UNIT – 9
INTRODUCTION
TO
DIGESTIVE SYSTEM
9.1 Definition:-Digestion , Digestive system
9.2 Structure and function of digestive organs
involved in digestive system:- Mouth,
oesophagus, stomach, small intestine, Large
intestine, Rectum, Anus
9.3 Structure and function of & its accessory
organs:- Pairs of salivary glands, pancreas,
liver, biliary duct
9.4 Types/ structure/ function of teeth:Temporary/ permanent
9.5 Function of digestive system
9.6 Physiology of digestion
• Every cell in the body require food for heat energy , growth and repair
of tissue. For that reason we need to eat food and digest it. So the
groups of organs work for ingestion, digestion, absorption and
excretion of food collectively called digestive system.
• As food passes through the digestive tract it is broken by physical
and chemical means until it is in a form suitable for absorption into
the blood stream and utilization within the body.
• There are certain constituents of the diet , which can not be digest and
absorbed therefore they are exerted in the form of feces.
• The continue process or serial act of mechanism is comes under the
system of digestive.
• The digestive system is collective name used to describe the
alimentary canal and accessory organs and varies of digestive
processes.
• The alimentary canal is a long tube about 8-10 meter extending from
mouth to anus.
• The largest structure of the digestive system is
the gastrointestinal tract (GI tract). This starts at the mouth and
ends at the anus, covering a distance of about nine (9) metres.
• The largest part of the GI tract is the colon or large intestine.
Water is absorbed here and remaining waste matter is stored prior
to defecation.
• Most of the digestion of food takes place in the small intestine.
• A major digestive organ is the stomach. Within its mucosa are
millions of embedded gastric glands. Their secretions are vital to
the functioning of the organ.
• There are many specialised cells of the GI tract. These include the
various cells of the gastric glands, taste cells, pancreatic duct
cells, enterocytes and microfold cells.
• The human digestive system consists of the gastrointestinal tract
plus the accessory organs of digestion (the tongue, salivary
glands, pancreas, liver, and gallbladder). In this system, the
process of digestion has many stages, the first of which starts in
the mouth (oral cavity).
• The human digestive system perform s four major activities.
i. Ingestion
ii. Digestion
iii. Absorption
iv. Excretion
• Ingestion:- Ingestion means taking food into alimentary tract. i e
mouth
• Digestion:- Digestion involves the breakdown of food into small
pieces, which makes ready to absorption is known as digestion.
Digestion can be divided into two process:
i. Mechanical digestion
ii. Chemical digestion
Mechanical digestion:-Mechanical digestion means
physical breakdown of food ,this includes mastication ,swallowing
and the peristaltic movement of the alimentary tract, which mix the
food with digestive juice and propel it along the tract.
Chemical digestion:- Chemical digestion is achieved by the
chemical substance called enzyme which is present in secretion
produced by gland of the digestive system , these secretion are saliva
from the salivary gland , gastric juice, from the stomach, intestinal
juice from the small intestine, bile from the liver, pancreatic juice
from the pancreas.
( Enzyme is a chemical substance secreted by the gland of alimentary
canal ,Which causes or speeds up a chemical change in other
substance , without itself being changed. Each enzyme has a specific
action on particular food )
• Absorption:- This is a process by which the digested substance
passes through the wall of some organ or digestive tract into the
blood and lymph capillaries.
• Excretion:- Excretion of unwanted or unabsorbed substance from the
bowel as faeces.
Function of digestive system
• The function of the digestive system is ingestion and
digestion of food .
• Secretion of several kinds of juice and mucus.
• Absorption of necessary nutrient materials.
• Excretion of unwanted or harmful substance.
• Movement of food or bolus onward by means of
peristaltic movement.
• Regulation of acid base balance.
• Maintenance of water balance.
Organs of digestive systems
• The organs of digestive system can be divided
into two parts.
i. The alimentary or Gastrointestinal tract
ii. The accessory gland or organs
The alimentary or Gastrointestinal tract
It is a long tube of about 8-10 meters, start at mouth and terminates
at the anus through which food passes, absorb and excretes.
There are various part
i. Mouth:- Tongue , teeth
ii. Pharynx
iii. Esophagus
iv. Stomach
v. Small intestine:- Duodenum, jejunum, ileum
vi. Large intestine:- Caeccum, Ascending colon, Transverse colon,
Descending colon, Pelvic or sigmoid colon, Rectum.
vii. Anal canal
The accessory gland or organs
• There are the glands situated outside the alimentary tract. Their
function is to secretes digestive juices which are poured into GI
tract by ducts. They are
a.
b.
c.
d.
The salivary glands
The pancrease
Liver
The gall bladder and bile ducts.
Mouth
• The mouth is the first part of the gastrointestinal tract .It is also
called buccal cavity and oral cavity.
• These include salivary glands, teeth and the tongue.
• The mouth consists of two regions, the vestibule(outer part)
and the oral cavity proper(inner central part). The vestibule
is the area between the teeth, lips and cheeks, and the rest is the
oral cavity proper, which communicated with the oro-pharynx
and contains the tongue, mouth proper .
• Most of the oral cavity is lined with(non keratinized stratified
squamous epithelium) oral mucosa, a mucous membrane that
produces a lubricating mucus, of which only a small amount is
needed.
Organ associated with the mouth
The mouth is a cavity bounded by mucous and bones.
• Anteriorly:-By the muscles of lips(Oblicularies orises)
• Posteriorly:- It is connected with the pharynx(Oropharynx)
• Laterally:- By the muscles of checks (Buccinators, massaetor)
• Superiorly:- By the bony hard and muscular soft plate.
• Inferiorly:- By the muscular tongue and the muscles and soft
tissue of the mouth.
• The palate is the roof of the mouth in humans and other mammals.
It separates the oral cavity from the nasal cavity. The palate is
divided into two parts, the anterior bony portion of plate (2/3) is
called hard palate, which is formed by the superior maxillae and
the palatine. The reminder (1/3) posterior portion is known as soft
palate, the soft palate is muscular , curves downwards from the
posterior end of the hard palate blends with the walls of the pharynx
at the sides .
• There is a cone shaped prolongation ,which are curved folds of
muscles covered with mucous membrane and hanging down from
the middle of the border of the soft palate, is known as uvula.
• Curving downwards from either side of the uvula, there are two
folds of mucus membrane ; these are called anterior and posterior
pillars of fauces (palatine arches or pillars).
• The posterior folds ,one on each side ,are the palatoglossal arches.
In between the arches, there is a collection of lymphoid tissue called
palatine tonsil.
The tongue
• The tongue is highly mobile, voluntary muscular structure which lies
on the floor of the mouth of most vertebrates that manipulates food
for mastication.
• It is the primary organ of taste, as much of its upper surface is covered
in taste buds. It is attached to the hyoid bone by a fold of the mucous
membrane covering, called the frenulum.
• The superior surface is covered with stratified squamous epithelial
,in which numerous minute elevation of mucous membrane is present
, which is known as papilla.
• These papillae consists of nerve ending of the sense of taste. Taste or
gestation is the sensory modality mediated by the chemoreceptor of
the tongue, mouth and pharynx.
• There are four primary taste qualities. Tip of tongue is sensitive to
sweet and salt, back of the tongue is sensitive to bitter and posterior
half of each sided of the tongue is sensitive to sour taste.
• A cluster of taste cells form taste buds. Taste buds are located on
the tongue papillae, hard palate, soft palate, epiglottis and in the
pharynx. There are three types of papillae.
1. Circumvallate (Vallate) papillae:- These are usually about 8 to
12 in number. They arrange in a inverted “V” shaped towards
the base of the tongue. These are the largest of the papillae and
are the most easily distributed because of their characteristics
design. It lies in front of sulcus terminalis.
2. Fungiform papillae:- These are situated mainly at the tip and
margin of the tongue. They are more numerous than vallate.
3. Filliform papillae:- They are the smallest and most numerous
than other papillae. They are found on the dorsum , edges and
the anterior two thirds of the tongue.
• The tongue plays in important part in:Chewing(mastication)
Swallowing(Deglutition)
Speech(Articulation) and
Taste
• Blood supply:- The tongue receives its blood supply primarily
from the lingual artery, a branch of the external carotid artery.
The lingual veins, drain into the internal jugular vein. There is
also a secondary blood supply to the tongue from the tonsillar
branch of the facial artery and the ascending pharyngeal artery.
• Nerve supply
• Motor supply of voluntary muscle tissue is by hypoglossal
nerve(CN XII)
• Anterior two thirds of tongue (anterior to the vallate papillae)
– Taste: facial nerve (CN VII)
– Sensation: mandibular division (V3) of the trigeminal
nerve (CN V)
• Posterior one third of tongue:
– Taste and sensation: glossopharyngeal nerve (CN IX) and
Vagus nerve
Mechanism of taste sensation
• The molecules of substance are attached with the molecular
receptor of the microvilli in the taste buds.
• The combination leads to some electrophysiological changes
to cause stimulation of receptor cell and then nerves fibers,
which emerge from the taste buds, are stimulated .
• The impulses then reach the appropriate part of the brain
through the various nerves, then perceived the sense of taste.
