A & P - Gastrointestinal Systmem, Digestion And Absorption Of Lipids And Fat-Soluble Vitamins

Front 1

Which are the fat-soluble vitamins?

Back 1

Vitamins A, D, E, and K are the fat-soluble vitamins.

Front 2

In what form is dietary fat normally found?

Back 2

Triglycerides

Front 3

Which enzyme is principally responsible for digesting fats in the stomach?

Back 3

Gastric lipase helps to kick off the digestion of fats in the stomach.

Gastric lipase is secreted by chief cells.

Front 4

Which cells of the gastric mucosa secrete gastric lipase?

Back 4

Chief cells

Front 5

All lipids are absorbed via which means of cell membrane transport?

Back 5

Simple diffusion

Front 6

In what form are lipids absorbed by enterocytes?

Back 6

Lipids are absorbed into enterocytes as monoglycerides and fatty acids (short or long chain).

Once inside enterocytes, however, they are re-assembled into triglycerides and packaged into chylomicrons which then enter the circulation by way of lacteals and the lymphatic system.

Front 7

Enzymes that split triglycerides and phospholipids are called...

Back 7

Lipases

Front 8

Name the three lipases involved in lipid digestion.

Back 8

1) Lingual lipase
2) Gastric lipase
3) Pancreatic lipase

Of these, pancreatic lipase does the bulk of the digesting.

Front 9

What is emulsification?

Back 9

Emulsification is the process by which a large globule of lipids is broken down into several small lipid globules.

Emulsification is achieved with the aid of bile salts. Through their amphipathic nature they are able to break the fat into many small globules.

The large surface area provided by these globules facilitates the work of pancreatic lipase.

Front 10

What are bile salts?

What is their role in lipid digestion and absorption?

Back 10

Bile salts are bile acids compounded with a cation, usually sodium.

Okay, so what are bile acids?

Bile acids are steroid acids found predominantly in the bile of mammals.

In humans, the salts of taurocholic acid and glycocholic acid (derivatives of cholic acid) represent approximately eighty percent of all bile salts.

The role of bile salts is twofold:

First bile salts aid in emulsification, or the breakdown of large fat globules into smaller globules. They achieve this through their amphipathic nature.

Secondly, bile salts also aid in absorption of lipids following their digestion.

Front 11

How do bile salts aid in the digestion of lipids?

Back 11

Bile salts aid the process of emulsification, or breakdown of large fat globules into smaller ones.

They are able to do this through their amphipathic nature. Each bile salt has a hydrophobic region and a hydrophilic region.

The hydrophobic regions of bile salts interact with the large lipid globule, while the hydrophilic regions interact with the watery intestinal chyme.

Front 12

What percentage of lipids entering the adult's small intestine are absorbed?

Back 12

95%

Front 13

What is a micelle?

Back 13

A micelle is a tiny sphere of bile acids containing digested lipid contents like fatty acids, monoglycerides, cholesterol, and fat-soluble vitamins.

Front 14

What's the name of the bile acid "ferry" that carries digested lipids to enterocytes for absorption?

Back 14

Micelle

Front 15

How are fat-soluble vitamins solubilized in the intestinal lumen?

Back 15

They are ferried through the intestinal lumen by micelles.

Front 16

Describe the route lipids take from ingestion to the circulation.

Back 16

Fat globules --> smaller fat globules --> fatty acids + monoglycerides within micelles in GI lumen --> fatty acids + monoglycerides in enterocytes --> triglycerides in enterocytes --> triglycerides within chylomicrons in enterocytes --> chylomicrons in lacteals --> chilomicrons in lymphatic system --> chylomicrons in circulation

1) Emulsification via mechanical separation and bile salts.

2) Digestion via lingual, gastric, and pancreatic lipases.

3) Ferrying to enterocytes by micelles

4) Diffusion out of micelles into enterocytes via simple diffusion

5) Recombination of fatty acids and monoglycerides to form triglycerides within enterocytes

6) Carriage of triglycerides out of enterocytes and into lacteals by chylomicrons

7) Entrance of chylomicrons into circulation

Front 17

What is the enterohepatic circulation?

Back 17

The enterohepatic circulation refers to the cycle of bile salt secretion by hepatocytes into bile, reabsorption of bile salts by the ileum, and re-secretion of bile salts by the hepatocytes into bile.

Front 18

Through what portion of the GI tract are bile salts reabsorbed?

Back 18

90-95% of bile salts are reabsorbed through active transport in the DISTAL ILEUM.

Front 19

Describe the fate of bile salts after they are secreted into bile.

Back 19

After their secretion by hepatocytes into bile, bile salts aid in the digestion and absorption of lipids in the small intestine.

They are subsequently reabsorbed via active transport in the distal ileum and returned by the blood to the liver through the hepatic portal system for recycling.

Front 20

Absorption of fat-soluble vitamins is absolutely dependent on...

Back 20

Absorption of fat-soluble vitamins (A, D, E, K) depends on the absorption of fat. Any condition in which fat digestion and absorption is decreased will eventually lead to a deficiency in these vitamins.

Front 21

In which regions of the GI tract are lipids absorbed?

Back 21

Almost all dietary fat is absorbed in the duodenum and jejunum.

Any fat in the stools (in the absence of steatorrhea) is from desquamated epithelial cells or from bacterial flora of the gut.

Note that fat-soluble vitamins, on the other hand, are absorbed in the distal jejunum and ileum.

Front 22

What is the principle source of most vitamin K?

Back 22

Most of the vitamin K we receive is synthesized by intestinal bacterial flora.