Lipids
Classification of lipids:
Lipids are classified
into simple, complex(compound) and derived lipids.
A.
Simple lipids:
1. Fats
and oils:
2. Waxes:
B.
Compound(complex) lipids:
1. Phospholipids
2. Glycolipids(glycophospholipids)
3. Lipoproteins
4. Sulpholipids
5. Aminolipids(proteolipids)
C.
Derived lipids:
1. Fatty
acids.
2. Monoglycerides
and diglycerides.
3. Alcohols
e.g. cholesterol.
Cholesterol
Sources of cholesterol:
1-Endogenous:
Cholesterol
is formed in the body almost in all nucleated cells from acetyl CoA.
2-Exogenous animal origin such as
egg yolk, meat, liver, and brain. Diet supplies about 400 mg/day.
Biochemical functions
1. It
is structural component of cell membrane.
2. Cholesterol
is the precursor for synthesis of steroid hormone(estrogen, progesterone,
testosterone, androgens,
glucocorticoids, and mineralocorticoids), vit D3, and bile acids
3. fatty
acids are transported to liver for oxidation as cholesteryl esters.
Plasma cholesterol:
Cholesterol present in plasma as free
or esterified (cholesteryl ester).
Total
plasma cholesterol= 110-230 mg/dl,
Plasma cholesterol abnormalities
A. Hypercholestererolemia
It
is increased plasma cholesterol concentration above 230 mg/dl due to.
a. Diet rich in carbohydrate and saturated fatty
acid.
b. Hypothyroidism(Myxoedema):
c. Diabetes
mellitus:
d. Nephrotic
syndrome: Increase in plasma globulin concentration is characteristic feature
of nephritic syndrome. Hypercholesterolemia is due to increase in plasma
lipoprotein fractions in this disorder.
e. Obesity.
f. Obstructive
jaundice Decreased excretion of cholesterol and bile acid s.
g. Familial
hypercholesterolemia, this is due to
h. Alcohol
consumption for long period enhances synthesis of cholesterol.
B. Hypocholesterolemia
It is decreased plasma cholesterol concentration below
110 mg/dl due to
a. Prolonged
fasting
b. diet
rich in unsaturated fatty acids and poor in saturated fatty acids,
carbohydrate, and cholesterol.
c. Hyperthyroidism.
d. liver
diseases.
e. chronic
infection as tuberculosis
Triglycerides
Triacylglycerol consists of a glycerol esterified with
three fatty acids. Simple triacylglycerols have three same fatty acids. Mixed
triglycerides have two or three different fatty acids. The triglycerides are
found in the adipose tissue which is storage site for lipids. Therefore,
triglycerides are the major energy store and the major dietary lipid in human.
Excessive accumulation of lipids
especially triglyceride in liver, result in fatty liver, while atherosclerosis
is due to accumulation of lipids, particularly cholesterol in inner arterial
wall.
Plasma triglyceride:
Plasma triglyceride< 200mg/dl.
Hypertriglyceridemia:
a)
Familial Hypertriglyceridemia (Types 1, 2b, 3, 4, and 5
hyperlipoproteinemias)
b)
Alcohol excess
c)
Chronic renal failure
d)
Poorly controlled Diabetes mellitus
e)
Metabolic syndrome
f)
Glycogen storage disease e.g. von Gierke’s type 1
g)
Certain drugs e.g. estrogens
Hypotriglyceridemia
a)
Malnutrition
b)
a beta lipoproteinemia
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