Digestive
System
Digestive Tract
Also
called alimentary canal
Hollow tube roughly 8 meters in length
Structure of the Wall
Lumen
- hollow center of tube
Mucosa - epithelial layer with mucoussecreting cells
Submucosa - connective tissue layer
rich with blood vessels, lymphatic
vessels, and nerves
Muscular layer - smooth muscle layer
 Circular-
adjust lumen diameter
 Longitudinal- adjust tract length
Serosa
- outermost layer; secretes
serous fluid
Movements of the Tube
Types of Digestion
Mechanical
 Physical
breakdown of food into
smaller pieces
Chemical
 Breakdown
of food molecules
into more simple molecules by
enzymes
Mouth
Receives
food
Pushes into the remaining digestive
tract
Includes: lips, teeth, cheeks, tongue,
and palate
Two cavities:
 1)
Oral cavity
 2)
Vestibule
 Space
between palate and tongue
 Cavity
between teeth and lips and cheeks
1.
7.
Exit Slip
2.
8.
3.
9.
4.
10.
5.
11.
6.
Cheek and Lips
 Cheeks
 Contain
muscles used during chewing
 Stratified squamous epithelial tissue
inside
 Lips
 Highly
mobile skeletal muscles rich in
sensory receptors
 Aid in sensing temperature and texture
of food
Tongue
 Functions:
 Keeps
food underneath teeth
 Mixes food with saliva
 Moves bolus to the back of the
mouth during swallowing
 Muscular
structure covered with
mucous membrane
 Root is attached to hyoid bone
 Attached to floor of mouth by
frenulum
 Papillae provide surface friction
and contain taste buds
Palate
 Forms
roof of oral cavity
 Hard palate
 Anterior
 Soft
portion
palate
 Posterior
 Soft
portion; includes uvula
palate raises during
swallowing to close off nasal
cavity
Tonsils
 Masses
of lymphatic tissue
 Lingual

On the tongue
 Pharyngeal

Posterior wall of pharynx;
also called adenoids
 Palatine

Back of mouth on either
side of tongue; associated
with palate
Teeth
 Two
sets:
 1) Primary - 20 teeth
 Lost/shed, nonpermanent
 2) Secondary - 32 teeth
 Permanent, come in after primary teeth are
lost/shed
 Function:
 Begin
mechanical digestion of food
Anatomy of Tooth
Crown - section above gingiva (gum)
Root -section below gingiva
Enamel - outer covering on crown
Dentin - bone-like substance that fills
most of the tooth
Pulp cavity - connective tissue that
contains blood vessels and nerves
Root canal - tubular extension that
brings blood vessel and nerve to the
pulp cavity
Cementum and periodontal ligament hold tooth in alveolar process of jaw
bone
Salivary Glands
 Functions:
 Moistens
food
 Binds food together
 Dissolves food (so it can be tasted)
 Cleanses mouth and teeth
 Begins digestion of carbohydrates
 Two
 1)
types of cells
Serous cells
 Secretes
 2)
serous fluid with enzyme amylase
Mucous cells
 Secretes
mucous
Salivary Glands (cont)
3
Types:
 1)
Parotid glands:
Largest glands; anterior and inferior to
ear; secrete watery saliva rich in amylase
 2) Submandibular:
Located in floor of mouth just inside
lower jaw
 3) Sublingual:
Smallest glands; inferior to tongue;
secrete saliva in mucous concentration
Pharynx
 Cavity
located posterior to oral cavity
 Provides connection to larynx and
esophagus
 Three parts:
 1)
Nasopharynx - upper potion connecting
to nasal cavity
 2) Oropharynx - middle section posterior to
palate
 3) Laryngopharynx - lower portion posterior
to larynx opening; leads to esophagus
Swallowing Action
1.
2.
3.
4.
5.
6.
7.
Bolus stimulates sensory receptors in
pharyngeal opening
Soft palate raises- closes nasal cavity
Larynx elevates; epiglottis closes off
larynx
Tongue presses against palate
Longitudinal muscle pull pharynx
towards food
Muscles relax near esophagus to open
the tube
Peristalsis moves food into esophagus
Esophagus
 Hollow
collapsible tube
 Move food from pharynx to stomach
 Passes through diaphragm in opening called
esophageal hiatus
 When food reaches opening of stomach, lower
esophageal sphincter opens
Stomach
 J-shaped
pouch in
abdomen
 Holds
about 1 liter of food
 Functions:
 Mix
food with gastric juices
 Begin protein digestion
 Responsible for limited
absorption
 Moves food into small intestine
Stomach (cont)
Rugae
 Thick
folds of mucosa and submucosa
allow for expansion of stomach wall
Regions
of the stomach
 Cardiac - portion near esophagus
 Fundic - portion lateral to cardiac where
stomach ballons
 Body - main portion of stomach between
cardiac and pyloric
 Pyloric - portion near opening to
duodenum
 Pyloric Sphincter - thick muscle band
controlling entrance into duodenum
Stomach
Gastric Secretions
Mucosa
is studded with gastric pits
Gastric pits are the opening to gastric
glands
Gastric glands have three types of
secreting cells:
 1)
Mucous cells - secrete mucous; helps
prevent stomach from digesting itself
 2) Chief cells - secrete pepsinogen
 3) Parietal cells - secrete HCl and intrinsic
factor
Gastric secretions
(cont)
 As
food enters stomach, mixing actions
occur to breakdown food into chyme
 Gastric juices are added

