Monday, January 24, 2011

CHOLESTEROL S. BY PALLAVI AND GROUP

Cholesterol The cholesterol is a lipidic molecule, indispensable to the body because:
it is one of the main components of the cellular membranes, brain and nerve cells, and bile, which helps the body absorb fats and fat-soluble vitamins.
it is a precursor of steroid hormones (oestrogens, androgens…).
The body uses cholesterol to make vitamin D.
Cholesterol is synthetized by the liver, but some also comes from the animal fats of the diet.
Structure
Synthesis and metabolism
Transport of cholesterol in the bloodThere is always a flow of cholesterol in the blood, to satisfy the requirements of the different organs. Because of its lipidic structure that makes it insoluble, it is carried along inside large molecules, the lipoproteins, that are soluble in the blood. There are 4 main types of lipoproteins, synthetized by the intestinal cells and/or by the liver. They are classified according their respective density. (The higher the density is, the less lipids they contain).
chylomicrons
VLDL (Very Low Density Lipoproteins)
LDL (Low Density Lipoproteins)
HDL (High Density Lipoproteins : compared to LDL, they have an opposite role. They collect cholesterol in excess throughout the body, and bring it back to the liver that will store, redispatch or eliminate it through the bile. Here we speak about " good cholesterol ".
these are VLDL, once they have " delivered " their triglycerides. Then they supply the hepatic cholesterol to the organs and tissues. It is commonly called the " bad cholesterol " .
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they are mainly in charge to dispatch the triglycerides synthetized in the liver to the different organs of the body.
: exclusively produced by the small intestine cells after a meal. They go through the lymphatic vessels before reaching the general circulation. Their major role is to transport dietary triglycerides up to the liver.
Cholesterol is then mostly carried along by LDL and HDL. In man, the most important lipoproteins are LDL. These are the ones that can cause fat deposits inside the arteria (atheroma), and be at the origin of so common diseases in man: coronary diseases, myocardial infarction… On the contrary, in dogs and cats, there are twice as much HDL than LDL, and 80 % of the total cholesterol is binded to HDL. Here, the " good cholesterol " is the most important. This physiological difference could explain why atheromatosis is so rare in these species.
Disorders of the lipidic metabolismThe fact that cholesterol does not deposit in the vascular system does not mean that there is no possible disorder in the lipidic metabolism of cats and dogs.
When there is a global excess of lipids in the blood, one speaks about hyperlipemia. In that case, the serum is cloudy, with a " strawberry milk " colour. After sedimentation during one night, a white " creamy " appears on the surface. A clear serum does not mean however that everything is normal. When there is only an excess of cholesterol in the blood, there is no modification of the serum visible. Only the dosage of cholesterol and triglycerides (after 12 hours fasting), can confirm hyperlipemia.
Those troubles of the lipidic metabolism are scarcely observed alone. Only a few cases are known: in miniature Schnauzer and in cats. In general, it is rather the consequence of another disbalance, mostly from hormonal origin.
Htpothyroidism70 % of hypothyroidism cases induce an abnormal rise in blood cholesterol- Dogs with hypothyroidism aren't producing enough T3 hormone. T3 stimulates the liver's LDL cholesterol receptors, which scrub LDL from the blood and thyroid harmone increases HMG-CoA reductase activity. A lack of T3 hormone means a higher LDL level. Dysfunctionment of surrenal glands (hypercorticism) . The adrenal glands of dogs with hypradrenocorticism produce excessive amounts of corticosteroids. These hormones increase the dog's lipase production to levels that raise cholesterol by releasing stored fat into the bloodstream.Glucocorticoids decrease HMG-CoA reductase activity.Diabetes- A dog's pancreas normally produces the enzyme lipase, which helps metabolize dietary fats. With diabetes mellitus, a dog doesn't release enough insulin to stimulate normal lipase production, causing elevated levels of cholesterol.Also, insulin increases HMG-CoA reductase activity. Acute pancreatitis-
Nephrotic Syndrome-Nephrotic syndrome is a kidney disorder that raises both HDL and LDL cholesterol
Drug intoxication
Hepatic deficiency
In obese animals, such as obese cats that suddenly stop eating, one can notice an elevation of blood cholesterol and triglycerides, but it is not a constant phenomenon
(fat storage in excess in cats): hypercholesterolemia can be one the first signs of an hepatic disorder If the liver itself is diseased, it may not be able to excrete cholesterol at all- Obstruction of the bile ducts (cholestasis). It should not be neglected.
: steroid anti-inflammatory drugs, contraceptive hormones…
Necrotic pancreas is thought to release inhibitors of lipoprotein lipase and both cholesterol and triglyceride concentration increases.
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An increase level of cholesterol affects dogs more than cats. Dogs and cats with high cholesterol are however not predisposed to
Hyperlipidemia is diagnosed if your pet has a fasted triglyceride level greater than 500mg/dl and/or a fasted cholesterol level greater than 300mg/dl
Conclusion On a dietetic aspect, the dietary fats have to be drastically restricted. However, the supply of essential fatty acids must not be forgotten. Increasing the fiber content of the diet is also advised. Fibers adsorb biliary salts and prevent from the recycling of cholesterol contained in these salts.
1.The principle regulatory enzyme in the pathway of cholesterol synthesis is HMG-CoA reductase2.Cholesterol is transported in plasma in lipoproteins.
3.Cholesterol is excreated from body in bile.
4.In
5.Good cholesterol is HDL6.
7.Glucagon or glucocorticoids decrease HMG-CoA reductase activity
8.Cheif synthetic and catabolic organ for cholesterol is liver.9.Primary or inherited disorders in cholesterol metabolism are seen in Miniature Schnauzer dogs    
Dogs, cholesterol is binded to HDL which contributes to their general resistance to atherosclerosis. Plasma cholesterol values greater than 750 mg/dl predispose dogs to atherosclerosis despite their natural resistance.
heart disease as in people. Warning symptoms and signs such as abdominal pain, seizures, patches on the skin, yellow bumps filled with a greasy, fatty fluid(cutaneous xanthomata) and nervous system abnormalities may be an indication that your pet has high cholesterol. Plasma cholesterol values greater than 750 mg/dl predispose dogs to atherosclerosis despite their natural resistance

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