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I. Processes overview
Taking in food
2) Movement
Transporting food material and waste down the digestive tract
3) Digestion
Breaking food material down into smaller parts: Two processes
Breaking food down using physical processes: chewing and
Enzymes break food macromolecules down into small
Starch into glucose; proteins into amino acids.
4) Absorption
The subunits are absorbed into the blood stream
5) Defecation
Waste material is eliminated from the body.
II. Organization
1) Organs of the gastrointestinal (GI) tract
Pharynx, esophagus, stomach, Small intestine, large intestine
2) Accessory structures
Teeth, tongue, salivary glands, liver, gallbladder, pancreas.
III. GI tissue
A mucous membrane that
lines the lumen of the
digestive tract
! Most of the length simple
columnar epithelium.
! Oral and anal ends:
nonkeratinzed stratified
lamina propria
! This is a layer of CT under
the epithelium
muscularis mucosae
! Under the lamina: a thin
layer of smooth muscle
! Folds of the mucosa
! Increases surface area
! Allows the digestive
organs to expand.
III. GI tissue
connective tissue
Areolar (loose)
blood vessels
and lymphatics
! Submucosal glands
! Secrete enzymes and
Muscularis externa
! Two layers:
! Outer longitudinal
! Inner circular
Serosa adventitia
Ootermost layer
Also called the viseceral
III. GI tissue
Visceral peritoneum
Is the inner membrane
that covers organs in
the abdominal cavity.
Forms part of the …
The serous membrane of
the abdominal cavity;
similar to the pericardial
and pleural membranes.
Peritoneum is the outer
membrane which lines the
Peritoneal cavity
The potential space between
the two membranes; filled
with a serous fluid.
III. GI tissue
Of the peritoneum extend
throughout the
abdominal cavity
Double-layered folds of the
Bind the organs together.
Anchor them to the
posterior wall
Falciform and coronary
Attaches the liver to the
anterior abdomen and
the diaphragm
Lesser and greater omentum
The former: suspends the
stomach from the liver.
Latter: hangs down in front
of the intestines.
IV-V. Mouth and tongue
Oral cavity
Entry into the digestive
Consists of accessory
organs that start
Teeth for mastication
Tongue to manipulate food
and generate speech.
Also taste buds are
located here.
Salivary glands secrete
into the oral cavity.
Place where swallowing
reflex is initiated.
IV-V. Mouth and tongue
Lingual frenulum
! Attaches the tongue to the
floor of the mouth.
Bumps of mucosal and CT on
dorsal surface of the
Give it rough texture.
Manipulate food
Salivary glands
Produce saliva
Three sets:
! Largest: Ant/inf to ears
! Medial surface of the
! Under the floor of the
IV-V. Mouth and tongue
98% water
ions: Na+, Cl-, bicarbonate
mucin ( protein, lubrication)
salivary amylase
Enzyme which breaks down starch into maltose (a disaccharide)
1) Dissolves food chemicals
2) Moistens and lubricates food
3) Carbohydrate digestion starts here
IV-V. Mouth and tongue
Or the swallowing reflex.
A mass of chewed food mixed with
Deglutition starts with…
Buccal stage
Or voluntary stage.
The tongue moves the bolus
towards the oropharynx.
Pharyngeal stage
The bolus in the pharynx triggers a
series of reflexive contractions.
Forces the bolus into the
Esophageal stage
Contractions carry the bolus down
the esophagus.
The esophageal sphincter at the
distal end opens.
VI. Esophagus
Muscular tube: 2.5x25 cm
Extends from the pharynx to the stomach
Function: transport a bolus to the stomach.
Similar to the mucosa describe before.
Muscularis layer is very prominent.
Involuntary waves of smooth muscle contraction.
Moves a bolus through the GI tract.
Esophageal sphincter
Located: distal esophagus, just before stomach.
Constricts to prevent back flow of stomach contents.
If the sphincter fails, backflow or acid reflux occurs.
Also called…
Irritation of esophageal lining.
VII. Stomach
Food storage
Chyme production
Protein digestion
Mucus production
Absorption of nutrients
(very little)
Bulges above the entrance of the esophagus.
Around the opening of the esophagus.
The open area below the fundus: about 2/3 of the stomach volume.
Lesser curvature- concave medial border.
Greater curvature- convex lateral border
Pyloric region
Narrow region distal to the body
Pyloric sphincter- between the duodenum and the pyloric region
VII. Stomach
Adaptations of the stomach
for digestion.
