6- Intestines

Question 1

Describe the state of chyme when it enters the intestines

Answer 1

Isotonic
Neutral
Nearly completely digested

Question 2

Describe intestinal epithelia

Answer 2

Simple columnar epithelium - enterocytes
Goblet cells
Within intestinal gland:
Enteroendocrine cells
Paneth cells (antibacterial)
Stem cells (cells mature as they migrate to the surface)

Question 3

How are carbohydrates digested?

Answer 3

Polysaccharides broken down into monosaccharides by brush border enzymes
Monosaccharide absorbed with Na

Question 4

Describe how starch is broken down

Answer 4

Maltase breaks a1,4 bonds to form maltose (glucose+glucose) and alpha dextrins, strands of amylopectin still with a1,6 bonds in tact
Isomaltase breaks a1,6 bonds to form glucose

Question 5

Describe how lactose is broken down

Answer 5

Lactase breaks it down into glucose and galactose

Question 6

Describe how sucrose is broken down

Answer 6

Sucrase breaks it down into glucose and fructose

Question 7

Describe the structure of starch

Answer 7

Made up of two molecules - straight chained amylose with A1,4 bonds
Branched amylopectin with A1,6

Question 8

How are monosaccharides absorped?

Answer 8

Basolateral Na/K ATPase maintaines low intraceullular Na
SGLT-1 binds to Na, allows glucose to bind and move into enterocyte
GLUT2 transports glucose out of enterocyte (fructose uses GLUT5)

Question 9

Why is Na and glucose given in oral rehydration?

Answer 9

Uptake of Na generates an osmotic gradient, water follows

Glucose uptake stimulates Na uptake

Question 10

Describe protein digestion in the stomach

Answer 10

Pepsinogen released from chief cells
Converted to pepsin by HCl
Pepsin breaks down proteins into amino acids

Question 11

What happens when trypsinogen is released from the pancreas?

Answer 11

Enteropeptidase converts trypsinogen into trypsin

Trypsin then activates other proteases

Question 12

Define exopeptidases

Answer 12

Exopeptidases break bonds at the ends of polypeptides to produce dipeptides/single amino acids

Question 13

Define endopeptidases

Answer 13

Endopeptidases break bonds in the middle of polypeptide to produce shorter polypeptide

Question 14

Give examples of endo and exopeptidases

Answer 14

Endopeptidases:
Trypsin 
Chymotrypsin 
Elastase 
Exopeptidases:
Carboxypeptidase A and B

Question 15

Why are amylase plasma levels tested?

Answer 15

In acute pancreatitis, amylase is released into blood

Question 16

Describe the absorption of protein products

Answer 16

Amino acids transported into eclls by Na co-transporter
Majority - Dipeptides moved into cell by H+ co-transporter PepT1, when cytosolic peptidases break them down into amino acids

Question 17

Describe water uptake in the intestines

Answer 17

Both small and large have Na/K ATPase basolaterally
Apically:
Small: Na co-transporter (most reabsorbed here)
Large: Na+ channels, induced by aldosterone, diffuses

Question 18

Describe the uptake of calcium in the duodenum

Answer 18

When calcium intake is low
Active transcellular transport, Ca enters via facilitated diffusion - Ca ATPase removes Ca from basolateral membrane
Vitamin D activates calbindin (Ca intracellular transport protein) and is activated by parathyroid horomone
When calcium intake is high
Passive paracellular absorption

Question 19

Where is iron stored in the body?

Answer 19

Half in haemoglobin

Half in ferritin complexes in bone marrow, liver and spleen

Question 20

How is iron absorbed?

Answer 20

In haem, absorbed across apical membrane by co-transport with H+

Question 21

Why do proton pump inhibitors affect iron absorption?

Answer 21

Gastric acid cotransporter, so needed to drive reuptake. PPIs inhibit gastric acid secretion

Question 22

How is iron uptaken when levels are high and low?

Answer 22

High: Iron contained in ferritin complexes within cell, lost when enterocyte is replaced
Low: Iron binds to transferrin, transported to stores

Question 23

Describe vit b12 uptake and what can affect it

Answer 23

Absorbed in terminal ileum and bound to intrinsic factor, which is secreted by gastric parietal cells.
Gastritis, terminal ileal removal (for Cronn’s disease) and PPIs all decrease absorption

Question 24

Describe the disease process of coeliac disease

Answer 24

Intolerance of gliadin fraction of gluten
Causes immune response that damages intestinal mucosa:
Lose intestinal villi
Lengthen intestinal crypts
Lymphocytes infiltrate epitheliumm, impairing digestion

Question 25

Explain the cause of the symptoms of coeliac disease

Answer 25

Damaged mucosal cells - osmotic content in gut - water not reabsorbed - diahorrea
Malabsorption - undigested carbohydrates fermented by bacteria produce gas - flatulence and bloating