HCl creates acidic environment
 Shortens
pepsin

(activates) pepsinogen and makes it
Helps with vitamin B12 absorption
Gastric secretions
(cont)
 Limited




absorption of the following occur:
Water
Salts
Alcohol
Lipid-soluble drugs
 Chyme
is moved to pyloric sphincter and
pushed through
Control of Gastric
Secretions
 Digestion
is controlled by medulla
oblongata
 Parasympathetic NS:

Increases gastric secretions
 Sympathetic

Decreases gastric secretions
 Hormones:


NS:
Gastrin - stimulates production of gastric juices
Cholecystokinin - released when small intestine
fills with food; decreases gastric motility
Review Quiz
Mouth->Stomach
Contains rugae (folds)?
2. Contains lower sphincter and opens to stomach?
3. Mixes food with gastric juices?
4. Provides connection to larynx and esophagus?
5. Begins mechanical digestion of food?
1.
1.
2.
3.
4.
5.
Stomach
Esophagus
Stomach
Pharynx
Teeth
Pancreas
Has
endocrine and exocrine function (Ch
11!)
Nestled in C-shaped curve of duodenum
Pancreatic acinar cells
 Secrete
pancreatic juices
 Clustered around tubes that eventually empty
into pancreatic duct
Pancreatic
pancreas
 Empties
duct run the length of the
the juice into the duodenum
Hepatopancreatic
 Controls
emptying
sphincter
Pancreatic Enzymes
Carbohydrates:
 Pancreatic
amylase
Breaks polysaccharides into
dissaccharides
Lipids:
 Pancreatic
lipase
Breaks fats into glycerol and fatty acids
Nucleic
Acids:
 Nucleases
Breaks
nucleic acids into nucleotides
Pancreatic Enzymes
(cont)
 Protein:
3
enzymes (break them down into amino
acids)
Trypsin
 Chymotrypsin
 Carboxypeptidase

 Stored
forms

in zymogen granules in inactive
Ex: Trypsin’s inactive form is trypsinogen and is activated
by enterokinase which is secreted by mucosa of
duodenum
Control of Pancreatic
Juices and Enzymes

Parasympathetic NS control:


Acidic chyme:



Stimulate release of pancreatic juices
Stimulates release of secretin into the bloodstream
Stimulates release of pancreatic juice high in
bicarbonate ions
Chyme high in protein and fat


Stimulates release of cholecystokinin into
bloodstream
Stimulates release of pancreatic juice high in
digestive enzymes
Liver
Functions:
 Controlling
carbohydrate metabolism
 Lipid metabolism
 Protein metabolism
 Storage
 Blood filtering
 Detoxification
 Secretion of bile
Liver Structure
 Connective
tissue divides liver into larger right lobe
and smaller left lobe
 Liver is further divided into lobules
 Hepatic cells radiate around a central vein
 Spaces between the hepatic cells are called
hepatic sinusoids
Liver Structure (cont)
 Blood
from digestive track enters sinusoids from
hepatic portal vein
 Kupffer cells