1)! Rugae
Prominent longitudinal
folds of the stomach
Easily seen when the
stomach is empty.
Allows the stomach to
distend with food.
2)! Gastric pits (3 million)
Openings to collections
of gastric glands (15
Allow gastric juice to
enter the stomach
VII. Stomach
Gastric glands contain
1)! Parietal cells secrete
Instrisic factor
Aids in vitamin B12 absorption
HCl- hydrochloric acid
pH ~2
For break down of cells
(bacteria, plant).
2)! Enteroendocrine cells or G cells
Produce hormones which regulate
gastric function such as gastrin.
3)! Chief cells
Produce pepsinogen
Precursor to pepsin, a proteolytic
(breaks down proteins) enzyme
VII. Stomach
Gastric juice
Made by gastric glands.
Consists of mucous, HCl, water, pepsinogen, and intrinsic factor.
You make about 1500 ml/day
Gastric juice mixed with food is called acidic chyme.
Also have the enzymes rennin and gastric lipase in gastric juice.
Important for the digestion of milk proteins and milk fat, respectively.
VII. Stomach
Regulation of gastric function
Cephalic phase (“head” phase)
ANS is stimulated by thoughts of food or smells, time of day.
Stimulates the release of gastric juice.
Prepare the stomach for the arrival of food.
Also release of the hormone gastrin which stimulates:
chief and parietal cells
Contractions in the stomach wall
VII. Stomach
Gastric phase (“stomach” phase)
When food arrives, stretches the stomach.
Stimulates release of gastrin and gastric juice.
Also triggers “mixing waves”; contractions of the stomach wall to mix food
and gastric juice.
Also increases intestinal motility (movement.)
Start protein digestion.
VII. Stomach
Intestinal phase
Gastric emptying.
Acidic chyme is passed into the first part of small intestine (duodenum.)
Only small amounts are released.
Distention of the duodenum releases CCK which affects the liver and
VII. Stomach
Regulatory functions are inhibitory to the stomach.
Called enterogastric reflexes.
Acidic chyme distends the duodenum
Inhibits gastrin production
Reflexes shutdown gastric activity
until the chyme passes further down the small intestine.
Contractions in the stomach (mixing waves) are inhibited.
Gives time for the duodenum to deal with the acidic chyme.
Several hormone are released by the duodenum when chyme arrives from the
Secretin and CCK (cholecystokinin)
These affect the pancreas and liver, respectively.
More on these later.
VII. Stomach
Gastric activity.
Or reverse peristalsis.
The stomach lining becomes overly irritated
strong contractions occur
Chyme is propelled in the opposite direction, up the esophagus.
Function: to remove irritant from the stomach.
Of nutrients is not a major function.
Stomach absorbs
Some ions, only if they are severely depleted
VIII. Pancreas
The pancreas is a heterocrine organ
Has 2 Functions:
1)! Endocrine: release of the hormones insulin and glucagon
2)! Exocrine: the formation of pancreatic juice, which contains digestive
enzymes, water, bicarbonate and other substances.
VIII. Pancreas
Gross anatomy
Location: inf/post to
Near the duodenum
(proximal part of the
small intestine)
Pancreatic duct- leads
from the pancreas
towards the
Hepatopancreatic duct or
ampulla is formed by
a union of the
pancreatic duct with
the common bile duct.
This common duct
empties into the
VIII. Pancreas
Control of pancreatic juice
•" Acidic chyme (from the stomach) enters the duodenum
•" Triggers the release of secretin (hormone) from the duodenum
•" Secretin stimulates the pancreas to release pancreatic juice.
•" The secretion enters the duodenum
•" Starts to digest the chyme
•" Acidic chyme also stimulates the duodenum to release
cholecystokinin (CCK).
VIII. Pancreas
Pancreatic juice contains many
pancreatic enzymes which digest different food materials.
•" Alpha-amylase
Breaks down starch to disaccharides (2 glucose molecules)
•" Pancreatic lipase
Breaks down fat into fatty acids and glycerol
•" Nucleases
Digest DNA and RNA molecules
VIII. Pancreas
Proteinases or proteolytic enzymes
Trypsin, chymotrypsin, carboxypeptidase, elastase
All break down proteins into amino acids.
•" Proezymes
Proteinases are released in an inactive form a called proenzymes.
Trypsinogen, chymotrypsinogen, procarboxypeptidase,
These are inactive, otherwise they would digest pancreatic cells.
