Lecture 22: The small intestine

Question 1

What are the three main regions of the small intestine?

Answer 1

1st section = Duodenum ~ 25cm
2nd section = Jejunum ~ 2.5m
3rd section = Ileum ~ 3.5m

Question 2

What is the role of the duodenum?

Answer 2

• receives acidic chyme from stomach
• where enzymes & bicarbonate get added from pancreas
• where bile from liver gets added

Question 3

What is the main role of the Jejunum and Ileum?

Answer 3

Digestion and absorption

Question 4

Where is each section of the small intestine and what holds it in place?

Answer 4

• Initial segment of small intestine (duodenum) is
  retroperitoneal
• Rest of small intestine is in the lower abdominal cavity below the stomach, held in place by mesentery - Allows movement, but prevents tangling

Question 5

What structures does the mesentery contain?

Answer 5

Mesentery contains arteries, veins, nerves and lymphatics

Question 6

What is the drainage pathway for blood from the small intestine and where does lymph travel?

Answer 6

• Nutrient rich, deoxygenated blood from small intestine
  enters mesenteric veins
• These drain to the hepatic portal vein
• Lymph lacteals ultimately drain into cisterna chyli,
  thoracic duct, then left subclavian vein (see CVS)

Question 7

How does the small intestine achieve high SA to allow for optimal absorption?

Answer 7

Achieved in 4 key ways:
1. Length
2. Folding of intestinal wall (plicae circulares)
3. Extensions of mucosa (villi)
4. Extensions of epithelial cells (microvilli)

Question 8

What are plicae circulares?

Answer 8

• Permanent large folds of of small intestine
• Had a core of submucosa with overlying mucosa

Question 9

What allows movement of villi?

Answer 9

Muscularis mucosae allows villi movement

Question 10

Where are villi found and what layer of the gut tube are they apart of?

Answer 10

• Numerous villi, found on the surface of the plicae circulares
• Part of mucosa

Question 11

What is the core of the villi made of and what do they contain?

Answer 11

Core of each villus is made of lamina propria

Contains:
* Lymph lacteal (absorbs products of fat digestion)

• Capillary network (absorbs products of protein and carbohydrate digestion)

Question 12

What epithelium does the small intestine have and what do they have on the surface of the cells?

Answer 12

• Epithelium of the small intestine is simple columnar
• The absorptive cells (enterocytes) have microvilli on apical surface (faces the lumen)

Question 13

What is the role of glycocalyx in the small intestine?

Answer 13

• Glycoproteins – branched filaments
• Tether enzymes

Question 14

What is the role of the microvilli brush border?

Answer 14

Contact digestion:
involves enzymes - attached to brush border

Question 15

Describe the plasma membrane of the small intestine epithelial cells:

Answer 15

The plasma membrane is a barrier:
* Selectively permeable
* Has proteins
* channels
* transporters

Question 16

What are the intercellular connections found in the epithelial cells of the small intestine?

Answer 16

Tight junctions - allow small molecules to diffuse through the cell layer

ALSO HAS (not sure if this is as important)

• Adhesion belts
• Gap junctions
• Desmosomes
• Hemidesmosomes - attach cell to base layer

Question 17

What are the five types of epithelial cells can be found in the small intestine?

Answer 17

EGPES (Elephants Prefer Green Eggplant Smoothies)
Enterocytes - Absorptive cells

Goblet cells - Secrete mucous for protection

Paneth cells - granules, antibacterial enzymes

Endocrine cells - secrete hormones

Stem cells - Make all cell types

Question 18

What structure allows passage from the small intestine to the large intestine?

Answer 18

• The ileocecal valve
• Regulates the passage of material into the large intestine