Large macrophages (filter out pathogens from sinusoids)
 Hepatic

cells
Take out excess nutrients
 Blood
enters central vein and continues on its path
back to the heart
What is Bile?
 Yellowish-green
cells
 Includes:

liquid secreted by liver
Bile salts, bile pigments, cholesterol, and
electrolytes
What does bile do?
 Emulsification


Breaks fats globules into smaller droplets
Smaller droplets are easier for lipases to
digest
 Enhances
absorption of fatty acids,
cholesterol, and fat-soluble vitamins A, D,
E, and K
Bile (cont)
Sequence
Hepatic
of travel:
cells → Bile canaliculi → Bile
Ductules → Bile duct → Hepatic duct
→ Common hepatic duct →
Hepatopancreatic sphincter →
Duodenum
Gallbladder



Between meals, bile up in common hepatic
duct and into the cystic duct that attaches to it
Bile is backed up into gallbladder that is
attached to the
cystic duct
Gallbladder also
absorbs excess
water in bile therefore
concentrating it
Control of Bile Release
 Chyme

high in protein and fat
Stimulates release of cholecystokinin into
bloodstream which stimulates release of
bile
 Where
peristalsis reaches
hepatopancreatic sphincter, it relaxes
and bile squirts into duodenum
Small Intestine
Structure
 Three
 1)
parts:
Duodenum
First part after stomach; forms a Cshape
 2) Jejunum
More active than ileum
 3) Ileum
Leads to large intestine
Small Intestine
Structure (cont)
 Mesentary


Holds loops of intestine to posterior abdominal wall
Supports blood vessels, lymphatic vessels, and nerves
associated with intestine
 Greater



omentum
Double fold of membrane covering intestines
Helps wall off infected area
Prevent spread throughout cavity
Structure of
Intestinal
Wall
Wall
has many projections called villi
 Increase digestive surface area
 Most numerous in duodenum and
first part of
jejunum
 Covered with simple columnar epithelium
 Have a connective tissue core
 Contains blood vessels, a lymphatic vessel
called a lacteal, and nerves
 At the base are pockets called intestinal
glands
Small Intestine Secretions
 Mucosa
 Goblet
cells secrete mucos
 Mucous
 Secreting
mucous
 Intestinal
 Secrete
cell in submucosa - secrete alkaline
gland
watery substance
 Epithelial
cells of mucosa (all release enzymes)
 Peptidase
 Sucrase,
maltase, and lactase
 Intestinal lipase
Control of Small Intestine
Secretions
 Parasympathetic

NS:
Triggers release when intestine wall is
expanded
 Other
glands are stimulated by chyme
(both mechanically and chemically)
Sm. Intes. Absorption
 Small
intestines = 95% of absorption of nutrients
 Absorption follows release of chemicals:

Chemicals mix with chyme to help digestion and
absorption
 Bile
 Pancreatic
juices
 Intestinal enzymes (maltase, lactase, sucrase, trypsin and
chymotrypsin)
Absorption (cont)
 Carbohydrates:
 Simple
sugars are moved into the blood stream
by diffusion or active transport
 Proteins:
 Amino
acids are actively transported into the
blood stream
Lipids
 Fatty acids and glycerol diffuse into cell of villi
 Fatty acids with short chains diffuse into blood
stream
 Other are synthesized into fats and packed with
protein (chylomicron) by the ER
 These enter the lacteal and are carried to the
blood
Movements of Sm Intes
 Mixing

movements
Contractions move chyme from side to side
to mix it
 Peristalsis

Movement toward large intestine; very slow
 Peristaltic

Forceful contraction if intestine if irritated or
over distended; pushes chyme to large
intestine without much absorption’ leads to
diarrhea
 Ileocecal

rush
sphincter
Controls movement between ileum and
cecum; normally closed; open after a meal
Structure of Large
Intestine
 Large
diameter lumen
 Composed of:







