Lipid Metabolism
Introduction
Lipid metabolism is
the synthesis and break down of lipids in cells, involving the breakdown or storage of fats
for energy and the synthesis of structural and functional lipids. Lipid
metabolism includes the metabolism of fats, phospholipids, sterol and
glycolipids.
Functions
of lipid metabolism
Fat is very important
for body due to its higher calorigenic value than protein and carbohydrate.
Some points of its importance are given below:
1. Much of the
carbohydrate of the diet is converted into fats for its utilization for supply
of energy as the body’s capacity to store glycogen is limited.
2. Some organs use fat
as a fuel in place of carbohydrate.
3. As the calorific
value of fat is over twice as great than carbohydrate and protein, i.e., 9.3
Cal/gm, so the fat is stored in the tissue as fat depots e.g. adipose tissue,
subcutaneous fat etc as principal form of energy.
4.It supplies essential
fatty acid (polyunsaturated fatty acid) and fat-soluble vitamins -A, D, E, and
K.
5. It is required in
diet for absorption of essential fatty acid (polyunsaturated fatty acid) and fat-soluble
vitamins -A, D, E, and K.
6. Phospholipids,
cholesterol and glycolipids are used to form essential structural constituent
of various organs in the body.
7. 10% of fats (the glycerol part) may be
converted into glucose during the synthesis of carbohydrates.
8. Amino acids can be synthesized
from fatty acids and ammonia in the liver.
9. Being a poor heat
conductor the subcutaneous fat helps in regulation of body temperature.
10. The depot fats act
mechanically in protecting the vital organs and also act as cushions and
packing tissues.
Types
The
types of lipids involved in lipid metabolism include-
A. Membrane lipids
I.
Phospholipids- Phospholipids are a major component of the lipid
bilayer of the cell membrane and are found in many parts of the body.
II.
Sphingolipids- Sphingolipids are mostly found in the cell membrane
of neural tissue.
III.
Glycolipids-
The main role of glycolipids is to maintain lipid bilayer stability and
facilitate cell recognition.
IV.
Glycerophospholipids- Neural tissue
(including the brain) contains high amounts of Glycerophospholipids.
B. Other types of lipids
I.
Cholesterols- Cholesterols are the main precursors for different
hormones in our body such as progesterone and testosterone. The main function
of cholesterol is controlling the cell membrane fluidity.
II.
Steroid- Steroids are one of the important cell
signaling molecules.
III.
Triacylglycerols- Triacylglycerides are the major form of energy
storage in human body.
IV.
Fatty acids-
Fatty acids are one of the precursors used for lipid membrane and cholesterol
biosynthesis. They are also used for energy.
V.
Bile salts- Bile salts are
secreted from liver and they facilitate lipid digestion in the small intestine.
VI.
Eicosanoids-
Eicosanoids are made from fatty acids in the body and they are used for cell
signaling.
VII.
Ketone bodies- Ketone bodies are made from fatty acids in the
liver. Their function is to produce energy during periods of starvation or low
food intake.
Blood
Fats-
Following fat types are found in blood-
·
Neutral fats
·
Phospholipids
·
Cholesterol esters
·
Free cholesterol
·
Free fatty acids
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