Teeth
• The teeth are embedded in the alveoli or sockets of the alveolar
ridges of the mandible and the maxillae. Each individual develops
two sets of teeth during his life; the temporary teeth of childhood
and permanent teeth of adult. At birth dentitions are present in
immature from in the mandible and maxilla.
1. The temporary teeth:- The temporary teeth are also known as
deciduous or milk teeth. These are 20 in number , 10 in each jaw.
They begin to erupt from the age of 6 months and should all be
presented by the end of 24 months.
2. The permanent teeth:- These begin to replace the deciduous teeth
. They start to erupt from the age of 6 years and should be
completed by the age of 24 years old. They are 32 permanent
teeth, 16 in the upper and 16 in the lower jaw(Or 8 in each half
of each jaw)
•
•
•
•
•
•
There are several types of teeth, and each performs its own special function
in the chewing process, depending on its size, shape and location within the
jaws.
Starting at the midline, the permanent dentition is comprised of incisors,
canines, premolars and molars. The primary dentition is the same except it
has no premolars
The four front teeth in each arch are called incisors, and their function is to
cut food with their sharp thin edges. On each side of the incisors, at the
corners of the mouth, are the canines. These teeth have one cusp, or pointed
edge, and are used for holding or grasping food, and are very strong, stable
teeth.
Behind the canines are the premolars, which are designed for holding food
like the canines because they have cusps, but they also function to crush
food. Sometimes these teeth are referred to as bicuspids, meaning two
cusps, but this is not always accurate because some premolars may have
three cusps.
Therefore the term premolar is preferred. The teeth farthest back in the
mouth are the molars. These teeth have broad chewing surfaces with four or
five cusps, and are designed for grinding food.
The incisors and canines are called anterior teeth, because they are located
in the front of the mouth, while the premolars and molars are called posterior
teeth because they are located in the back of the mouth.
Structure of teeth
• The structure of tooth can be divided into two ways,
ie
1. External portion
2. Internal portion
The external portion can be divided into 3 parts
Crown:- The crown is part which protrudes from the
gum.
Root:- The root is part which embedded in the bone.
Neck:-The neck is the slightly constricted part where
the crown emerges with the root.
Internal portion
•
In center of the tooth, there is a pulp cavity containing blood
vessels, lymph vessels and nerves and surrounding this there is a hard
like substance called dentine.
•
Dentine is secreted by odonoblast (one of the connective tissue
cells that deposit dentin and form the outer surface of the dental pulp
adjacent to the dentin.).
•
Outside the dentine of the crown, there is a thin layer of hard
substance, the enamel which is secreted by
ameloblast.(Ameloblasts are cells present only during tooth
development that deposit tooth enamel, which is the hard outermost
layer of the tooth forming the surface of the crown)
• The root of the tooth on the other hand ,is covered with substance
resembling bone , called cement, which fixes the tooth in its socket.
Blood vessels and nerves passes to the tooth through small foramen at
the apex of each root which is called apical foramen.
• Blood supply:- Most of the arterial blood supply to the teeth is
by branches of the maxillary arteries . The venous drainage is
by a number of veins, which empty into the internal jugular
veins.
• Nerve supply:- The nerve supply to the upper teeth is by
branches of the maxillary nerve and to the lower teeth by the
branches of the mandibular nerve. These are both branches of
the trigeminal nerve (5th cranial nerve).
Mechanism of Mastication
• The Mastication or chewing is the process by which
food is crushed and ground by teeth. It is the first step
of digestion, and it increases the surface area of foods to allow
more efficient break down by enzymes.
• The act of mastication is mostly due to the movement of lower
jaw(Mandible)Various types of movement of the mandible e.g :simple, closing , side to side movement etc are made possible by
different muscles like the masseter, temporal and the internal as
well as the external pterygoids.
• These muscles are all voluntary and are supplied by the trigeminal
(5th cranial ) nerve.
• During mastication, the pressure exerted on the food matter
particularly those by the molar teeth may be truly considerable.
• During the mastication process, the food is positioned by the
cheek and tongue between the teeth for grinding.
• The muscles of mastication move the jaws to bring the teeth into
intermittent contact, repeatedly occluding and opening.
• As chewing continues, the food is made softer and warmer, and
the enzymes in saliva begin to break down carbohydrates in the
food.
• After chewing, the food (now called a bolus) is swallowed. It
enters the esophagus and via peristalsis continues on to the
stomach, where the next step of digestion occurs.
• Mastication may be regarded as a voluntary as well as a reflex
act. Area in the brain are found in the cerebral cortex,
amygdaloidal nuclei and medulla.
Function of Mastication
a. Enables the food bolus to be easily swallowed.
b. Enhances the digestibility of food by:
 Decreasing the size of particles to increase the surface
area for enzyme activity.
 Reflexively stimulating the secretion of digestive juice
(saliva and gastric juice)
c. Mixes the food with saliva , initiating digestion by the
activity of salivary amylase.
d. Prevent irritation of the GI system be large food mass.
e. Ensures healthy growth and development of the oral
tissues.
f. Increase is digestive efficiency, the primary purpose of
mastication.
Pharynx
In humans the pharynx is part of the digestive system
and also of the conducting zone of the respiratory
system. The pharynx is expanded muscular tube lying
behind the nose and mouth.
The pharynx in cone shaped fibro muscular
tube of 12-14 cm ( inch) in length. It is extending
from the inferior surface of the base of the skull to the
level of the sixth cervical vertebrae. It is continuous
with the esophagus .
Organs associated with the pharynx
Superior:-The skull
Inferior:-Esophagus
Anterior :-Nasal cavity, mouth and the larynx
Posterior:-Sixth cervical vertebrae.
Pharynx is anatomically divided into three parts:
The nasopharynx,
The oropharynx and
The laryngopharynx
• The upper portion of the pharynx, (the nasopharynx), extends from the
base of the skull to the upper surface of the soft palate . It includes the
space between the internal nares and the soft palate and lies above the
oral cavity.
Anterior join with nasal cavity, posterior oropharynx , laterally
auditory tube which contuning to the middle ear.
• The oropharynx lies behind the oral cavity, extending from the uvula to
the level of the hyoid bone(3rd cervical vertebra).It provide common
pathway diverges into the respiratory (larynx) and digestive
(esophagus) pathways. It is anterior aspect is opened to the mouth and
is bounded by the anterior pillars of the fauces.
• The laryngopharynx, also known as hypo pharynx, is the caudal part of
the pharynx; it is the part of the throat that connects to the esophagus
(3rd to 6th cervical vertebra).
• The nasopharynx is not a functional part of alimentry tract but belongs
to respiratory system. The oropharynx is a shared entrance for both
respiratory and digestive tracts where oropharynx and laryngo pharynx
are responsible for digestive system.
The pharynx is composed of 3 layer of tissue:• The inner lining membrane(Mucous membrane):- It is squamous
epithelial , continuous with the lining of the mouth at one end
and with the esophagus at other end.
• The middle layer:- It consist of fibrous tissue which becomes
thinner towards the lower end, containing blood and lymph
vessels and nerves.
• The outer layer:-Consists of number of involuntary constriction
muscle layer, which are involved in swallowing. When food
reaches the pharynx, swallowing is no longer under voluntary
control
Arterial blood supply:-Facial arteries
Venous return:-Facial and internal jugular vein
Nerve supply:-Nerve supply is from the
pharyngeal plexus and consists of sympathetic
and parasympathetic nerves. Parasympathetic
supply is mainly by the glossopharyngeal and
Vagus nerve and sympathetic from the cervical
ganglia.
Function of pharynx
 The pharynx is a common pathway for air and food. The
pharynx opens into two pathways, one that leads to the
esophagus or food passage .
Mechanism of swallowing(Deglutition)
• Swallowing, sometimes called deglutition, is the process in the
human or animal body that makes something pass from
the mouth, to the pharynx, and into the esophagus.
• Swallowing is an important part of eating and drinking. If the
process fails and the material (such as food, drink, or medicine)
goes through the trachea, then choking or pulmonary
aspiration can occur.
• In the human body the automatic temporary closing of the
epiglottis is controlled by the swallowing reflex.
• The portion of food, drink, or other material that will move
through the neck in one swallow is called a bolus.
Deglutition has been divided into three phases
(Stages)
I. 1st stage (Oral stage)
II. 2nd stage(Pharyngeal stage)
III. 3rd stage (Esophageal stage)
Swallowing is a complex mechanism using both
skeletal muscle (tongue) and smooth muscles of the pharynx
and esophagus.
The autonomic nervous system (ANS) coordinates this
process in the pharyngeal and esophageal phases.
I.
a.
b.
c.
d.
1st stage (Oral stage):The food is rolled adequately on the upper surface of the
tongue to form a “bolus” by suitable movement of the tongue.
The admixture of saliva with the food matter also contributes
to the formation of the bolus.
The soft palate rises ; the posterior wall of the nasopharynx
also approaches towards the soft palate. Therefore the
nasopharynx is sealed off and thus the nasal regurgitation is
prevented.
The respiratory is reflexbly stopped.
Ultimately the bolus is pushed to the posterior part of the
tongue . The initiation of the first stage is voluntary.
II. 2nd stage(Pharyngeal stage):- In this stage the bolus enter the
esophagus and not in the respiratory tract. It should be
understood that if the food enters the respiratory tract, it might
lead to severe coughing/bronchospasm (choking),obstruction of
a bronchial tube and atelectasis or even death.
