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I. Primary functions are:
A. Digestion of food particles to small nutrient molecules
B. Absorption of nutrient molecules
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II. Digestive Processes:
A. Ingestion: done only by the mouth.
B. Propulsion: movements force food through the canal in order to promote digestion.
1) swallowing
2) peristalsis – esophagus, stomach ,small and large intestine
- moves food distally by “waves of contraction”
C. Mechanical Digestion: Movements physically break food particles into smaller particles. All performed by muscular layer of digestive organs.
1) mastication by mandible/maxillae and teeth.
2) mixing by the tongue
3) churning in the stomach
4) segmentation – intestines
D. Chemical Digestion:
1emulsification – Bile from the liver disperses fat droplets in small intestine.E. Absorption:
end-products of digestion (sugar, amino acids, fatty acids, nucleotides, water,
vitamins, minerals) are absorbed into the blood or lymph. Food molecules must
be smaller to be absorbed.
F. Defecation/egestion:
Non-absorbed material must be eliminated to allow room for more food.
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III. Histology of the Alimentary Canal: (Esophagus, stomach, small intestine,
large intestine.)
A. Mucosa: lines the lumen, typically simple columnar epithelium with goblet
cells (similar to respiratory epithelium but without cilia)
This layer provides all of the secretions for digestion (water, enzymes, gastric
acid)
B. Submucosa: dense CT,
This layer contains blood and lymph vessels, nerves, and lymphatic tissue. (Peyer’s
Patches – lymphatic tissue in submucosa of small intestine)
C. Muscularis: smooth muscle.
This layer provides all movements (digestive and propulsive) as well as valves
and sphincters (thickenings of the circular layer) that control food passage
from one organ to the next.
D. Serosa = the visceral peritoneum.
This layer produces serous fluid to lubricate outside of these moving organs.
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IV . Blood Supply:
A. Arterial Supply:
splenic, gastric, mesenteric and the common hepatic arteries supply the spleen, stomach, small/large intestine and liver, respectively.
B. Hepatic Portal System:
hepatic portal vein collects nutrient rich blood draining from the stomach and intestines and delivers it to the liver for processing. Also receives blood from spleen.
IV. Organs of the Alimentary Canal:
A. Mouth/Oral Cavity:
lined by a stratified squamous epithelium
Functions: mastication, deglutition (swallowing)
Salivary amylase from the salivary glands breaks large carbohydrates like glycogen (animal carbs) and starch (plant carbs)-starch digestion begins here
B. Pharynx:
receives food from mouth, air from nose
lined by stratified squamous epithelium
Functions in deglutination.
C. Esophagus:
posterior to the trachea.
lined by stratified squamous epithelium
Functions to move food down to stomach via peristalsis.
D. Stomach
1) Cardiac region– surrounds the opening from esophagus.
2) Pylorus – opening into duodenum
Rugae are large, longitudinal folds of mucosa and submucosa that allow distension
for storage of food
3) Sphincters:
a) lower esophageal-prevents backflow into esophagus
b) Pyloric – controls stomach emptying into small intestine
stomach acts to store food,
protein digestion begins here with pepsin and hydrochloric acid
pepsin enzyme breaks large proteins, HCl activates this enzyme.
HCl also unravels larger proteins so that enzymes can cut up easier.
E. Small Intestine:
The major digestive organ with most digestion and absorption occuring here.
1) Regions:
a) Duodenum
Bile and pancreatic enzymes dumped here.
b) Jejunum:
c) Ileum: Joins the large intestine at the ileocecal valve.
2) Sphincters:
a) Hepatopancreatic sphincter/Sphincter of Oddi: Controls the entry of bile
and pancreatic
juice into the duodenum.
b) Ileocecal Valve: controls emptying of small intestine into large intestine
3) Histology:
Villi: finger-like projections of mucosa to promote absorption
Small intestine: major organ of both digestion and absorption.
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F. Large Intestine:
1) Subdivisions:
a) Cecum – saclike first part, below ileocecal valve
b) Appendix – hangs from cecum
c) Ascending colon – up right side
d) Transverse colon – crosses abdomen
from right to left.
e) Descending colon – down the left side
f) Sigmoid colon – S-shaped, enters pelvis
g) Rectum – anterior to the sacrum
h) Anal Canal
lined by a stratified squamous epithelium
2) Sphincters:
a) Internal anal sphincter – smooth muscle,
involuntary.
b) External – skeletal, voluntary.
VI. Accessory Digestive Organs:
A. Teeth: mandible and maxillae.
B. Tongue: skeletal muscle, stratified squamous epithelium
C. Salivary Glands: three pairs
D. Liver:
On the right side of the abdominal cavity.Almost entirely in the rib cage.
Produces Bile which emulsifies lipids in the duodenum.
The liver also stores glycogen, makes plasma proteins, and rids the blood of ammonia.
E. Gall Bladder:
It is on the liver’s inferior surface.
stores bile.
F. Pancreas:
It extends from the duodenum across the abdomen to
the spleen and is deep to the stomach.
Acinar cells make most enzymes used during digestion.They are delivered to
the duodenum via the
main pancreatic duct.
Acinar cells also produce bicarbonate to reduce acidity of gastric chyme.
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Professor Thomas M. Lancraft
Human Anatomy Courses
at St. Petersburg College
St. Petersburg/Gibbs Campus
6/2006