Digestion & Absorption

Question 1

Where does protein digestion start?

Answer 1

In stomach (pepsin and HCl)

Question 2

What cell releases pepsinogen?

Answer 2

Peptic/chief cell

Question 3

What cell releases HCl?

Answer 3

Parietal/oxyntic cell

Question 4

What does chyme from the stomach contain?

Answer 4

Solubilised, slightly digested carbohydrates and proteins

Slightly digested fats

Intrinsic factor

Question 5

Describe protein digestion in the duodenum. (4)

Answer 5

1. Enterokinase activates pancreatic trypsinogen to trypsin which activates other pancreatic proteases
2. Pancreatic trypsin, elastase and chymotrypsin cleave interior peptide bonds
3. Pancreatic carboxypeptidases remove amino acids from carboxyl ends
4. Aminopeptidases remove amino acids from amino ends

Question 6

Where is enterokinase found?

Answer 6

Brush border of duodenal enterocytes

Question 7

Where are aminopeptidases found?

Answer 7

Brush border of duodenal enterocytes

Question 8

What type of protease is chymotrypsin?

Answer 8

Endopeptidase

Question 9

How are amino acids absorbed in the small intestine?

Answer 9

Na-linked luminal transporters and exit on BL membrane

Question 10

How are di/tripeptides absorbed in the small intestine?

Answer 10

H-linked luminal transporters

Hydrolysed to amino acids

Exit on BL membrane

Question 11

Why is the infant small intestine wall permeable to peptides?

Answer 11

Allows absorption of growth factors and antibodies from colostrum

Question 12

What substance makes up dietary fibre?

Answer 12

Cellulose

Question 13

How is starch digested?

Answer 13

Salivary amylase in mouth begins process

Pancreatic amylase cleaves straight chains to from short oligosaccharides, maltose and maltriose

Further digestion of these and other disaccharides by brush border enzymes

Question 14

What transporters are involved in monosaccharide absorption? (4)

Answer 14

Driven by BL Na/K-ATPase

Apical SGLT - Na-linked glucose and galactose secondary active transport

Apical GLUT5 - fructose facilitated diffusion

Basolateral GLUT2 - facilitated diffusion of all three hexoses

Question 15

What enzymes are involved in lipid digestion?

Answer 15

Mainly pancreatic lipase with some gastric lipase

Question 16

What aids lipid digestion in the duodenum?

Answer 16

Colipase

Bile salts

Question 17

What is beta-lipoprotein used for?

Answer 17

Package absorbed lipids into chylomicrons for export

Question 18

Describe fat digestion in the duodenum. (4)

Answer 18

1. Fat emulsification using bile salts
2. Lipase actions converts TG to FA and MG
3. Formation of micelles (FA, MG, bile salts…)
4. Diffusion of micelles to epithelial brush border

Question 19

Describe fat absorption in the duodenum. (4)

Answer 19

1. Simple diffusion of free FA and MG into cell
2. Intracellular resynthesis of TG in SER
3. Incorporation of TG into chylomicrons together with beta-lipoprotein, cholesterol…
4. Exocytosis of chylomicrons into nearby lacteals

Question 20

Where is the majority of bile reabsorbed?

Answer 20

Terminal ileum

Question 21

What is enterohepatic recirculation of bile salts?

Answer 21

Reabsorption of bile salts in terminal ileum

Transported back to liver via hepatic portal vein to be re-extracted by hepatocytes to be re-exported in bile juice

Question 22

What is the overall percentage loss of bile salts?

Answer 22

5-10%

Question 23

What hormone stimulates water reabsorption in the colon?

Answer 23

Aldosterone

Question 24

What is produced by the resident microflora in the colon?

Answer 24

Vitamin K and folic acid

Question 25

Where are the fat-soluble vitamins generally absorbed?

Answer 25

In small intestine with lipids

Question 26

In what state are drugs best absorbed?

Answer 26

Non-ionised

Question 27

Where are drugs absorbed?

Answer 27

Small intestine and colon

Question 28

What can cause failure to digest macromolecules in chyme? (3)

Answer 28

Interruption of enterohepatic recirculation of bile salts (fats) Failure to deliver pancreatic enzymes Poor coordination of gastric emptying with delivery of pancreatic and biliary secretions

Question 29

What can cause failure to absorb lactose?

Answer 29

Absence of brush border lactase (alactasaemia)

Question 30

What can cause failure to absorb lipids?

Answer 30

Lack of beta-lipoproteins Failed lipid digestion

Question 31

What can cause insufficient water absorption?

Answer 31

Increased solute load Increased salt and water secretion by bacterial infection

Question 32

What does vit. B12 malabsorption in the ileum cause?

Answer 32

Fewer, immature, but macrocytic RBCs (pernicious anaemia)

Question 33

What can cause vit. B12 malabsorption?

Answer 33

Lack of intrinsic factor due to gastric atrophy or an autoimmune condition

Question 34

What does Fe2+ malabsorption cause?

Answer 34

Microcytic RBCs due to insufficient Hb

Question 35

How can anaemia affect the oral appearance?

Answer 35

Pale gums Glossitis and changes to tongue surface

Question 36

What is osmotic diarrhoea? (4)

Answer 36

Increased solute load in lumen causes water retention Increased volume of lumen contents causes increased peristalsis Undigested fats have laxative effect Undigested material fermented in colon by microflora = distension

Question 37

What is secretory diarrhoea?

Answer 37

Response to bacterial infection Increased secretory activity of intestinal crypt cells which affects Na movement

Question 38

What diseases can cause intestinal mucosal damage (causing diarrhoea)?

Answer 38

Coeliac disease Crohn's disease

Question 39

What is characteristic of the small intestine in Coeliac disease (gluten)?

Answer 39

Crypt hyperplasia Decreased surface area (villous atrophy)

Question 40

What is Crohn's disease?

Answer 40

Inflammatory condition mainly affecting ileum and colon