The events in the end stages are as follows,
a. By the movement of the tongue backward, the bolus is pushed
back against the epiglottis.
b. Almost immediately the epiglottis deflects in transverse
direction
c. The laryngeal opening is closed by closure of vocal cords. The
larynx is elevated. The respiration in the meantime has already
stopped.
d. The upper esophageal sphincter relaxes and the bolus enters the
esophageal tube.
III. 3rd stage (Esophageal stage):- The esophagus has two sphincters
upper, situated at the upper end of the esophagus and lower,
situated near where esophagus open into the stomach.
Both the sphincters are normally closed. At the end of the 2nd
stage of deglutition, the upper sphincter opens and the bolus
enter the esophagus.
After the bolus has passed this sphincter closed again . Now a wave
of peristalsis is initiated at the upper end of the esophagus and
travels downward propelling the bolus downward. This
downward movement of the food is helped considerably by the
action of gravity, provided the subject in an erect position.
As the bolus reaches the lower end of the esophagus, the
LES(Lower esophageal sphincter) relaxes and the food enter the
stomach. When the bolus has passed out and entered the
stomach , the LES constricts again. This makes the end of the
Deglutition.
I.
Oral phase:1) Moistening
2) Mastication
3) Trough formation
4) Movement of the bolus posteriorly
ii. Pharyngeal phase:5) Closure of the nasopharynx
6) The pharynx prepares to receive the bolus
7) Opening of the auditory tube
8) Closure of the oropharynx
9) Laryngeal closure
10) Hyoid elevation
11) Bolus transits pharynx
iii. Esophageal phase
12) Esophageal peristalsis
13) Relaxation phase
Esophagus
• The esophagus or oesophagus , commonly known as the food
pipe or gullet, is a hollow muscular tube that transports saliva,
liquids, and foods from the mouth to the stomach. When the
patient is upright, the esophagus is usually between 18 to 25
centimeters in length, while its width averages 1.5 to 2 cm.
• The esophagus is one of the upper parts of the digestive
system. At the mouth opening, it is continuous with the back of
the oral cavity, passing downwards through the rear part of
the mediastinum, through the diaphragm, and into the stomach.
• In humans, the esophagus generally starts around the level of
the sixth cervical vertebra (C6) behind the cricoid cartilage,
enters the diaphragm at about the level of the tenth thoracic
vertebra (T10), and ends at the cardia of the stomach, at the
level of the eleventh thoracic vertebra (T11).
• During swallowing the epiglottis tilts backwards to prevent food
from going down the larynx. The esophagus travels behind
the trachea and heart, passes through the diaphragm and empties
into the cardia (the uppermost region) of the stomach.
• The muscular layers that form the esophagus are closed tightly at
both ends by sphincter muscles, to prevent food or liquids from
leaking from the stomach back into the esophagus or mouth.
When the patient swallows, the sphincters temporarily relax to
allow passage of the food through.
• The esophagus passes close to the trachea (breathing tube) and
the left side of the heart. This means that problems with the
esophagus, such as eating something too hot, can sometimes feel
like a pain close to or in the heart or throat.
• The most common problem is gastroesophageal reflux
disease (GERD), when the sphincter at the base of the
esophagus does not close properly, allowing stomach contents
to leak back into the esophagus and irritate or damage it over
time. With prolonged GERD, esophageal ulcer is likely to
occur.
• The upper and lower ends of the esophagus are closed by
sphincter muscles. The upper cricopharyngeal sphincter
prevents air passage into the esophagus during inspiration and
the aspiration of esophagus contents . The lower esophageal
sphincter prevents the reflex of the acid (Gastric content) into
the esophagus.
Structure of the esophagus
The esophagus is formed by four layer of tissue.
I. The outer layer
II. The muscle layer
III. The sub mucous layer
IV.The inner lining mucous membrane
I. The outer layer:- Covered with elastic fibrous tissue.
II. The muscle layer :- It consists of outer coat longitudinal and
inner coat circular layer of fibers. The muscle of the upper third
of the esophagus is skeletal muscle but their action is
involuntary, whilist that of the middle third is mixed skeletal and
visceral muscle and the lower third contains only visceral
muscle fibers. At the lower end of the esophagus, the circular
fibers are thickened to become the cardiac sphincter.
III. The sub mucous layer:- It consists of alveolar tissue, which
contains blood and lymph vessels, and nerves of the autonomic
nervous system.
IV. The inner lining mucous membrane:- The proximal third is lined
with stratified squamous epithelium with mucous secreting
glands , which have tiny by columnar epithelium and middle
third by mixed of both.
Functions of esophagus
• Swallowing:- In humans and other animals, food
is ingested through the mouth. During swallowing, food passes
from the mouth through the pharynx into the esophagus. The
esophagus is thus one of the first components of the human
digestive system and the human gastrointestinal tract. After
food passes through the esophagus, it enters the stomach.
• Reducing gastric reflux:- The stomach generates strong
acids, including hydrochloric acid (HCl), and enzymes to aid
in food digestion. This digestive mixture is called gastric juice.
Constriction of the upper and lower esophageal sphincters help
to prevent reflux of gastric contents and juices into the
esophagus, protecting the esophageal mucosa. In addition, the
acute angle of His and the lower crura of the diaphragm helps
this sphincteric action.
Arterial blood supply:-The cervical parts of the esophagus and the
upper esophageal sphincter receive blood from inferior thyroid
artery, the parts of the esophagus in the thorax from the bronchial
arteries and branches directly from the thoracic aorta, and the
lower parts of the esophagus and the lower esophageal sphincter
receive blood from the left gastric artery and the left inferior
phrenic artery.
Venous return:-The venous drainage also differs along the course of
the esophagus. The upper and lower parts of the esophagus drain
into the azygos and hemiazygos veins, and blood from the middle
part drains into the left gastric vein. All these veins drain into
the superior vena cava, with the exception of the left gastric vein,
which is a branch of the portal vein.
Nerve supply:-The esophagus is supplied by parasympathetic and
sympathetic fibers and branches of the vagus nerve.
Stomach
• The stomach is a muscular, hollow, dilated part of the digestive
system which functions as an important organ of the digestive
tract in many animals. It is involved in the second phase of
digestion, following mastication (chewing).
• In most vertebrates, the stomach is located between
the esophagus and the small intestine. It secretes proteindigesting enzymes called proteases and gastric acid to aid in
food digestion, through smooth muscular contractions
• In adult humans, the stomach has a relaxed, near empty volume
of about 45 ml. Because it is a distensible organ, it normally
expands to hold about 1 liter of food, but can hold as much as 23litres. The stomach of a newborn human baby will only be able
to retain about 30ml.
• The stomach is “J” shaped structure having 25 cm longs.
Organ associated with the stomach
• Anteriorly:- Left lobe of liver and anterior abdominal wall.
• Posteriorly :-Abdominal aorta, pancreas, spleen, left kidney
and adrenal gland .
• Superiorly:-Diaphragm, esophagus, and left lobe of liver.
• Inferiorly:-Transverse colon and small intestine.
• To the left:- Diaphragm and spleen.
• To the right:- Liver and duodenum
structure
The stomach has two opening:a. The cardiac
b. The pyloric orifice
It has also two curvatures:a. The greater curvature
b. The lesser curvature
• The esophagus enters the stomach at the cardiac oriffice, which
is situated at the upper end of the lesser curvature which
terminates at the pyloric orifice. The greater curvature begins
where the esophagus enters the curves downwards to the
pylorus. The lesser is shorter and extends from the cardiac
orifice to the pylorus.
•
a.
b.
c.
Parts of the stomach
Fundus
Body
Pyloric antrum
• Parts of the stomach
a. Fundus:- The part of the stomach above the cardiac orifice is
fundus . It is dome shaped, Which generally contains a double
of air.
b. Body:- The main part of the stomach is body.
c. Pyloric antrum:- This is a narrow part of the body, from this
point the stomach joins with the duodenum.
• The wall of the stomach is made up of 4 layer of tissue.
I. The outer layer
II. The muscle layer:- Longitudinal muscles fibers, Circular
muscle fibers, Inner oblique fibers.
III. The sub mucous layer
IV. The inner lining mucous membrane
I.
II.
The outer layer:- Covering of serous membrane (The peritoneum)
The sub mucous layer:- When actually consists of three layer of visceral
muscle fibers:
Longitudinal muscles fibers are the most superficial and are continuous with the
longitudinal fibers of the esophagus.
Circular muscle fibers form the middle layer. They are continuous with those of
the esophagus and are thickened around the pylorus forming the pyloric
sphincter.
The Inner oblique fibers muscle.
III. The sub mucous layer:- Consisting of loose areolar tissue carrying blood
vessels, lymphatic and nerves.
IV. The inner lining mucous membrane:- Which is thick and has a smooth , soft,
Velvety surface. When the stomach is empty , it is thrown into numerous
irregular folds, Which is called rugae. A numerous gastric secretary cells are
located on the surface and in the glands that are buried within the mucosa.
There are two types of gastric glands:
a.
Oxyntic glands and
b. Pyloric gland.
a.



b.
