Lecture 32 - Intestinal Function

Question 1

Where are the sites of absorption in the GI tract?

Answer 1

mouth and esophagus
stomach
intestine

Question 2

What absorption happens in the small intestine?

Answer 2

bulk absorption of isosmotic fluid
nutrients

Question 3

What absorption happens in the proximal colon of the large intestine?

Answer 3

absorption of products of fermentation
fluid and electrolytes

Question 4

What absorption happens in the distal colon of the large intestine?

Answer 4

selective absorption of fluid and electrolytes

Question 5

What is the nutrient dependent Na+ absorption in the small intestine?

Answer 5

Na+ coupled solute absorption of monosaccharides and amino acids
Specialised absorption
- bile salts
- vitamins

Question 6

What is the nutrient dependent Na+ absorption in the proximal colon?

Answer 6

Na+ dependent absorption of short chain fatty acids

Question 7

Where do we have the nutrient independent Na+ absorption?

Answer 7

small intestine
large intestine

Question 8

What channels are involved in the nutrient dependent Na+ absorption in the small intestine?

Answer 8

Na+-coupled solute absorption
(SGLT1, amino acids)

Question 9

What channels are involved in the nutrient independent Na+ and Cl- absorption in the small intestine?

Answer 9

Na+/H+ exchanger (NHE3)
Cl-/HCO3- exchanger

Question 10

What occurs in the proximal colon?

Answer 10

Na+ absorption
Fermentation of indigestible sugars and proteins

Question 11

How do we have the fermentation of indigestible sugars and proteins?

Answer 11

generation of short chain fatty acids
- acetate, propionate and butyrate

Question 12

What is Na+ absorption associated with in proximal colon?

Answer 12

absorption of short chain fatty acid

Question 13

What is Na+ absorption in the proximal colon?

Answer 13

Electroneutral NaCl absorption
- paired Na+/H+ and Cl-/HCO3- exchangers as in small intestine

Question 14

What transporter for SCFA is found in the apical membrane of the proximal colon?

Answer 14

Sodium monocarboxylate transporter

Question 15

What is SCFA?

Answer 15

short chain fatty acid

Question 16

What is SCFA used by?

Answer 16

Colonocytes for intracellular metabolism

Question 17

What is the function of the distal colon?

Answer 17

Regulation of composition of faeces

Question 18

What does Na+ absorption variation depend on?

Answer 18

Fluid and electrolyte status

Question 19

What are the plasma levels of aldosterone in salt depleted conditions?

Answer 19

High

Question 20

What are the plasma levels of aldosterone in salt replete conditions?

Answer 20

Low

Question 21

What is the normal volume of intestinal secretions per day?

Answer 21

1-2 L

Question 22

What type of secretion occurs in the duodenum?

Answer 22

Cl- secretion
HCO3- secretion

Question 23

What type of secretion occurs in the jejunum?

Answer 23

Cl- secretion

Question 24

What type of secretion occurs in the ileum and proximal colon?

Answer 24

Cl- and HCO3- secretion

Question 25

What type of secretion occurs in the distal colon?

Answer 25

Cl- secretion

Question 26

Where is the main mechanism for electrogenic Cl- secretion in intestinal secretion?

Answer 26

small intestine & colon

Question 27

What does active Cl- secretion drive?

Answer 27

Active Cl- secretion drives movement of Na+ and water - Result: isotonic solution of NaCl

Question 28

What transporter is found in the basolateral membrane of the small intestine and colon in the secretion of Cl-?

Answer 28

NKCC1cotransporter - accumulates Clin the cell above electrochemical equilibrium

Question 29

What transporter is found in the apical membrane of the small intestine and colon in the secretion of Cl-?

Answer 29

Cl- channel - CFTR - exit pathway for Cl-

Question 30

What is CFTR activated by?

Answer 30

cAMP

Question 31

What is vibrio cholerae?

Answer 31

Bacteria that multiples in small intestine that secretes cholera toxin

Question 32

What is the mechanism of cholera toxin?

