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Medicine > Small Intestine > Flashcards

Small Intestine Flashcards

1
Q

Which of the GI tract functions are applicable to the small bowel?

A

Mechanical processing
Digestion
Secretion
Absorption

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2
Q

What are the three parts of the small intestine called, in order?

A

Duodenum, Jejunum, Ileum

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3
Q

What are the ridges in the structure of the small intestine called?

A

Plica circulares

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4
Q

What do villi and microvilli do?

A

amplify the surface area available for interaction with food

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5
Q

What do crypts do?

A

secrete bicarbonate-rich fluid

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6
Q

Brush border enzymes - name their structure, location and function.

A

Integral membrane proteins

On surfaces of intestinal microvilli

Break down materials in contact with brush border

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7
Q

What is peristalsis?

A

Waves of muscular contractions which move contents along the length of the GI tract

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8
Q

What are the 3 stages of peristalsis?

A

Circular muscles contract behind bolus, while circular muscles ahead of bolus relax

Longitudinal muscles ahead of bolus contract,shortening adjacent segments

Wave of contraction in circular muscles forces bolus forward

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9
Q

What is segmentation?

A

Alternate contraction of neighbouring segments

  • Churn and fragment the bolus
  • Mix contents with intestinal secretions
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10
Q

What is a Migrating Motor Complex?

A

When the gut is relatively empty, MMCs are generated roughly every 90 minutes. Stimulated by motilin, a 22 aa peptide secreted by M cells (and by erythromycin). Suppressed by feeding.

For a few minutes, a series of strong, slow, peristaltic waves will sweep down, mostly from the stomach, and along the small bowel.

Pyloric sphincter is relaxed, allowing larger things to pass

These waves are thought to help keep the gut clean, prevent reflux, and reduce bacterial growth.

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11
Q

Which hormones are secreted from APUD cells?

A

CCK from I cells
Secretin from S cells
Motilin from M cells
Gastrin from G cells

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12
Q

What is secreted from pancreatic duct cells?

A

Bicarbonate secretion

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13
Q

Which nutrients can be absorbed without processing?

A

Water
Electrolytes
Vitamins

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14
Q

Which bonds can soluble amylases break?

A

internal α1,4 bonds.

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15
Q

What is actively absorbed by SGLT1?

A

glucose and galactose

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16
Q

How is fructose absorbed?

A

passively, via Glut5 transporter

17
Q

Where is pepsin deactivated?

A

In the duodenum

18
Q

From which cells is enterokinase secreted?

A

crypt cells

19
Q

Which endopeptidases are cut within the protein chain?

A

Trypsin
Chymotrypsin
Elastase

20
Q

Which exopeptidases are cut at the last peptide bond?

A

Carboxypeptidases

21
Q

What happens to small peptides produced by soluble proteases ?

A

They diffuse to the brush border, where membrane-bound peptidases chop them up into amino acids and dipeptides.

22
Q

What happens to amino acids in the small intestine?

A

They are taken up by sodium-linked secondary active transporters

23
Q

How are Di- (and sometimes tri-) peptides are absorbed?

A

By proton-linked secondary active transporters.

24
Q

What is the importance of how some protein is not degraded in M cells overlying Peyer’s patches?

A

May be important in delivering antigen out of the gut to the immune system.

25
Q

What breaks up lipid droplets to increase surface area?

A

Bile salts

26
Q

What does pancreatic lipase do?

A

cleaves off “outside” fatty acids, leaving a monoglyceride, plus 2 free fatty acids

27
Q

What are mixed micelles and what do they do?

A

Mixed micelles are monoglycerides and fatty acid complexes with bile salts, which solubilise them. They diffuse close to the brush border, delivering their contents to the membrane.

28
Q

What happens to triglycerides inside the cell?

A

They are resynthesised and packaged into chylomicra, which are exocytosed into the interstitium.
They can’t get into capillaries, but can get into lymphatic lacteals.

29
Q

How are conjugated bile salts recycled?

A

They are actively absorbed in the distal ileum.
Some escape to the colon, and may be deconjugated by bacteria, making them lipophilic and allowing passive reabsorption. About 5% are lost in the faeces.

30
Q

Describe the absorption of Ca2+

A

Ca2+ is actively reabsorbed in the duodenum

Regulated by Vit. D

In the rest of the small bowel, it is reabsorbed paracellularly

31
Q

Which 4 vitamins are fat-soluble?

A

A, D, E, and K

32
Q

How are water-soluble vitamins absorbed?

A

They require special transport proteins, usually Na+-linked

33
Q

What is absorbed only when bound to intrinsic factor (secreted by gastric parietal cells) ?

A

Vitamin B12

34
Q

What hormone is Na+ and K+ secretion in the colon regulated by?

A

aldosterone

Medicine (25 decks)

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