Oxyntic glands :- These are located in the fundus and body of the stomach.
They contain three types of cells namely,
Parietal or Oxynite cells:-Which secretes hydrochloric acid (HCL)and
intrinsic factor.
Peptic or chief cells:- Which secrete pepsinogen (a substance which is
secreted by the stomach wall and converted into the enzyme pepsin by
gastric acid) and
Mucus cells:- Secrete mucus.
Pyloric gland:- They are located in the antrum and pyloric region of the
stomach. They Contain G- Cells, Which secrete gastrin. Gastrin is
hormone, Which stimulates parietal cell to secrete HCL. HCL secretion is
stimulated by acetylcholine, histamine and gastrin and inhibited by
somatostatin.
There are several digestive enzymes present in the gastric juice; pepsin,
rennin, gastric lipase ferment and intrinsic factor. Intrinsic factors is an
enzyme which is necessary for the absorption of vitamin B12 through the
wall of the intestine. Deficency of intrinsic factor leads to pernicious
anemia due to vitamin B12 and folic acid deficiency.
Blood supply
• The lesser curvature of the stomach is supplied by the right gastric
artery inferiorly, and the left gastric artery superiorly, which also supplies the
cardiac region. T
• he greater curvature is supplied by the right gastro-omental artery inferiorly
and the left gastro-omental artery superiorly. The fundus of the stomach, and
also the upper portion of the greater curvature, is supplied by the short gastric
artery which arises from the splenic artery.
• Venous drainage into the portal vein and thence to the
liver.
• Nerve supply :- The sympathetic supply to the
stomach is mainly from the celiac plexus and the
parasympathetic supply is from the vagus nerves.
Sympathetic stimulation reduces the motility of the
stomach and the secretion of gartric juice ; Vagal
stimulation has the opposite effect.
Functions of stomach
• It acts as a temporary reservoir for food, allowing the digestive enzyme to
act.
• It produce gastric juice , which begins the chemical digestion of proteins.
• Muscular action of stomach mixes the food with gastric juice. When the mix
contents reaches its suitable degree of acidity and liquefaction then the
matter is known chyme. Chyme is passed through into the duodenum in
small jest when the pyloric sphincter relaxs and the muscular walls of the
stomach contract.
• absorption is mainly a function of the small intestine, some absorption of
certain small molecules nevertheless does occur in the stomach through its
lining. This includes:
Water, if the body is dehydrated
Medication, like aspirin
Amino acids
10–20% of ingested ethanol (e.g. from alcoholic beverages)
Caffeine
• Churns the food into small pieces, which helps for complete
digestion.
• Secrete intrinsic factor which is necessary for binding Vit B12 in
the stomach and needed for its absorption in the terminal ileum.
• Iron absorption takes place in the small intestine it is dissolved out
of foods most effectively in the stomach in the presence of HCL
• A other very important function of the stomach is the destruction
of contaminants that the food may contain – bacteria and other
micro-organisms. Very little is absorbed into the bloodstream
straight through the stomach walls – aspirin and alcohol being
exceptions to this rule.
Gastric juice
 Gastric juice is a clear , watery , strong acid fluid containing
hydrochloric acid , enzyme, mineral salts and mucus. A total
quantity of 1.5 to 2 liters is secreted each day.
 This is secreted by special secretary glands in the mucous and
consists of water , mineral salts(Secreted by gastric glands) ,
mucus(secreted by goblet cells), Hydrochloric acid and intrinsic
factor (Secreted by parietal cells in the gastric glands), enzyme
( pepsinogen ) secreted by chief (Peptic or zymogemic) cells in
the glands.
Functions of Gastric juice
• Water further liquefies the food.
• HCL:- Acidified the food and stop the action of ptyalin(secreted in
saliva), Kills many microbes , which may be harmful to the body.
Provide the acid environment needed for effective digestion by
pepsin.
• Pepsinogens are activated to pepsin by Hcl (Which is already
present in stomach) . They begin the digestion of protein, breaking
them into smaller molecules . Pepsin act most effectively at ph 1.53.5.
• Intrinsic factor(a protein compound)is necessary for the absorption
of vitB12 (The anti anemic factor) is present in gastric juice.
• Mucus prevents mechanical injury to the stomach wall by
lubricating the contents.
Secretion of gastric juice
• There is always a small quantity of gastric juice present in the
stomach, even when it contains no food . This is known as fasting
juice. Maximum level of secretion reaches an hour after a meal
then declines to the fasting level after about 4 hours.
•
a.
b.
c.
There are three phases of secretion of gastric juice:Cephalic phase
Gastric phase
Intestine phase
a. Cephalic phase:- The flow of juice occurs before food reaches the
stomach and is due to reflex stimulation of the vagus nerves
initated by the sight, smell or taste of food. When the vagus nerve
have been cut, this phase of gastric secretion stops.
b. Gastric phase :- When stimulated by the presence of food , the
cells in the pyloric antrum and duodenum secrete gastrin, a
hormone which passes directly into the stomach , stimulates the
gastric gland to produce more gastric juice. Gastric phase secretion
is suppressed when the PH in the pyloric antrum falls to about 1.5
c. Intestine phase:- When the partially digested content of the
stomach reach the small intestine , a hormone complex,
enterogastrone, is produce which slow down the secretion of
gastric juice and reduce gastric motility . By slowing the emptying
rate of the stomach , the content of duodenum become more
thoroughly mixed with the bile and pancreatic juice . This phase of
gastric secretion is most marked when the meal has had high fat
contents.
Secretion of Gastric juice
Small intestine:• The small intestine is a tubular structure within the abdominal
cavity that carries the food in continuation with the
stomach and the large intestine, and is where most of the
digestion and absorption of food takes place.
• It is approximately 5 m (16feet) long and lies in abdominal
cavity , surrounded by the large intestine.
• The small intestine has three distinct regions –
a. The duodenum,
b. jejunum and
c. Ileum.
• The duodenum is a short structure (about 20–25 cm long or 10 inch)
continuous with the stomach and shaped like a "C". It surrounds the
head of the pancreas. It receives gastric chyme from the stomach,
together with digestive juices from the pancreas (digestive enzymes)
and the liver(bile). The digestive enzymes break down proteins and
bile emulsify fats into micelles. The duodenum contains Brunner's
glands, which produce a mucus-rich alkaline secretion
containing bicarbonate. These secretions, in combination with
bicarbonate from the pancreas, neutralizes the stomach acids
contained in gastric chyme.
• The jejunum is the midsection of the small intestine, connecting the
duodenum to the ileum. It is about 2.5 m long(8 feet), and contains
the plicae circulares(folds within the wall of small intestine that
increase the absorptive surface area), and villi that increase its surface
area. Products of digestion (sugars, amino acids, and fatty acids) are
absorbed into the bloodstream here.
• The ileum: The final section of the small intestine. It is about 3
m long(12 feet), and contains villi similar to the jejunum. It
absorbs mainly vitamin B12and bile acids, as well as any other
remaining nutrients. The ileum joins to the cecum of the large
intestine at the ileocecal junction.
Structure
• There are four layer of tissue forming the walls of the intestine.
I. The outer layer:- Covering of peritoneum called messentry.
II. The muscle layer:- There are two layer of smooth muscle
fibers under the serous membrane.
a. Longitudinal muscles fibers(Superficial layer)
b. Circular muscle fibers(Deep layer)
III. The sub mucous layer:- It consists of alveolar tissue, which
contains blood and lymph vessels, and nerves of the autonomic
nervous system.
IV. The inner lining mucous membrane:- The surface area of the
small intestine is greatly increased by two peculiarities in the
arrangement of the mucous membrane.
• The circular folds:-Unlike the rugae of the stomach , the circular fold
are not smooth out when the small intestine is distended.
• The villi:-When are tiny finger like projection into the lumen of the
organ .Their wall consists of columnar epithelial cells which encloses
a network of blood and lymph capillary are called lacteals.
Absorption of nutrient materials takes place across the wall of the
villus into the blood and lymph capillaries.
• Intestinal glands:- These are simple tubular gland, Which lies
between the villi. They secrete intestinal juice ,containing the
enzyme ,which complete the chemical digestion of carbohydrates,
protein and fats.
• Lymph nodes:-There are numerous lymph nodes in the mucous
membrane situated at irregular intervals through out the length of
small intestine. The smaller ones known as solitary lymphatic
nodules and about 20- 30, larger nodules situated towards the
distal end of the illeum , are called aggregated lymphatic
nodules(Payers patches)
• Blood supply:- The arterial blood is supplied by superior
mesenteric artery , which is a branch of the abdominal
aorta(Branch of descending aorta) .
• Venous drainage is through superior mesenteric vein , which
empties its impure blood into the portal vein.
• Nerve supply:-The nerve supply to the small intestine is through
sympathetic and parasympathetic nerves.
Functions
• Onward movement of its content, which is produced by peristaltic,
segmental and pendular movement.
• Secretion of intestinal juice.
• To complete the digestion of carbohydrates, proteins and fats in the
enterocytes of the villi.
• To protect against infection by microbes that have survived the
antimicrobial action of the HCL in the stomach , by the solitary lymph
follicles and aggregated lymph follicles.
