Digestion And Absorption Of Lipids Flashcards
Digestion in oral cavity (enzyme, site and salivary gland function)
-Enzyme: Lingual Lipase
-Site: Secreted by Sublingual and Parotid
-Salivary Glands Function: Lingual Lipase breaks down the ester bond
-TG → monoacylglycerol (MAG) + 2 free fatty acids (FFA)
Digestion in the stomach (enzyme, site, and function)
-Enzyme: Gastric Lipase
-Site: Secreted by chief Cells
-Chief Cells also secret Pepsinogen
-Function: Gastric Lipase breaks down the ester bond
-TG → monoacylglycerol (MAG) + 2 free fatty acids (FFA)
-Not large amount of lipids is broken down by Lingual Lipase and Gastric lipase enzymes due to small surface area and short exposure time
Digestion in small intestine
Duodenum
➡️watery environment (intestinal chyme)
➡️ triglyceride, cholesterol, phospholipids aggergate
➡️from fat globules
Bile (digestion)
-Produced by liver
-Stored and concentrated by Gallbladder Bile Composition:
-Bile Acids
-Cholic Acid and Chenodeoxycholic acid
-Synthesized in the liver from Cholesterol
-Bile Acids are conjugated with Glycine or Taurine
to form bile salts and become water soluble.
-Phospholipids → Lecithin
-Others (e.g., Bilirubin, Biliverdin, cholesterol, water, ions)
Bile pathway to the duodenum
Produced in the liver
➡️hepatic duct
➡️go to gallbladder where it is stored and concentrated
➡️cystic duct
➡️common bile duct
➡️fuse w/ pancreatic duct
➡️ampulla of vater
➡️surrounded by sphincter of Oddi (=hepatopancreatic sphincter)
➡️into the duodenum
Bile role in lipid digestion
-bile= emulsification agent
➡️enhance the breaking down of the large fat globule into small fatty droplets
-bile salts and lecithin are amphipathic molecules
➡️they have both polar (hydrophilic) and nonpolar (hydrophobic) parts
Bile role in lipid digestion steps
1)Lecithin forms a layer around the fat globule
➡️more hydrophilic
➡️distributed into intestinal chyme
➡️small fatty droplets
2)Bile salts which have hydrophilic and hydrophobic sites bind to the complex and make it more hydrophilic
→Enhance Colipase Binding
3)Protein called colipase bind to the droplets coated with lecithin and bile salts→ Enhance Pancreatic Lipase interaction
Digestion: pancreatic secretions
-Pancreatic Lipase
-Bind with the colipase → Break down the Triglycerides (TG) → monoacylglycerol (MAG) + 2 free fatty acids (FFA)
-Phospholipase A2- PLA2
-Break down Phospholipids → FFA + Glycerol
-Cholesterol Ester Hydroxylase
-Break down Cholesterol Ester → FFA + Cholesterol
Digestion: micelles
-Very small fatty droplets, Made up of Monoacylglycerol, Free fatty acids, cholesterol, Phospholipids and Bile salts
-They can also contain Lipid soluble vitamins (Vitamin A, K, D, E)
Enterocyte mostly found in what organ?
Small intestine
Absorption of lipids: from lumen to enterocyte
As the micelles get close to the cell membrane of the enterocytes
-Bile Salts → 94% recycled → Go back to the liver via Enterohepatic Circulation
-Cholesterol, MAG, FFA and vitamins move to the cell via Passive Diffusion
Absorption of lipids: inside the enterocyte: smooth ER
-MAG + FFA → Reconvert to TG
-Vitamins
-Free cholesterol
-Cholesterol +FFA →Reconvert to Cholesterol esters
-Phospholipids
Absorption of lipids: inside the enterocyte: rough ER
A collection of lipid soluble vitamins, TG, Cholesterol, Cholesterol Ester, Phospholipids → Make some Modifications → Add protein to the outer part APO-B48
Absorption of lipids: inside the enterocyte (golgi)
Packaging➡️ chylomicrons
Absorption of lipids: from enterocyte into circulation: chylomicrons
-Chylomicrons leave the enterocyte via Exocytosis
-Chylomicrons are too large to pass through the blood capillaries→ thus they enter lymph
-Chylomicrons move through Lacteals (=Lymphatic Capillaries) → Lymphatic vessels, Trunks → Thoracic Duct → enter the blood circulation where the left subclavian vein and the Left internal Jugular vein meet and make the Brachiocephalic veins → Target tissues (Skeletal Muscles, Adipose tissue) and some go to the liver
Absorption of lipids: from enterocyte into the circulation: skeletal muscle
Lipoprotein lipase → Special Enzyme located in the capillary endothelium of the skeletal muscle → Cleave TG into FFA→ FFA enter the skeletal Muscle → Skeletal Muscle can use FFA as source of Energy
Absorption of lipids: from enterocyte into the circulation: adipose tissue
Lipoprotein lipase → Special Enzyme located in the capillary endothelium of the adipose tissue → Cleave TG into FFA→ FFA enter the Adipose tissue → stored as TG (Lipogenesis)
Absorption of lipids: from enterocyte into the circulation: liver
Make VLDL → push back to the circulation → other tissues
