ANATOMY AND PHYSIOLOGY
FINALS
LECTURE | First Semester
UNIT 1: THE RESPIRATORY AND DIGESTIVE SYSTEM
➢ In the cells, metabolic reactions that
consume O2 and give off CO2 during the
production of ATP is termed cellular
respiration
Coverage:
•
Respiration
Process of supplying the body with O2 and
removing CO2
Cellular respiration
•
Steps of Respiration
•
•
•
•
Pulmonary Ventilation
➢ Breathing, is the which is the movement
of air into (inspiration) and out
(expiration) of the lungs. Inhalation
permits O2 to enter the lungs and
exhalation permits CO2 to leave the
lungs.
External (pulmonary) Respiration
➢ The exchange of oxygen (O2) and
carbon dioxide (CO2) between the air in
the lungs and the blood.
➢ O2 diffuses from the lungs to the blood.
Pulmonary capillary blood gains O2 and
loses CO2.
➢ CO2 diffuses from the blood to the
lungs.
Transport of respiratory gases
➢ The cardiovascular system transports
gases using blood as the transporting
fluid.
➢ O2 is transported from the lungs to the
tissue cells of the body.
➢ CO2 is transported from the tissue cells
➢ to the lungs.
Internal (tissue) respiration
➢ Exchange of gases between blood in
systemic capillaries and tissue cells.
➢ O2 diffuses from blood to tissue cells
and CO2 diffuses from the tissue cells to
blood (blood loses O2 and gains CO2)
Actual use of oxygen and production of
carbon dioxide by tissue cells. The
cornerstone of all energy-producing
chemical reaction in the body.
Function of the Respiratory System
•
•
•
•
Supply oxygen and dispose of carbon
dioxide.
Air movement past the vocal cords makes
sound and speech possible.
The sensation of smell occurs when airborne
molecules are drawn into the nasal cavity
The respiratory system protects against
some microorganisms and other pathogens
(Innate Immunity)
Anatomy of Respiratory System
Components of the Respiratory System
a) Upper Respiratory System
➢ Nose
➢ Nasal Cavity
➢ Pharynx
➢ Associated structures
b) Lower Respiratory System
➢ Larynx
➢ Trachea
➢ Bronchi
➢ Lungs
Two Parts of the Respiratory System
Conducting Zone (CZ)
➢ Series of interconnecting cavities and tubes
both outside and within the lungs.
➢ Airways that serve as a conduit to move air.
ANATOMY AND PHYSIOLOGY
LECTURE | First Semester
Parts of the body that include the CZ
o Nose
o Nasal Cavity
o Pharynx
o Larynx
o Trachea
o Bronchi
o Bronchioles
o Terminal Bronchioles
Function:
•
Filter, warm, and moisten air and
conduct it inro the lungs.
Respiratory Zone (RZ)
➢ Tubes and tissues within the lungs where
gas exchange occurs
FINALS
•
•
•
•
•
Provides an airway for respiration
Moistens and warms entering air
Filters and cleans inspired air
Serves as a resonating chamber for
speech
Houses the olfactory (smell) receptors.
Parts of the Nose
External Nose
➢ Visible on the face and
consists of a supporting framework of bone
and hyaline cartilage covered with muscle
and skin and lined by a mucous membrane.
➢ The external openings of the nose, the
nostrils or nares are bounded laterally by
the flared alae.
Skeletal Framework
Parts of the body that consists the RZ
o Respiratory bronchioles
o Alveolar ducts
o Alveolar sacs
o Alveoli
➢ Root (area between the eyebrows),
bridge, and dorsum nasi (anterior
margin), the latter terminating in the
apex (tip of the nose).
Respiratory Tract
Bony Framework
➢ Passageways that carry air to and
from the exchange surfaces of the
lungs.
➢ Form by the frontal bone, nasal
bones, and maxillae.
➢ help to keep the vestibule and nasal
cavity patent, that is, open or
unobstructed.
Otorhinolaryngology
The branch of medicine that deals with the
diagnosis and treatment of diseases of the ears,
nose, and throat (ENT)
Cartilaginous framework
➢ Flexible.
➢ help to keep the vestibule and nasal
cavity patent, that is, open or
unobstructed.
Upper Respiratory System
Nose
➢ The only externally visible part of the
respiratory system.
➢ Consists of the external nose and the nasal
cavity.
➢ Primary passageway for air entering the
respiratory system.
Functions of the Nose
•
•
•
Septal nasal cartilage
o forms the anterior portion of the nasal
septum
Lateral nasal cartilages
o inferior to the nasal bones
Alar Cartilages
ANATOMY AND PHYSIOLOGY
LECTURE | First Semester
o Forms a portion of the walls of the
nostrils.
External Nares (Nostrils)
➢ Air normally enters here.
Nasal Vestibules
➢ Space contained within the flexible tissues
of the nose.
➢ The epithelium of the vestibule contains
coarse hairs (vibrissae) that extend across
the external nares.
▪ Large airborne particles, such as
sand, sawdust, or even insects,
are trapped in these hairs and
prevented from entering the
nasal cavity
➢ Air passes through here first.
Functions of the interior structures of the external
nose
•
•
•
Warming, moistening, and filtering
incoming air
Detecting olfactory stimuli
Modifying speech vibrations as they pass
through the large, hallow resonating
chambers.
▪ Resonance refers to
prolonging, amplifying, or
modifying a sound by
vibration.
Nasal Cavity (internal nose)
➢ Large space in the anterior aspect of the
skull that lies inferior to the nasal bone and
superior to the oral cavity
➢ Lined with muscle and mucous
membrane.
➢ Extends from the nares to the choanae
➢ The nasal cavity merges with the external
nose
➢ Space contained within the flexible tissues
of the nose.
➢ The nasal cavity is divided into a larger,
inferior respiratory region and a smaller,
superior olfactory region.
FINALS
Respiratory Region
➢ Lined with ciliated pseudostratified
columnar epithelium with numerous goblet
cells.
➢ Lies here are olfactory receptor cells,
supporting cells, and basal cells.
o These cells make up the olfactory
epithelium. It contains cilia but no
goblet cells.
Olfactory Region
➢ superior portion of the nasal cavity.
➢ It includes the areas lined by olfactory
epithelium:
(1) the inferior surface of the
cribriform plate
(2) the superior portion of the
nasal septum.
(3) the superior nasal conchae.
Receptors in the olfactory epithelium
provides your sense of smell
Nasal Septum
➢ Divides the nasal cavity into right and left
sides.
➢ The anterior portion consists primarily of
hyaline cartilage.
➢ The remainder is formed by the septal
cartilage (anterior). The vomer and the
perpendicular plate of the ethmoid,
maxillae, and palatine bones (posterior).
Nasal Cavity opens into the nasopharynx through
the connection known as the internal nares.
Internal Nares (Choanae)
➢ Openings of the pharynx.
➢ Where the nasal cavity communicates with
the pharynx.
Superior, middle, and inferior nasal conchae
o Protruding medially from each
lateral wall of the nasal cavities
o Scroll like mucosa covered
projections
ANATOMY AND PHYSIOLOGY
LECTURE | First Semester
Paranasal Sinus
air-filled spaces within bone
Located in the frontal, sphenoid,
ethmoid, and maxillary bones.
Open into the nasal cavity and are
lined with a mucous membrane.
➢ They reduce the weight of the skull, produce
mucus, and influence the quality of the voice
by acting as resonating chambers
➢ Drain mucus
➢ Help keep the surfaces of the nasal cavity
moist and clean.
➢
➢
➢
➢
Nasolacrimal Ducts
➢ Drains tears
➢ Sensory receptors for the sense of smell are
in the superior part of the nasal cavity
Nasal Meatus
FINALS
o
o
o
o
As air moves out of the respiratory tract,
it again passes over the epithelium of the
nasal cavity.
This air is warmer and more humid than
the air that enters.
It warms the nasal mucosa, and
moisture condenses on the epithelial
surfaces.
In this way, breathing through your nose
helps prevent heat loss and water loss.
Epistaxis (Nose bleed)
➢ Extensive vascularization of the nasal cavity
and the vulnerable position of the nose
makes.
➢ Bleeding generally involves vessels of the
mucosa covering the cartilaginous portion
of the septum
Function of the Conchae and Nasal Mucosa
➢ Groovelike air passageways inferior to each
concha
➢ To pass from the vestibule to the internal
nares, air tends to flow through the
superior, middle, and inferior meatuses.
➢ greatly increase the mucosa) surface area
exposed to air and enhance air turbulence in
the cavity.
Conchae and meatuses increase surface area in the
internal nose and prevents dehydration by trapping
water droplets during exhalation.
o
o
o
o
o
Inhaled air whirls around the conchae
and meatuses, it is warmed by blood in
the capillaries.
Mucus secreted by the goblet cells
moistens the air and traps dust particles.
Drainage from the nasolacrimal ducts
also helps moisten the air, and is
sometimes assisted by secretions from
the paranasal sinuses.
Cilia move the mucus and trapped dust
particles toward the pharynx.
At this point, they can be swallowed
or spit out, thus removing the particles
from the respiratory tract.
During inhalation
•
Filter, heat, and moisten
the air
During exhalation
•
Reclaim this heat and
moisture.
Nasal Mucosa
➢ Prepares inhaled air for arrival at the lower
respiratory system.
➢ Richly supplied with sensory nerve endings,
o As a result, a contact with irritating
particles (dust, pollen, and the like)
triggers a sneeze reflex.
o Sensory receptors detect the foreign
substances, and action potentials are
conducted along the trigeminal nerves
to the medulla oblongata, where the
reflex is triggered
• During the sneeze reflex, the
uvula and the soft palate are
depressed, so that rapidly
flowing air from the lungs is
directed primarily through the
ANATOMY AND PHYSIOLOGY
LECTURE | First Semester
nasal passages, although a
considerable amount passes
through the oral cavity
o The sneeze forces air outward in a
violent burst-a crude but effective way to
expel irritants.
Photic sneeze reflex
➢ stimulated by exposure to bright
light, such as the sun.
➢ Fancifully called ACHOO
(Autosomal-dominantcompelling-helio-ophthalmicoutburst)
Pupillary Reflex
➢ Causes the pupils to constrict in
response to bright light.
➢ Complicated “wiring” of the
pupillary and sneeze reflexes is
intermixed in some people, so
that, when bright light activates a
pupillary reflex, it also activates a
sneeze reflex
Lamina Propria
➢ contains an abundance of arteries,
veins, and capillaries that bring
nutrients and water to the secretory
cells.
➢ Lamina propria of the internal
conchae contains an extensive
network of large and highly
expandable veins.
Types of Mucous membrane that line the Nasal
Cavity
Olfactory mucosa
➢ lines the slit like superior region of the nasal
cavity and contains smell receptors in its
olfactory epithelium.
FINALS
scattered goblet cells, that rests on a lamina
propria richly supplied with seromucous
nasal glands.
➢ Epithelial cells secrete defensins, a natural
antibiotic that help kill invading microbes.
➢ Lines the conducting portion of the
respiratory system.
Mucosa
➢ It is a mucous membrane.
➢ Consists of an epithelium and an
underlying layer of areolar tissue.
Lamina Propria
➢ The underlying layer of areolar
tissue that supports the respiratory
epithelium.
Upper Respiratory Function
➢ Contains mucous glands that
discharge their secretions
onto the epithelial surface.
Conduction Zone
➢ Contains bundles of smooth
muscle cells. At the
bronchioles, the smooth
muscles form thick bands
that encircle or spiral around
the lumen.
Structure of the Respiratory Epithelium
➢ It changes along the respiratory tract
Pseudostratified Ciliated Columnar Epithelium (w/
mucous cells)
➢ Nasal Cavity and the superior part of
the Pharynx
➢ Superior portion of the lower
respiratory system.
Respiratory Mucosa
➢ lines most of the nasal cavity. The
respiratory mucosa is a pseudostratified
ciliated columnar epithelium, containing
Stratified Squamous Epithelium
➢ Inferior portions of the Pharynx
ANATOMY AND PHYSIOLOGY
LECTURE | First Semester
Cuboidal Epithelium with scattered cilia.
➢ Smaller bronchioles
Simple Squamous Epithelium
➢ Exchange surfaces of the alveoli
Other, more specialized cells are scattered
among the squamous cells and together they
form the alveolar epithelium.
Seromucous Nasal Glands
➢ contain mucus-secreting mucous cells and
serous cells that secrete a watery fluid
containing enzymes.
➢ Secrete mucus containing lysosome.
Pharynx (Throat)
➢ Funnel-shaped that connects the nasal
cavity and mouth superiorly to the larynx
and esophagus inferiorly.
➢ chamber shared by the digestive and
respiratory systems.
➢ starts at the internal nares and extends to
the level of the cricoid cartilage, the most
inferior cartilage of the larynx
➢ wall is composed of skeletal muscles and is
lined with a mucous membrane.
➢ passageway for air and food, provides a
resonating chamber for speech sounds, and
houses the tonsils
Three anatomical regions
Nasopharynx
➢ Superior portion of the pharynx and lies
posterior to the nasal cavity and extends to
the soft palate.
➢ lined with ciliated pseudostratified
columnar epithelium
➢ Lined with nonkeratinized stratified
squamous epithelium because it is prone to
abrasion by food particles.
➢ Connected to the posterior portion of the
nasal cavity through the internal nares
FINALS
Soft Palate
➢ forms the posterior portion of the
roof of the mouth
➢ arch-shaped muscular partition
between the nasopharynx and
oropharynx that is lined by mucous
mem
➢ Separates the pharynx from the oral
cavity
➢ Elevated during swallowing which
then closes the nasopharynx to
prevent food from entering the oral
cavity into the nasopharynx.
Uvula
➢ Posterior extension of the
soft palate
Pharyngotympanic tubes
➢ Which drains the middle ears, open
into the nasopharynx
Five Openings
o
o
o
Two internal nares
Two openings that lead into the
auditory (pharyngotympanic)
tubes (commonly known as the
eustachian tubes)
The opening into the
oropharynx.
Pharyngeal tonsil (adenoid)
➢ Located on the posterior wall of the
nasopharynx.
➢ left and right auditory tubes open into the
nasopharynx on either side of this tonsil.
Passageway of air
Nasopharynx receives air from the nasal cavity
along with packages of dust-laden mucus.
The cilia move the mucus down toward the most
inferior part of the pharynx.
ANATOMY AND PHYSIOLOGY
LECTURE | First Semester
There is an exchange of small amounts of air with
the auditory tubes to equalize air pressure between
the middle ear and the atmosphere.
Oropharynx
➢ intermediate portion of the pharynx
➢ posterior to the oral cavity and extends from
the soft palate inferiorly to the level of the
hyoid bone
➢ the boundary between the nasopharynx and
the oropharynx, the epithelium changes to
stratified squamous epithelium
➢
Fauces
➢ the only opening. This is the opening
from the mouth
FINALS
Lower Respiratory System
Larynx (Voice box)
➢ Short passageway that connects the
laryngopharynx with the trachea.