• To secrete the hormones
a. Cholecystokinin pancreozymine(CCK-PZ)(hormones secreted by
duodenum that stimulates secrection of pancreatic juice and
stimulates the gall bladder contraction) and
b. Secretin (hormones secreted by duodenum that stimulates secrection
of pancreatic juice rich in bicarbonate and stimulates the liver to
increase bile output)
• To absorb the end product of nutrient matrials.
Intestinal Juice(Succus entericus)
• Intestinal juice refers to the clear to pale yellow watery secretions from
the glands lining the small intestine walls. The secretion is about 3 liters
daily with having PH 7.8 to 8. It consists of
• hormones,
• digestive enzymes,
• mucus,
• water and
• Enteropeptide (enterokinase) , Enzyme in the intestinal juice that
converts inactive trypsinogens into active trypsin
Traces of other enzyme found in intestinal juice are believed
to be released following the breakdown of cells brushed off the villi.
Secretion:- Mechanical stimulation of the intestinal glands by chyme is
believed to be the main stimulus to the secrection of intestinal juice ,
although the hormones secretine may be involved.
Function
1.
Alkaline intestinal juice assists in raising the PH of the
intestinal contents in between 6.5 to 7.5
2. Enteropeptidase activates pancreatic peptidase which convert
some polyptidase to amino acids and some to smaller molecule
peptides. The final stage of breakdown to amino acids of all
peptides occurs inside the cells of the villi.
3. Lipase complete the digestion of fats to fatty acids and
glycerol partly in the intestine and partly in the cells of the
villi.
4. Sucrose, maltose and lactase complete the digestion of
carbohydrate by converting disaccharide to monosaccharide
inside the cells of the villi.
Large intestine
• The large intestine, also called the colon or the large bowel, is
the last part of the digestive system in vertebrates. Water is
absorbed here and the remaining waste material is stored as
feces before being removed by defecation.
• in humans, the large intestine is about 1.5 meters (4.9 ft) long,
which is about one-fifth of the whole length of
the gastrointestinal tract.
• The lumen is lager than the small intestine . It forms and arch
rounded the coiled up small intestine . For descreptive purpose ,
it can be divided into following parts.
• The cecum and the verniform appendix
• The ascending colon
• The transverse colon
• The descending colon
• The pelvic or sigmoid colon
• Rectum and anal canal
• Caeccum:- Beginning on the right side of the abdomen, the large
intestine is connected to the ilium of the small intestine via the
ileocecal sphincter. From the ileocecal sphincter, the large
intestine forms a sideways “T,” extending both superiorly and
inferiorly. The inferior region of the large intestine forms a short
dead-end segment known as the cecum that terminates in the
vermiform appendix. It is about 13 cm in length.
• Ascending colon:- The superior region forms a hollow tube known
as the ascending colon that climbs along the right side of the
abdomen.
• Transverse colon :- Just inferior to the diaphragm, the ascending
colon turns about 90 degrees toward the middle of the body at the
hepatic flexure(The hepatic flexure is the point of the colon
where the liver touches the large intestine in the upper right
abdomen) and continues across the abdomen as the transverse
colon.
• Descending colon:- At the left side of the abdomen, the
transverse colon turns about 90 degrees at the splenic flexure
and runs down the left side of the abdomen as the descending
colon.
• Pelvic or sigmoid colon:- At the end of the descending colon,
the large intestine bends slightly medially at the sigmoid
flexure to form the S-shaped sigmoid colon before
straightening into the rectum.
• Rectum :- The rectum is the enlarged final segment of the large
intestine that terminates at the anus.
Layer of large intestine
• The innermost layer, known as the mucosa, is made of simple
columnar epithelial tissue. The mucosa of the large intestine is
smooth, lacking the villi found in the small intestine. Many
mucous glands secrete mucus into the hollow lumen of the large
intestine to lubricate its surface and protect it from rough food
particles.
• Surrounding the mucosa is a layer of blood vessels, nerves and
connective tissue known as the submucosa, which supports the
other layers of the large intestine.
• The muscularis layer surrounds the submucosa and contains two
layers of muscle cells that contract and move the large intestine.
a) The longitudinal fibers do not form a smooth continuous
layer of tissue but are collected into three bands called taeniae
coli
b) The circular muscle fibers:- A thin layer , which completely
surrounded s the colon. Thickening of these circular fibers
forms the anal canal sphincters
• Finally, the serosa forms the outermost layer. The serosa is a
thin layer of simple squamous epithelial tissue that secretes
watery serous fluid to lubricate the surface of the large
intestine, protecting it from friction between abdominal organs
and the surrounding muscles and bones.
Functions of Large intestine
• The large intestine performs the vital functions of converting
food into feces, absorbing essential vitamins produced by gut
bacteria, and reclaiming water from feces.
• The absorption of water, electrolytes, and salts by the large
intestine.
• While chyme moves through the large intestine, bacteria digest
substances in the chyme that are not digestible by the human
digestive system. Bacterial fermentation converts the chyme into
feces and releases vitamins including vitamins K, B1, B2, B6,
B12, and biotin.
• finally stored in the rectum and sigmoid colon until it can be
eliminated from the body through the process of defecation.
Anal canal
• The anal canal is a short canal about 3.8 cm long in the adult
and leads from the rectum to the exterior.
• There are two sphincter muscles, which control the anus. The
internal sphincter consisting the smooth muscle fibers, which
is under the control of the autonomic nervous system and the
external sphincter formed by striated muscles, is under
voluntary nerve control.
Mechanism of Defecation
• Defecation is the final act of digestion, by which organisms eliminate
solid, semisolid, and/or liquid waste material from the digestive
tract via the anus.
• Humans expel feces with a frequency varying from a few times daily
to a few times weekly. Waves of muscular contraction (known as
peristalsis) in the walls of the colon move fecal matter through the
digestive tract towards the rectum. Undigested food may also be
expelled this way, in a process called egestion
• Defecation may be involuntary or under voluntary control. Young
children learn voluntary control through the process of toilet
training. Once trained, loss of control called fecal incontinence, may
be caused by physical injury, nerve injury, prior surgeries (such as
an episiotomy), constipation, diarrhea, loss of storage capacity in
the rectum, intense fright ,inflammatory bowel
disease, psychological or neurological factors, birth, or death
• Defecation is the expulsion of faeces from the anal canal. The rectum is
usually empty until mass peristaltic movements propel faecal matter
from the pelvic colon into the rectum. This is known as mass movement
and it is often precipitated by the entry of food into the stomach. This
combination of stimulus and response is called the gastro colic reflex.
• The entry of faeces into the rectum distends the walls of the cavity and
causes nervous impulses to pass to the lower part of the spinal cord.
• Reflex signals are transmitted through the several parasympathetic
nerves, causing contraction of the descending colon , sigmoid flexure
and rectum and relaxation of internal anal sphincter.
• At the same time impulses are sent to the brain , where they arouses the
concious sensation of the desire to defecation.
• If the time is appropriate , the external sphincture is relaxed by concious
control and defecation takes place .
• If the time is not suitable or individual ignored to the defecation, the
external sphincter muscles is controled by will.
• Then the rectum accommodates itself to the contents by relaxation of its
muscular walls , nerves impulses cease and the desire passes off.
• The arrival of more fecal material in the rectum causes further distension
and initiates the defecation reflex again.
During defecation the following action
occure
I.
II.
III.
IV.
The sphincter muscles of the anus relax.
The muscular wall of the rectum contract.
The muscles of the pelvic floor contract.
The intra abdominal pressure is raised by holding
the breath and contracting the diaphragm and
abdominal muscles.
Peritoneum
• peritoneal cavity(abdominal cavity) – The peritoneum is the largest
serous membrane of the body . It is closed sac ,containing a small
amount of serous fluid ,within the abdominal cavity.
• The interior of the peritoneum; a potential space between layers of the
peritoneum bounded by the diaphragm above; it is lined by the
parietal layer of the serous peritoneum and contains the abdominal
organs (stomach, intestines , spleen, liver, pancreas, adrenal glands ).
• It is richly supplied with blood and lymph vessels, and contain many
lymph nodes.
• It provide a physical barrier to local spread of infection.
• It has two layer:• The outer layer, called the parietal peritoneum, is attached to the
abdominal wall and the pelvic walls. The cavity is filled with a serous
fluid ,secreted by the cells, which prevents friction of the layer.
• The inner layer, the visceral peritoneum, is wrapped around the
internal organs that are located inside the intraperitoneal space.
Function of peritoneum
• It gives support to the abdominal organs.
• The presence of peritoneal fluid secrete by the cell of
peritoneum prevents friction of the organs from each other.
• It act as a protection against infection due to presence of
lymph nodes and the ability of greater omentum to isolate an
area of inflamation . It is also known as “Abdominal
policeman”
• It forms a protective covering for the abdominal organs.
• It acts as a storage for fat.
• It has the power to absorb fluid in large quantities.
The salivary glands
• The salivary glands in mammals are exocrine glands, glands with
ducts, that produce saliva. They also secrete amylase, a digestive
enzyme that break down starch into maltose and glucose.
• Parotid glands :-The two parotid glands are major salivary glands
wrapped around the mandibular ramus in humans. The largest of the
salivary glands, they secrete saliva to facilitate mastication and
swallowing, and amylase to begin the digestion of starches. They
produce 20% of the total salivary content in the oral cavity.
