1. Biology 212 Anatomy & Physiology 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 oropharynx
which leads to
laryngopharynx
Which opens inferiorly into esophagus

6. Paired Salivary Glands:
Parotid
Submandibular
Sublingual

7. Saliva:
97% - 99% water
Solutes: Ions (electrolytes)
Antibodies
Lysozyme (antibacterial)
Amylase (enzyme – digests carbohydrates)
Mucous
Lubricates
Cleans mouth and teeth
Immune surveillance
Begins carbohydrate digestion

8. Swallowing

9. 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

10. Esophagus:
Propels food from pharynx to stomach
Posterior to trachea & heart

11. 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

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

13. Stomach:
Storage: Highly distensible
Delivers chyme slowly to duodenum
Secretion of mucous, hydrochloric acid
Secretion of enzyme pepsin - Digestion of proteins
Secretion of gastric lipase – Digestion of lipids
Secretion of intrinsic factor – Absorption of B12

14. Stomach:
Fundus
Cardiac
Region
Pyloris
Body

15. Stomach:
Lesser
Curvature
Greater
Curvature

16. Stomach:

17. Stomach:
Mucosa thrown into folds called rugae

18. Stomach:
Pyloric sphincter releases chyme slowly into duodenum

19. Small Intestine:
Total length: 6 to 7 meters
Diameter: 2.5 to 3 centimeters
Duodenum
Jejunum
Ileum

20. Small Intestine:
DUODENUM: ~ 25 cm long
Receives secretions of liver (bile)
pancreas (enzymes)
Secretes mucous
digestive enzymes
bicarbonate – neutralize HCl
JEJUNUM: ~ 2.5 m long
Specialized for absorption
ILEUM: ~ 3.5 m long

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

22. Mucosa specialized three ways to increase surface area for absorption
Small Intestine:
Mucosa specialized three ways to increase surface area for absorption 3.
1. All layers of mucosa thrown into folds called plicae circulares

23. 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 3.

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

25. Mucosa specialized three ways to increase surface area for absorption
Small Intestine:
Mucosa specialized three ways to increase surface area for absorption 3.
Nutrients, ions, etc. are absorbed through these plasma membranes and pass through the cells to the deeper lamina propria, where they are absorbed into capillaries & lymphatic vessels.

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

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

28. Right colic (hepatic) flexure
Left colic (splenic) flexure
Sigmoid flexure

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

30. 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

31. Liver
Digestive functions: Regulate metabolism
Store excess carbohydrate
protein
lipid
Secrete bile:
Produced from cholesterol
Stored in gall bladder
via cystic duct
Transported to duodenum
through common bile duct
Emulsifies fats

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

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. Pancreas:
Produces many different digestive enzymes:
Amylases: starches & monosaccharides
glycogen & disaccharides
Proteases: proteins amino acids
Lipases: diglycerides & fatty acids
triglycerides & glycerol
Nucleases: nucleic acids nucleotides

35. 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

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

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

39. Intraperitoneal organs have a serosa which includes the visceral layer of the peritoneum.
Retroperitoneal organs are not covered by the visceral layer of the peritoneum, so the connective tissue on their external surface is an adventitia.
Mesentery
In reality, many retroperitoneal organs (no mesentery) have a serosa (visceral peritoneum) covering part of their wall and an adventitia (no visceral peritoneum) covering part of their wall.

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

41. Intestinal Motility:
Moves liquid distally by peristalsis
Mixes chyme from stomach with
- Intestinal enzymes
- Pancreatic enzymes
- Bile from liver
Increases contact of liquid with intestinal mucosa for absorption

42. Digestion:
Breakdown of food into molecules small enough to be absorbed from the lumen of the intestine into its blood vessels.
Four types of molecules = more than 95% of total:
Water
Sugars (carbohydrates)
Amino acids
Fatty acids
Also: Nucleic acids
Ions (electrolytes, minerals)
Vitamins
? Others ?

43. Mechanical digestion In mouth (teeth)
Chemical digestion Begins in mouth
Continues through intestine
Absorption of nutrients Primarily in
electrolytes small intestine
vitamins
Absorption of water Both small intestine &
large intestine
Salivary glands produce amylases
Stomach secretes proteases
Small intestine secretes proteases
Liver secretes bile
Pancreas secretes amylases, proteases, lipases, nucleases

44. All absorbed molecules must pass through epithelial cells
of intestinal mucosa.
Tight junctions prevent anything from passing between cells.

45. 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