➢ It lies in the midline of the neck anterior to
the esophagus and the fourth through sixth
cervical vertebrae (C4–C6).
➢ Composed of nine pieces of cartilage
Occur singly
▪ Thyroid Cartilage
▪ Epiglottis
▪ Cricoid cartilage
Occur in pairs
▪
Functions:
➢ common passageway for air, food,
and drink.
Two pairs of tonsils in the Oropharynx
Palatine (2)
➢ Located in the lateral walls near the
border of the oral cavity and
oropharynx
Lingual tonsils (2)
➢ Located on the surface of the
posterior part of the tongue
Laryngopharynx (Hypopharynx)
➢ Inferior portion of the pharynx
➢ Lined by nonkeratinized stratified
squamous epithelium.
➢ A respiratory and digestive pathway
➢ Begins at the level of the hyoid bone
Inferior end it opens into the
esophagus posteriorly
The larynx (voice
box) anteriorly
▪
▪
Arytenoid
➢ the most important because
they influence changes in
position and tension of the
vocal folds.
Cuneiform
Corniculate cartilages
Extrinsic Muscles
➢ Connect the cartilages to other
structures in the throat.
Intrinsic Muscles
➢ Connect the cartilages to one
another.
Cavity of the larynx
➢ Space that extends from the
entrance into the larynx down to the
inferior border of the cricoid
cartilage
Laryngeal vestibule
➢ portion of the cavity of the
larynx above the vestibular
folds (false vocal cords)
Infraglottic cavity
ANATOMY AND PHYSIOLOGY
FINALS
LECTURE | First Semester
➢ Portion of the cavity of the
larynx below the vocal folds
➢Inhaled air leaves the
pharynx and enters the
larynx through here.
Cartilages in the Larynx
Rima Glottis
➢ space between
the two
mucous
membrane.
Thyroid cartilage (Adam’s apple)
➢ Consists of two fused plates of hyaline
cartilage that form the anterior wall of the
larynx and give it a triangular shape.
➢ Present in both male and female but larger
in males.
➢ largest laryngeal cartilage
➢ Together with the cricoid cartilage they
protect the glottis and the entrance of the
trachea
Thyrohyoid membrane
➢ Ligament that connects the thyroid
cartilage to the hyoid bone.
Epiglottis
➢ Large, leaf-shaped piece of elastic cartilage
that is covered with epithelium.
Stem
➢tapered inferior portion that
is attached to the anterior
rim of the thyroid cartilage.
Leaf
➢unattached and is free to
move up and down like a trap
door.
During swallowing, the pharynx and larynx rise.
Elevation of the pharynx widens it to receive food
or drink; elevation of the larynx causes the
epiglottis to move down and form a lid over the
glottis, closing it off.
Glottis
➢consists of a pair of folds of
mucous membrane, the vocal
folds.
Swallowing routes liquids and foods into the
esophagus and keeps them out of the larynx and
airways. When small particles of dust, smoke,
food, or liquids pass into the larynx, a cough reflex
occurs.
usually expelling the material
Cricoid cartilage
➢ ring of hyaline cartilage that forms the
inferior wall of the larynx.
➢ greatly expanded, providing support in
the absence of the thyroid cartilage
➢ Landmark for making an emergency airway
called a tracheotomy.
Cricotracheal ligament
I.
this connects the thyroid cartilage
and cricoid cartilage.
Arytenoid Cartilage (Paired)
➢ triangular pieces of mostly hyaline cartilage
➢ located at the posterior, superior border of
the cricoid cartilage.
➢ Form synovial joint with the cricoid
cartilage and have a wide range of mobility.
Corniculate Cartilage (Paired)
➢ horn-shaped pieces of elastic cartilage
➢ Located at the apex of each arytenoid
cartilage.
Cuneiform Cartilage (Paired)
➢ club-shaped elastic cartilages anterior to the
corniculate cartilages.
ANATOMY AND PHYSIOLOGY
LECTURE | First Semester
➢ support the vocal folds and lateral
aspects of the epiglottis
Lining of the Larynx
o
o
lining of the larynx superior to the vocal
folds is nonkeratinized stratified squamous
epithelium.
lining of the larynx inferior to the vocal folds
is ciliated pseudostratified columnar
epithelium consisting of ciliated columnar
cells, goblet cells, and basal cells.
The Structures of Voice Production
Mucous membrane of the larynx forms two pairs of
folds.
Vestibular folds (false vocal cords)
➢ superior pair
➢ function in holding the breath against
pressure in the thoracic cavity, such as
might occur when a person strains to lift a
heavy object
➢ fairly inelastic
➢ help prevent foreign objects from entering
the glottis
Vocal Folds (true vocal cords)
➢ inferior pair
➢ principal structures of voice production
➢ Deep in the mucous membrane, is
nonkeratinized stratified squamous
epithelium, bands of elastic ligaments
stretched between the rigid cartilages of the
larynx
Rima vestibuli
➢ space between the vestibular folds
Laryngeal ventricle
➢ lateral expansion of the middle portion of
the laryngeal cavity inferior to the vestibular
folds and superior to the vocal folds.
Sound Production
FINALS
Intrinsic laryngeal muscles are attached to the rigid
cartilages and the vocal folds. When these muscles
contract they move the cartilage then pulls the
elastic ligaments tight. This stretches the vocal folds
out into the airways as a result the Rima glottides
are narrowed.
Air passing through the larynx vibrates the folds
and produces sound (phonation)
Phonation
➢ sound production at the larynx
Variation in the pitch of the sound is related to the
tension in the vocal folds.
Greater the pressure of air, the louder the sound
produced by the vibrating vocal folds.
Intrinsic muscles of the larynx contract, they pull
on the arytenoid cartilages, which causes the
cartilages to pivot and slide.
Contraction of the posterior cricoarytenoid
muscles:
a) moves the vocal folds apart (abduction),
as a result the rima glottidis opens.
b) contraction of the lateral cricoarytenoid
muscles moves the vocal folds together
(adduction), as a result the rima
glottidis closes.
Due to androgens, vocal folds are usually thicker
and longer in males than in females, and therefore
they vibrate more slowly.
The pharynx, mouth, nasal cavity, and paranasal
sinuses all act as resonating (producing) chambers
that give the voice its human and individual quality.
Muscles of the face, tongue, and lips help us
enunciate words.
Whispering
➢ closing all but the posterior portion of the
rima glottidis because vocal folds do not
vibrate.
The Laryngeal Maculate
ANATOMY AND PHYSIOLOGY
LECTURE | First Semester
1) muscles of the neck and pharynx, which
position and stabilize the larynx
2) Smaller intrinsic muscles that control
tension in the vocal folds or open and close
the glottis
Trachea (Windpipe)
➢ tubular passageway for air.
➢ located anterior to the esophagus and
extends from the larynx to the superior
border of the fifth thoracic vertebra (T5),
where it divides into right and left primary
bronchi.
➢ epithelium of the trachea is continuous with
that of the larynx.
➢ Lined with pseudostratified columnar
epithelium, which contains numerous cilia
and goblet cells.
Layers of the tracheal wall (Deep to Superficial)
a) Mucosa
➢ Consists of an epithelial layer of
ciliated pseudostratified columnar
epithelium and a layer of lamina
propria that contains elastic and
reticular fibers
➢ protection against dust
b) Submucosa
➢ thick layer of connective tissue
➢ consists of areolar connective tissue
that contains seromucous glands
and their ducts.
➢ contains mucous glands that
communicate with the epithelial
surface through a number of
secretory ducts.
c) Hyaline Cartilage
➢ Resembles the letter C which are
stacked one above the other and are
connected by dense connective
tissue.
o open part of each C-shaped
cartilage ring faces
posteriorly toward the
esophagus and spanned
FINALS
by a fibromuscular
membrane.
o Within the membrane are
transverse smooth muscle
fibers called trachealis
muscle.
o Elastic connective tissue that
allow the diameter of the
trachea to change subtly
during inhalation and
exhalation, which is
important in maintaining
efficient airflow.
o solid C-shaped cartilage rings
provide a semirigid support
to maintain patency so that
the tracheal wall does not
collapse inward.
d) Adventitia (areolar connective tissue)
➢ consists of areolar connective tissue
that joins the trachea to surrounding
tissues.
The normal diameter of the trachea changes from
moment to moment, primarily under the control of
the sympathetic division of the ANS. Sympathetic
stimulation increases the diameter of the trachea
and makes it easier to move large volumes of air
along the respiratory passageway.
Tracheotomy
➢ If the obstruction is above the level of the
larynx.
➢ skin incision is followed by a short
longitudinal incision into the trachea below
the cricoid cartilage. A tracheal tube is then
inserted to create an emergency air
passageway
Intubation
➢ tube is inserted into the mouth or nose and
passed inferiorly through the larynx and
trachea.
➢ lumen of the tube provides a passageway for
air; any mucus clogging the trachea can be
suctioned out through the tube.
ANATOMY AND PHYSIOLOGY
FINALS
LECTURE | First Semester
Bronchi
➢ columnar, nonciliated cells
interspersed among the epithelial
cells
➢ protect against harmful effects of
inhaled toxins and carcinogens,
produce surfactant
➢ function as stem cells (reserve cells),
which give rise to various cells of the
epithelium.
Main bronchi contain incomplete rings of cartilage
and are lined by ciliated pseudostratified columnar
epithelium
Right Primary Bronchus
➢ Goes to the right lung
➢ more vertical, shorter, and wider
➢ An aspirated object is more likely to enter
and lodge in the right main bronchus than
the left
Left Primary Bronchus
➢ Goes to the left lung
Bronchial Tree
➢ Extensive branching from the trachea
through the terminal bronchioles. Beyond
the branches of the bronchial tree are the
respiratory bronchioles and alveolar ducts.
Respiratory Bronchioles
Carina
➢ where the trachea divides into right and left
main bronchi an internal ridge.
➢ formed by a posterior and somewhat
inferior projection of the last tracheal
cartilage
➢ The mucous membrane of the carina is one
of the most sensitive areas of the entire
larynx and trachea for triggering a cough
reflex
Lobar secondary bronchi
➢ Right lungs have 3 lobes while the left lung
has 2.
➢ Continue to branch into smaller bronchi
➢ thinnest and most delicate branches of the
bronchial tree.
➢ hey deliver air to the gas exchange surfaces
of the lungs.
The respiratory passages from the trachea to the
alveolar ducts contain about 23 generations of
branching. From the trachea into the main bronchi
is called the first generation, that from main
bronchi into lobar bronchi is called secondgeneration branching.
During the branching there are several changes in
the structures.
o
Segmental tertiary bronchi
➢ supply the specific bronchopulmonary
segments within the lobes.
➢ Divides into bronchioles
Terminal Bronchioles
➢ smaller tubes of the branch out bronchioles.
➢ Contain Clara cells.
Clara Cells
o
o
o
ciliated pseudostratified columnar
epithelium (main bronchi, lobar bronchi,
and segmental bronchi) to:
Ciliated simple columnar epithelium with
some goblet cells in larger bronchioles
To mostly ciliated simple cuboidal
epithelium with no goblet cells in smaller
bronchioles
To mostly nonciliated simple cuboidal
epithelium in terminal bronchioles.
Function of ciliated epithelium
• removes inhaled particles in 2 ways
▪ mucus produced by goblet
cells traps the particles
ANATOMY AND PHYSIOLOGY
FINALS
LECTURE | First Semester
▪ cilia move the mucus and
trapped particles toward the
pharynx for removal
▪ In nonciliated simple
cuboidal epithelium inhaled
particles are removed by
macrophages
o Plates of cartilage replace the incomplete
rings of cartilage in main bronchi and
disappear in the distal bronchioles
o Cartilage decrease so smooth muscles
increases. Since there is no supporting
cartilage, muscle spasms can close off the
airways. This is what happens
during an asthma attack.
➢ Acts as a lubricant which
reduces friction between the
membranes which allow
them to slide easily over one
another during breathing.
➢ Helps hold pleural
membranes together.
Surface Tension
➢ A phenomenon caused by
pleural fluid in which the two
membranes to stick to one
another.
Visceral Pleura
➢ The deep layer.
➢ Covers the lungs
Lungs
➢ are paired cone-shaped organs in the
thoracic cavity
➢ Separated from each other by the heart and
other structures of the mediastinum. There
are two anatomically distinct chambers.
➢ If trauma causes one lung to collapse, the
other may remain expanded.
Pulmonologist
➢ specialist in the diagnosis and
treatment of lung diseases.
Pleural Membrane
➢ This enclosed and protect the lungs. It is a
double-layered serous membrane.
Parietal pleura
➢ superficial layer
➢ Lines the wall of the thorax,
diaphragm, and mediastinum.
Pleural cavity
➢ Between the parietal and visceral
pleura.
➢ Contains a small amount of
lubricating fluid secreted by the
membranes
Pleural Fluid
Base
➢ broad inferior portion of the lung
➢ concave
Apex
➢ narrow superior portion of the lung
Costal Surface
➢ surface of the lung lying against the ribs
Mediastinal Surface
➢ Each of the lung has a region called hilum.
Hilum
➢ through which bronchi, pulmonary
blood vessels, lymphatic vessels, and
nerves enter and exit.
Root
➢ attaches to the mediastinum and fixes the
positions of the major nerves, blood vessels,
and lymphatic bessels.
Cardiac Notch
➢ a concavity where the apex of the heart lies.
➢ Present in the left lung
Apex of the Lungs
ANATOMY AND PHYSIOLOGY
LECTURE | First Semester
➢ lies superior to the medial third of the
clavicles
➢ only area that can be palpated (can be used
to examine for thoracic and abdominal
examinations)
FINALS
➢ Separates the superior lobe
from the inferior lobe in the
left lung.
Each lobe receives its own lobar bronchus
Right main bronchus
Thoracentesis
➢ Removal of excessive fluid in the pleural
cavity without injuring lung tissue by
inserting a needle anteriorly through the
seventh intercostal space.
➢ gives rise to three lobar bronchi
called the superior, middle, and
inferior lobar bronchi.
Left Main Bronchus
➢ gives rise to superior and
inferior lobar bronchi.
Lobar Bronchi
➢ Within the lungs this gives the rise to
segmental bronchi.
➢ There are 10 segmental
bronchi.
Bronchopulmonary segment
➢ portion of lung tissue that each segmental
bronchus supplies.
Lobes, Fissures, and Lobules
Fissures
➢ One or two fissures divide each lung into
sections called lobes
Oblique fissure
➢ Both lungs have this.
➢ Extends inferiorly and anteriorly
Right Lung
➢ Has horizontal fissure.
➢ superior part of the oblique
fissure separates the superior
lobe from the inferior lobe
➢ inferior part of the oblique
fissure separates the inferior
lobe from the middle lobe
Left Lung
Lobules
➢ small compartments of the
bronchopulmonary segment.
➢ each lobule is wrapped in elastic
connective tissue.
➢ contains a lymphatic vessel, an
arteriole, a venule, and a branch
from a terminal bronchiole.