Released by the epithelium of the duodenum.
Converts the proenzyme trypsinogen into trypsin.
Trypsin converts the other proenzymes into their active forms.
Active enzymes require an alkaline environment.
Pancreatic enzymes cannot function in acidic chyme (~pH 2.)
Bicarbonate of pancreatic juice converts the acidic chyme alkaline
chyme (~pH 8.)
Enzymes can function normally.
IX. Liver
The liver has three major functions
1)! Metabolic regulation
Carbohydrate metabolism
Helps to maintain proper blood glucose levels.
Lipid metabolism- maintain blood fatty acid, triglycerides and
Amino acid metabolism-removes extra amino acids
Detoxifies blood
Vitamin and mineral storage
2)! Hematological function
Makes plasma proteins
Removes hormones
Removes antibodies
Removal of bilirubin
3)! Bile production
IX. Liver
Synthesis and production of bile
Bile consists of
Bilirubin- made from the breakdown of the heme- gives bile it’s green
Bile salts- a collection of lipids
These lipids (some derived from cholesterol) are important in
making fats soluble- a process called…emulsification.
This processes causes large fat droplets to break into tiny
particles- makes it easier for lipases to break down fat.
Without emulsification fats are difficult to digest.
IX. Liver
Gross anatomy
Location: right hypochondriac and epigastric region
Largest visceral organ
Two major lobes (right and left) divided by the falciform ligament.
Porta hepatis (“doorway to the liver”)
Located on the posterior surface.
The site where the hepatic artery and the hepatic portal vein connect to
the liver. Gallbladder attaches here.
IX. Liver
Bile passes through the
hepatic ducts, common
bile duct, into the cystic
duct, into the
Bile is stored until
needed, when it is
passed out through the
cystic duct, common
bile duct and into the
IX. Liver
Functional unit of the liver
Is called a lobule, which consists of:
Hepatocytes- liver cells, regulate circulating nutrients/waste levels in the
The vessels that supply and the ducts that drain the lobules enter at a
site called the portal area.
This consists of
1.! The portal vein; a branch of the hepatic portal vein.
This carries nutrient and toxic laden blood from the intestinal tract.
2. Hepatic artery, which supplies O2 to the hepatocytes.
3. Bile duct tributaries which carry bile into the main bile duct.
IX. Liver
Sinusoids of the liver carry the blood from the portal veins slowly past the
The blood is processed and then passed into the central vein.
This leads to the hepatic veins and then into the inferior vena cava.
The waste material and bile is passed into bile duct tributaries, then into
the bile duct.
The liver makes about 1 lt of bile per day.
X. Gall bladder
1.! Bile storage: about 40-80 ml
2.! Bile modification
Most of the water in bile is removed.
Bile becomes concentrated
Post/inf to the liver
X. Gall bladder
CCK in th blood causes the
•" The gallbladder to
•" The biliary
sphincter to open
•" This forces bile into
the duodenum
Fat droplets becomes
emulsified by bile salts.
Bile helps fat digestion.
X. Gall bladder
Gallstones (biliary calculi)
Caused by the deposits of cholesterol and/or bile salts in the
gallbladder and ducts.
May cause cholecystitis- inflammation of the gallbladder
If the stones are large or numerous enough they can block the bile duct.
This may cause …
Jaundice (obstructive)
Where the bile backs up into the liver and bilirubin can’t be
removed from the blood.
This builds up and causes a discoloration of the skin and other
Cholecystitis and the 4 Fs
XI. The Small intestine
Consists of
1.! Duodenum
2.! Jejunum
3.! Ileum
Extends from the…
Pyloric sphincter
Distal end of the stomach, to the…
Ileocecal valve
Entrance to the large intestine
2.5 cm by 5-7 m
Function: most of digestion and absorption of nutrients occurs here.
XI. The Small intestine
1.! Duodenum
Shortest: 25-30cm in length
Most of digestion is initiated here
Submucosal glands
Are prominent: provide mucus to
protect the intestinal wall
from acid.
Large, circular folds of the mucus
Extend around the lumen.
Increase surface area nd allows
Millions of finger like projections
(0.2 - 1.0 mm).
Extend from the mucosa.
Greatly inc surface area.
XI. The Small intestine
Are found w/I each villus.
Consist of a capillary network and a lymph
Droplets of lipid molecules from fat digestion.
Found in the lymph fluid of the lacteal.
Transports fat around the body.
