7.3 Lipid Digestion, Absorption, and Transport

Question 1

What is the problem with lipid Digestion, Absorption, and Transport?

Answer 1

Lipids do not like water as they are non-polar (will not dissolve).

Question 2

What is the general process of lipid digestion?

Answer 2

Mouth: Lingual lipase digests med and short chain fatty acids + mechanical digestion
Stomach: Gastric lipase digests med and short chain fatty acids
Small intestine: majority of digestion. bile emulsifies lipids, pancreatic lipase digests remaining lipids
Large intestine: minimal lipid digestion and absorption

Question 3

Triglycerides must be first broken down into what during digestion?

Answer 3

glycerol and fatty acids

Question 4

How are lipids absorbed in the small intestine?

Answer 4

1. Micelle (from lipid + bile emulsification) breaks down. Lipid content is absorbed into small intestine cells through passive diffusion.
2. Lipids are wrapped in phospholipids as they exist the small intestine cell and enter the centre of the villus. This makes a chylomicron, a type of lipoprotein
3. Chylomicrons enter lacteals as they are too large to enter blood

Question 5

_____ vessels are types of lymphatic vessels that bypass the liver, but eventually lead to blood

Answer 5

Lacteal

Question 6

What are lipoproteins? What is their use?

Answer 6

Lipid transporters that carry lipids around the body. We need them as lipids are hydrophobic and cannot be dissolved in the small intestine, blood, and lymph

Question 7

Why are lipoproteins called as such?

Answer 7

Phospholipid outside, lipid content inside, proteins embedded throughout

Question 8

What are the 4 types of lipoproteins?

Answer 8

Chylomicron
VLDL
LDL
HDL

Question 9

What is the lifecycle of a chylomicron?

Answer 9

Takes lipids from the small intestine, delivers them to cells, and then comes to the liver to be broken down into VLDL or HDL.

Question 10

What is the lifecycle of a VLDL?

Answer 10

Made in liver, delivers triglycerides to body cells, becomes LDL as it loses triglycerides

Question 11

What is the lifecycle of LDL?

Answer 11

Made from VLDL, delivers cholesterol OR return to the liver OR gets deposited in artery walls (leading to CVD)

Question 12

What is the lifecycle of HDL?

Answer 12

Made in liver, picks up cholesterol from body cells, returns it to the liver

Question 13

What does density have to do with the lipoproteins?

Answer 13

Low density - low mass (triglycerides) for their volume. As triglycerides are lost, density increases.

High density - High in protein, which are dense.

Question 14

What are the 8 steps in lipoprotein transport and delivery?

Answer 14

1. Chylomicrons (CM) deliver TGs from small intestine to body cells.
2. At tissues, lipoprotein lipase (LPL) breaks down TGs into fatty acids (FAs) and glycerol so they can be absorbed out of the CM and into the tissue. CM becomes smaller
3. Remaining CM return to liver where it breaks down into its components
4. Liver reassembles TFs, cholesterol, proteins, and phospholipids into VLDL.
5. During fat delivery to tissues, LPL breaks down TGs, allowing its components to enter cells
6. As VLDL loses TGs, it becomes smaller and denser to form LDL
7. 3 ends for LDL: 1. Cells with LDL-receptors take up entire LDL structures, where cholesterol and other contents are used. 2. LDL return to liver to be broken down. 3. If LDL levels are high, more likely to be oxidized and stick to artery walls. Increases risk for atherosclerosis (main case if heart attacks and strokes)
8. Liver makes HDL (high in proteins, low in TGs). HDL picks up cholesterol from body cells and lipoproteins and returns it to the liver.