• Submandibular glands:- The submandibular glands are a pair of
major salivary glands located beneath the lower jaws, superior to
the digastric muscles. The secretion produced is a mixture of
both serous fluid and mucus, and enters the oral cavity via
the submandibular duct or Wharton duct. Approximately 65-70% of
saliva in the oral cavity is produced by the submandibular glands.
• Sublingual glands:- The sublingual glands are a pair of major
salivary glands located inferior to the tongue, anterior to the
submandibular glands. The secretion produced is mainly mucous in
nature, however it is categorized as a mixed gland. Unlike the other
two major glands. Approximately 5% of saliva entering the oral
cavity come from these glands.
Structure of salivary gland
• A fibrous capsule surrounds all the glands. They consists of a
number of lobules made up of small alveoli lined with secretary
cells. The secretion are poured into small ducts , which join up
to form larger ducts leading into the external jugular veins.
Blood supply: Arterial blood supply by various branches from the external
carotid arteries.
 Venous drainage is into the external jugular veins.
Nerve supply:All of the glands are supplied by sympathetic and parasympathetic
nerves fibers .
Parasympathetic:- Stimulates secretion
Sympathetic:- Depress secretion
Saliva
• Saliva is the mixed secretion of three pairs of salivary glands. It
is a fluid consisting of 90% of water and contain the enzyme
ptyalin(Salivary amylase),which begins the digestion of
carbohydrates. It is also contains mucin, a thick lubricants and
1.5 lit saliva is secreted per day.
• It has small amount of calcium salts, pH is about 5.4 to 7.5 . It
consists of water. Minerals salt, enzyme, mucus, lysosomes,
immunoglobulin, blood clotting factors etc.
Secretion of saliva
The secretion of saliva is under the control of the superior and
inferior salivary nuclei in the brain. All salivary glands are
supplied by both sympathetic and parasympathetic nerves fibers .
Parasympathetic nerves Stimulates secretion of saliva while
Sympathetic nerve inhibits its production .
The sight , smell or thought of food stimulates an initial increase in
the secretion of saliva, when food is place in the mouth there is a
further increase in the output of saliva . The teeth are essential for
mastication of food so that a greater surface area of the food is
exposed to the saliva . The tongue aids mastication by moving the
food about in the mouth.
Inhibition of the secretion of saliva is caused by activity of the
sympathetic nerve fibers as in fear or excitement; leading to
dryness of mouth . Dehydration and some drug(atropin) also
decreased the secretion of saliva.
Functions of saliva
• It helps to moistens the mouth and tongue.
• It moistens and lubricates food so that it can be rolled into a soft
mass or bolus , suitable for swallowing.
• Ptyalin begins to act on cooked starch and converts them to
dextrin's and maltose.
• Saliva dissolves part of the food , which stimulates the taste
buds.
• It has a cleansing action and helps to keep the mouth and teeth
free of debris.
• Saliva contains lysozymes, immunoglobulin, which prevents
infections.
liver
• Liver is the largest gland in the body , weighting about 1.5 to 2.5
kg and is heavier in male than in female.
• It is occupies 2% of total body weight in adult and about 5% of
body weight in newborn.
• It is wedge shaped (triangular) organ lying immediately below the
diaphragm in the right hypochondriac and epigastrium and
extending into the left hypochondrium. Its upper and anterior
surface are smooth and fit the under surface of the diaphragm; Its
posterior surface is irregular in outline . Liver is a store house for
glycogen .
Organ associated with the liver
• Superiorly and Anteriorly:- Diaphragm and anterior abdominal
wall.
• Inferiorly :-Stomach , bile duct, duodenum, right hepatic flexure
of the colon , right kidney and right supra renal gland.
• Posteriorly:-Esophagus inferior venacave ,abdominal aorta , gall
bladder, vertebral column, and the diaphragm.
• Laterally:-The lower ribs and the diaphragm.
• Liver divided into two lobes by falciform ligament anteriorly and
posteriorly.
1. The right lobe
2. The left lobe
The right lobe is 5/6 and left lobe is 1/6 of total liver. The
right lobe is subdivided into caudate and quadrate lobe by the porta.
Caudate lobe lies between inferior venacava ligamentum venosum
and porta hepatis(hilium or door of the liver).
Quadrate lobes lies between gall bladder fossa, ligamentum teres of the
door of the livers, in a deep ,transverse fissure that admit portal vein ,
hepatic vein, right and left hepatic duct , blood vessels, lymph vessels
and nerves to and from the liver.
The surface of the liver
• The liver has two surfaces separated from each other by the sharp
inferior border except posteriorly.
I. The diaphragmatic surface and
II. The visceral surface
On the diaphragmatic surface, apart from a large triangular bare area
where it connects to the diaphragm, the liver is covered by a thin
double-layered membrane, the peritoneum, that help reduces
friction against other organs.
The visceral surface or inferior surface, is uneven and concave. It is
covered in peritoneum apart from where it attaches the
gallbladder and the porta hepatis(The central area or hilum,
known as the porta hepatis is where the common bile duct, hepatic
portal vein, and the hepatic artery proper enter the liver.).
Structure of the liver
• The liver composed of a large number of hexagonal lober, each about
1 mm in diameters and formed by cubical shaped known as
hepatocytes(A hepatocytes is a cell of the main parenchymal tisssue
of the liver).
• A small branches of the hepatic vein extends through the centers of
each lobule.
• The liver cells are arranged in plate or sheets, one cell thick, around
the central vein. The plates of cells form an irregular anatomizing
system throughout the liver between the places of cells lie space,
which contains the sinusoids(A tiny endothelium- lined passage for
blood in the tissue of an organ).
• The sinusoids are blood vessels with incomplete wall and are irregular
in shape and wider than blood capillaries.
• They are lined by the thin endometrium and kuffers cells(hepatic
macrophages), which are phagocytes and remove cellular debries and
bacteria from the blood.
• Each lobes are branches of hepatic artery , the portal vein.
And the hepatic bile duct.
• The blood vessels from small branches which pass between
lobules and enter the sinusoids . Thus sinusoids receive
oxygenated blood form hepatic artery and blood rich in
nutrients from the portal vein.
• The sinusoids drain into the central vein which joins the vein
from adjacent lobules to form the hepatic veins , which drain
the blood from the liver into the inferior venacava.
• The hepatic cells are polyhedral(have many sides) which
secretes the bile
• Artery:- Hepatic artery
Vein:- Hepatic vein and hepatic portal vein
Nerve:- Celiac ganglia and vagus nerve
Functions of liver
1. Deaminates amino acids(Urea formation):- To remove the
nitrogenous portion from the amino acids which is excreted in
the urine.
2. Carbohydrate metabolism:a. Glycogenesis:- Conversion of glucose to glycogen in the
presence of insulin for storage.
b. Glycogenolysis:- Conversion of glycogen to glucose in the
presence of glucagone and release of glucose into the blood.
c. Gluconeogenesis:- Formation of glucose from protein or fat ;
glucocorticoids have accelerating effect on glucogenesis.
3. Desaturation of fats:- Converting stored fat to a form in which it
can be used by the tissue to provide energy,
• Glycogen:- One form in which body fuel is stored primarily in
the liver and broken down into glucose when needed by the
body.
• Glucagone :- A hormone secreted by the pancrease: stimulates
increases in blood sugar levels in the blood(opposing action of
insulin)
• Insulin:- Hormone secreted by the islets of langerhans in the
pancrease ; regulated storage of glycogen in the liver and
accelerates oxidation of sugar in cells.
• Glucocorticoids:- A steroid hormone that is produced by the
adrenal cortex of animal; affects functioning of gonads and has
anti inflammatory activity.
3. Heat production:- Liver has a high metabolic rate and produce heat .
It is main heat producing organ of the body and distribute to other
body organ through blood stream.
4. Secretion of bile:- Liver secrete approximately 600- 1000ml bile/day.
6. Storage of
a. Vit. B12(anti anemic factor)
b. Fat soluble vitamins A, D, E,K
c. Water soluble vitamins ; Riboflavin, niacin, pyridoxine ,folic acid
d. Iron
e. Copper and vitamin D
7. Synthesis of vitamins A from carotene:- The provitamin or carotene
found in green vegetables are changes into retinol in liver.
8. Production and synthesis of amino acids, plasma protein:- About 9095% of the plasma protein and remaining 5- 10 % are gamma
globulin and most of the blood clotting factors i.e. clotting factors V,
VII, IX and X
7. Detoxification:- Liver is able to destroy or modify toxic
substance in the body. Many drugs , toxins, noxious
substances are chemically reduced to simpler non toxins
compound.
8. Inactivation of hormone:- Some hormones like insulin,
glucagon, thyroxin, cortisol, aldesterone and sex hormones are
either chemically altered or excreted by the liver.
9. Metabolize ethanol :- In alcoholic drinks.
The biliary tract
• The biliary tract, (biliary tree or biliary system) refers to
the liver, gall bladder and bile ducts, and how they work together
to make, store and secrete bile.
• The biliary tract is the common anatomical term for the path by
which bile is secreted by the liver then transported to the first part
of the small intestine, also known as the duodenum.
