Lecture 22: The small intestine Flashcards

1
Q

What are the three main regions of the small intestine?

A

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

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2
Q

What is the role of the duodenum?

A
  • receives acidic chyme from stomach
  • where enzymes & bicarbonate get added from pancreas
  • where bile from liver gets added
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3
Q

What is the main role of the Jejunum and Ileum?

A

Digestion and absorption

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4
Q

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

A
  • 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
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5
Q

What structures does the mesentery contain?

A

Mesentery contains arteries, veins, nerves and lymphatics

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6
Q

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

A
  • 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)
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7
Q

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

A

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)

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8
Q

What are plicae circulares?

A
  • Permanent large folds of of small intestine
  • makes up the core of submucosa with overlying mucosa
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9
Q

What allows movement of villi?

A

Muscularis mucosae allows villi movement

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10
Q

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

A
  • Numerous villi, found on the surface of the plicae circulares
  • Part of mucosa
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11
Q

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

A

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)
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12
Q

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

A
  • Epithelium of the small intestine is simple columnar
  • The absorptive cells (enterocytes) have microvilli on apical surface (faces the lumen)
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13
Q

What is the role of glycocalyx in the small intestine?

A
  • Glycoproteins – branched filaments
  • Tether enzymes
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14
Q

What is the role of the microvilli brush border?

A

Contact digestion:
involves enzymes - attached to brush border

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15
Q

Describe the plasma membrane of the small intestine epithelial cells:

A

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

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16
Q

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

A

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
17
Q

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

A

EGPES (Every Good Person Enjoys Sausage)
Enterocytes - Absorptive cells

Goblet cells - Secrete mucous for protection

Paneth cells - granules, antibacterial enzymes

Endocrine cells - secrete hormones

Stem cells - Make all cell types

18
Q

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

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