Lipid Metabolism

Biochemistry

2nd stage
Dr.Lamees Majid Al-Janabi
LIPID METABOLOSIM
Brief review about lipid chemistry:
-Fatty Acids structure

- Cholesterol

Normal serum cholesterol < 200 mg/dl

We have two types of cholesterol :
1) Endogenous: greater of the body cholesterol is provided
by synthesis of about 700 mg/day ( MORE THAN HALF )
2) Exogenous: daily intake of the cholesterol usually less
than 1g/day of which 40-70 % is absorbed.

Uses:

One of the main compound of the cell membrane. Precursor in the steroid hormones ,bile acids ,vitamin D synthesis .(The body can't break the steroid nucleus ,body can eliminate cholesterol either as unchanged or converted to bile acids ).

Triglyceride

Normal serum TG concentration is<150 mg\dl .

Uses: energy store
Sources:

1) Exogenous: main component of the diet ,daily intake is between 100-200 g, by the action of pancreatic Lipase will be hydrolyzed to monoglycerides and 2 fatty acid, these will be absorbed and the TG resynthesised in the mucosal cell and incorporated in structure called "Chylomicron" and release into intestinal lymph and reach systemic circulation through thoracic duct .

2) Endogenous: the liver is the major site for synthesis from glycerol and fatty acid which incorporated into Lipoproteins and release into the circulation to utilized by peripheral tissue as energy source or stored in adipose tissue.TG that are carried by Lipoprotein and stored by adipose tissue can't be utilized without prior hydrolysis to glycerol and fatty acid.

- Phospholipids

Serum level: 120-390 mg/dl

mainly synthesized in the liver and small intestine ,it's amphipathic molecule (contain polar and non polar portion) and consequently ideally suited as main component of the cell membrane.
PL have specialized function e.g.
*Lecithin is the major component of lung surfactant.
* Also inositol PL in cell membrane act as a precursor of hormone second messenger

-Free Fatty Acids

normal range 6-16 mg\dl .
Mainly derived from daily TG, but the body is able to synthesis most of the fatty acids except essential fatty acids(poly unsaturated F.A.).F.A. is an alteration energy source of glucose. Polyunsaturated F.As. is substrate for prostaglandin.