1. Biology 322 Human Anatomy I
Digestive System

2. Functions:

3. Organs
Two functional groups:
1. Alimentary Canal or Gastrointestinal tract
Organs which ingest, propel, digest, absorb, & eliminate
Oral cavity, pharynx, esophagus, stomach,
small intestine, large intestine, anus
2. Accessory Digestive Organs
Assist with digestion
Teeth, tongue, salivary glands,
liver, gall bladder, pancreas

4. Organs:

5. Oral Cavity:
Includes: teeth
tongue
Opens posteriorly into pharynx
Which opens inferiorly into esophagus

6. Three Pairs of Salivary Glands:
Parotid
Submandibular
Sublingual

7. From esophagus to anus: 4 concentric layers or tunics
Alimentary Canal:
From esophagus to anus:
4 concentric layers or tunics
Serosa or Adventitia
Muscularis Externa
Submucosa
Mucosa
Epithelium
Lamina propria
Muscularis mucosa

8. Esophagus:
Propels food from pharynx to stomach
Posterior to trachea & heart
Mucosa: Nonkeratinized stratified squamous epithelium
Many mucous-secreting cells
Thin lamina propria
Thin muscularis mucosa
Submucosa: Thick layer of dense irregular CT
Muscularis Externa: Upper third = skeletal muscle
Middle third = mixed
Lower third = smooth muscle
Adventitia: Thin layer of connective tisssue

9. Esophagus:
Passes from thorax to abdomen through diaphragm, enters stomach (left of midline).

10. Stomach:
Storage: Highly distensible
Delivers chyme slowly to duodenum

11. Stomach
Lesser
Curvature
Greater
Curvature

12. Stomach: Regions
Fundus
Cardiac
Region
Pyloris
Body

13. Stomach:

14. Stomach:
Mucosa thrown into folds called rugae

15. Stomach:
Pyloric sphincter releases chyme slowly into duodenum

16. Small Intestine:
Total length: 6 to 7 meters
Diameter: 2.5 to 3 centimeters

17. Small Intestine: Three parts

18. Small Intestine: Serosa or Adventitia Muscularis Externa Submucosa
Epithelium
Lamina propria
Muscularis mucosa

19. Mucosa specialized three ways to increase surface area for absorption
Small Intestine:
Mucosa specialized three ways to increase surface area for absorption 1.
All layers of mucosa thrown into folds called plicae circulares

20. Mucosa specialized three ways to increase surface area for absorption
Small Intestine:
Mucosa specialized three ways to increase surface area for absorption 2.
Epithelium and lamina propria form finger-like villi

21. Mucosa specialized three ways to increase surface area for absorption
Small Intestine:
Mucosa specialized three ways to increase surface area for absorption
Plasma membranes of epithelial cells form finger-like microvilli 3.

22. Small Intestine: Nutrients, ions, etc. are absorbed through
these plasma membranes & passed through the cell to the deeper lamina propria, where they are absorbed into capillaries & lymphatic vessels.

23. Large Intestine (colon):
From ileocecal junction to anus
~ 2 meters long
~ 5 to 8 cm diameter
Most digestion has already occurred in the small intestine
Colon primarily absorbs water and electrolytes
forms feces for elimination

24. Transverse colon
Ascending colon
Descending colon
Sigmoid colon
Cecum
Rectum

25. Right Colic or “Hepatic” Flexure
Left Colic or “Splenic” Flexure
Sigmoid Flexure

26. Just like all other organs of the alimentary canal:
Serosa or Adventitia
Muscularis Externa
Submucosa
Mucosa
Epithelium
Lamina propria
Muscularis mucosa

27. Abdominal Accessory Organs:
Liver,
Gall bladder,
Pancreas,
& associated ducts

28. Liver
Most superior organ in abdomen
Immediately inferior to diaphragm
Partially protected by ribs
Develops from embryonic intestine
Mass ~ 1.5 kg

29. Liver
Most superior organ in abdomen
Immediately inferior to diaphragm
Partially protected by ribs
Develops from embryonic intestine
Mass ~ 1.5 kg
Four lobes
Blood supply:
Hepatic artery from celiac trunk
Hepatic portal vein from stomach
intestine
pancreas
spleen

30. Liver:
Hepatic artery
Hepatic portal vein
Common bile duct
Enter / exit together on inferior surface

31. Gall Bladder and Ducts
Bile produced in liver:
a) May be sent directly
to duodenum through
common bile duct
b) May be sent through
the cystic duct to be
stored in the
gall bladder

32. Pancreas:
Inferior & posterior to stomach
Fits into concavity of duodenum
Both endocrine (Insulin, glucagon)
exocrine (digestive enzymes)

33. Pancreas:
Inferior & posterior to stomach
Fits into concavity of duodenum
Both endocrine (Insulin, glucagon)
exocrine (digestive enzymes)
Enzymes transported to duodenum by pancreatic duct
(shares opening with
common bile duct)

34. The abdominal cavity is
lined by a double-layered
serous membrane called
the peritoneum.
Visceral layer – surrounds and
is firmly attached to
abdominal organs
Parietal layer – attached to
inner surface of body wall
Between these = Peritoneal cavity

35. Mesentary – fold of peritoneum
connecting visceral
& parietal layers

36. More terminology:
Intraperitoneal organs Retroperitoneal organs
connected to body wall posterior to peritoneal
by mesentaries cavity

38. Intraperitoneal Retroperitoneal
Stomach
Duodenum
Jejunum
Ilium
Cecum & Appendix
Ascending colon
Transverse colon
Descending colon
Sigmoid colon
Rectum
Liver
Gall bladder
Pancreas

39. Alimentary Canal:
Since contents include many foreign substances, including microorganisms, your immune system considers it “outside” so
Lined by many lymphatic and immune tissues in lamina propria and submucosa