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 " . :: 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.--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

STRESS

What Is Stress?
Stress is a feeling that's created when we react to particular events. It's the body's way of rising to a challenge and preparing to meet a tough situation with focus, strength, stamina, and heightened alertness.
The events that provoke stress are called stressors, and they cover a whole range of situations — everything from outright physical danger to making a class presentation or taking a semester's worth of your toughest subject.
The human body responds to stressors by activating the nervous system and specific hormones. The hypothalamus signals the adrenal glands to produce more of the hormones adrenaline and cortisol and release them into the bloodstream. These hormones speed up heart rate, breathing rate, blood pressure, and metabolism. Blood vessels open wider to let more blood flow to large muscle groups, putting our muscles on alert. Pupils dilate to improve vision. The liver releases some of its stored glucose to increase the body's energy. And sweat is produced to cool the body. All of these physical changes prepare a person to react quickly and effectively to handle the pressure of the moment.
This natural reaction is known as the stress response. Working properly, the body's stress response enhances a person's ability to perform well under pressure. But the stress response can also cause problems when it overreacts or fails to turn off and reset itself properly.
Good Stress and Bad Stress
The stress response (also called the fight or flight response) is critical during emergency situations, such as when a driver has to slam on the brakes to avoid an accident. It can also be activated in a milder form at a time when the pressure's on but there's no actual danger — like stepping up to take the foul shot that could win the game, getting ready to go to a big dance, or sitting down for a final exam. A little of this stress can help keep you on your toes, ready to rise to a challenge. And the nervous system quickly returns to its normal state, standing by to respond again when needed.
But stress doesn't always happen in response to things that are immediate or that are over quickly. Ongoing or long-term events, like coping with a divorce or moving to a new neighborhood or school, can cause stress, too.
Long-term stressful situations can produce a lasting, low-level stress that's hard on people. The nervous system senses continued pressure and may remain slightly activated and continue to pump out extra stress hormones over an extended period. This can wear out the body's reserves, leave a person feeling depleted or overwhelmed, weaken the body's immune system, and cause other problems.
What is the healthy response to stress?
A key aspect of a healthy adaptational response to stress is the time course. Responses must be initiated rapidly, maintained for a proper amount of time, and then turned off to ensure an optimal result. An over-response to stress or the failure to shut off a stress response can have negative biological consequences for an individual. Healthy human responses to stress involve three components:
The brain handles (mediates) the immediate response. This response signals the adrenal medulla to release epinephrine and norepinephrine.

The hypothalamus (a central area in the brain) and the pituitary gland initiate (trigger) the slower maintenance response by signaling the adrenal cortex to release cortisol and other hormones.

Many neural (nerve) circuits are involved in the behavioral response. This response increases arousal (alertness, heightened awareness), focuses attention, inhibits feeding and reproductive behavior, reduces pain perception, and redirects behavior.
The combined results of these three components of the stress response maintain the internal balance (homeostasis) and optimize energy production and utilization. They also gear up the organism for a quick reaction through the sympathetic nervous system (SNS). The SNS operates by increasing the heart rate, increasing blood pressure, redirecting blood flow to the heart, muscles, and brain and away from the gastrointestinal tract, and releasing fuel (glucose and fatty acids) to help fight or flee the danger.
What is the role of the hypothalamus-pituitary-adrenal (HPA) axis (grouping) in stress?
The HPA axis is a grouping of responses to stress by the brain and the pituitary and adrenal glands. First, the hypothalamus (a central part of the brain) releases a compound called corticotrophin releasing factor (CRF), which was discovered in 1981. The CRF then travels to the pituitary gland, where it triggers the release of a hormone, adrenocorticotrophic hormone (ACTH). ACTH is released into the bloodstream and causes the cortex of the adrenal gland to release the stress hormones, particularly cortisol, which is a corticosteroid hormone. Cortisol increases the availability of the body's fuel supply (carbohydrate, fat, and glucose), which is needed to respond to stress. However, if cortisol levels remain elevated for too long, then muscle breaks down, there is a decreased inflammatory response, and suppression of the immune (defense) system occurs.
Because they suppress the immune system, corticosteroids in measured doses are used to treat many illnesses that are characterized by inflammation or an overactive immune system, such as asthma and inflammatory bowel disease. For the same reason, they are used to help reduce the chances that our body will immunologically reject a transplanted organ. Corticosteroids also can cause fluid retention and high blood pressure. Therefore, it is critical that the response to corticosteroids be carefully controlled (modulated). This control usually is accomplished by a feedback mechanism in which increased cortisol levels feeding back to the hypothalamus and pituitary turn off production of ACTH. In addition, extremely high levels of cortisol can cause mental changes, including depression and psychosis, which disappear when the levels return to normal.


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