Absorption

Question 1

Carbohydrates absorption

Answer 1

(broken into monosaccharides for digestion)
1. Glucose and galactose - co-transporter with Na across apical membrane and GLU2 across basolateral
2. Fructose - GLUT5 across apical and GLUT 2 across basoateral

Question 2

Proteins absorption

Answer 2

(digested into AA/peptides in digestion)
1. Peptides - H dependant transporter across apical and hydrolysed to AA inside
2. AA - sodium co-transporter across apical and fac diff across basal

Question 3

Lipids absoption

Answer 3

(broken into free fatty acids, glycerol, monoglycerides, and cholesterol in dig)
1. Glycerol - passive diffusion
2. short fatty acids - diffusion
3. Long fatty acids/monoglycerides - diffuse into cell and re-synthesised into triglycerides inside then exocytosed as chylomicron at the basal membrane
4. Cholesterol - endocytosed into clarthrin pits

Question 4

Ca2+ absorption

Answer 4

1. Passive transport through whole SI
2. Active transport when in chyme

Question 5

Iron absorption

Answer 5

(Fe3+ reduced to Fe2+ in digestion)
1. Fe2+ is H+ co-transported (or transported through haem) into cell and inside, combines with apoferratin to be stored as ferratin in oxidised Fe3+ form.
2. Fe2+ is protein transported into blood and oxidised by ferroxidase into Fe3+ at basolateral membrane where it is picked up by transferrin for transport

Question 6

B12 absorption

Answer 6

When bound to intrinsic factor it is endocytosed into cell

Question 7

Fat soluble vitamins (A, D, E, K) absorption

Answer 7

Diffuse into cell where they are incorporated into chylomicron and exocytosed into lymphatics

Question 8

Water soluble vitamins (C, H, B) absorption

Answer 8

Na transporter into and out of cell

Question 9

Sodium absoprtion

Answer 9

1. Na/H exchange - duodenum and jejunum
2. Na/glucose co-transporter - jejunum
3. Na/AA co-transporter - jejunum
4. parallel Na/H and Cl/HCO3 exchange - ileum and proximal colon
5. Epithelial Na Channels - distal colon
   - Na/K ATPase for basolateral membrane

Question 10

Chlorine absorption

Answer 10

1. Electrochemical gradient absortion due to Na/AA and Na/glucose transporter whole length of small intestine
2. Electrochemical gradient absorption due to ENaC in the large intestine
3. parallel Na/H and Cl/HCO3 exchange - ileum and proximal colon
4. Cl/HCO3 exchange - ileum, proximal and distal colon

Question 11

Chlorine secretion

Answer 11

Apical membrane - CTFR channels
Basolateral membrane - Na co-transport
Parietal cells - Cl and HCO3 undergo antiport and then H+ is released to bind to HCl in a canaliculus to be released

Question 12

Chylomicron transport and digestion (in blood)

Answer 12

(chylomicron are the exocytosed form of tryglycerides)
1. they are transported into lymphatic system
2. If they are metabolised, it is by lipoprotein lipase
3. Albumin carries the products of the metabolism (free fatty acids and glycerol)