Gastrointestinal Physiology: Absorption

Question 1

How are monosaccharides absorbed?

Answer 1

Diffuse passively down concentration gradient via paracellular patway

or cotransport with Na+

Question 2

What is the driving force for the absorption of monosaccharides?

Answer 2

Concentration gradient/Na+/K+ ATPase

Question 3

This is the monosaccharide transporter in the apical membrane.

Answer 3

Na+ monosaccharide transporter

Question 4

This is the monosaccharide carrier in the basolateral membrane.

Answer 4

glucose carrier

Question 5

How are amino acids passively absorbed?

Answer 5

Diffusion down a concentration gradient via paracelullar pathway

Question 6

How are amino acids actively absorbed?

Answer 6

Cotransport with Na+ via Na+/K+ATPase

Question 7

How are di and tri peptides actively absorbed?

Answer 7

Cotransport with H+ via Na+/K+ ATPase
(apical membrane = H+/peptide cotransporter)
(basolateral membrane = amino acid carrier)
(cytoplasmic peptidases)

Question 8

The rate of absorption is proportional to the?

Answer 8

Surface area: the greater the surface area, the faster the rate of absorption

Question 9

What are the 4 anatomical adaptations that maximises the surface area?

Answer 9

Length of intestine, plicae circulares, villi and microvilli

Question 10

This is a pathway whereby solutes do not cross cell membranes. Only barrier is tight junctions binding cells together. This is a non-selective pathway and requires a gradient.

This is a pathway in between cells.

Answer 10

Paracellular pathway

Question 11

This is a pathway whereby solutes must cross two cell membranes (apical and basal membrane). Cellular membrane is usually made of phospholipid bilayer - if solute is not lipid soluble, it requires a transport protein

This pathway is across cell membranes.

Answer 11

Transcellular pathway

Question 12

Water absorption mainly occurs through what process? And what pathway?

Answer 12

Osmosis via paracellular pathway

Question 13

The osmotic gradient is set up by the absorption of what 2 molecules?

Answer 13

Salts and nutrients

Question 14

Na+ absorption mainly occurs through what process and what pathway?

Answer 14

1) passive movement via paracellular pathway (down its concentration gradient)

2) active transport via cells in transcellular pathway (via co-transport with carbohydrates and proteins)

Question 15

What is the driving force for Na+ absorption?

Answer 15

Na+/K+ATPase

Question 16

This is the passage of substances from the GI lumen across the lining of the intestine into the interstitial fluid and then into the bood or lymph.

Answer 16

Absorption

Question 17

What is the main site of absorption?

Answer 17

Small intestine

Question 18

What binds the epithelial cells together?

Answer 18

Tight junctions

Question 19

Bile salts are absorbed in the?

Answer 19

Ileum

Question 20

How are products of fat digestion absorbed?

Answer 20

1) Diffusion of FFA and monoglycerides from micelle into the cell.
2) Resynthesis of FFA and monoglycerides into triglycerides in the ER
3) Packaged in golgi as chylomicrons, then transported to basolateral membrane
4) Exocytosed from basolateral membrane into lymph
5) Enters lymph via lymph lacteals of the villi

Question 21

How are the products of fat digestion secreted from the golgi?

Answer 21

As chylomicrons

Question 22

Why are FFA and monoglycerides resynthesized to triglycerides?

Answer 22

To maintain gradient for apical diffusion.

Question 23

How is vitamin B12 usually absorbed?

Answer 23

Through transcellular pathway by binding to intrinsic factor (specific transporter for intrinsic factor in the ileum)

Question 24

Where is Vitamin B12 absorbed in the small intestine?

Answer 24

Ileum