Digestion and absorption of nutrients

Question 1

Definition of oligopeptides

Answer 1

Peptide whose molecules contain a relatively small no of amino acid residues

Question 2

Name the 4 layers of the GI tract and the features of each

Answer 2

Mucosa

• villi, brush border
• arterial, venous, lacteal vessels

Submucosa

• v fenestrated arterial, venous, lymph plexuses
• Meissner’s plexus
• separated from mucosa with muscularis mucosa

Muscular externa

• inner circular muscle
• Auerbach’s plexus
• outer longitudinal muscle layer

Serosa

Question 3

Name the 2 cells lining the villi and their functions

Answer 3

Absorptive cells
-nutrient uptake

Goblet cells
-mucus secretion

Question 4

Name the 3 main cells lining the crypt and their functions

Answer 4

Paneth
-antimicrobicidal secretions

Stem
-regeneration of GI epithelia

Enterochromaffin
-seretonin secretion => increased Cl secretion from CFTR => increased Na and water in lumen

Question 5

Describe the digestion pathway of carbohydrates

Answer 5

Salivary and pancreatic amylase => maltose, sucrose

Disaccharases in brush border => glucose, fructose, galactose

Question 6

Describe the absorption of glucose/galactose and fructose

Answer 6

Glucose/galactose

• SGLUT with Na => enter cell
• GLUT 2 => leave cell
• Na grad established by NaKATPase

Fructose

• GLUT 5 => enter cell
• GLUT 2 => leave cell

Question 7

Describe the digestion pathway of proteins

Answer 7

Gastric pepsin => AA, oligopeptides

Intestinal brush border, pancreatic enzymes => AA, di/tripeptides

Question 8

Describe the absorption of AA and di tripeptides

Answer 8

AA

• cotransported with Na => into cell
• FD => out of cell

Di tripeptides

• Cotransported with H => into cell
• hydrolysed into AA
• FD => out of cell

Question 9

What happens in

• Hartnup
• Cystinuria

Answer 9

Hartnup
-decreased uptake of non polar AA

Cystinuria
-decreased uptake of basic AA and cysteine

Question 10

Describe the absorption pathway of fat soluble vitamins

Answer 10

ADEK transported to epithelium via micelle

Diffuses into epithelium => chylomicron => lymph

Question 11

Describe the absorption pathway of water soluble vitamins

Answer 11

Cotransport with Na => into cell
FD => out of cell
Gradient established by NaKATPase

Question 12

Describe the absorption pathway of B12

Answer 12

Low pH and pepsin release B12 bound to protein

Haptocorrin released from salivary glands binds and protects B12 from acid

IF secreted from parietal cells

Haptocorrin B12 complex broken down by bile
Haptocorrin degraded

IF binds to CBL, complex absorbed in ileum

Question 13

Describe the absorption pathway of calcium

Answer 13

FD => into cells
Binds to calbindin to control [free Ca in cell]
CaATPase and NaCa exchange release Ca into ISS