Interlobular septa
➢ finest partitions
➢ divide the lung into
pulmonary lobule
The terminal bronchioles and lobule subdivide into
microscopic branches called respiratory
bronchioles.
ANATOMY AND PHYSIOLOGY
FINALS
LECTURE | First Semester
Alveoli participate in gas exchange, and thus
respiratory bronchioles begin the respiratory zone
of the respiratory system.
phospholipids
and
lipoproteins.
➢ Function:
Lowers the
surface
tension of
alveolar fluid,
which reduces
the tendency
of alveoli to
collapse and
thus
maintains
their patency
Epithelial lining changes from simple cuboidal to
simple squamous.
Respiratory bronchioles in turn subdivide into
several (2–11) alveolar ducts, consists of simple
squamous epithelium.
Alveolar Sacs and Alveoli
Alveolar Sac
➢ terminal dilation of an alveolar duct
➢ composed of alveoli.
Alveolus (singular)
➢ Consists of two types of alveolar
epithelial cells:
Type I alveolar (squamous
pulmonary epithelial) cells
➢ More numerous
➢ simple squamous epithelial
cells that form a continuous
lining of the alveolar wall.
➢ main sites of gas exchange
➢ Underlying the layer is an
elastic basement membrane
Type II alveolar cells (Septal cells)
➢ Fewer
➢ Found between type I
alveolar cells
➢ cuboidal epithelial cells with
free surfaces containing
microvilli
o secrete alveolar fluid,
which keeps the
surface between the
cells and the air.
o Within the alveolar
fluid is surfactant.
Surfactant
➢ Complex
mixture of
Alveolar macrophages
➢ phagocytes that remove fine
dust particles and other
debris from the alveolar
space.
➢ fibroblasts that produce
reticular and elastic fibers.
The lobule’s arteriole and venule disperse into a
network of blood capillaries that consist of a single
layer of endothelial cells and basement membrane.
Exchange of O2 and Co2 in the air spaces in the
lungs and blood takes place by diffusion across the
alveolar and capillary walls, which together form
the respiratory membrane.
Respiratory Membrane
➢ Very thin to allow rapid diffusion of gases
➢ Gas exchange between the air and blood
takes place.
➢ Formed by the walls of the alveoli and the
surrounding capillaries.
Respiratory Membrane’s layer
1) Thin layer pf fluid lining the alveolus
2) A layer of type I and type II alveolar cells
and associated alveolar macrophages that
constitutes the alveolar wall
ANATOMY AND PHYSIOLOGY
LECTURE | First Semester
3) The alveolar epithelium, composed of
simple squamous epithelium
4) An epithelial basement membrane
underlying the alveolar wall
5) A capillary basement membrane
6) The capillary endothelium, composed of
simple squamous epithelium
FINALS
o
Blood supply to the Lung
One supplies the respiratory portion of the lungs.
The other perfuses the conducting portion.
Respiratory exchange surfaces receive blood from
arteries of the pulmonary circuit
o
o
o
o
o
Receives blood from two arteries:
Pulmonary arteries and bronchial arteries.
Deoxygenated blood passes through the
pulmonary trunk, which divides into a left
pulmonary artery that enters the left lung
and a right pulmonary artery that enters the
right lung.
• The pulmonary arteries are the only
arteries in the body that carry
deoxygenated blood.
They enter the lungs at the hilum and
branch with the bronchi as they approach
the lobules.
Each lobule receives an arteriole and a
venule, and a network of capillaries
surrounds each alveolus
Oxygen-rich blood from the alveolar
capillaries passes through the pulmonary
venules and then enters the pulmonary
veins, which deliver the blood to the left
atrium.
Alveolar Capillaries
➢ primary source of angiotensinconverting enzyme (ACE), which
converts circulating angiotensin I to
angiotensin II.
o This enzyme plays an
important role in regulating
blood volume and blood
pressure.
o
o
o
Return of the oxygenated blood to the heart
occurs by way of the four pulmonary veins,
which drain into the left atrium
• Constriction occurs in pulmonary
blood vessels in response to hypoxia.
Ventilation–perfusion coupling
➢ vasoconstriction in
response to hypoxia
diverts pulmonary blood
from poorly ventilated
areas of the lungs to well
ventilated regions for
more efficient gas
exchange.
➢ the perfusion (blood
flow) to each area of the
lungs matches the extent
of ventilation (airflow) to
alveoli in that area
Bronchial arteries, which branch from the
aorta, deliver oxygenated blood to the lungs.
most blood returns to the heart via
pulmonary veins.
Some blood drains into bronchial veins,
branches of the azygos system, and returns
to the heart via the superior vena cava.
Pulmonary vessels can easily become blocked
by small blood clots, fat masses, or air bubbles
in the pulmonary arteries.
Conducting
o
o
o
tissues of conducting passageways of your
lungs receive oxygen and nutrients from
capillaries supplied by the bronchial
arteries, which branch from the thoracic
aorta.
venous blood from these bronchial
capillaries empties into bronchial veins or
anastomoses and then into pulmonary veins
Blood flow outside the pulmonary veins
bypasses the rest of the systemic circuit and
dilutes the oxygenated blood leaving the
alveoli.
Very small blood clots occasionally form in the
venous system. These are usually trapped in the
ANATOMY AND PHYSIOLOGY
LECTURE | First Semester
pulmonary capillary network, where they soon
dissolve
Pulmonary embolism
➢ blockage of a branch of a pulmonary artery
stops blood flow to a group of lobules or
alveoli
➢ If the blockage occurs in a major pulmonary
vessel rather than a minor branch,
pulmonary resistance increases.
Patency of the Respiratory System
Structures that help maintain patency of the
respiratory system
➢ bony and cartilaginous frameworks of
the nose, skeletal muscles of the
pharynx, cartilages of the larynx, Cshaped rings of cartilage in the trachea
and bronchi, smooth muscle in the
bronchioles, and surfactant in the
alveoli.
Factors the compromise patency
➢ crushing injuries to bone and cartilage, a
deviated nasal septum, nasal polyps,
inflammation of mucous membranes,
spasms of smooth muscle, and a
deficiency of surfactant
Pulmonary Ventilation (Breathing)
➢ flow of air into and out of the lungs.
➢ air flows between the atmosphere and the
alveoli of the lungs
o because of alternating pressure
differences created by contraction
and relaxation of respiratory muscle
➢ rate of airflow and the amount of eff ort
needed for breathing are also influenced by
alveolar surface tension, compliance of the
lungs, and airway resistance.
Pressure Changes during Pulmonary Ventilation
Air moves into the lungs when the air pressure
inside the lungs is less than the air pressure in the
atmosphere
FINALS
Air moves out of the lungs when the air pressure
inside the lungs is greater than the air pressure in
the atmosphere
Respiratory Cycle
➢ single cycle of inhalation and exhalation.
Inhalation
➢ Breathing in
➢ the air pressure inside the lungs is equal to
the air pressure of the atmosphere.
o At sea level the atmospheric
pressure is 760 millimeters of
mercury (mmHg), or 1 atmosphere
(atm).
➢ For air to flow into the lungs, the pressure
inside the alveoli must become lower than
the atmospheric pressure.
➢ the diaphragm and external intercostals
contract, the lungs expand, and air moves
into the lungs
Boyle’s Law
➢ Inverse relationship between volume and
pressure
➢ pressure of a gas in a close container
is inversely proportional to the
volume of the container. This means
that if the size of a closed container
is increased, the pressure of the gas
inside the container decreases, and
that if the size of the container is
decreased, then the pressure inside
it increases
For inhalation to occur, the lungs must expand,
which increases lung volume and thus decreases
the pressure in the lungs. The diaphragm contracts,
the chest expands, the lungs are pulled outward,
and alveolar pressure decreases
1) contraction of the main muscle of
inhalation, the diaphragm, with resistance
from external intercostals.
o most important muscle of inhalation
is the diaphragm. It is innervated by
fibers of the phrenic nerves, which
ANATOMY AND PHYSIOLOGY
LECTURE | First Semester
emerge from the spinal cord at
cervical levels 3, 4, and 5.
o next most important muscles of
inhalation are the external
intercostals. When these muscles
contract, they elevate the ribs. As a
result, there is an increase in the
anteroposterior and lateral
diameters of the chest cavity
2) Contraction of the diaphragm causes it to
flatten, lowering its dome. This increases
the vertical diameter of the thoracic cavity.
3) During normal quiet inhalation produce a
pressure difference of 1–3 mmHg and the
inhalation of about 500 mL of air
4) As the diaphragm and external intercostals
contract and the overall size of the thoracic
cavity increases, the volume of the pleural
cavity also increases, which causes
intrapleural pressure to decrease to about
754 mmHg
Intrapleural pressure
➢ pressure within the pleural cavity
➢ ways a negative pressure (lower than
atmospheric pressure), ranging from
754–756 mmHg during normal quiet
breathing.
➢ The pleural cavity has a negative
pressure, it essentially functions as a
vacuum.
➢ The elastic fibers cannot recoil so
➢ much, however. The reason is that
they are not strong enough to
overcome the fluid bond between the
parietal and visceral pleurae.
➢ If the thoracic cavity increases in
size, the lungs also expand; if the
thoracic cavity decreases in size, the
lungs recoil (become smaller).
5) As the thoracic cavity expands, the parietal
pleura lining the cavity is pulled outward in
all directions, and the visceral pleura and
lungs and pulled along with it
Alveolar (intrapulmonic) pressure
FINALS
➢ the pressure of air within the alveoli of the
lungs drops from 760 to 758 mmHg
➢ Air pressure within the alveoli, is equal to
the atmospheric pressure, which is pressure
outside the body.
Most of the increase in volume appears to be due to
the lengthening and expansion of the alveolar ducts
and the increase in size of the openings into the
alveoli.
The accessory muscles of inhalation
1) Sternocleidomastoid muscles
o elevate the sternum
2) Scalene
o elevate the first two ribs
3) Pectoralis minor muscles
o elevate the third through fifth rib
Exhalation
➢ Breathing out
➢ The pressure in the lungs is greater than
the pressure of the atmosphere
➢ results from elastic recoil of the chest wall
and lungs, both of which have a natural
tendency to spring back after they have been
stretched
Directed forces that contribute to elastic recoil
1) The recoil of elastic fibers that were
stretched during inhalation
2) The inward pull of surface tension due to
the film of intrapleural fluid between the
visceral and parietal pleurae
Steps of Exhalation
1) Starts when the inspiratory muscles relax.
2) the diaphragm relaxes, its dome moves
superiorly owing to its elasticity.
3) As the external intercostals relax, the ribs
are depressed.
4) These movements decrease the vertical,
lateral, and anteroposterior diameters of the
thoracic cavity, which decreases lung
volume.
ANATOMY AND PHYSIOLOGY
LECTURE | First Semester
5) the alveolar pressure increases to about 762
mmHg
6) Air then flows from the area of higher
pressure in the alveoli to the area of lower
pressure in the atmosphere.
Muscles used in Exhalation
1) internal intercostal and transversus thoracic
muscles
o Depress the ribs. This action reduces
the width and depth of the thoracic
cavity.
2) Abdominal muscles. (including the external
and internal oblique, transversus
abdominis, and rectus abdominis muscles)
o assist the internal intercostal
muscles in exhalation by
compressing the abdomen. This
action forces the diaphragm upward.
FINALS
➢ reduces the tendency of the lungs to
collapse
➢ If not present it causes the alveoli to
recoil ten times greater.
Compliance
➢ how much effort is required to stretch the
lungs and chest wall.
➢ The greater the compliance, the easier it is
to fill the lungs.
o
o
Factors Affecting Compliance
•
Other Factors affecting Pulmonary Ventilation
Surface Tension of Alveolar Fluid
➢ arises at all air–water interfaces because the
oppositely charged ends of polar water
molecules are more strongly attracted to
each other than they are to gas molecules in
the air
➢ When liquid surrounds a sphere of air, as in
an alveolus or a soap bubble
➢ Soap bubbles “burst” because they collapse
inward due to surface tension.
➢ They pull on the alveolar walls causing the
alveoli to assume the smallest possible
diameter and recoil
➢ During breathing, surface tension must be
overcome to expand the lungs during each
inhalation
Surfactant
➢ Mixture of phospholipid and
lipoproteins, produced by secretory cells
of the alveolar epithelium.
➢ reduces its surface tension below the
surface tension of pure water
High compliance means that the
lungs and chest wall expand easily
Low compliance means that they
resist expansion.
•
•
The Connective Tissue of the Lungs.
o The loss of supporting tissues due to
alveolar damage, as in emphysema,
increases compliance.
The Level of Surfactant Production.
o On exhalation, the collapse of alveoli
due to inadequate surfactant, as in
respiratory distress syndrome,
reduces compliance.
The Mobility of the Thoracic Cage.
o Arthritis or other skeletal disorders
that affect the articulations of the
ribs or spinal column also reduce
compliance.
Airway Resistance
➢ The walls of the airways, especially the
bronchioles, offer some resistance to the
normal flow of air into and out of the lungs.
o during inhalation, the bronchioles
enlarge because their walls are
pulled outward in all directions
o Airway resistance then increases
during exhalation as the diameter of
bronchioles decreases.
ANATOMY AND PHYSIOLOGY
LECTURE | First Semester
Role of the CNS in airway resistance
ANS
➢ Signals to cause relaxation of bronchiolar
smooth muscle (bronchodilation) which
results in decreased resistance.
PNS
➢ Signals to cause contraction of bronchiolar
smooth muscle (bronchoconstriction)
resulting in increased resistance.
Hallmark of asthma or chronic obstructive
pulmonary disease (COPD)—emphysema or
chronic bronchitis—is increased airway resistance
due to obstruction or collapse of airways.
Breathing Patterns
Eupnea
➢ Term for quiet breathing.
➢ Consists of shallow, deep, or combined
shallow and deep breathing.
➢ expansion of the lungs stretches their elastic
fibers.
Costal Breathing
➢ pattern of shallow (chest) breathing.
➢ upward and outward movement of the
chest due to contraction of the external
intercostal muscles.
➢ Thoracic volume changes because the
rib cage alters its shape
➢ Exhalation takes place passively when
these muscles relax.
Diaphragmatic Breathing
➢ pattern of deep (abdominal) breathing
➢ consists of the outward movement of the
abdomen due to the contraction and
descent of the diaphragm.
FINALS
➢ contraction of the diaphragm provides
the necessary change in thoracic volume
➢ Air is exhaled passively when the
diaphragm relaxes
Forced Breathing (hyperpnea)
➢ involves active inspiratory and expiratory
movements
➢ our accessory muscles assist with
inhalation, and exhalation involves
contraction of the internal intercostal
muscles
➢ maximum levels of forced breathing, our
abdominal muscles take part in exhalation.
o contraction compresses the
abdominal contents, pushing them
up against the diaphragm. This
action further reduces the volume of
the thoracic cavity
Lung Volumes and Capacity
Varying amounts of air move into and out of the
lungs.
Respiratory Rate
➢ number of breaths you take each minute.
