Physiology of the small intestine Flashcards Preview

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Flashcards in Physiology of the small intestine Deck (23)
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1
Q

What glands in the small intestine secrete mucus?

A

Brunner’s glands

2
Q

What is the function of motilin hormone?

A

Stimulates migrating motor complexes (MMCs) via both the enteric and autonomic nervous systems.

3
Q

What is the function of Vasoactive intestinal peptide (VIP) hormone?

A

Increases blood flow to the GI tract

4
Q

What is the function of CCK (cholecystokinin) and secretin?

A

Inhibits gastric motility and secretion and controls pancreatic and biliary secretion.

5
Q

What are the main secretions of the small intestine?

A

Mucus, water and hormones

6
Q

Name the hormones secreted by the small intestine.

A
Motilin
Vasoactive intestinal peptide (VIP)
Gastric inhibitory peptide (GIP)
Cholecystokinin (CCK)
Secretin
7
Q

What cells (x2) in the pancreas secrete enzymes/alkali?

A

Acinar cells - enzymes (zymogens) (activated by membrane bound enterokinase)
Duct cells - alkali

8
Q

How is HCO3- secreted from the pancreatic duct into the intestinal lumen?
(CO2 + H2O H2CO3 HCO3- + H+)

A

HCO3- secreted into duct lumen

H+ are pumped out of duct cells and released into the blood

9
Q

How are fats digested in the small intestine?

A

1) Fats are emulsified by bile salts and phospholipids
2) Triglycerides are digested by pancreatic lipase to monoglycerides and fatty acids.
3) Held in micelles

10
Q

How are fats absorbed in the small intestine?

A

1) Monoglycerides and fatty acids diffuse into epithelial cell
2) Reassembled into triglycerides
3) Packaged into chylomicrons
4) Leave intestinal villus via its lymph vessel (thoracic duct - LSV)

11
Q

Describe how starch is converted to monosaccharides.

A

Pancreatic amylase converts starch to maltose. Brush border enzymes (maltase, sucrose and lactase) break down products to glucose, fructose and galactose. Absorbed into blood.

12
Q

How are dissacharides formed from monosaccharides?

A

Glycosidic bond by eliminating water

13
Q

Glucose, galactose and fructose are absorbed from the intestinal lumen via what transporters and exit into the blood via which transporters?

A

Glucose + galactose - SGLT-1
Fructsoe - GLUT5 (facilitated diffusion)
All exit into blood via GLUT2 (facilitated diffusion)

14
Q

How are proteins absorbed in the small intestine?

A

1) proteins digested by: trypsin, chymotrypsin and carboxypeptidase
2) Further by: dipeptidase and aminopeptidase into tri/dipeptides and free AAs
3) Enter epithelial cells and usually hydrolysed to AAs by cytosolic peptidase

15
Q

Di/tripeptides and free AAs are absorbed from the intestinal lumen via what transporters and exit into the blood via which transporters?

A

AAs - Na+-amino acid cotransporters
Di/tripeptides - H+-dependent co-transporters
Exit into blood by facilitated diffusion

16
Q

How is Ca2+ absorbed?

A

1) Enters intestinal lumen via Ca2+ channel
2)Ca2+ exits via both:
plasma membrane Ca2+-ATPase
Na+/Ca2+ exchanger

17
Q

What 2 forms is dietary iron present as?

A

Haem iron

Free iron

18
Q

How is haem iron abserbed into blood?

A

Haem is absorbed by receptor-mediated endocytosis then digested to release Fe3+.
Fe3+ reduced to Fe2+
Fe2+ exits via the transmembrane protein ferroportin 1.

19
Q

How is free iron absorbed into blood?

A

Fe3+ reduced to Fe2+ by membrane ferrireductase (FR).
Fe2+ crosses membrane via divalent metal transporter 1 (DMT1).
Fe2+ exits via the transmembrane protein ferroportin 1.

20
Q

How is vitamin B12 absorbed from the intestine?

A

Stomach - binds to R protein.
Duodenum/ jejunum - released and binds to intrinsic factor (IF)
Terminal ileum - vit B12-IF complex is absorbed by receptor-mediated endocytosis

21
Q

Explain lactose intolerance

A

Bacteria ferments lactose into gases etc - bloating

22
Q

Explain how excessive vomiting can lead to metabolic alkalosis.

A

leads to large losses of secreted acids from the body.

23
Q

Explain how excessive diarrhea can lead to metabolic acidosis.

A

excessive loss of fluid (and hence NaHCO3) in faeces.