57. Catabolism and absorption of lipids

Question 1

The majority of the lipid in the food is

Answer 1

The majority of the lipid in the food is triglyceride, but it also contains sterine, sterine-ester and phospholipids in a smaller amount.

Question 2

• Pancreatic lipase

Answer 2

• Pancreatic lipase is a water-soluble molecule which can digest lipids at the lipid-water interphase.
• The surface of this interphase is extremely enhanced by emulsification
• Bile acids can emulsify lipids inefficiently by it self, but with the help of lecithin (excreted with bile), the emulsification is appropriate.

Question 3

• Fat digestion

Answer 3

• Fat digestion results in 2 fatty acids and one 2-monoglyceride which form the so-called micelles combined with bile salts.
• In this form the digested products get to the brush border, where they can easily get through the fat-soluble membrane.

Question 4

Fatty acids in the sER

Answer 4

• Products that enter the enterocyte is transported into the sER.
• Fatty acids in the sER are re-esterified, in which process species specific triglycerides are synthesized by binding the appropriate fatty acids to the 2-monoglyceride.
• The re-synthesized triglyceride aggregates in the sER, absorbs cholesterol and phospholipid in a way to place the hydrophilic part towards the environment (chylomicrons).

Question 5

Apolipoproteins

Answer 5

• Apolipoproteins emerge onto the surface of the chylomicrons and direct its further transport and metabolism.
• The size of the chylomicrons is bigger than would allow them to enter into the capillaries.
• Chylomicrons with the attached apolipoproteins get out of the cell by exocytosis though the basolateral side to the intracellular space, where they get into the lymphatic capillaries (having large fenestrations), and are transported by the lymph into the blood.

Question 6

Fat droplets

Answer 6

• Fat droplets appear due to body heat and gastric motility, however any tendency to form emulsions with phospholipids or other natural emulsifying agents is inhibited by the high acidity.
• Because fats tend to separate out into an oily phase, they tend to be emptied from the stomach later than the other gastric content.
• The lipid content of the duodenum inhibits gastric motility → helps the digestion and emulsification processes in the duodenum.