Digestion and Absorption of Lipids

What are lipids?

- triglycerides

- cholesterol

- fatty acids

- phospholipids

Are lipids insoluble or soluble in water?

insoluble

With lipids being insoluble in water, what does this mean?

they cannot circulate freely

How is lipids important for the cell membrane?

they are a structural component

How is lipids important for the diet?

healthy part of it, if taken in proper amounts

What is major function of lipids other than structural support for the cell membrane?

help in providing energy and producing hormones

What are the 3 lipid polymers?

1. triglycerides

2. cholesterol ester

3. phospholipids

How are the lipid polymers broken down into monomers?

catabolic pathways

Can our body absorb monomers or polymers?

monomers

What are the monomers formed from the Triglyceride polymer?

1. monoacylglycerol (MAG)

2. Free Fatty Acid

What are the monomers formed from the Cholesterol ester polymer?

cholesterol

What are the monomers formed from the phospholipid polymer?

1. glycerol

2. free fatty acid

3. phosphate

When food is ingested in the mouth, what enzyme breaks down fats/lipids?

salivary lipase

In the process of breaking down the fats/lipids with salivary lipase, what bonds does the enzyme specifically attack?

ester bonds

When the ester bonds get attacked and broken down from salivary lipase, what happens?

breaks down triglycerides into free fatty acids and MAG

Does salivary lipase degrade all of the ester bonds?

no because food is not in our mouths very long

Where does the food go to, to get further degradation of the ester bonds?

the stomach

What enzyme is present in the stomach to further degrade the ester bonds?

gastric lipase

What is gastric lipase released from?

chief cells in the stomach

When the ester bonds get attacked and broken down from gastric lipase, what happens?

breaks down triglycerides into free fatty acids and MAG

Where does the chyme from the stomach go to, to get further degradation of the ester bonds?

duodenum where it also interacts with the pancreas

What all does pancreatic lipase degrade?

ester bonds in triglycerides and phospholipids

Can pancreatic lipase work alone?

no

What does pancreatic lipase need?

coplipase

Colipase

protein co-enzyme required for optimal enzyme activity of pancreatic lipase

What helps the lipid globule to enter the intestinal chyme?

bile

What does the bile salt do?

very important for emulsification of lipid globule

Bile acids/Salts are synthesized where?

liver

Bile acids/Salts are synthesized in the liver and secreted into what?

intestinal lumen via gallbladder

Bile salts are reabsorbed in what?

ileum

Bile salts are reabsorbed in the ileum and returned to?

liver by enterhepatic circulation

What is chyme made of?

water and dissolved foods

Since lipids are not soluble in water, when the it reaches the intestines where does it sit?

on surface of intestinal wall

In order to get the fat lobule (lipids) to sink down into the chyme, what must be released?

bile salts from the liver gallbladder where it attaches to the fat

When the bile salt/acid attaches to the fat lobule, what happens?

it sinks down into the chyme

After the bile salt attaches to the fat lobule and sinks, what is released?

colipase

Where is the colipase released from?

pancreas

Why is colipase released?

to help the lipase further work

What does pancreatic lipase and colipase do?

breaks triglycerides into free fatty acids, monoglycerides, and cholesterol

With all these attached to the fat lobule (colipase, lipase, and bile salts), what occurs due to bile salts being present on the fat lobule?

emulsification

What do these emulsified lipid droplets have in them?

polymers

After emulsification, what are the fat droplets called?

micelles

What are micelles?

made of only monomers

What is the most important cell in the intestines?

enterocytes

Micelle will transport to where?

enterocytes at the brush border

When at the brush border of enterocytes, what happens to the bile salts?

they are recycled back to the liver or stored in gallbladder

What happens to the monomers when entering the enterocyte?

they first encounter the smooth ER

What does the smooth ER do to the monomers?

converts them into polymers

After they are converted to polymers, what happens?

encounter the rough ER

What does the rough ER do to the polymers?

packages them?

What transfers the polymers that are packaged?

MTP

Microsomal Triglyceride transfer protein (MTP)

binds triglycerides to Apo B

Chylomicron

a type of lipoprotein that carries digested fat and other lipids through the lymph system into the blood