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BMS13 > Digestion & Absorption > Flashcards

Digestion & Absorption Flashcards

1
Q

Where does protein digestion start?

A

In stomach (pepsin and HCl)

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2
Q

What cell releases pepsinogen?

A

Peptic/chief cell

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3
Q

What cell releases HCl?

A

Parietal/oxyntic cell

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4
Q

What does chyme from the stomach contain?

A

Solubilised, slightly digested carbohydrates and proteins

Slightly digested fats

Intrinsic factor

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5
Q

Describe protein digestion in the duodenum. (4)

A
  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
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6
Q

Where is enterokinase found?

A

Brush border of duodenal enterocytes

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7
Q

Where are aminopeptidases found?

A

Brush border of duodenal enterocytes

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8
Q

What type of protease is chymotrypsin?

A

Endopeptidase

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9
Q

How are amino acids absorbed in the small intestine?

A

Na-linked luminal transporters and exit on BL membrane

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10
Q

How are di/tripeptides absorbed in the small intestine?

A

H-linked luminal transporters

Hydrolysed to amino acids

Exit on BL membrane

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11
Q

Why is the infant small intestine wall permeable to peptides?

A

Allows absorption of growth factors and antibodies from colostrum

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12
Q

What substance makes up dietary fibre?

A

Cellulose

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13
Q

How is starch digested?

A

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

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14
Q

What transporters are involved in monosaccharide absorption? (4)

A

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

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15
Q

What enzymes are involved in lipid digestion?

A

Mainly pancreatic lipase with some gastric lipase

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16
Q

What aids lipid digestion in the duodenum?

A

Colipase

Bile salts

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17
Q

What is beta-lipoprotein used for?

A

Package absorbed lipids into chylomicrons for export

18
Q

Describe fat digestion in the duodenum. (4)

A
  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
19
Q

Describe fat absorption in the duodenum. (4)

A
  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
20
Q

Where is the majority of bile reabsorbed?

A

Terminal ileum

21
Q

What is enterohepatic recirculation of bile salts?

A

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

22
Q

What is the overall percentage loss of bile salts?

A

5-10%

23
Q

What hormone stimulates water reabsorption in the colon?

A

Aldosterone

24
Q

What is produced by the resident microflora in the colon?

A

Vitamin K and folic acid

25
Q

Where are the fat-soluble vitamins generally absorbed?

A

In small intestine with lipids

26
Q

In what state are drugs best absorbed?

A

Non-ionised

27
Q

Where are drugs absorbed?

A

Small intestine and colon

28
Q

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

A

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

29
Q

What can cause failure to absorb lactose?

A

Absence of brush border lactase (alactasaemia)

30
Q

What can cause failure to absorb lipids?

A

Lack of beta-lipoproteins

Failed lipid digestion

31
Q

What can cause insufficient water absorption?

A

Increased solute load

Increased salt and water secretion by bacterial infection

32
Q

What does vit. B12 malabsorption in the ileum cause?

A

Fewer, immature, but macrocytic RBCs (pernicious anaemia)

33
Q

What can cause vit. B12 malabsorption?

A

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

34
Q

What does Fe2+ malabsorption cause?

A

Microcytic RBCs due to insufficient Hb

35
Q

How can anaemia affect the oral appearance?

A

Pale gums

Glossitis and changes to tongue surface

36
Q

What is osmotic diarrhoea? (4)

A

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

37
Q

What is secretory diarrhoea?

A

Response to bacterial infection

Increased secretory activity of intestinal crypt cells which affects Na movement

38
Q

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

A

Coeliac disease

Crohn’s disease

39
Q

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

A

Crypt hyperplasia

Decreased surface area (villous atrophy)

40
Q

What is Crohn’s disease?

A

Inflammatory condition mainly affecting ileum and colon

BMS13 (7 decks)

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