Respiratory Minute Volume
➢ amount of air moved each minute
multiplied by the respiratory rate f
by the tidal volume
Lung Volumes
➢ measured directly by use of a spirometer
Spirometer
➢ apparatus used to measure volumes
and capacities. The record is called
spirogram.
Tidal Volume
➢ volume of one breath
➢ In a typical adult, about 70% of
➢ the tidal volume (350 mL) actually
reaches the respiratory zone and the
other 30% (150 mL) remains in the
conducting zone.
ANATOMY AND PHYSIOLOGY
FINALS
LECTURE | First Semester
Minimal Volume
Anatomic Dead Space
➢ conducting airways with air that
does not undergo respiratory
exchange.
Inspiratory Reserve Volume
➢ Additional inhaled air when in deep
breathing.
➢ about 3100 mL in an average adult
male and 1900 mL in an average
adult female.
Expiratory Reserve Volume
➢ extra 1200 mL in males and 700 mL
in females
➢ amount of air that you can
voluntarily expel after you have
completed a normal, quiet
respiratory cycle
Forced expiratory volume in 1 second
➢ the volume of air that can be exhaled
from the lungs in 1 second with
maximal eff ort following a maximal
inhalation.
➢ chronic obstructive pulmonary
disease (COPD) greatly reduces
FEV1
considerable air remains in the lungs because the
sub atmospheric intrapleural pressure keeps the
alveoli slightly inflated, and some air remains in the
noncollapsible airways.
Residual Volume
➢ volume which cannot be measured
by spirometry
➢ amount of air that remains in your
lungs even after a maximal
exhalation
If the thoracic cavity is opened, the intrapleural
pressure rises to equal the atmospheric pressure
and forces out some of the residual volume.
➢ Air remaining
➢ provides a medical and legal tool for
determining whether a baby is born
dead (stillborn) or died after birth.
Lung Capacities
➢ combinations of specific lung volumes
Inspiratory capacity
➢ amount of air that you can draw into
your lungs after you have completed
a quiet respiratory cycle.
➢ sum of tidal volume and inspiratory
reserve volume
Functional residual capacity
➢ amount of air remaining in your
lungs after you have completed a
quiet respiratory cycle.
➢ the sum of residual volume and
expiratory reserve volume
Vital capacity
➢ maximum amount of air that you
can move into or out of your lungs in
a single respiratory cycle.
➢ the sum of inspiratory reserve
volume, tidal volume, and expiratory
reserve volume
Total lung capacity
➢ total volume of your lungs.
➢ the sum of vital capacity and
residual volume
Minute ventilation
➢ total volume of air inspired and
expired each minute—is tidal volume
multiplied by respiratory rate
➢ not all of the minute ventilation can
be used in gas exchange because
some of it remains in the anatomic
dead space
ANATOMY AND PHYSIOLOGY
FINALS
LECTURE | First Semester
Alveolar ventilation
➢ volume of air per minute that actually
reaches the respiratory zone/reaches the
alveoli
The respiratory minute volume can be increased by
increasing either the tidal volume or the respiratory
rate. In other words, you can breathe more deeply
or more quickly or both.
Exchange of Oxygen and Carbon Dioxide
The exchange of oxygen and carbon dioxide
between alveolar air and pulmonary blood occurs
via passive diffusion.
Dalton’s Law
➢ each gas in a mixture of gases exerts its
own pressure as if no other gases were
present.
DIGESTIVE SYSTEM
group of organs that break down the food we eat
into smaller molecules that can be used by body
cells.
Gastrointestinal (GI) tract (alimentary canal)
➢ continuous tube that extends from the
mouth to the anus through the thoracic and
abdominopelvic cavities.
➢ GI tract organs are in a state of tonus
(sustained contraction)
Organs of the GI tract
1.
2.
3.
4.
5.
6.
Mouth
Pharynx
Esophagus
Stomach
Small Intestine
Large Intestine
Accessory Digestive organs
➢ never come into direct contact with food.
➢ produce or store secretions that flow into
the GI tract through ducts that aid chemical
breakdown of food.
➢ Enzymes secreted by accessory digestive
organs and cells that line the tract break
down the food chemically.
Organs of the Accessory Digestive Organs
1.
2.
3.
4.
5.
6.
Teeth
Tongue
Salivary Glands
Liver
Gallbladder
Pancreas
Digestive Processes/Functions
1. Ingestion
➢ taking foods and liquids into the
mouth (eating).
2. Secretion
➢ release of water, acid,
➢ buffers, and enzymes into lumen of
GI tract.
ANATOMY AND PHYSIOLOGY
LECTURE | First Semester
3. Mobility
➢ Ability of the GI tract to mix food
and secretions and move them
toward the anus
4. Digestion
➢ process of breaking down ingested
food into small molecules that can
be used by body cells.
Mechanical Breakdown
➢ Before food is swallowed,
teeth cut and grind it. The
smooth muscles of the
stomach and small intestine
churn the food to help the
process it on. As a result,
food molecules dissolve and
mix thoroughly with
digestive enzymes.
Chemical Breakdown
➢ Large carbohydrate, lipid,
protein, and nucleic acid
molecules in food are split
into smaller molecules by
hydrolysis
➢ Digestive enzymes produced
catalyze these catabolic
reactions.
5. Absorption
➢ Movement of the products of
digestion from the lumen of the GI
tract into blood or lymph.
➢ substances circulate to cells
throughout the body.
➢ Can be absorbed without digestion
are vitamins, ions, cholesterol, and
water.
6. Defection
➢ materials that were not absorbed in
their journey through the digestive
tract leave the body through the
anus.
➢ Feces is the eliminated wastes
FINALS
LAYERS OF THE GI TRACT
Mucosa
➢ The inner lining of the GI tract and a
mucous membrane
Function:
1) Secrete mucus, digestive enzymes, and
hormones
2) Absorb the end products of digestion into
the blood
3) Protect against infectious disease
Composition
1) Epithelium
➢ nonkeratinized stratified squamous
epithelium that serves a protective
function.
➢ Simple columnar epithelium, which
functions in secretion and
absorption. Present in the stomach
and small intestine.
➢ Located in the epithelium are
exocrine cells that secrete fluid and
mucus into the lumen.
➢ Enteroendocrine cells are also
present which secretes hormones.
2) Lamina Propria
➢ areolar connective tissue containing
many blood and lymphatic vessels.
➢ routes by which nutrients absorbed
into the GI tract reach the other
tissues of the body
➢ supports the epithelium and binds it
to the muscularis mucosae
➢ Contains mucosa-associated
lymphatic tissue (MALT), nodules
contain immune system cells that
protect against disease
➢ present all along the GI tract,
especially in the tonsils, small
intestine, appendix, and large
intestine.
3) Muscularis mucosae
➢ thin layer of smooth muscle fibers
ANATOMY AND PHYSIOLOGY
LECTURE | First Semester
➢ Transforms mucous membrane into
small folds which increases the
surface area for digestion and
absorption
➢ ensure that all absorptive cells are
fully exposed to the contents of the
GI tract
Submucosa
➢ consists of areolar connective tissue that
binds the mucosa to the muscularis.
➢ Has blood and lymphatic vessels that
receive absorbed food molecules.
➢ Located in the submucosa are extensive
network of neurons known as the
submucosal plexus
➢ may also contain glands and lymphatic
tissue
➢ Its abundant elastic fibers enable the
stomach, for example, to regain its normal
shape after temporarily storing a large meal.
Muscularis
➢ In the mouth, pharynx, superior and middle
part of the esophagus contains skeletal
muscle that produces voluntary swallowing.
o Skeletal muscles forms the external
anal sphincter, which permits
voluntary control of defecation
➢ The rest of the tract, the muscularis consists
of smooth muscle that are found in two
sheets
I.
inner sheet of circular fibers
II.
outer sheet of longitudinal fibers.
➢ Between the layers of the muscularis is a
second plexus of neurons—the myenteric
plexus
➢ Involuntary contractions of the
smooth muscle help break down food, mix it
with digestive secretions, and travel along
the tract
Serosa
➢ portions of the GI tract that are suspended
in the abdominal cavity have a superficial
layer.
FINALS
➢ serous membrane composed of areolar
connective tissue and mesothelium.
➢ Also called the visceral peritoneum which
forms a portion of the peritoneum
• esophagus lacks a serosa;
instead, only a single layer of
areolar connective tissue
called the adventitia forms
the superficial layer of this
organ.
NEURAL INNTERVENTION OF THE GI TRACT
GI tract is regulated by an intrinsic set of nerves
known as the enteric nervous system and by an
extrinsic set of nerves that are part of the
autonomic nervous system.
Enteric Nervous System
➢ Brain of the Gut
➢ Neurons extend from the esophagus and
anus.
➢ ENS are arranged into two plexuses:
Myenteric
➢ located between the
longitudinal and circular
smooth muscle layers of the
muscularis
➢ mostly controls GI tract
motility (movement)
Submucosal Plexus
➢ found within the submucosa.
➢ supply the secretory cells of
the mucosal epithelium,
controlling the secretions of
the organs of the GI tract
o consist of motor neurons,
interneurons, and sensory neurons
o Interneurons of the ENS
interconnect the neurons of the
myenteric and submucosal plexuses.
o sensory neurons of the ENS supply
the mucosal epithelium and contain
receptors that detect stimuli in the
lumen of the GI tract.
Wall of the GI Tract contains the following:
ANATOMY AND PHYSIOLOGY
LECTURE | First Semester
1) Chemoreceptors
➢ which respond to certain chemicals
in the food present in the lumen
2) Mechanoreceptors
➢ stretch receptors, that are activated
when food distends (stretches) the
wall of a GI organ.
Autonomic Nervous System
➢ vagus (X) nerves supply parasympathetic
fibers to most parts of the GI tract except
the half portion of the large intestine which
is supplied by parasympathetic fibers from
the sacral spinal cord.
➢ parasympathetic nerves that supply the GI
tract form neural connections with the ENS
➢ Located in the plexus are parasympathetic
preganglionic neurons of the vagus or pelvic
splanchnic nerves synapse with
parasympathetic postganglionic neurons
and Sympathetic postganglionic neurons
synapse with neurons
➢ stimulation of the parasympathetic nerves
that innervate the GI tract causes an
increase in GI secretion and motility by
increasing the activity of ENS neurons.
➢ Sympathetic nerves that supply the GI tract
arise from the thoracic and upper lumbar
regions of the spinal cord
➢ Sympathetic nerves that supply the GI tract
cause a decrease in GI secretion and
motility by inhibiting the neurons of the
ENS.
➢ Emotions such as anger, fear, and anxiety
may slow digestion because they stimulate
the sympathetic nerves.
Gastrointestinal Reflex Pathways
➢ initial components of a typical GI reflex
pathway are sensory receptors
➢ axons of these sensory neurons can synapse
with other neurons located in the ENS, CNS,
or ANS, informing these regions about the
nature of the contents and the degree of
distension (stretching) of the GI tract.
FINALS
➢ neurons of the ENS, CNS, or ANS
subsequently activate or inhibit GI glands
and smooth muscle, altering GI secretion
and motility
Peritoneum
➢ the largest serous membrane of the body.
➢ consists of a layer of mesothelium with an
underlying supporting layer of areolar
connective tissue.
➢ contains large folds that weave between the
viscera.
➢ folds bind the organs to one another and to
the walls of the abdominal cavity.
➢ Contain blood vessels, lymphatic vessels,
and nerves that supply the abdominal
organs.
Division of Peritoneum
1) Parietal Peritoneum
➢ lines the wall of the abdominal cavity
2) Visceral Peritoneum
➢ covers some of the organs in the
cavity and is their serosa
Peritoneal Cavity
➢ Slim space containing lubricating serous
fluid that is between the parietal and
visceral portions of the peritoneum
Retroperitoneal
➢ covered by peritoneum only on their
anterior surfaces; they are not in the
peritoneal cavity. The organs are kidneys,
ascending and descending colons of the
large intestine, duodenum of the small
intestine, and pancreas.
Five Major Peritoneal Folds
1) Greater omentum
➢ coils of the small intestine like a
“fatty apron” and drapes over the
transverse colon
➢ Longest peritoneal fold.
ANATOMY AND PHYSIOLOGY
LECTURE | First Semester
➢ double sheet that folds back on itself
which has 4 layers.
➢ Contains adipose tissues which can
greatly expand with weight gain,
contributing to the characteristic
“beer belly”
➢ Lymph nodes contribute
macrophages and antibodyproducing plasma cells that help
combat and contain infections of the
GI tract
2) Falciform ligament
➢ Attaches from the liver to the
anterior abdominal wall and
diaphragm
3) Lesser omentum
➢ pathway for blood vessels entering
the liver and contains the hepatic
portal vein, common hepatic artery,
and common bile duct, along with
some lymph nodes.
➢ Connects the stomach and
duodenum.
4) Mesentery
➢ Fan-shaped fold
➢ binds the jejunum and ileum of the
small intestine to the posterior
abdominal wall
➢ most massive peritoneal fold
➢ typically, laden with fat and
contributes extensively to the large
abdomen in obese individuals.
Functions:
• provide routes for blood
vessels, lymphatics, and
nerves to reach the digestive
viscera.
• hold organs in place.
• store fat
5) Mesocolon
➢ Two separate folds
➢ bind the transverse colon (transverse
mesocolon) and sigmoid colon
(sigmoid mesocolon) of the large int
and posterior abdominal wall.
➢ Carries blood and lymphatic vessels
to the intestines.
FINALS
➢ The mesentery and mesocolon work
together to keep the intestines
loosely in place, allowing movement
as muscular contractions mix and
move luminal contents along the GI
tract.
Mouth
➢ formed by the cheeks, hard and soft palates,
and tongue
Cheeks
➢ covered externally by skin and internally by
a mucous membrane, which consists of
nonkeratinized stratified squamous
epithelium
➢ Buccinator muscles and connective tissue lie
between the skin and mucous membranes of
the cheeks.
Lips (Labia)
➢ folds surrounding the opening of the mouth.
➢ contain the orbicularis oris muscle
➢ Contraction of the buccinator muscles in the
cheeks and orbicularis oris muscle in the
lips helps keep food between the upper and
lower teeth. These muscles also assist in
speech.
labial frenulum
➢ Mucous membrane where the inner
surface of each lip is attached to its
corresponding gum.
Oral Vestibule
➢ Space between the cheeks, lips, gums, and
teeth
➢
Oral cavity proper
➢ space that extends from the gums and teeth
to the fauces.
Fauces is the opening between the oral
cavity and oropharynx.
Palate
ANATOMY AND PHYSIOLOGY
LECTURE | First Semester
➢ wall that separates the oral cavity from the
nasal cavity, and forms the roof of the
mouth.
➢ This structure makes it possible to chew and
breathe at the same time.
Hard Palate (bony)
➢ Formed by the maxillae and palatine
bones
➢ Forms most of the roof of the mouth
➢ forms a bony partition between the
oral and nasal cavities.
Soft Palate (muscular)
➢ an arch-shaped muscular partition
between the oropharynx and
nasopharynx that is lined with
mucous membrane.
