GI10 Lipid Digestion

Question 1

1) What breaks down lipids in the stomach?
2) Describe the rate of stomach emptying for lipids +why?
3) What is the impact of this on glucose absorbtion?

Answer 1

1)Gastric lipase hydrolyses triglyceride
2)  Lipid is slowly emptied from stomach, as+
Lipid in duodenum inhibits gastric emptying,
3) (2) slows absorption time of other molecules to so won’t get glucose peak

Question 2

What happens to lipid in Duodenum and Jejunum?

Answer 2

1) Lipid is emulsified by bile salts and lecithin to increase the surface area for the water soluble enzymes to act
2) Enzymes in pancreatic juice lipolytic enzymes are released by acinar cells.
3) they are acted on by bile salts, when the concentration of bile salts is greater than critical micelle concentration = micelles form. This happens in the duodenum
4) Most the micelles in the juodenum enter the epithelial cells via diffusion or transport proteins

Question 3

Name the enzymes that are Pancreatic juice lipolytic enzymes?

Answer 3

1 Pancreatic lipase
2 Co-lipase
3 Cholesterol esterase
4 Phospholipase A

Question 4

What does pancreatic lipase breakdown (+product)?

Answer 4

triglyceride to = 2-monoglyceride and 2* non-esterified fatty acids (NEFA)

Question 5

What does cholesterol esterase do?

Answer 5

Cleaves a fatty acid from cholesterol ester, producing NEFA and a free cholesterol

Question 6

What does Phospholipase A2 breakdown (+product)?

Answer 6

phophospolipid to lysophospholipid + NEFA

Question 7

What does NEFA stand for?

Answer 7

non-esterified fatty acid

Question 8

What affects the rate of micelle absorption?

Answer 8

the rate they pass through the unstirred layer of the small intestine (deep to the BBM) as the the convoluted surface means the aqueous surroundings move more slowly and do not mix with luminal contents.

Question 9

Which constituent of micelle absorbed last?

2) How does the micelle enter the epithelium?
3) where are most micelles absorbed?

Answer 9

1) Cholesterol
2) diffusion
3) jejunum

Question 10

A) What happens before micelle absorbtion:
B)How are the following asbsorbed:
1) cholesterol
2) long-chain fatty acids
3) the rest

Answer 10

A) they diffuse along the brushborder membrane for a bit- who knows why?
B) 1)
then brush border membrane contains 2 transporters :
1) cholesterol transporter mediates facilitated diffusion
2) Microvillus membrane fatty acid binding protein transports long-chain fatty acids by 2nd active transport
3) diffusion across and directly into epithelail cell

Question 11

What happens to lipids once they enter the epithelium?

Answer 11

1) Fatty acid binding protein and sterol carrier proteins transport products of lipid digestion to smooth endoplasmic reticulum
2) In the smooth ER lipids are re-esterified forming phospholipid and cholesterol ester (from 1 NEFA) , and triglycerides (from 2)
3) then chlosterol ester, phospholipid and triglyceride form pre-chylomicron
4) the pre-chylomicron goes to the golgi then after processing leaves as a chylomicron
5) chylomicron is exocytosed and enters lacteal then blood via thoracic duct

Question 12

Why doesn’t chylomicrons enter blood directly?

2) Does this influence time taken for fat to appear in blood stream?

Answer 12

they are too large to transverse basement membrane where cappillaries are,
2) yes as after a fatty meal blood lipids take an hour or 2 to appear.

Question 13

1) Where are bile salts reabsorbed?
2) How are unconjugated bile salts absorbed?
3) how are conjugated bile salts absorbed?
4) Bile salts may be conjugated to….

Answer 13

1) terminal ileum
2) diffuse across brush border membrane
3) Conjugated bile salts are actively taken up by an Na+ bile salt co-transporter
4) glycine or taurine

Question 14

How do bile salts return to liver?

Answer 14

Bile salts re-enter portal blood, mostly bound to albumin, and return to liver