Lipid digestion and the absorbtion of calcium, iron and vitamins

Question 1

What is in lipids?

Answer 1

Fats/oils (TAG)
Phospholipids
Cholesterol and cholesterol esters
Fatty acids

Question 2

How does digestion occur for lipids?

Answer 2

Mouth - lingual phase
Stomach - gastric phase
Small intestine - emulsification by bile synthesised by the liver, pancreatic lipase - hydrolyses TAGs to monoglyceride and free fatty acid

Question 3

What occurs in the gastric phase of lipid digestion?

Answer 3

Heat an dmovements in the stomach mix food with gastric lipase which begins digestion and forms an emulsion. Emulsified fats are ejected from the stomach to the duodenum

Question 4

What occurs in the duodenum for lipid digestion?

Answer 4

Pancreatic lipase - main lipid digestive enzyme
Aided by bile salts from gall bladder
Bicarbonae in pancreatic juice neutralises stomach acid

Question 5

What does a free fatty acid stimulate?

Answer 5

CCK release from the duodenum and secretion of pancreatic lipase

Question 6

What pancreatic cells secrete pancreatic lipase?

Answer 6

Acinar cells in reponse to CCK

Question 7

What does full activity of pancreatic lipase require?

Answer 7

Colipase co-factor
Alkaline pH
Ca2+
Bile salts
Fatty acids

Question 8

What is the function of bile salts?

Answer 8

They act as detergents to emulsify large lipid droplets to small droplets to allow for an increased SA for action of lipase

Question 9

What does failure to secrete bile salts result in?

Answer 9

Lipid malabsorbion (steatorrhoea) 
Secondary vitamin deficieny due to failure to absorb lipid vitamins

Question 10

What is the function of colipase?

Answer 10

It is an amphipathic polypeptide that is secreted with lipase by the pancreas and binds to bile salts and lipase to allow access by lipase to tri and di glycerides

Question 11

What is contained within the hydrophobic core of a mixed micelle?

Answer 11

TAGs and esterified cholesterol

Question 12

What is contained with the outside of the mixed micelle?

Answer 12

Monoglyceride
Cholesterol
Fatty acid
Bile salts
Phospholipid

Question 13

How do fatty acids enter the enterocyte from the mixed micelle?

Answer 13

Passive diffusion throught the apical membrane

Question 14

How do short chained fatty acids leave the enterocyte?

Answer 14

Via basolateral membrane where they enter the villus capillaries

Question 15

How do long chained fatty acids leave the enterocyte?

Answer 15

They are resynthesised with monoglycerides to triglycerides in the ER and are incorporated into chylomicrons

Question 16

What makes up a chylomicron?

Answer 16

Triglyceride
Cholesterol ester
Phospholipids
ApoB-48

Question 17

Where doe shte chylomicron enter the systemic circulation?

Answer 17

Into the subclavian vein via the thoracic duct and distributed to the tissues

Question 18

Where are chylomicrons mtabolised?

Answer 18

In the capillaries by lipoprotein lipase present on endothelial cells

Question 19

How do free fatty acids and glyerol reach the tissues?

Answer 19

They bind to albumin are are taken up by tissues

Question 20

What is left of the chylomicron?

Answer 20

Chylomicron remnant, enriched with phospholipids and cholesterol

Question 21

What happens to the chylomicron remnant?

Answer 21

It undergoes endocytosis by hepatocytes

Question 22

What happens to the cholesterol in the hepatocytes?

Answer 22

Stored
Secreted unaltered in bile
Oxidised to bile salts

Question 23

How is cholesterol absorbed?

Answer 23

Transport by endocytosis in clatherin coated pits by NPC1L1 proteins

Question 24

What is the mode of action of ezetimibe?

Answer 24

Binds to NPC1L! to prevent internalization and thus cholesterol absorbtion