➢ Forms the posterior portion of the
mouth
Uvula
➢ Fingerlike muscular structure which is
hanging
➢ The soft palate and uvula close the
nasopharynx and preventing swallowed
foods and liquids from entering the nasal
cavity
Salivary Glands
➢ gland that releases a secretion called saliva
into the oral cavity.
➢ Composed of two types of secretory cells:
serous and mucous
Serous Cells
➢ produce a watery secretion containing
enzymes, ions, and a tiny bit of mucin
Mucous Cells
➢ produce mucus, a stringy, viscous solution
Saliva
FINALS
➢ Secreted to keep the mucous membranes of
the mouth and pharynx moist and to cleanse
the mouth and teeth.
➢ Glands that have a contribution to saliva
includes: labial, buccal, and palatal glands
in the lips, cheeks, and palate, respectively,
and lingual glands in the tongue. These are
called Minor or intrinsic salivary glands.
➢ Most of saliva is secreted by major salivary
glands.
➢ Contains IgA antibodies, Lysozyme, and
defensins which protects against
microorganisms.
Mucins
➢ Glycoproteins give saliva its lubricating
action
Major Salivary glands
➢ Located beyond the oral mucosa into ducts
that lead to the oral cavity.
➢ paired compound alveolar or tubuloalveolar
glands that develop from the oral mucosa
and remain connected to it by ducts
Pairs of the major salivary glands.
➢ Parotid gland
➢ Located inferior and anterior to the
ears, between the skin and the
masseter muscle.
➢ secretes saliva into the oral cavity via
a parotid duct
➢ consist of serous acini only
➢ Branches of the facial nerve run
through the parotid gland on their
way to the muscles of facial
expression
➢ Contains mostly serous cells
➢ secrete a watery (serous) liquid
containing salivary amylase.
Mumps
➢ inflammation of the parotid glands
caused by a viral infection.
➢
➢ Submandibular gland
ANATOMY AND PHYSIOLOGY
LECTURE | First Semester
➢ Found in the floor of the mouth
➢ submandibular ducts, run under the
mucosa on either side of the midline
of the floor of the mouth and enter
the oral cavity proper lateral to the
lingual frenulum
➢ consist mostly of serous acini
(serous fluid–secreting portions of
gland) and a few mucous acini
(mucus-secreting portions of gland)
➢ Contains mostly serous cells plus
some mucous cells
➢ secrete a fluid that contains amylase
but is thickened with mucus
➢ Sublingual glands
➢ beneath the tongue and superior to
the submandibular glands
➢ lesser sublingual ducts, open into the
floor of the mouth in the oral cavity
proper
➢ consist of mostly mucous acini and a
few serous acini
➢ contain mostly mucous cells.
➢ secrete a much thicker fluid that
contributes only a small amount of
salivary amylase.
About 70 percent of saliva comes from the
submandibular salivary glands. Another 25 percent
comes from the parotids, and 5 percent from the
sublingual salivary glands
Composition and Functions of Saliva
➢ Made up of 99.5% water and 0.5% solutes.
➢ solutes are ions, including sodium,
potassium, chloride, bicarbonate, and
phosphate
➢ provides a medium for dissolving foods so
that they can be tasted by gustatory
receptors
➢ Chloride ions in the saliva activate salivary
amylase
➢ Salivary glands help remove waste
molecules from the body, which is because
of the presence of urea and uric acid in
saliva
➢
FINALS
Salivary amylase
➢ enzyme that starts the breakdown of starch
in the mouth into maltose, maltotriose, and
α-dextrin
Immunoglobulin A
➢ prevents attachment of microbes so they
cannot penetrate the epithelium
Salivation
➢
➢
➢
➢
secretion of saliva
controlled by the autonomic nervous system
parasympathetic stimulation promotes
continuous secretion of a moderate amount
of saliva, which keeps the mucous
membranes moist and lubricates the
movements of the tongue and lips during
speech.
➢
➢ Sympathetic stimulation dominates during
stress, resulting in dryness of the mouth.
➢ chemoreceptors and mechanoreceptors in
the mouth send signals to the salivatory
nuclei in the brain stem (pons and medulla).
➢ Returning parasympathetic impulses in
fibers of the facial (VII) and
glossopharyngeal (IX) nerves stimulate the
secretion of saliva.
➢ In contrast to Parasympathetic control, the
sympathetic division (specifically fibers in
T1-T3) causes release of a thick, mucin-rich
saliva.
➢ Strong activation of the sympathetic
division constricts blood vessels serving the
salivary glands and almost completely
inhibits saliva release, causing a dry mouth.
Tongue
➢ accessory digestive organ composed of
skeletal muscle covered with mucous
membrane.
➢ divided into symmetrical lateral halves by a
median septum
ANATOMY AND PHYSIOLOGY
FINALS
LECTURE | First Semester
➢ Each half of the tongue consists of an
identical complement of extrinsic and
intrinsic muscles
Extrinsic muscles for the tongue
➢ move the tongue from side to side and in
and out to maneuver food for chewing,
shape the food into a rounded mass, and
force the food to the back of the mouth for
swallowing
➢ connective tissues in the tongue, include the
hyoglossus, genioglossus, and styloglossus
muscles
Intrinsic muscles of the tongue
➢ alter the shape and size of the tongue for
speech and swallowing.
➢ intrinsic muscles include the longitudinalis
superior, longitudinalis inferior, transversus
linguae, and verticalis linguae muscles
Lingual frenulum
➢ fold of mucosa
Ankyloglossia
➢ lingual frenulum is abnormally short
or rigid
➢ person is said to be “tongue-tied”
because of the resulting impairment
to speech. It can be corrected
surgically.
2. contain keratin, which stiffens them
and gives the tongue its whitish
appearance.
Fungiform papillae
➢ mushroorn-shaped
➢ Each has a vascular core that gives it a
reddish hue.
Vallate papillae
➢ resemble the fungiforrn papillae but
have an additional surrounding furrow.
Foliate Papillae
➢ located on the lateral aspects of the
posterior tongue
Fungiform, vallate, and foliate papillae house taste
buds.
Terminal sulcus
➢ groove that distinguishes the portion of the
tongue that lies in the oral cavity from its
posterior portion in the oropharynx
Lingual glands
➢ secrete both mucus and a watery serous
fluid that contains the enzyme lingual lipase
Lingual lipase
➢ acts on as much as 30% of dietary
triglycerides (fats and oils) and
converts them to simpler fatty acids
and diglycerides.
➢ enabling it to start lipid digestion
immediately
➢ continue to break down lipids—
specifically, triglycerides—for a
considerable time after the food
reaches the stomach
Papillae
➢ covers the dorsum (upper surface) and
lateral surfaces of the tongue
➢ the lamina propria covered with stratified
squamous epithelium
➢ lack taste buds, but they contain receptors
for touch
Filiform papillae
1. roughen the tongue surface, helping
us lick semisolid foods and providing
friction for manipulating foods
Teeth
➢ surfaces carry out chewing, or mastication
of food.
ANATOMY AND PHYSIOLOGY
LECTURE | First Semester
➢ Accessory digestive organs located in
sockets of the alveolar processes
Gingivae (Gums)
➢ covers the alveolar processes
Periodontal ligament
➢ lines the sockets
➢ Consists of dense fibrous connective tissue
that anchors the teeth to the socket walls
and acts as a shock absorber during
chewing.
Major external regions
Crown
➢ the visible portion above the level of the
gums.
Roots
➢ one to three sockets are embedded here.
Neck
➢ constricted junction of the crown and root
near the gum line.
FINALS
➢ contains unique radial striations called
dentinal tubules.
o tubule contains an elongated process
of an odontoblast, cell type that
secretes and maintains the dentin.
Enamel
➢ covers the dentin
➢ consists primarily of calcium phosphate and
calcium carbonate
➢ higher content of calcium salts
➢ hardest substance in the body
➢ nonliving and cannot repair itself
Function
➢ serves to protect the tooth from the wear
and tear of chewing.
➢ protects against acids that can easily
dissolve dentin.
Cementum
➢ attaches the root to the periodontal
ligament
➢ also covers the dentin
Pulp Cavity
➢ space inside the dentin
➢ lies within the crown and is filled with pulp
Pulp
➢ connective tissue containing blood
vessels, nerves, and lymphatic
vessels
Root Canals
Dentin
➢ forms the majority of the tooth
➢ consists of a calcified connective tissue that
gives the tooth its basic shape and rigidity.
➢ higher content of hydroxyapatite (70%
versus 55% of dry weight).
➢ Narrow extensions of the pulp cavity
➢ has an opening at its base, the apical
foramen.
▪ Through the foramen the
blood vessels, lymphatic
vessels, and nerves enter a
tooth.
▪ The blood vessels bring
nourishment, the lymphatic
ANATOMY AND PHYSIOLOGY
FINALS
LECTURE | First Semester
vessels offer protection, and
the nerves provide sensation
All deciduous teeth should be lost between the ages
6 and 12 and are replaced by the permanent teeth.
Endodontics
Permanent Dentition
➢ concerned with the prevention, diagnosis,
and treatment of diseases that affect the
pulp, root, periodontal ligament, and
alveolar bone
Orthodontics
➢ branch of dentistry that is concerned with
the prevention and correction of abnormally
aligned teeth
Periodontics
➢ branch of dentistry concerned with the
treatment of abnormal conditions of the
tissues immediately surrounding the teeth,
such as gingivitis.
Dentitions
Humans have two set of teeth: deciduous and
permanent.
Deciduous Teeth
➢ called primary teeth, milk teeth, or baby
teeth
➢ Begins at 6 months of age. Two teeth appear
each month after the other until 20 are
present.
Incisors
➢ chisel-shaped and adapted for
cutting into food.
Canines (cuspids or eye-teeth)
➢ Pointed surface called a cusp.
Canines are used to tear and shred
food.
Premolars (bicuspids)
➢ have four cusps
➢ Maxillary (upper) molars have three
roots; mandibular (lower) molars
have two roots.
➢ crush and grind food to prepare it
for swallowing.
➢ contains 32 teeth that erupt between age 6
and adulthood.
➢ deciduous molars are replaced by the first
and second premolars
o have two cusps and one root and are
used for crushing and grinding.
➢ Permanent molars don’t replace premolars
o first permanent molars at age 6 (sixyear molars)
o the second permanent molars at age
12 (twelve-year molars)
o third permanent molars (wisdom
teeth) after age 17 or not at all.
Teeth disease
Dental caries (tooth decay)
➢ result of breakdown of enamel by acids
produced by bacteria on the tooth surface
Periodontal disease
➢ inflammation and degeneration of the
periodontal ligaments, gingiva, and alveolar
bone.
Mechanical and Chemical Digestion in the Mouth
Mastication
➢ Mechanical digestion in the mouth
➢ food is manipulated by the tongue, ground
by the teeth, and mixed with saliva.
➢ partly voluntary and partly reflexive
Bolus
➢ easily swallowed food mass
Salivary amylase and Lingual lipase contribute to
chemical digestion in the mouth.
Salivary amylase initiate breakdown of starch. Only
monosaccharides can be absorbed into the
bloodstream. Thus, ingested disaccharides and
starches must be broken down into
ANATOMY AND PHYSIOLOGY
LECTURE | First Semester
monosaccharides. Salivary amylase is to begin
starch digestion by breaking down starch into
smaller molecules such as the disaccharide maltose,
the trisaccharide maltotriose, and short-chain
glucose polymers called α-dextrins.
Lingual lipase, which is secreted by lingual glands
in the tongue. Enzymes becomes activated in the
acidic environment of the stomach and starts to
work after food is swallowed. It breaks down
dietary triglycerides (fats and oils) into fatty acids
and diglycerides. A diglyceride consists of a glycerol
molecule that is attached to two fatty acids.
Pharynx
➢ composed of skeletal muscle and lined by
mucous membrane.
➢ The nasopharynx functions only in
respiration, but both the oropharynx and
laryngopharynx have digestive as well as
respiratory functions.
Oropharynx
➢ Where swallowed food passe3s through
from the mouth.
Laryngopharynx
➢ muscular contractions of these areas help
propel food into the esophagus and then
into the stomach.
Muscles in the Pharynx
1. The pharyngeal constrictor muscles push
the bolus toward
2. and into the esophagus.
3. The palatopharyngeus and stylopharyngeus
muscles elevate the larynx.
4. The palatal muscles elevate the soft palate
and adjacent
5. portions of the pharyngeal wall.
Esophagus
FINALS
➢ pierces the diaphragm through an opening
called the esophageal hiatus
➢ joins the stomach at the cardial orifice
o Cardial orifice is surrounded by the
gastroesophageal or cardiac
sphincter
o acts as a sphincter
o Mucous cells on both sides of the
sphincter help protect the esophagus
from reflux of stomach acid.
Histology of Esophagus
Mucosa
➢ consists of nonkeratinized stratified
squamous epithelium, lamina propria
(areolar connective tissue), and a
muscularis mucosae (smooth muscle)
➢ The mucosa of the esophagus near the
stomach consists of mucous glands.
➢ stratified squamous epithelium give
protection against abrasion and wear and
tear from food particles that enter the
mouth.
Submucosa
➢ contains areolar connective tissue, blood
vessels, and mucous glands.
➢ contains mucus-secreting esophageal
glands.
o secrete mucus that "greases" the
esophageal walls and aids food
passage.
Muscularis
➢ the superior third of the esophagus is
skeletal muscle
➢ intermediate third is skeletal and
smooth muscle
➢ inferior third is smooth muscle
➢ At each end of the esophagus,
muscularis becomes slightly more
prominent and forms two sphincters:
Upper esophageal sphincter (UES)
➢ collapsible muscular tube
➢ consists of skeletal muscle
ANATOMY AND PHYSIOLOGY
LECTURE | First Semester
➢ regulates the movement of
food from the pharynx into
the esophagus
Lower esophageal (cardiac)
sphincter (LES)
➢ consists of smooth muscle
and is near the heart
➢ Regulates the movement of
food from the esophagus into
the stomach.
Adventitia
➢ Superficial layer of the esophagus
➢ attaches the esophagus to surrounding
structures.
➢ areolar connective tissue of this layer is not
covered by mesothelium
➢ composed entirely of connective tissue,
which blends with surrounding structures
along its route
Physiology of the Esophagus
➢ secretes mucus and transports food into the
stomach
➢ does not produce digestive enzymes, and it
does not carry on absorption
Swallowing (Deglutition)
➢ mechanism that moves food from the mouth
into the stomach.
Swallowing reflex
➢ begins when tactile receptors on the palatal
arches and uvula are stimulated by the
passage of the bolus.
Swallowing center
➢ information is relayed to the swallowing
center of the medulla oblongata over the
trigeminal (CN V) and glossopharyngeal
(CN IX) nerve
Divided into three phases: Voluntary, Pharyngeal
stage, esophageal stage.
FINALS
Voluntary Stage
➢ bolus is forced to the back of the oral cavity
and into the oropharynx by the movement
of the tongue upward and backward against
the palate
Pharyngeal Stage
➢ passage of the bolus into the oropharynx.