Answer 32

Binds to intestine Enters villous and crypt cells Stimulates adenylate cyclase irreversibly Elevation of cAMP Stimulates Cl- secretion in crypts Inhibits nutrient-independent Na+ absorption in villi Secretory diarrhea - Loss of isotonic fluid

Question 33

The absorption of Na+ and water in the small intestine A. is mainly facilitated by channels. B. is nutrient dependent. C. is entirely nutrient independent. D. is facilitated by CFTR.

Answer 33

B. is nutrient dependent.

Question 34

What are the different types of dietary sugars>

Answer 34

polysaccharides - glycogen and starch disaccharides - sucrose, lactose and maltose monosaccharides - glucose, fructose

Question 35

What percentage of dietary sugars do polysaccharides comprise?

Answer 35

45-60%

Question 36

What percentage of dietary sugars do disaccharides comprise?

Answer 36

30-40%

Question 37

What percentage of dietary sugars do monosaccharides comprise?

Answer 37

10%

Question 38

What dietary sugar is absorbed?

Answer 38

Monosaccharides

Question 39

What are the main monosaccharides absorbed?

Answer 39

Glucose, galactose, fructose

Question 40

What is glucose and galactose absorbed by?

Answer 40

Na+-dependent mechanism (SGLT1)

Question 41

What is fructose absorbed by?

Answer 41

Na+ -independent mechanism (GLUT5)

Question 42

What are the two steps in the digestion of sugars to release monosaccharides?

Answer 42

Luminal digestion Contact or brush boarder digestion

Question 43

What is the luminal digestion of sugar?

Answer 43

Mouth - a amylase Small intestine – pancreatic amylase Products: - a-limit dextrins - short oligosaccharides and some disaccharides

Question 44

What is the contact or brush border digestion of sugar?

Answer 44

Enzymes attached to apical membrane of epithelial cells Release monosaccharides - glucose, galactose, fructose

Question 45

The absorption of glucose via SGLT1 is against the concentration gradient, BECAUSE basolateral glucose absorption is mediated by facilitated diffusion.

Answer 45

A - Both true and causally related

Question 46

Why do we have the digestion and absorption of proteins?

Answer 46

NOT for energy Required for amino acids

Question 47

What are our sources of proteins (%)?

Answer 47

50% diet 25% sloughed cells 25% digestive enzymes

Question 48

What are the stages of digestion and absorption of fat?

Answer 48

Emulsification and stabilization Digestion Formation of micelles Absorption Re-esterification – synthesis of triglycerides Formation of chylomicrons

Question 49

What is the emulsification and stabilization of fat?

Answer 49

Reduction in size to droplets - motility - important as it increases the surface area available for digestion

Question 50

What is the emulsification and stabilization of fat in the stomach?

Answer 50

crude emulsion

Question 51

What is the emulsification and stabilization of fat in the small intestine?

Answer 51

Emulsion stabilized by emulsification agents - bile salts, phospholipids, cholesterol, lecithin

Question 52

What are the minor enzymes in digestion?

Answer 52

gastric and lingual lipases

Question 53

What are the major enzymes in digestion?

Answer 53

pancreatic lipase/colipase secreted by the pancreas into the small intestine

Question 54

What are the fat soluble vitamins and how are they absorbed?

Answer 54

Fat soluble vitamins A,D & E - absorbed in the same fashion as fats

Question 55

What are examples of water soluble vitamins?

Answer 55

Vitamin C Vitamin B12

Question 56

What is the transport process of vitamin B12?

Answer 56

IF is released in stomach In duodenum B12 binds to IF IF/B12 complex attaches to specific receptors in terminal ileum Complex absorbed by endocytosis and degraded to release B12 into portal blood

Question 57

Protein A. digestion starts in the mouth. B. digestion occurs mainly in the stomach. C. digestion is reduced during the gastric phase. D. absorption is facilitated by brush border membrane peptidases.

Answer 57

D. absorption is facilitated by brush border membrane peptidases.