Lipid Metabolism. Digestion & absorption . Introduction Fat is a good source of energy as 1 gm supplies 9.1 calories, which is over double that supplied by carbohydrates or protein. Dietary lipids are ingested in form of
Digestion & absorption
supplies 9.1 calories, which is over double
that supplied by carbohydrates or protein.
triglycerides,phosholipids,cholesterol and free fatty acids.
R-COOH + R-OH RCOOR + H2O
Fatty acid + Alcohol Ester + Water
These are carboxylic acids
their general formula R- COOH.
fatty acids are classified into
according to absence or presence of double bonds.
CH3 - COOH is acetic acid,
CH3 – CH2 – COOHis propionic acid
CH3 – CH2 – CH2 – COOH butyric acid and so on.
They have one or more double bonds.
1- Energy production, dietary lipids supply the body with about 25% of calories needed every day.
2- They provide the body with
Fats under the skin are used as insulater protecting the body against external temp.
1- Digestion of triglycerides:
1-Lingual lipase: Is secreted by the dorsal surface of the tongue (Ebner's glands),
but this enzyme is not of much significance in humans as compared with rat or mouse.
In the stomach some digestion occurs by gastric lipase
hydrolyzing triglycerides containing short, medium and unsaturated long chain fatty acids
to form FFA and 1,2 diglycerides
assist emulsification by lowering surface tension
exposing large area of triglycerides
pancreatic lipase will dissolve fatty acids.
acts on finely emulsified lipid droplets
in presence of
1- bile salts.
2- colipase (a protein present in pancreatic
3- phospholipase A2 (Ca++ is necessary for
phospholipase A2 activity).
Pancreatic lipase hydrolyses the primary ester bond with the production of 2FFA + β-monoglyceride.
this process is very slow. So the major digestion products of TGareβ-monoglyceride and FA.
Act within intestinal mucosal cells where it may hydrolyse primary monoglyceride
glycerol and FFA.
which remove FA in position 2 to form lysophospholipids.
may complete the hydrolysis of lysophospholipids
glycerol + FA + phosphoric acid
Cholesterol ester are hydrolyzed by cholesterol ester hydrolase (cholesterol esterase) into FA and free cholesterol
1- Short(less than 10 carbon atoms) and medium chain fatty acids (10-12C) together with free glycerol are water soluble
2- monoacylglycerol +long chain fatty acids + cholesterol and lysophosphoatide
are absorbed through the plasma membrane of the intestinal cells (jejunum and ileum) together withbile salts
forming soluble complexes with them(Micelles).
This known as enterohepatic circulation of bile salts.
T.G are formed also from free glycerol in intestinal cells from dihydroxyacetone phosphate (from glycolysis).
Activated by glycerokinase enzyme
Resynthesis of phospholipids & cholesterol esters by combination of cholesterol and lysophospholipids absorbed with acyl-CoA.
a protein (apolipoprotein B48) to formchylomicrons
which enter lacteals and pass with lymphatic drainage to the thoracic duct to reach systemic circulation.
chylomicrons to glycerol and FFA.
Free fatty acids are carried by plasma albumin to adipose tissues liver and other tissues for metabolism.