This is where the pharyngeal stage begins.
➢ bolus stimulates receptors in the
oropharynx, which send impulses to the
deglutition center in the medulla oblongata
and lower pons of the brain stem.
➢ returning impulses cause the soft palate and
uvula to move upward to close off the
nasopharynx
o which prevents swallowed foods and
liquids from entering the nasal
cavity.
➢ epiglottis closes off the opening to the
larynx
o which prevents the bolus from
entering the rest of the respiratory
tract.
➢ bolus moves through the oropharynx and
the laryngopharynx
➢ Upper esophageal sphincter relaxes, the
bolus moves into the esophagus.
Esophageal Stage
➢ Begins when the bolus enters the
esophagus.
➢ Peristalsis pushes the bolus onward.
o Peristalsis progression of
coordinated contractions and
relaxations of the circular and
longitudinal layers of the muscularis
▪ occurs in other tubular
structures, including other
parts of the GI tract to the
anus and the ureters, bile
ducts, and uterine tubes; in
the esophagus it is
▪ controlled by the medulla
oblongata
ANATOMY AND PHYSIOLOGY
LECTURE | First Semester
➢ circular muscle fibers contract, constricting
the esophageal wall and squeezing the bolus
toward the stomach
➢ Longitudinal fibers inferior to the bolus also
contract, which shortens this inferior
section and pushes its walls outward so it
can receive the bolus.
➢ contractions are repeated in waves that
push the food toward the stomach. Steps are
repeated until the bolus reaches the lower
esophageal sphincter muscles.
➢ lower esophageal sphincter relaxes and the
bolus moves into the stomach
➢ Secrets mucus which lubricates esophagus
for smooth passage of bolus
Stomach
➢ directly inferior to the diaphragm in the
abdomen.
➢ connects the esophagus to the duodenum,
the first part of the small intestine.
➢ forces a small quantity of material into the
first portion of the small intestine.
➢ digestion of starch and triglycerides
continues, digestion of proteins begins, the
semisolid bolus is converted to a liquid, and
certain substances are absorbed
➢ served by the autonomic nervous system.
o Sympathetic fibers from thoracic
splanchnic nerves are relayed
through the celiac ganglion
o Parasympathetic fibers are supplied
by the vagus nerve
➢ arterial supply of the stomach is provided by
branches (gastric and splenic) of the celiac
trunk
Gastroenterology
➢ medical specialty that deals with the
structure, function, diagnosis, and
treatment of diseases of the stomach and
intestines
Physiology of the Stomach
➢ serve as a mixing chamber and holding
reservoir.
FINALS
➢ Mixes saliva, food, and gastric juice to form
chyme
➢ Secretes gastric juice, which contains HCl
(kills bacteria and denatures proteins),
pepsin (begins the digestion of proteins),
intrinsic factor (aids absorption of vitamin
B12), and gastric lipase (aids digestion of
triglycerides).
➢ Secretes gastrin into blood.
Anatomy of the Stomach
Main Regions:
1) Cardia
➢ surrounds the surrounds the cardial
orifice into the stomach
➢ abundant mucous glands.
➢ secretions coat the connection with
the esophagus and help protect that
tube from the acid and enzymes of
the stomach.
2) Fundus
➢ rounded portion superior to and to
the left of the cardia
3) Body
➢ Inferior to the fundus
➢ the large central portion of the
stomach
➢ acts as a mixing tank for ingested
food and secretions produced in the
stomach
➢ Gastric (gaster, stomach) glands in
the fundus and body secrete most of
the acid and enzymes involved in
gastric digestion
4) Pyloric Part
➢ Glands present in here secrete
mucus and important digestive
hormones, including gastrin, a
hormone that stimulates gastric
glands
➢ Has three regions:
Pyloric Antrum (1st region)
➢ connects to the body of the
stomach
Pyloric Canal (2nd region)
➢ leads to the third region
ANATOMY AND PHYSIOLOGY
FINALS
LECTURE | First Semester
Pylorus (3rd region)
➢ which in turn connects to the
duodenum
➢ riddled with fat deposits which give
the appearance of a lacy apron.
➢ contains large collections of lymph
nodes.
Pyloric Glands
➢ contain D cells, which release somatostatin.
o a hormone that inhibits the release
of gastrin.
Rugae
➢ a large fold where the mucosa of the
stomach lies when it’s empty because the
stomach collapses inward
Pyloric sphincter
➢ Where the pylorus communicates with the
duodenum of the small intestine
➢ A smooth muscle sphincter
➢ Opens to permit passage of chyme into
duodenum.
o Regulates passage of chyme from
stomach to duodenum; prevents
backflow of chyme from duodenum
to stomach.
Lesser Curvature
➢ concave medial border of the stomach
Greater Curvature
➢ convex lateral border
Omenta
➢ extends from the curvatures
➢ help tether the stomach to other digestive
organs and the body wall
Lesser omentum
➢ From the liver to the lesser curvature
of the stomach, where it becomes
continuous with the visceral
peritoneum covering the stomach.
Greater omentum
➢ drapes inferiorly from the greater
curvature of the stomach to cover
the coils of the small intestine
Histology of the Stomach
Mucosa
➢ surface of the mucosa is a layer of simple
columnar epithelial cells called surface
mucous cells
➢ Contains a lamina propria (areolar
connective tissue) a muscularis mucosae
(smooth muscle)
➢ Epithelial cells extend down which form
columns of secretory cells called gastric
glands.
Gastric Glands
➢ open into the bottom of narrow
channels called gastric pits
➢ Secretion from the gastric glands
flow to each gastric pit and then into
the lumen
➢ contain three types of exocrine gland
cells:
Mucous neck cells
➢ secrets mucus
o Forms protective
barrier that prevents
digestion of stomach
wall
o Small quantity of
water, ions, shortchain fatty acids, and
some drugs enter
bloodstream.
Parietal cells
➢ produce intrinsic factor
o Needed for
absorption of vitamin
B12 (used in red
blood cell formation,
or erythropoiesis).
➢ Secrete hydrochloric acid.
ANATOMY AND PHYSIOLOGY
LECTURE | First Semester
o
FINALS
Kills microbes in
food; denatures
proteins; converts
pepsinogen into
pepsin
o
Chief cells (Zymogenic cells)
➢ secrete pepsinogen
o Pepsin (activated
form) breaks down
proteins into
peptides.
➢ Secrete gastric lipase
o Splits triglycerides
into fatty acids and
monoglycerides
➢ stomachs of newborn infants
(but not of adults) produce
rennin, also known as
chymosin, and gastric lipase.
o Rennin coagulates
milk proteins. Gastric
lipase initiates the
digestion of milk fats
Enteroendocrine cells
➢ release a variety of chemical
messengers directly into the
interstitial fluid of the lamina
propria.
o for example,
histamine and
serotonin, act locally
as paracrine
➢ Produce Gastrin
➢ hormone, plays essential
roles in regulating
sto1nach secretion and
motility
➢ Produced by G cells
Gastric Juice
➢ form by the secretion of the
mucous, parietal, and chief
cells
Stimulates parietal
cells to secrete HCl
and chief cells to
secrete pepsinogen;
contracts lower
esophageal sphincter,
increases motility of
stomach, and relaxes
pyloric sphincter.
Submucosa
➢ composed of areolar connective tissue.
Muscularis
➢ has three layers of smooth muscle:
• an outer longitudinal layer
• a middle circular layer
• an inner oblique layer.
o limited primarily to the body
of the stomach.
Serosa
➢ composed of simple squamous epithelium
(mesothelium) and areolar connective tissue
➢ portion of the serosa covering the stomach
is part of the visceral peritoneum
Mechanical and Chemical Digestion in the Stomach
Propulsion
➢ Process where peristaltic wave moves
gastric contents from the body of the
stomach down into the antrum.
Retropulsion
➢ a process where pyloric sphincter normally
remains almost, but not completely, closed.
Because most food particles in the stomach
initially are too large to fit through the
narrow pyloric sphincter, they are forced
back into the body of the stomach.
➢ Another round of propulsion then occurs,
moving the food particles back down into
the antrum. If the food particles are still too
ANATOMY AND PHYSIOLOGY
LECTURE | First Semester
large to pass through the pyloric sphincter,
retropulsion occurs again as the particles
are squeezed back into the body of the
stomach.
o result of these movements is that
gastric contents are mixed with
gastric juice.
Chyme
➢ a soupy liquid when gastric contents are
reduced
Gastric emptying
➢ the passage of enough chyme through the
pyloric sphincter.
➢ a slow process: only about 3 mL of chyme
moves through the pyloric sphincter at a
time.
Churning action mixes chyme with acidic gastric
juice, inactivating salivary amylase and activating
lingual lipase produced by the tongue, which starts
to digest triglycerides into fatty acids and
diglycerides.
Secretion of hydrochloric acid is the net effect of
secretion of hydrogen ions and chloride ions
separately into the stomach lumen.
Proton Pumps
➢ Powered by H+–K+ ATPase
➢ This actively hydrogen ion (H+) into the
lumen while bringing potassium ions into
the cell.
➢ Cl− and K+ diff use out into the lumen
through Cl− and K+ channels
Carbonic anhydrase
➢ An enzyme which is plentiful in the parietal
cells.
➢ Catalyzes the formation of carbonic acid
(H2CO3) from water (H2O) and carbon
dioxide (CO2).
HCl secretion by parietal cells can be stimulated by
several sources:
FINALS
1) acetylcholine (ACh) released by
parasympathetic neurons
2) gastrin secreted by G cells
3) histamine, which is a paracrine substance
released by mast cells in the nearby lamina
propria
a. histamine acts synergistically,
enhancing the effects of
acetylcholine and gastrin.
Receptors for all three substances are present in the
plasma membrane.
Histamine receptors – H2
➢ used to treat gastric ulcers caused by
hyperacidity.
HCl partially unfolds proteins in food and
stimulates the secretion of hormones that promote
the flow of bile and pancreatic juice
Pepsin
➢ only proteolytic (protein-digesting) enzyme
in the stomach
➢ Secreted by parietal cells
➢ “Cut” certain peptide bonds between amino
acids, breaking down a protein chain of
many amino acids into smaller peptide
fragments.
➢ most effective in the very acidic
environment of the stomach (pH 2); it
becomes inactive at a higher pH.
➢ secreted in an inactive form called
pepsinogen
o cannot digest the proteins in the
chief cells
o Pepsinogen is not converted into
active pepsin until it comes in
contact with hydrochloric acid
secreted by parietal cells or active
pepsin molecules.
Gastric lipase
ANATOMY AND PHYSIOLOGY
LECTURE | First Semester
➢ splits triglycerides (fats and oils) in fat
molecules into fatty acids and
monoglycerides.
➢ which has a limited role in the adult
stomach, operates best at a pH of 5–6.
Monoglycerides
➢ consists of a glycerol molecule that is
attached to one fatty acid molecule.
Pancreatic lipase
➢ enzyme secreted by the pancreas into the
small intestine
Epithelial cells are impermeable to most materials
which is why only small amounts of nutrients are
absorbed in the stomach. Mucous cells of the
stomach absorb some water, ions, and short-chain
fatty acids, as well as certain drugs (especially
aspirin) and alcohol.
FINALS
Tail
Pancreatic Juice
➢ secreted by exocrine cells into small ducts
that ultimately unite to form two larger
ducts, the pancreatic duct and the accessory
duct.
Pancreatic Duct
➢ larger of the two ducts
➢ joins the common bile duct from the liver
and gallbladder and enters the duodenum
Hepatopancreatic Duct (ampulla of Vater)
➢ dilated common duct
➢ opens on an elevation of the duodenal
mucosa known as the major duodenal
papilla
Sphincter of the hepatopancreatic ampulla
Regulation of Gastric Activity
➢ a mass of smooth muscle
surrounding the ampulla
➢ regulates the passage of pancreatic
juice and bile through the
hepatopancreatic ampulla into the
duodenum of the small intestine.
1) controlled by the CNS
2) Regulated by short reflexes of the enteric
nervous system, coordinated in the wall of
3) the stomach regulated by hormones of the
digestive tract
Pancreas
➢ accessory digestive organ
➢ a retroperitoneal gland
Anatomy of the Pancreas
➢ consists of a head, a body, and a tail and is
usually connected to the duodenum of the
small intestine by two ducts.
Head
➢ expanded portion of the organ near the
curve of the duodenum
Body
➢ superior to and to the left of the head
Accessory Duct
➢ leads from the pancreas and empties into
the duodenum
Histology of the Pancreas
➢ made up of small clusters of glandular
epithelial cells
Acini
➢ Constitute the exocrine portion of the organ
➢ Cells within secrets a mixture of fluid and
digestive enzymes called pancreatic juice.
Pancreatic islets
➢ form the endocrine portion of the pancreas.
ANATOMY AND PHYSIOLOGY
LECTURE | First Semester
➢ secrete the hormones glucagon, insulin,
somatostatin, and pancreatic polypeptide
Composition and Functions of Pancreatic Juice
Pancreatic juice
➢ a clear, colorless liquid consisting mostly of
water, some salts, sodium bicarbonate, and
several enzymes.
➢ sodium bicarbonate gives pancreatic juice a
slightly alkaline pH
Enzymes
1. Pancreatic amylase
• starch-digesting enzyme
2. Trypsin, chymotrypsin,
carboxypeptidase, elastase
• digest proteins into peptides
• Trypsin acts on the inactive
precursors (called
• chymotrypsinogen,
procarboxypeptidase, and
proelastase) to produce
chymotrypsin, carboxypeptidase,
and elastase, respectively.
3. pancreatic lipase
• triglyceride–digesting enzyme in
adults
4. ribonuclease
• nucleic acid–digesting enzymes
5. deoxyribonuclease
• digest ribonucleic acid (RNA)
and deoxyribonucleic acid (DNA)
into nucleotides
Trypsinogen
➢ inactivated form which secretes trypsin
➢ reaches the lumen of the small intestine, it
encounters an activating brush-border
enzyme called enterokinase
o splits off part of the trypsinogen
molecule to form trypsin.
Trypsin inhibitor
FINALS
➢ secreted by Pancreatic acinar cells
➢ t combines with any trypsin formed
accidentally in the pancreas or in pancreatic
juice and blocks its enzymatic activity
Liver and Gallbladder
Liver
➢ heaviest gland of the body
Anatomy of Liver
➢ Divided into two principal lobes
Right lobe
➢ visible on all liver surfaces
Left lobe
➢ include an inferior quadrate lobe
and a posterior caudate lobe
Falciform ligament
➢ a mesentery
➢ separates the right and left lobes anteriorly
and suspends the liver from the diaphragm
and anterior abdominal wall
Ligamentum teres
➢ remnant of the umbilical vein of the
fetus
➢ fibrous cord extends from the liver to
the umbilicus.
Right and left coronary ligaments
➢ narrow extensions of the parietal
peritoneum that suspend the liver from the
diaphragm.