Cecum
Ascending colon
Transverse colon
Descending colon
Sigmoid colon
Rectum
Anal Canal
Structure of Large Intestine
Wall
 Longitudinal
muscle
occurs in three
bands called teniae
coli
 Tension in teniae coli
creates pouches
called haustra in
intestine
Functions of Large Intestine
 Mucous



secretion
Protects walls
Bind fecal matter
Controls pH
 Absorption

Absorb water and electrolytes in proximal portion
 Habitat


for bacteria
Bacteria digest parts of fecal matter that is indigestible
to us;
Synthesize vitamins that are then absorbed
Movements of Large Intestine
 Mixing
 Same
movements
as small intestine
 Peristalsis
 Waves
meals
occur only a few time a day; usually after
 Defecation
reflex
 Feces
are forced into rectum; internal anal
sphincter is relaxed
 Pressure
is increased in abdomen which
squeezes the rectum
 External anal sphincter is relaxed
Composition of Feces
 Water
 Undigested
material
 Electrolytes
 Mucous
 Intestinal
 Bacteria
Cells
Thumbs up, Thumbs Down
The large intestines houses bacteria such as E coli?
Thumbs up!
2. The liver can absorb excess water in bile.
Thumbs down! Gallbladder
3. The small intestines contains mesentery which helps bind
and support.
Thumbs up!
4. The large intestines helps perform peristalsis and
peristaltic rush.
Thumbs down! Small intestines
5. The liver metabolizes proteins and lipids and filters blood.
Thumbs up!!
1.
Review of Digestive Tract
Digestive Nutrients
 Macronutrients



Carbohydrates
Protein
Lipids
 Micronutrients


Vitamins
Minerals
 Essential

Nutrients
Nutrients that body cannot produce itself
Carbohydrates
 Process

of Digestion:
Complex carbohydrate (Polysaccharide) →
Disaccharide → Monosaccharide
 Indigestible

carbohydrates:
Ex: Cellulose - provides roughage (or fiber)
to diet
Carbohydrates (cont)
 Fructose
and galactose are converted to glucose
by the liver
 Excess glucose

Liver converts glucose to glycogen or to fats
 Deficiency

of Glucose
Liver converts glycogen, fats, or proteins to glucose
 Requirements
for carbohydrates varies depending
upon energy expenditures


More energy = more carbohydrate requirement
Ex: Athletes will consume pasta before event for more
energy
Lipids

Process of Digestion:


Fat → Glycerol + Fatty Acids
Use of Lipid Products:






Used to synthesize glucose
Converted to acetyl CoA and enters
Krebs/Citric acid cycle (of cellular respiration)
Stored in adipose tissue (insulation)
Used in building cellular structures (cell and
organelle membranes)
Used to synthesize some hormones (steroid)
Animation
Protein
 Process

Polypeptide → Amino Acids
 Uses




of Digestion:
of Amino Acids:
Used to create enzymes
Used to create structural proteins (muscle, etc)
Various other uses
Deaminated (removal of amine group from amino
acid) by liver
 Converted
respiration)
into products used in citric acid cycle (cellular
Proteins (cont)
 Nonessential

Can be synthesized by body; do not need to be in diet
 Essential

amino acids
Cannot be synthesized by body; do need to be in diet
 Complete

proteins
Dietary proteins that contain enough of the essential amino
acids
 Incomplete

proteins
Dietary proteins that don’t contain enough of the essential
amino acids
 Partially

amino acids
complete proteins
Contain enough essential proteins to sustain life but not enough
to promote growth
Vitamins
 Organic
compounds requires in small
amounts for normal metabolism
 Fat-soluble: A, D, E, and K

Accumulate in tissues and can
lead to overdoses
 Water-soluble:

B and C
Excess is often excreted
Minerals
 Elements
other than carbon needed for
human metabolism
 Concentrated in bones and teeth; parts
of structural components and enzymes;
free-floating ions
 Major Minerals: Ca, P, K, S, Na, Cl, and Mg
 Trace Elements: Fe, Mn, Cu, I, Co, Zn, F, Cr
Diseases and disorders
Hepatitis:
 Inflammation
of liver
 Caused by class of viruses (usually)
 Names
of hepatitis (A-G) come from virus
 Symptoms:
 Lack
of appetite
 Nausea and vomiting
 Low fever and mild headache
 Stiff joints and rash
 Upper right quadrant pain in
abdomen
 Dark/foamy urine
 Yellowish skin/sclera of eye
Diseases and disorders
 Lactose



Intolerance:
Lactose sugar unable to be broken down
Caused by lack of production of lactase (enzyme
which breaks down lactose)
Symptoms:
 Bloating
 Intestinal
cramps
 Diarrhea

Avoidance:
 Avoid
lactose sugar (drink soy/almond milk)
 Take lactase pills before eating lactose