Physiology of the small intestine

Question 1

Which section of the small intestine is the main site of absorption?

Answer 1

Jejunum

Question 2

The mucosa of the small intestine is folded into which structures?

Answer 2

Plicae circulares

Question 3

What 2 things do cells of Paneth secrete?

Answer 3

Lysozyme and Ig

Question 4

Is chyme hyper- or hypotonic?

Answer 4

Hypertonic

Question 5

How is the hypertonicity of chyme corrected in the duodenum?

Answer 5

Duodenum secretes Na+, Cl- and HCO3-. Water follows by osmosis

Question 6

What are the 5 hormones secreted by the small intestine?

Answer 6

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

Question 7

What is the function of motilin?

Answer 7

Stimulates migrating motor complexes (MMCs)

Question 8

What effect does gastric inhibitory peptide (GIP) have on gastrin and insulin?

Answer 8

Inhibits gastrin secretion
Stimulates insulin secretion

Question 9

What triggers the release of CCK?

Answer 9

Fats and partially digested proteins in the duodenum

Question 10

What triggers the release of secretin?

Answer 10

Low pH from chyme in the duodenum

Question 11

What are the 2 functions of secretin?

Answer 11

Stimulates pancreas to produce HCO3-

Stimulates liver to produce bile

Question 12

What are the 2 functions of CCK?

Answer 12

Stimulates pancreas to produce digestive enzymes

Stimulates gallbladder contraction

Question 13

Once in the duodenum, fats (triglycerides) are emulsified by what 2 things?

What does this form?

Answer 13

Bile salts
Phospholipids

Emulsion droplets

Question 14

Once in emulsion droplets, fats (triglycerides) are digested by what to form what?

Answer 14

Digested by pancreatic lipase to form monoglycerides and fatty acids

Question 15

What 4 things are held in micelles?

Answer 15

Monoglycerides
Fatty acids
Bile salts
Phospholipids

Question 16

Once inside the enterocytes, what happens to monoglycerides and fatty acids?

Answer 16

They are reassembled into triglycerides and packaged into chylomicrons

Question 17

Chylomicrons leave the intestinal villus via what?

Answer 17

Lymph vessel

Question 18

Starch is digested in the small intestine by which enzyme?

Answer 18

Pancreatic amylase

Question 19

Pancreatic amylase breaks down what to form what?

Answer 19

Breaks down starch to form disaccharides

Question 20

How are disaccharides digested to form monosaccharides?

Answer 20

By brush border enzymes - maltase, lactase, sucrase

Question 21

How do glucose and galactose enter enterocytes?

Answer 21

SGLT1 (secondary active transport, coupled to Na+/K+ATPase on the basolateral membrane)

Question 22

How does fructose enter enterocytes?

Answer 22

GLUT 5 (facilitated diffusion)

Question 23

How do glucose, galactose, and fructose leave enterocytes to enter the blood?

Answer 23

GLUT 2 (facilitated diffusion)

Question 24

Proteins are digested in the small intestine by which 3 enzymes?

What are the products?

Answer 24

Trypsin
Chymotrypsin
Carboxypeptidase

Peptide fragments

Question 25

Peptide fragments are digested by which 2 brush border enzymes? What are the products?

Answer 25

Dipeptidase Aminopeptidase Tripeptides, dipeptides, free amino acids

Question 26

How do amino acids enter enterocytes?

Answer 26

Secondary active transport (Na+/amino acid co-transporters, coupled to Na+/K+ATPase on the basolateral membrane)

Question 27

How do tripeptides and dipeptides enter enterocytes?

Answer 27

H+ dependent co-transporters

Question 28

By what mechanism do amino acids leave enterocytes to enter the blood?

Answer 28

Facilitated diffusion

Question 29

How does calcium enter enterocytes?

Answer 29

Calcium channels

Question 30

Once inside enterocytes, what does calcium bind to?

Answer 30

Calbindin

Question 31

An enterocytes capacity to absorb calcium is dependent on what?

Answer 31

Amount of calbindin in the cell's cytosol

Question 32

By which 2 ways does calcium leave enterocytes to enter the blood?

Answer 32

Plasma membrane Ca2+/ATPase (PMCA) Na+/Ca2+ exchanger (NCX)

Question 33

In which 3 ways does vitamin D3 aid in the absorption of calcium?

Answer 33

1. Increases the number of calcium channels on luminal membrane 2. Increases the amount of calbindin 3. Increases the activity of calcium transporters on the basolateral membrane

Question 34

What are the 2 forms of iron and what are their sources?

Answer 34

Haem iron - animal products Non-haem (free) iron - plants and vegetables

Question 35

How does haem iron enter enterocytes?

Answer 35

Receptor-mediated endocytosis

Question 36

How does non-haem (free) iron enter enterocytes?

Answer 36

Reduced from Fe3+ to Fe2+ by membrane ferrireductase Fe2+ enters cell via divalent metal transporter 1 (DMT1)

Question 37

Once inside enterocytes, what can iron bind to?

Answer 37

Ferritin

Question 38

How does iron leave enterocytes to enter the blood?

Answer 38

Ferroportin 1

Question 39

Describe the absorption of vitamin B12.

Answer 39

Vitamin B12 binds to R protein in the stomach. In the duodenum + jejunum, vitamin B12 is released and binds to IF. In the terminal ileum, vitamin B12-IF complex is absorbed by receptor-mediated endocytosis.

Question 40

By what mechanism does vitamin B12 enter enterocytes?

Answer 40

Receptor mediated endocytosis

Question 41

In what way can vomiting affect acid-base balance?

Answer 41

Loss of H+ ions - can lead to increased blood pH and metabolic alkalosis

Question 42

In what way can diarrhoea affect acid-base balance?

Answer 42

Loss of fluid (bicarbonate) in faeces - can lead to decreased blood pH and metabolic acidosis

Question 43

Which cells of the pancreas secrete alkali?

Answer 43

Duct cells

Question 44

Which cells of the pancreas secrete digestive enzymes?

Answer 44

Acinar cells

Question 45

Zymogens are activated in the small intestine by which enzyme?

Answer 45

Enterokinase