Intestinal Crypts or glands
Collections of cells between the villi within the
Secrete enzymes and hormones.
Such as Enterokinase (enzyme) and
secretin and CCK (hormones):
Basic function
Produce intestinal juice.
starts protein digestion (see pancreas and
Increase digestiive secretion and motility
(secretin and CCK)
XI. The Small intestine
2. Jejnum
Second segment.
1-1.5 m
Larger plicae; lots of surface area.
Most of nutrient absorption occurs here and in the next segment.
3. Ileum
Last part: 2-2.5 m long.
Intestinal secretions or juice
Consist of water and enzymes.
These secretions combine with pancreatic juice to complete digestion.
lactase, breaks down milk sugar lactose into monosaccharides.
Intestinal lipases, amylases, peptidases.
XI. The Small intestine
Hormones and CNS stimulate secretions
Cephalic phase (CNS/ANS) triggers
gastric secretions.
Hormones such as gastrin (from
stomach), secretin and CCK (from
duodenum) regulate their target organs.
Stomach, pancreas and liver,
Duodenal ulcers
The lining of the duodenum is eroded by
too much acid.
Pyloric valve may not work properly; lets
too much chyme in.
Bicarb from the pancreas can’t neutralize
the acid.
XI. The Small intestine
Intestinal movements
Peristaltic movements; moves a bolus more distally.
Gastroenteric reflex (stomach/intestine)
Food arriving in the stomach triggers intestinal movements.
This moves chyme down the intestinal tract.
Gastroileal reflex
Opens the ileocecal valve.
Allows feces to enter the large intestine.
Both reflexes speed up movement of material distally in the intestine.
80% of digestion occurs in the small intestine.
XII. Large intestine
1.! Absorbs 80-90% of
the water/
electrolytes from the
2.! Absorbs vitamins: K,
riboflavin, thiamin.
3.! Produces feces
Large intestine extends
The ileocecal valve to
the anus.
7.5 cm x 1.5 m
XII. Large intestine
Major parts
Cecum; ascending, transverse
and descending colon;
1.! Cecum
Pouch below the level of the
ileocecal valve.
Haustre: bulging sacs caused by
the contraction of bands of
smooth muscle
Ileocecal sphincter: a valve that
regulates the flow of chyme
from the ileum into the large
Appendix: vestigial organ; blind
ended sac filled with
lymphoid tissue.
Appendicitis: inflammation of the
XII. Large intestine
2. Colon
Ascending colon: passes
superiorly from the cecum.
Right colic flexture is
where the colon turns
Transverse colon: crosses the
abdomen to the left side. At
the …
Left colic flexture the
colon turn downward into
Descending colon
Sigmoid colon: is formed
when the descending colon
makes an s-shaped turn
before passes into the
XII. Large intestine
3) Rectum
Last 12-13 cm of the
digestive tract.
Ends at the anal canal and
opens to the exterior at the
Muscles of the rectum
At the distal end of the
rectum are two sets of
Internal anal sphincter:
smooth muscle, involuntary
External anal sphincter:
skeletal muscle, voluntary
XII. Large intestine
Colon wall
No villi or plicae.
Reduced surface area.
Intestinal gland
Produce no digestive
enzymes or hormones.
Only mucus.
Colonic movements
Both gastroenetric and
gastroileal reflexes
causes contraction to
occur in the large
intestine. These strong
smooth muscle
contractions, called…
Mass movements, move
feces towards the rectum
and trigger the
defecation reflex.
XII. Large intestine
Large intestine excretes waste as feces.
75-80% water
Solid material
Organic and inorganic residues
Cell debris
Roughage (fiber)
When feces has too little water and bulk.
Difficult to trigger the defection reflex.
When feces has too much water and bulk.
Triggers a string defection reflex.
Cholera toxin
Stimulates intestinal motility and reduces the absorption of water in
the large intestine.
This creates large amounts of very watery feces and severe water
Can be lethal if not treated quickly.
XII. Large intestine
Defecation reflex.
The arrival of feces in the rectum triggers a
There are two feedback loops
1. Stretch
Distension of the rectal wall by the
Stimulates smooth muscle contractions
in the rectum.
Moves feces towards the anus.
2. ANS
Triggers mass movements to push
feces from the descending and
sigmoid colon into the rectum.
Internal anal sphincter (involuntary) opens
External anal sphincter (voluntary) closes
Requires conscious effort to open the ext.
anal sphincter.
Val salva manuver
“Straining at the stool”