• The biliary tract consist of
a. Right and left hepatic ducts
b. The common hepatic ducts
c. The gall bladder the cystic duct
d. The common bile duct
Structure of Biliary tract
• The walls of the bile ducts consist of following layer:I. The outer covering – peritoneum
II. The middle layer – Smooth muscles layer which exhibits
peristaltic contraction.
III. The inner layer – Lining of mucous membrane
The gall bladder and bile ducts
• The gallbladder is a long sac that stores bile produced by the
liver. Sitting under the liver, the gallbladder controls the
expulsion of bile into the duodenum plays an important role in
the digestion of fats.
• The gallbladder is a pear shaped sac attached to the posterior
surface of the liver by connective tissue. It is about 7 to 10
centimeters long (3 to 4 inches) and 2 to 3 centimeters wide
(about 1 inch). It has the ability to hold about 50- 60 milliliters
of bile which can be emptied via the cystic duct (gallbladder
duct) into the common bile duct. From here, the bile will
empty into the lumen of the duodenum.
Structure
• The wall of the gallbladder has three coats
I. Peritoneum:II. Muscles layer:III. Mucous membrane:• Parts of the Gallbladder
• The gallbladder has 3 parts – fundus, body and neck. The fundus
is the bottom of the gallbladder that protrudes from under the
liver and visible anteriorly. The body is the main dilated portion
of the gallbladder that lies between the fundus and cystic duct.
The neck of the gallbladder is the narrower part that tapers into
the cystic duct
Blood supply
• Arterial blood supply to the gallbladder is via the cystic
artery which arises from the right hepatic artery.
• Venous drainage is via the cystic veins in to portal vein
• Nerves supply of the Gallbladder :- Nerve impulses are
conveyed by sympathetic and parasympathetic nerves fibers.
Functions
• The gallbladder stores bile.
• The lining membrane adds mucus to the bile
• It is also able to concentrate the bile from the liver so that the a
large volume of the bile constituents can be stored in a small
space (1 liter of bile concentrated into 50 ml).
• The gallbladder secretes bile by muscular contractions of its wall
in response to both neural and hormonal factors stimulated by
food, especially fatty foods, in the duodenum.
• Cholecystokinin pancreozymine(CCK-PZ) hormones secreted
by duodenum stimulates the gall bladder contraction
Bile
• A bitter brownish-yellow or greenish-yellow secretion produced
by the liver, stored in the gall bladder, and discharged into the
duodenum, where it aids the process of digestion.
Composition of bile
•
•
•
•
•
•
•
•
•
•
•
Bile produced by the liver is made up of
water (97%)
bile salts – 0.7%
Bile pigments – 0.2%
Cholesterol- 0.06%
Inorganic salts - 0.7%
Fatty acids - 0.7%
Lecithin – 0.1%
fats – 0.1%
mucus and
Alkaline phosphate
Functions Bile
• Bile acts as a surfactant, helping to emulsify the fats in the food .
• This increases the surface area of the fat, allowing greater access by the
pancreatic enzymes that break down fats.
• Bile increases the absorption of fats,
• It is an important part of the absorption of the fat-soluble vitamins, such as the
vitamins D, E, K, and A.
• Besides its digestive function, bile serves also as the route
of excretion for billirubin a waste byproduct of red blood cells recycled by the
liver.
• The presence of bile in small intestine is necessary for the absorption of vitamin
k and digested fat.
• Bile colors and deodorize the feaces.
• Bile has mild laxative and purgative action
• The alkaline bile also has the function of neutralizing any excess stomach acid
before it enters the ileum, the final section of the small intestine.
• Bile salts also act as bactericides, destroying many of the microbes that may be
present in the food.
The pancreas
• The pancreas is a pale yellowish grey gland , weight about 60gm
and having 10- 15 cm long. It is situated in the epigastric and the
left hypochondriac region of the abdominal cavity.
• It consists of three parts
a. Head:- Which lies in the curve(C shaped) of the duodenum and
is closely attached to it.
b. A body which lies behind the body of the stomach.
c. Tail, it is a narrow part , which lies in front of the left kidney
and which just reaches the spleen.
The abdominal aorta and inferior venacava pass behind the gland.
The anterior surface of the pancrease is covered by perotoneum.
• Blood supply:-The splenic and messentaric arteries supply
arterial blood to the pancrease .
• Venous return:- the vein of the same names and joins other
veins to form the portal vein
• Nerve supply:- Parasympathetic stimulates increase the
secretion of pancreatic juice and sympathetic stimulation
depress it.
Functions of pancreas
1. Exocrine function:- The acinar cells of the pancrease secrete
pancreatic juice containing digestive enzyme that digest the
carbohydrates , protein, and fats .
2. Endocrine function:- The alpha beta and gamma cells secrete
hormones .
Pancreatic juice
• Pancreatic juice is a liquid secreted by the pancreas, which
contains a variety of enzymes, including trypsinogen,
chymotrypsinogen, elastase, carboxypeptidase, pancreatic
lipase, nucleases and amylase.
• Pancreatic juice is alkaline in nature due to the high
concentration of bicarbonate ions. Bicarbonate is useful in
neutralizing the acidic gastric acid, allowing for effective
enzymic action.
Composition of pancreatic juice
• Water
• Mineral salt
• Enzymes including trypsinogen, chymotrypsinogen, elastase,
carboxypeptidase, pancreatic lipase, nucleases and amylase.
Secretion
• Pancreatic juice secretion is regulated by the hormones secretin and
cholecystokinin, which is produced by the walls of
the duodenum upon detection of acid food, proteins, fats and
vitamins.
• Pancreatic secretion consists of an aqueous bicarbonate component
from the duct cells and enzymatic component from the acinar cells.
• A clear alkaline secretion of the pancreas containing enzymes that
aid in the digestion of proteins, carbohydrates, and fats.
Function
a. Trypsinogen and chymotrypsinogen are inactive enzymes until
they come in contact which entrokinase of the intestinal juice
which converts them into trypsin and chemotrypsin. These
enzymes converts peptones into peptides and polypeptides.
b. Amylase converts all polysaccharides ((starch) not affected by
ptyalin) to disaccharides(sugar)
c. Lipase converts fats into fatty acids and glycerol to aid the
action of lipase . Bile salts emulsify the fats , breaking the fat
down into smaller globules.
9.4 Physiology of digestion
• Digestion is the process by which the nutritional material (food
substance) are altered or change physically and chemically so that they
are reduced to simple chemical substances ready for absorption from
alimentary tract into the blood and lymph capillaries in the villi of the
small intestine. The process is divided into two main parts
a. Mechanical digestion
b. Chemical digestion
a. Mechanical digestion consists of the liquefying of food by the
digestive juice, mastication, swallowing, and thereafter onward
movement through the tract by peristalsis.
b. Chemical digestion takes place by break down of food through
chemical substances of enzyme present in the secretions of the
different organs of the GI tract.
•
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The different juice and enzymes are :Saliva in the mouth—Amylase( Ptylin)
Gastric juice in the stomach- Pepsinogen, Rennin
Pancreatic juice in the duodenum- Amylase, lipase,
trypsinogen, Chymotrypsinogen
 Bile in duodenum
 Intestinal juice in the small intestine enteropeptidase
enterokinase, maltase, Lactase, Sucrose, Isomaltose, Lipase.
Carbohydrate digestion
Organ
Digestive Juice
Enzyme and action
Mouth
Saliva
Ptyaline converts cooked
starch to maltose(A white
crystal sugar formed during the
digestion of starch)
Stomach
Gastric juice
Small intestine Pancreatic juice
HCL stops the action of
saliva amylase
Amylase converts all
starches to
disaccharides(sugar) two
monosaccharides
Small intestine Intestinal juice
(Enterocytes)
intestinal absorptive
cells
Sucrase, maltose lactase
converts all sugar to
monosaccaride(simple sugars)
Absorption of digested carbohydrate
• The monosaccharide resulting from digestion is easily
absorbed into the mucosal cells of small intestine and pass into
circulation via portal vein.
• A very small amount may also be absorbed by the lymph.
• The microvilli lining the mocousal cells greatly helps in
absorption by increasing the surface area.
• The absorption of glucose and galactose is now believed to
take place by active transport rather than by simple diffusion.
Utilization
I.
To maintain a constant blood glucose level so that all
body tissues has a constant supply.
II. Some of the excess is converted to glycogen in the
presence of insulin and stored in the liver and in the
muscles.
III. Any remaining glucose is converted into fat and
stored in the fat depots.
IV. Glucose is used in the body to provide energy and
heat. O2 is necessary for its complete break down
and the waste products left are carbon dioxide and
water .
Protein digestion
Organ
Digestive Juice
Enzyme and action
Mouth
Saliva
No action
Stomach
Gstric juice
HCL converts pepsinogen to pepsin;
pepsin converts all protein to
peptones.(water soluble compounds)
Rennin converts soluble casein to
insoluble caseinogen.(A protein present in milk)
Small intestine
Pancreatic juice
Enterokinase of intestinal juice converts
trypsinogen and chymotrypsin (secreted by
pancrease), which converts peptidase and
polypeptides.
Small intestine
(Enterocytes)
Intestinal juice
Peptidase converts peptidase and
polypeptides to amino acids.