Porta
➢ which blood vessels, ducts, and nerves enter
or exit the liver
Liver receives blood from 2 sources:
Hepatic artery
ANATOMY AND PHYSIOLOGY
LECTURE | First Semester
➢ takes oxygen-rich blood to the liver,
which supplies liver cells with
oxygen.
Hepatic veins
➢ where blood exits from the liver
which empty to the inferior vena
cava
Gallbladder
➢ a pear-shaped sac that is located in a
depression of the posterior surface of the
liver.
Anatomy of the Gallbladder
broad fundus
➢ projects inferiorly beyond the inferior
border of the liver
FINALS
endothelial-lined vascular spaces called
hepatic sinusoids
Bile
➢ a yellow, brownish, or olive-green liquid
secreted by hepatocytes, serves as both
an excretory product and a digestive
secretion.
Bile canaliculi
➢ small ducts between hepatocytes that collect
bile
Transportation of bile
Bile canaliculi
Bile ductules
Bile ducts
o
Body
➢ central portion
Neck
➢ tapered portion
Histology of the Liver and Gallbladder
Liver is composed of the following:
Hepatocytes
➢ major functional cells of the liver
➢ perform a wide array of metabolic,
secretory, and endocrine functions.
➢ Grooves in the cell membranes provide
spaces for canaliculi into which the
hepatocytes secrete bile.
Hepatic laminae
➢ formed by hepatocytes.
➢ Complex three-dimensional
arrangements
➢ highly branched, irregular structures.
➢ plates of hepatocytes one cell thick
bordered on either side by the
merge and eventually form the larger
right and left hepatic ducts
o which unite and exit the liver as
the common hepatic duct
Common bile duct
joins the cystic duct from the
gallbladder to form the common bile
duct.
Bile enters duodenum of the small intestine
to participate in digestion.
o
Hepatic sinusoids
➢ highly permeable blood capillaries
➢ Located between rows of hepatocytes that
receive from branches of the hepatic artery
and nutrient-rich deoxygenated blood from
branches of the hepatic portal vein.
➢ converge and deliver blood into a central
vein
o From central veins the blood flows
into the hepatic veins, which drain
into the inferior vena cava
ANATOMY AND PHYSIOLOGY
LECTURE | First Semester
Stellate reticuloendothelial cells (hepatic
macrophages)
➢ fixed phagocytes
➢ destroy worn-out white and red
blood cells, bacteria, and other
foreign matter in the venous blood
draining from the gastrointestinal
tract
Portal triad
➢ includes r, a bile duct, branch of the hepatic
artery, and branch of the hepatic vein
anatomical and functional units
Hepatic lobule
➢ functional unit of the liver.
➢ model is based on a description of the liver
of adult pigs.
➢ shaped like a hexagon
o its center is the central vein, and
radiating out from it are rows of
hepatocytes and hepatic sinusoids.
o In the three corners of the hexagon
is a portal triad.
Portal lobule
➢ emphasizes the exocrine function of the
liver, that is, bile secretion.
➢ bile duct of a portal triad is taken as the
center
➢ A triangular in shape defined by three
imaginary straight lines that connect three
central veins
Hepatic acinus
➢ smallest structural and functional unit of
the liver.
➢ preferred structural and functional unit of
the liver
➢ approximately oval mass that includes
portions of two neighboring hepatic lobules.
➢ short axis of the hepatic acinus is defined by
branches of the hepatic artery, vein, and bile
ducts
FINALS
➢ long axis of the acinus is defined by two
imaginary curved lines, which connect the
two central veins closest to the short axis
➢ Hepatocytes arranged in three zones around
the short axis, with no sharp boundaries
between them
Zone 1
➢ Cells in zone 1 are closest to the
branches of the portal triad and the
first to receive incoming oxygen,
nutrients, and toxins from incoming
blood.
➢ first ones to take up glucose and
store it as glycogen after a meal and
break down glycogen to glucose
during fasting
➢ first to show morphological changes
following bile duct obstruction or
exposure to toxic substances.
➢ Last ones to die if circulation is
impaired and the first ones to
regenerate
Zone 2
➢ structural and functional
characteristics intermediate between
the cells in zones 1 and 3
Zone 3
➢ zone 3 are farthest from branches of
the portal triad and are the last to
show the effects of bile obstruction
➢ first ones to show the effects of
impaired circulation, and the last
ones to regenerate.
➢ First to show evidence of fat
accumulation.
Hepatic acinus model provides a logical description
and interpretation of
(1) patterns of glycogen storage and release
(2) toxic effects, degeneration, and regeneration
relative to the proximity of the acinar zones to
branches of the portal triad.
ANATOMY AND PHYSIOLOGY
LECTURE | First Semester
Gallbladder
Mucosa
➢ consists of simple columnar epithelium
arranged in rugae.
➢ middle, muscular coat of the wall consists of
smooth muscle fibers.
o Contraction of the smooth muscle
fibers ejects the contents of the
gallbladder into the cystic duct.
Submucosa
➢ wall of the gallbladder lacks a submucosa
visceral peritoneum.
➢ gallbladder’s outer coat
Function of the Gallbladder
➢ store and concentrate the bile produced by
the liver (up to tenfold) until it is needed in
the duodenum.
➢ water and ions are absorbed by the
gallbladder mucosa. Bile aids in the
digestion and absorption of fats.
Functions of the Liver and Gallbladder
Bilirubin
➢ principal bile pigment
➢ waste product of the heme of hemoglobin
formed during the breakdown of worn-out
erythrocytes
phagocytosis of aged red blood cells liberates iron,
globin, and bilirubin. The iron and globin are
recycled; the bilirubin is secreted into the bile and
is eventually broken down in the intestine.
Stercobilin
➢ gives feces their normal brown color.
Bile
➢ partially an excretory product and partially
a digestive secretion.
FINALS
Bile salts
➢ primarily salts of cholic and
chenodeoxycholic acids, are cholesterol
derivatives. They play a crucial role in
emulsification
Emulsification
➢ breakdown of large lipid globules
into a suspension of small lipid
globules
Enterohepatic circulation
➢ recycling mechanism
➢ conserves bile salts
➢ minimize the amount of new bile
salts that must be synthesized
Other vital function of the Liver
Carbohydrate metabolism
➢ important in maintaining a normal blood
glucose level.
o blood glucose is low, the liver can
break down glycogen to glucose and
release the glucose into the
bloodstream.
➢ convert certain amino acids and lactic acid
to glucose, and it can convert other sugars,
such as fructose and galactose, into glucose
o blood glucose is high, as occurs just
after eating a meal, the liver converts
glucose to glycogen and triglycerides
for storage.
Lipid metabolism
➢ Hepatocytes store some triglycerides
➢ break down fatty acids to generate ATP
➢ synthesize lipoproteins
o transport fatty acids, triglycerides,
and cholesterol to and from body
cells
➢ synthesize cholesterol
➢ use cholesterol to make bile salts.
Protein metabolism
ANATOMY AND PHYSIOLOGY
LECTURE | First Semester
➢ Hepatocytes remove the amino group, NH2,
from amino acids so that the amino acids
can be used for ATP production or
converted to carbohydrates or fats.
➢ toxic ammonia (NH3) is then converted into
the much less toxic urea, which is excreted
in urine.
➢ synthesize most plasma proteins, such as
alpha and beta globulins, albumin,
prothrombin, and fibrinogen
Processing of drugs and hormones
➢ detoxify substances such as alcohol and
excrete drugs such as penicillin,
erythromycin, and sulfonamides into bile
➢ Chemically alter or excrete thyroid
hormones and steroid hormones
Excretion of bilirubin
➢ metabolized in the small intestine by
bacteria and eliminated in feces.
Phagocytosis
➢ stellate reticuloendothelial cells of the liver
phagocytize aged red blood cells, white
blood cells, and some bacteria.
Activation of vitamin D
➢ participate in synthesizing the active form of
vitamin D
Gallbladder
➢ bile storage
➢ Bile is released into the duodenum only
under the stimulation of the intestinal
hormone CCK
o Without CCK, the hepatopancreatic
sphincter remains closed, so bile
exiting the liver in the common
hepatic duct cannot flow through the
common bile duct and into the
duodenum, it enters the cystic duct
and is stored within the expandable
gallbladder
FINALS
chyme enters the duodenum, CCK is
released, relaxing the
hepatopancreatic sphincter and
stimulating contractions of the
gallbladder that push bile into the
small intestine
➢ Bile modification
o composition of bile gradually
changes as it remains in the
gallbladder:
▪ Much of the water is
absorbed, and the bile salts
and other components of bile
become increasingly
concentrated.
Gallstones
➢ bile becomes too
concentrated
➢ Formed crystals of insoluble
minerals and salts
o
Small Intestine
➢ Most digestion and absorption of nutrients
occur
Anatomy of the Small Intestine
Divided into three regions
Duodenum
➢ first part of the small intestine
➢ shortest region, and is retroperitoneal.
➢ starts at the pyloric sphincter of the stomach
and is in the form of a C-shaped tube until it
merges with the jejunum.
Jejunum
➢ means “empty,” which is how it is found at
death.
➢ extends to the ileum
Ileum
➢ joins the large intestine at a smooth muscle
sphincter called the ileocecal sphincter.
Histology of the Small Intestine
ANATOMY AND PHYSIOLOGY
LECTURE | First Semester
Mucosa
➢ consists of simple columnar epithelium that
contains many types of cells.
➢ contains many deep crevices lined with
glandular epithelium.
Absorptive cells
➢ the epithelium contains
enzymes that digest food and
possess microvilli that absorb
nutrients in small intestinal
chyme
➢ slough off into the lumen of
the small intestine, they
break apart and release
enzymes that help digest
nutrients in the chyme.
Goblet Cells
➢ Secrete mucus
FINALS
Lamina Propria
➢ contains areolar connective tissue
➢ embedded in the connective tissue are an
arteriole, a venule, a blood capillary
network, and a lacteal
➢ has an abundance of mucosa-associated
lymphoid tissue (MALT).
Solitary lymphatic nodules
➢ most numerous in the distal part
of the ileum
Aggregated lymphatic follicles
➢ Groups of lymphatic nodules
Mucscularis
➢ consists of smooth muscle.
Submucosa
➢ consists of two layers of smooth muscle
Granular Cells
➢ Help protect intestinal
epithelium from bacteria
Intestinal glands
➢ Formed by cells lining the crevices
➢ Secrete intestinal juice
Paneth cells
➢ secrete lysozyme capable of
phagocytosis.
➢ have a role in regulating the
microbial population in the small
intestine
Enteroendocrine Cells
➢ S cells, CCK cells, and K cells
o secrete the hormones
secretin
➢ cholecystokinin (CCK) and
glucose-dependent -dependent
insulinotropic peptide
insulinotropic peptide (GIP)
Outer and thicker layer
➢ contains longitudinal fibers
Inner and thinner layer
➢ contains circular fibers
➢ contains duodenal glands
Duodenal glands
➢ secrete an alkaline mucus that helps
neutralize gastric acid in the chyme.
➢ help protect the duodenal
epithelium from gastric acids and
enzymes
Increase their secretion in response
to
o local reflexes
o the release of the hormone
enteroendocrine by
enteroendocrine cells of the
duodenum
o parasympathetic stimulation
through the vagus nerves.
ANATOMY AND PHYSIOLOGY
LECTURE | First Semester
Serosa (visceral peritoneum)
➢ completely surrounds the small intestine
except the major portion of the duodenum
(retroperitoneal)
special structural features
Circular Folds
➢ folds of the mucosa and submucosa
➢ permanent ridges
➢ enhance absorption by increasing surface
area and causing the chyme to spiral
FINALS
Physiology of the Small Intestine
➢ Segmentations mix chyme with digestive
juices and bring food into contact with
mucosa for absorption; peristalsis propels
chyme through small intestine.
➢ Completes digestion of carbohydrates,
proteins, and lipids; begins and completes
digestion of nucleic acids.
➢ Absorbs about 90% of nutrients and water
that pass through digestive system.
Role of Intestinal Juice and Brush-Border Enzymes
Intestinal Juice
Villi
➢ fingerlike projections of the mucosa
➢ increases the surface area of the epithelium
available for absorption and digestion
➢ gives the intestinal mucosa a velvety
appearance
➢ covered by epithelium and has a core of
lamina propria
➢ Nutrients absorbed by the epithelial cells
covering the villus pass through the wall of a
capillary or a lacteal to enter blood or
lymph.
Lacteal
➢ lymphatic capillary
➢ together with the blood capillary
they have an important role in
transporting absorbed nutrients.
Microvilli
➢ projections of the apical (free) membrane of
the absorptive cells
➢ contains a bundle of 20–30 actin filaments.
➢ microvilli greatly increase the surface area
of the plasma membrane
➢ amounts of digested nutrients can diff use
into absorptive cells
Brush border
➢ a fuzzy line
➢ extending into the lumen
➢ contains several brush-border enzymes
➢ clear yellow fluid which is secreted each day
➢ contains water and mucus and is slightly
alkaline (pH 7.6)
o Alkaline pH is present due to high
concentration of bicarbonate ions
➢ Together with the pancreatic juice provide a
liquid medium that aids the absorption of
substances from chyme in the small
intestine
Brush-border enzyme
➢ absorptive cells of the small intestine
synthesize several digestive enzymes
➢ enzymatic digestion occurs at the surface of
the absorptive cells that line the villi rather
than the lumen
➢ four carbohydrate-digesting enzymes
o α-dextrinase
o maltase
o sucrase
o lactase
➢ peptidases
o protein-digesting enzymes
o aminopeptidase and dipeptidase
o Break the peptide bonds in proteins
to form amino acids
➢ two types of nucleotide-digesting enzymes
o nucleosidases
o phosphatases
ANATOMY AND PHYSIOLOGY
FINALS
LECTURE | First Semester
Mechanical Digestion in Small Intestine
along a short stretch of small intestine
before dying out
6. MMC slowly migrates down the small
intestine, reaching the end of the ileum
in 90–120 minutes. Then another MMC
begins in the stomach. Altogether,
chyme remains in the small intestine for
3–5 hours.
Two types of movements of the small intestine
Segmentations
➢ localized, mixing contractions that occur in
portions of intestine distended by a large
volume of chyme
➢ mix chyme with the digestive juices and
bring the particles of food into contact with
the mucosa for absorption. The don’t push
contents along the tract
➢ occur most rapidly in the duodenum, about
12 times per minute, and progressively slow
to about 8 times per minute in the ileum.
Process of Segmentation
1. starts with the contractions of circular
muscle fibers in a portion of the small
intestine, an action that constricts the
intestine into segments.
2. Muscle fibers that encircle the middle of
each segment also contract, dividing
each segment again.
3. Fibers that first contracted relax, and
each small segment unites with an
adjoining small segment so that large
segments are formed again.
4. meal has been absorbed, which lessens
distension of the wall of the small
intestine, segmentation stops and
peristalsis begins.
Migrating motility complex (MMC)
➢ type of peristalsis that occurs
in the small intestine
➢ waves of contraction and
relaxation of circular and
longitudinal smooth muscle
fibers passing the length of
the small intestine
➢ moves chyme toward
ileocecal sphincter.
