Alimentary canal and basic A&P

1. Anatomy and Physiology of
the Digestive System
ATS Unit 5

2. Goals
• Identify major organs and there functions
in the digestive tract.
• Discuss micro and macro anatomy and
physiology of the digestive tract.
• Discuss how the digestive tract impacts
and interacts with other systems.

3. Overview of the Digestive System
• Functions:
– Digestion of food substances
– Absorption of nutrients
– Excretion of waste
• The digestive system includes the entire
alimentary canal (oral cavity to anus,
approx. 30 feet) plus all of the accessory
organs which produce and store enzymes
or otherwise assist in digestion.

4. The Alimentary Canal
• Include (in order) the mouth, pharynx, esophagus,
stomach, small intestine and large intestine.
• The passageway has four layers:
– Innermost is called the mucosa, made of epithelium.
– Next is the submucosa, contains blood vessels, nerve
fibers and connective tissue.
– Third is the muscularis, which contains either skeletal
(voluntary) or smooth (involuntary) muscle.
– The outermost layer is is called the serosa, also
called the visceral peritoneum.

6. Physiology of the Alimentary Canal
• Primary function is PERISTALSIS
– Coordinated rhythmic muscle movements that
move food substance along in a bolus. It also
helps in mixing and digestive food.
– The upper GI tract has skeletal muscle that
allow for voluntary initiation of peristalsis. The
lower GI tracts acts automatically.

7. The Mouth and Accessory Organs
• Teeth and tongue assist with manual
breakdown of the food.
• Tongue also allows for the special sense of
taste which helps our bodies decide if food is
safe or good for us.
• Salivary Glands:
– Produce saliva, which is mostly water but also
contains lysozyme to kill bacteria and amylase
which begins digestion of sugars.
– Includes the parotid, submandibular and
sublingual glands

8. The Esophagus
• This is a 10 inch tube that connects the
lower portion of the pharynx to the
stomach. It passes through the diaphragm.
• It ends in a ring like muscular structure
called the cardiac sphincter that prevent
stomach contents from regurgitating.

9. The Stomach
• Located just below the diaphragm and has three
portions:
– Fundus (upper part)
– Body (greater and lesser curvature or middle portion)
– Pylorus (lower or distal portion)
• Has the same layers as the rest of the alimentary
canal, but he inner mucosa has lots of folds called
rugae.
• The pylorus ends in another sphincter (like the
esophagus) called the pyloric sphincter which
regulates food passing into the duodenum (small
intestine).

10. Small Intestine
• Continues the process of digestion and does
most of the absorption of nutrients. It has 3
portions:
– Duodenum (most proximal)
– Jejunum (middle)
– Ileum (most distal)
• Similar to the inner lining of the stomach, the
mucosa of the small intestine has folds called
plicae circularis (increase surface area). It is
also covered with villi.

11. Absorption in the Small Intestine
• As the food (now called chyme) bolus
moves toward the distal end of the small
intestine, more and more nutrients are
absorbed (after being broken down as
much as possible).
• The plicae and villi drastically increase
surface area which helps with this, and
each villus has capillaries which absorb
and transport he nutrients.

12. The Large Intestine
• About 5 feet long, this final part of the alimentary
canal focuses mostly on reabsorbing water and a
few nutrients such as B vitamins and vitamin K,
and producing/eliminating waste.
• It has 6 portions (proximal to distal)
– Cecum (pouch like area below the ileocecal valve,
attached is the appendix)
– Ascending Colon
– Transverse Colon
– Descending Colon
– Sigmoid Colon
– Rectum (including anus)

13. Physiology of the Large
Intestine
• Inner Mucosa produces lots of mucus to
allow the solidifying bolus of waste to
move easily.
• The colon is gathered by the teniae coli
(muscle bands) and formed into pockets
called haustra.
• Vitamin absorption and (possibly) immune
functions are heavily impacted by the large
amount of coliform bacteria that lives in
the large intestine.

14. Elimination of waste
• The Waste product we eliminate is called
either feces or stool and is comprised of
unabsorbable food parts like dense fiber and
seeds, bacteria, waste products from
metabolism, mucus, and gases.
• Cellulose if what we call fiber and is important
in keeping the bowels healthy and regular.
• Feces should be moderate to dark brown in
color. Other colors can mean disease, illness
or unhealthy diet.