Absorption of protein
• The amino acids obtained after the digestion of dietary
proteins are rapidly absorbed from the small intestine
into the portal blood by active transport.
• Pyridoxine (Vit B6) is required for the absorption of
amino acids .
• Large protein molecules are not absorbed in GI tract
normally.
Utilization
I.
In the liver, to form albumin , serum globulin, prothrombin,
and fibrogen.
II. Used in various combination by cells of the body for cell
multiplication, cell repair and the production of secretion e.g.
hormones, enzymes.
III. Amino acids , which are not required , are deaminated(one or
more of the groups of atoms containing nitrogen are removed)
in the liver. The nitrigenous part is converted into urea and
excreted in the urine, the remaining part is used to provide
energy and heat or deposited as fat in the fat depots.
IV. To maintain the amino acid pool.
Fat digestion
Organ
Digestive Juice
Enzyme and action
Mouth
Saliva
No action
Stomach
Gstric juice
No action
Small intestine
Pancreatic juice
Small intestine
Bile
Lipase converts fat to fatty
acids and glycerol
Bile salt emulsify fats
Small intestine
(Enterocytes)
Intestinal juice
Lipase completes the
digestion of fats to fatty
acids and glycerol
Absorption of Fat
• Last part of the duodenum and proximal portion of
the jejunum are the site for maximum absorption as
well as for intracellular resynthesis of triglycerides
from fatty acids.
Utilization
i.
In the presence of oxygen to provide energy and
heat , the waste products CO2 and H2O being
produced.
ii. Stored in the fats depots.
Physiology of metabolism
• Metabolism is the total of all the chemical reaction that occur
in the body , using absorbed nutrients to
a. Provide energy by chemical oxidation of nutrient.
b. Make new or replacement of body substances.
Metabolism consists of two major process
a. Catabolism
b. Anabolism
a. Catabolism:- Catabolism is the breaking down of
large molecules into smaller ones releasing
chemical energy, that is stored as adenosine
triphosphate and heat. Heat is used to maintain the
body at the optimum level for chemical activity.
Excess heat is displaced through the skin and excreta.
b. Anabolism:- Anabolism is building up, or synthesis
of large molecules from smaller ones and utilize
the energy stored as ATP[(adenosine triphosphate),
major source of energy for cellular reaction]
In healthy adults there is a balance between
catabolism and anabolism, Which is called the energybalance(ie energy produced equal energy used)
• Metabolic rate:- The metabolic rate is a method of
estimating the energy requirements of the body, is to
measure in terms of heat. The unit of the heat used for
this purpose is the calorie(Abbreviated to C).
• A calorie or (Kilocalorie) may be defined as the
amount of heat required to raise 1 liter of water through
1 degree centrigrade.
• 1 CALORIE= 4184 JOULES(J)= 4.184 KILIJOULES
• 1 grams carbohydrates = 4 calories (17 kilojuiles)
• 1grams protein = 4 calories (17 kilojuiles)
• 1 grams fat = 9 calories (38 kilojuiles)
• 1 grams alcohol = 7 calories (29.75 kilojuiles)
• Basal metabolic rate :- BMR is the rate of the body's energy
requirement (expenditure) Under “Basal condition”. This means
the individual is at rest mentally and physically , has not eaten for
at least 12 hours(Post absorptive state) and in a warm comfortable
environment.
• Under this condition the metabolic needs of the body are at their
lowest energy being used only to sustain vital function (Eg.
Breating ,the beating of the heart, Maintenance of normal body
temperature)
• The basal metabolic rate can be calculated by estimating the
amount of oxygen consumed in a given time . Since individual
vary greatly in size, the BMR is also differs. The BMR is
expressed in calories per square meter of body surface per hour.
• The body surface area is calculated from measurements of an
individuals weight and height.
Carbohydrates metabolism
• Carbohydrate is the term used to describe staches and sugar.
They are compounds of carbon, hydrogen and oxygen(C6 H12O6)
. Carbohydrates are absorbed through the villi of the small
intestine as glucose, fructose, and glactose . They are the primary
energy source of the body. The fructose and glactose converted to
glucose by the liver and returned to the blood stream.
• Glucose is used to provide energy for cellular activity. Before
oxidation of glucose in the cells , it must be transported across the
cell membrane by a process called facilitated diffusion , which
require the use of carrier substance. The presence of hormone
insulin accelerates this process. Failure of the pancrease to secrete
sufficient insulin , as in diabetes mellitus, means that only very
small amount of glucose are able to enter the cells.
• The maintenance of the blood glucose concentration at a
relatively constant level is essential for the survival and function
of brain cells. A fall in the blood glucose level rapidly results in
disturbance of the central nervous system and if uncorrected ,
leads to loss of consciousness and death within few hours.
• The liver and hormones regulates the blood glucose level.
1. Catabolism of glucose:- The catabolism of glucose by cells to
release energy occurs in two stage
a. An anaerobic stage, called glycolysis (Which does not require
oxygen and )
b. Aerobic stage, which require oxygen
a. Glycolysis:- The conversion of glucose or glycogen to pyruvate
and lactate is known as glycolysis. Lactate is produced from
pyruvate only when oxygen supply to tissue is insufficient.
B. Oxidation of glucose (citric acid cycle):- Under aerobic
condition , pyruvate is oxidized to CO2 and H2O through a
service of reaction, collectively called as citric acid cycle(Kerbs
cycle). It is most commonly pathway related with energy
production in animal system.
2. Glycogenesis:- The formation of glycogen in the body is called
glycogenesis . It takes place mainly in liver and muscle where
glycogen is stored in large amount on an average about 108gm
of glycogen are store in liver and about 245 gm in muscles.
3. Glycogenolysis:- The beak down of glycogen to glucose is called
glycogenolysis. This process takes place in liver and muscles
tissues which store glycogen as reserve carbohydrate.
4. Glyconeogenesis:- The formation of glucose from non
carbohydrate precursors, such as lactic acid, amino acids
(protein) and glycerol(fat) is called glyconeogenesis.
Protein metabolism
• Protein are complex organic compounds containing carbon,
hydrogen and oxygen with the addition of nitrogen , sulphur
and phosphorus. Large protein molecules consists of many
amino acids linked together to form chain known as peptide
bonds.
• Protein are essential to the body , they provide most of the
structural elements of the cells and the enzymes , which are
necessary for all biochemical reaction
• When the blood concentration of amino acids is high . Some
are absorbed in the liver cells and stored . As the amino acids
concentration of the blood falls to below normal . The stored
amino acids are release from the liver back into the blood. To
some extend most of the other body cells can also stored in this
way are referred to as the “amino acids pool”.
• Catabolism of protein :- The amino acids are utilized for heat and
energy. The first stage of protein catabolism is deanimation and takes
place in the liver.
Deanimation:- (Removal of an amino group from amino acid and
converted to ammonia)
The reconversion of an amino acids to a ketoacid with the liberation of
ammonia is called deanimation. It is accomplished mainly in liver and
kidney tissues by the following mechanism.
 Oxidation deanimation
 Non oxidative deanimation
The nitrogen portion is split off from the amino acids molecules to form
ammonia , which in turn combines with carbondioxide to form urea in
the liver. The urea is excreted by the kidneys into the urine.
The deanimated amino acids can be directly oxidized to form
carbondioxide and water with the release of heat and energy.
Fat metabolism
• Fats are absorbed as fatty acids and glycerol into the lacteals of
the villi in the small intestine, where they are recombined to
neutral fats and transported to the blood stream by lymphatic
vessels. Fats are compounds containing carbon and hydrogen
with very little oxygen.
• They constitute a more concentrated energy source than
carbohydrates
• 1 gmof fats yeild 9 calories of heat and energy.
• Catabolism of fats:- neutral fats are split by the liver to glycerol and
fatty acids. Glycerol is similar to the breakdown products of glucose
and can be converted to a compound that enters the glycoltic pathway
, Fatty acids are oxidazed to acetyl coenzyme A and provided that
carbohydrates are being metabolized, can enter the citric acid cycle.
• If carbohydrates are not available , as in starvation or when
carbohydrates cannot be metabolized as in diabetes mellitus, then the
accumulate in the body.
• The liver cells condense the acetyl coenzyme . A molucule to form
aceto- acetic acids . Some of which converted to beta
hydroxybutyric acids and acetone. These three substances are
collectively known as ketone bodies or ketoacids . Accumulation of
ketone bodies in the blood is called ketosis.
• Any fat which is not immediately required for heat and energy is
stored in the fat depots of the body.
• When fat is required to provide energy , it is withdrawn from the fat
depots and carried to the liver to be desaturated and split to glycerol
and fatty acids.
Question
• List the accessory organ of digestive system.
Write the function of salivary glands.
• Write the function of gastric juice ,what special
digestion takes place in small intestine ? Explain.
• Explain the physiology of protein digestion from
mouth to large intestine.
• Describe the function of stomach . Explain the
process of carbohydrate metabolism in small
intestine.
• Write the short notes :i. Mouth:- Tongue , teeth
ii. Pharynx
iii. Esophagus
iv. Stomach
v. Small intestine
vi. Large intestine
vii. Anal canal
a. The salivary glands
b. The pancrease
c. Liver
d. The gall bladder and bile ducts.