5. MMC begins the lower portion of the
stomach and pushes chyme forward
Chemical Digestion in the Small Intestine
Mouth
➢ salivary amylase converts starch (a
polysaccharide) to:
o maltose (a disaccharide)
o maltotriose (a trisaccharide)
o α-dextrins (short-chain, branched
fragments of starch with 5–10
glucose units).
Stomach
➢ pepsin converts proteins to peptides (small
fragments of proteins)
➢ lingual and gastric lipases convert some
triglycerides into fatty acids, diglycerides,
and monoglycerides
Small Intestine
➢ chyme entering the small intestine contains
partially digested carbohydrates, proteins,
and lipids.
➢ digestion of carbohydrates, proteins, and
lipids is a collective eff ort of pancreatic
juice, bile, and intestinal juice in the small
intestine.
Digestion of Carbohydrates
Pancreatic amylase
➢ enzyme in pancreatic juice that acts in the
small intestine
➢ split starch that has not already bean broken
down into maltose, maltotriose, and αdextrins
➢ acts on both glycogen and starches
ANATOMY AND PHYSIOLOGY
LECTURE | First Semester
➢ no effect on another polysaccharide called
cellulose
➢ digestible plant fiber that is
commonly referred to as “roughage”
as it moves through the digestive
system
➢ After amylase has split starch into smaller
fragments, a brush-border enzyme called αdextrinase acts on the resulting α-dextrins,
clipping off one glucose unit at a time.
➢ Three brush-border enzymes digest the
disaccharides into monosaccharides
Sucrase
➢ breaks sucrose into a molecule of
glucose and a molecule of fructose
Lactase
➢ digests lactose into a molecule of
glucose and a molecule of galactose
Maltase
➢ splits maltose and maltotriose into
two or three molecules of glucose
➢ Digestion of carbohydrates ends with the
production of monosaccharides, which the
digestive system is able to absorb
Digestion of Proteins
➢ digestion starts in the stomach, when
proteins are fragmented into peptides by the
action of pepsin
➢ Enzymes in pancreatic juice continue to
break down proteins into peptides.
➢ Protein digestion is completed by two
peptidases
Aminopeptidase
Splits off the amino acid at the
amino end of a peptide
Dipeptidase
o splits dipeptides (two amino acids
joined by a peptide bond) into single
amino acids
o
Digestion of Lipids
➢ most abundant lipids in the diet are
triglycerides
FINALS
➢ consist of a molecule of glycerol
bonded to three fatty acid molecules
Lipases
➢ Enzymes that split triglycerides and
phospholipids
➢ Lipid digestion occurs in the
stomach through the action of
lingual and gastric lipases, most
occurs in the small intestine through
the action of pancreatic lipase
➢ Types of Lipases
▪ lingual lipase
▪ gastric lipase
▪ pancreatic lipase
➢ Triglycerides are broken down by
pancreatic lipase into fatty acids and
monoglycerides
➢ Lipid globule containing
triglycerides can be digested in the
small intestine will undergo
emulsification
➢ bile contains bile salts
➢ Bile salts are amphipathic
▪ Each bile salt has a
hydrophobic (nonpolar)
region and a hydrophilic
(polar) region
▪ Amphipathic nature of bile
salts allow them to emulsify a
large lipid globule
▪ Hydrophobic regions of bile
salts interact with the large
lipid globule
▪ Hydrophilic regions of bile
salts interact with the watery
intestinal chyme.
➢ small lipid globules formed from
emulsification provide a large
surface area that allows pancreatic
lipase to function more effectively.
Digestion of Nucleic Acid
➢ Pancreatic juice contains two nucleases:
Ribonuclease
➢ digests RNA
Deoxyribonuclease
ANATOMY AND PHYSIOLOGY
LECTURE | First Semester
➢ digests DNA
➢ Two nucleases are further digested by
brush-border enzymes called nucleosidases
and phosphatases
➢ into pentoses, phosphates, and
nitrogenous bases.
➢ products are absorbed via active
transport
Absorption in the Small Intestine
➢ Absorption of materials occurs via diffusion,
facilitated diffusion, osmosis, and active
transport
➢ About 90% of all absorption of nutrients
occurs in the small intestine; the other 10%
occurs in the stomach and large intestine
➢ undigested or unabsorbed material left in
the small intestine passes on to the large
intestine.
Absorption of Monosaccharides
➢ carbohydrates are absorbed as
monosaccharides
➢ dietary carbohydrates that are digested
leaves only indigestible cellulose and fibers
in the feces.
➢ Monosaccharides pass from the lumen
through the apical membrane via facilitated
diffusion or active transport
➢ Fructose transported via facilitated
diffusion
➢ glucose and galactose transported into
absorptive cells of the villi via secondary
active transport that is coupled to the active
transport of Na+.
➢ move out of the absorptive cells through
their basolateral surfaces via facilitated
diffusion and enter the capillaries of the villi
Absorption of Amino Acids, Dipeptides, and
Tripeptides
➢ proteins are absorbed as amino acids via
active transport processes
o occur mainly in the duodenum and
jejunum
FINALS
➢ Half of the absorbed proteins are from food
and the other half came from the body.
➢ Some amino acids enter absorptive cells of
the villi via Na+-dependent secondary active
transport processes
➢ transported in the blood to the liver by way
of the hepatic portal system
➢ one symporter brings in dipeptides and
tripeptides together with H+
➢ peptides then are hydrolyzed to single
amino acids inside the absorptive cells
➢ Amino acids move out of the absorptive cells
via diffusion and enter capillaries of the
villus
Absorption of Lipids and Bile Salts
➢ dietary lipids are absorbed via simple
diffusion.
➢ triglycerides are mainly broken down into
monoglycerides and fatty acids
Small short-chain
➢ Fatty acids that are hydrophobic
➢ Can dissolve watery intestinal chyme
➢ pass through absorptive cells via
simple diffusion
➢ Same route taken by
monosaccharides and amino acids
into a blood capillary of a villus
Large short-chain fatty acids
➢ larger and hydrophobic
➢ not water-soluble
➢ their role in emulsification, bile salts
help make these large short-chain
fatty acids, long-chain fatty acids,
and monoglycerides more soluble
Micelles
➢ surrounds bile salts in the
intestinal chyme
➢ tiny speheres
➢ formed due to the
amphipathic nature of bile
salts
➢ solubilize other large
hydrophobic molecules such
as fat-soluble vitamins (A, D,
ANATOMY AND PHYSIOLOGY
LECTURE | First Semester
E, and K) and cholesterol and
aid in their absorption
Hydrophobic regions interact with the large shortchain fatty acids, long-chain fatty acids, and
monoglycerides.
Hydrophilic regions of bile salts interact with the
watery intestinal chyme. Micelles move from the
interior of the small intestinal lumen to the brush
border of the absorptive cells. At that point large
short-chain fatty acids, long-chain fatty acids, and
monoglycerides diffuse out of the micelles into the
absorptive cells, leaving the micelles behind in the
chyme
Chylomicrons
➢ Large spherical masses
➢ hydrophilic protein coat that surrounds
each chylomicron
o keeps the chylomicrons suspended
in blood and prevents them from
sticking to each other
Process
o Leave the absorptive cell via
exocytosis
o so large and bulky which cannot
enter blood capillaries
o enter lacteals, which have much
larger pores
o From lacteals transported by way of
lymphatic vessels to the thoracic
duct
o enter the blood at the junction of the
left internal jugular and left
subclavian veins
Lipoprotein lipase
➢ Removal of half of the chylomicrons is
because of this enzyme
➢ enzyme attached to the apical surface of
capillary endothelial cells
➢ breaks down triglycerides in chylomicrons
and other lipoproteins into fatty acids and
glycerol
FINALS
Enterohepatic circulation
➢ cycle of bile salt secretion by hepatocytes
into bile, reabsorption by the ileum, and
resecretion into bile.
Obstruction of the bile ducts or removal of the
gallbladder, can result in the loss of up to 40% of
dietary lipids in feces due to diminished lipid
absorption.
Benefits of fat
➢ delay gastric emptying, which helps a
person feel full.
➢ enhance the feeling of fullness by triggering
the release of a hormone called
cholecystokinin
➢ Necessary for the absorption of fat-soluble
vitamins
Absorption of Electrolytes
➢ Absorbed electrolytes in the small intestine
came from gastrointestinal secretions.
➢ Sodium ions are actively transported out of
absorptive cells (mechanism: basolateral
sodium–potassium pumps)
➢ Move into absorptive cells via diffusion and
secondary active transport.
➢ Sodium ins are reclaimed and not lost in the
feces
➢ Negatively charged ions are absorbed
actively in a process stimulated by calcitriol
➢ Other electrolytes are absorbed via active
transport mechanisms.
Absorption of Vitamins
➢ absorbed via simple diffusion.
➢ Vitamin B12, however, combines with
intrinsic factor produced by the stomach,
and the combination is absorbed in the
ileum via an active transport mechanism
Absorption of Water
➢ water absorption in the GI tract occurs via
osmosis from the lumen of the intestines
ANATOMY AND PHYSIOLOGY
LECTURE | First Semester
through absorptive cells and into blood
capillaries.
➢ Absorption of water from the small intestine
depends on the absorption of electrolytes
and nutrients to maintain an osmotic
balance with the blood
➢ Absorbed electrolytes, monosaccharides,
and amino acids establish a concentration
gradient for water that promotes water
absorption via osmosis
Large Intestine
➢ terminal portion of the GI tract
➢ overall function
o completion of absorption
o the production of certain vitamins
o the formation of feces
o the expulsion of feces from the body.
Proctology
➢ deals with the diagnosis and treatment of
disorders of the rectum and anus
Physiology of the Large Intestine
1) Haustral churning, peristalsis, and mass
peristalsis drive contents of colon into rectum.
2) Bacteria in large intestine convert proteins to
amino acids, break down amino acids, and produce
some B vitamins and vitamin K.
3) Absorption of some water, ions, and vitamins.
4) Formation of feces.
5) Defecation (emptying rectum)
Anatomy of the Large Intestine
Ileocecal sphincter
➢ fold of mucous membrane that guards the
opening from the ileum into the large
intestine
Four major regions of the Large Intestine
FINALS
Cecum
➢ Hanging inferior to the ileocecal valve
➢ Attached is the appendix which is a twisted,
coiled tube. Appendix contains masses of
lymphoid tissue, and as part of MALT
Mesoappendix
➢ mesentery of the appendix
➢ connects the appendix to the
ileum and cecum.
➢ merges with the cecum open end.
➢ divided into ascending, transverse,
descending, and sigmoid portions.
Ascending Colon
➢ retroperitoneal
➢ ascends on the right side of the
abdomen to the level of the right
kidney
➢ colon bends sharply to the left at the
right colic flexure, or hepatic flexure.
▪ bend marks the end of the
ascending colon and travels
across the abdominal cavity
as the transverse colon
Transverse Colon
➢ curves anteriorly from the right colic
flexure and crosses the abdomen
from right to left.
➢ supported by the transverse
mesocolon
➢ Near the spleen, the colon makes a
90° turn at the left colic flexure, or
splenic flexure, and becomes the
descending colon
Descending Colon
➢ proceeds inferiorly along the left side
until reaching the iliac fossa formed
by the inner surface of the left ilium.
➢ retroperitoneal and firmly attached
to the abdominal wall.
➢ At the iliac fossa, the descending
colon curves at the sigmoid flexure
and becomes the sigmoid colon.
ANATOMY AND PHYSIOLOGY
LECTURE | First Semester
Sigmoid Colon
➢ projects medially to the midline, and
terminates as the rectum at about the level
of the third sacral vertebra.
➢ The sigmoid colon empties into the rectum
Rectum
FINALS
➢ lamina propria consists of solitary
lymphatic nodules may extend through the
muscularis mucosae into the submucosa
➢ not have as many structural adaptations
➢ microvilli are present on the absorptive
cells.
Submucosa
➢ lies anterior to the sacrum and coccyx.
Anal Canal
➢ terminal 2–3 cm (1 in.) of the large
intestine
Anal columns
➢ mucous membrane is longitudinal
folds
➢ contain a network of arteries and
veins.
Anus
➢ opening of the anal canal to the exterior
➢ guarded by an
o internal anal sphincter of smooth
muscle (involuntary)
o external anal sphincter of skeletal
muscle (voluntary).
▪ Sphincters keep the anus
closed except during the
elimination of feces
Histology of The Large Intestine
Mucosa
➢ consists of simple columnar epithelium,
lamina propria (areolar connective tissue),
and muscularis mucosae (smooth muscle)
➢ epithelium contains mostly absorptive and
goblet cells
o Goblet cells secrete mucus that
lubricates the passage of the colonic
contents.
o located in tubular intestinal glands
➢ absorptive cells function primarily in water
absorption
o Located in tubular intestinal glands
➢ consists of areolar connective tissue
Muscularis
➢ Consists of an external layer of longitudinal
smooth muscle and an internal layer of
circular smooth muscle.
➢ Longitudinal muscles are thickened,
forming three conspicuous bands called the
teniae coli
o Separated by portions of the wall
with less or no longitudinal muscle
Haustra
➢ give the colon a puckered
appearance.
➢ Tonic contractions of the bands
gather the colon into a series of
pouches
Serosa
➢ part of the visceral peritoneum
omental (fatty) appendices.
o Fills the peritoneum with fat
attached to teniae coli
Mechanical Digestion in the Large Intestine
Passage of chyme from the ileum into the cecum is
regulated by the action of the ileocecal sphincter.
Valve remains partially closed so that the passage of
chyme into the cecum usually occurs slowly.
Gastroileal reflex
➢ intensifies peristalsis in the ileum and forces
any chyme into the cecum
➢ cecum is distended, the degree of
contraction of the ileocecal sphincter
intensifies
ANATOMY AND PHYSIOLOGY
LECTURE | First Semester
Movements of the colon begin when substances
pass the ileocecal sphincter. Food passes through
the ileocecal sphincter, it fills the cecum and
accumulates in the ascending colon.
Haustral churning
➢ One movement characteristic of the large
intestine
➢ occur mainly in the ascending and
transverse colon
➢ in the descending and sigmoid colon
promote the final drying out of the feces.
Process
➢ haustra remain relaxed and become
distended (swollen) while they fill up
➢ distension reaches a certain point,
the walls contract and squeeze the
contents into the next haustrum
➢ Peristalsis also occurs, although at a
slower rate
➢ These movements mix the residue,
which aids in water absorption
Mass peristalsis
➢ strong peristaltic wave that begins at
➢ about the middle of the transverse colon
and quickly drives the contents of the colon
into the rectum
➢ Food in the stomach initiates this
gastrocolic reflex in the colon
o mass peristalsis usually takes place
three or four times a day, during or
immediately after a meal
Chemical Digestion in the Large Intestine
Final stage through the activity of bacteria that
inhabit the lumen.
Mucus is secreted by the glands of the large
intestine, but no enzymes are secreted.
FINALS