John Jacob Abel was an American biochemist. He was born in 1857 at Cleveland, Ohio and died in 1938. He determined the molecular weight of cholesterol and in 1897 isolated the hormone adrenaline from the adrenal gland. In 1892 he discovered carbonic acid in horse urine and associated it with the production of urea. He also pioneered kidney dialysis.
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7-dehydrocholesterol (desmosterol) is a crystalline steroid alcohol that occurs chiefly in higher animals and man (as in the skin), that is made synthetically from cholesterol, and yields vitamin D3 on irradiation with ultraviolet light.
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Aneurysm is a balloon-like bulge that forms in a weakened area of the wall of an artery or vein. The most dangerous aneurysms are those that form in arteries, especially the arteries of the brain and the aorta. Most aneurysms result from atherosclerosis, a disease caused by cholesterol build-up in artery walls. Other causes of aneurysms include genetic disorders or other defects present at birth. The symptoms of an aneurysm vary with its location and size. There may be no symptoms, or pain may develop at the site of the aneurysm. Shortness of breath occurs if the aneurysm interferes with the heart's pumping ability. Some aneurysms press on nearby structures, producing a cough, hoarseness, or difficulty in swallowing. An aneurysm may worsen without the patient knowing and then suddenly rupture, causing a coma, paralysis, or death. Many strokes result from the rupture of an aneurysm in an artery of the brain.
Aneurysms can be detected with X-rays and, in many cases, can repair them surgically. Surgeons remove the diseased portion of the blood vessel. If it is a minor vessel, they tie off the loose ends. In a major artery or vein, they replace the diseased portion with a plastic tube, a fabric patch, or a piece of another blood vessel.
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Atherosclerosis is a form of arteriosclerosis. Atherosclerosis is the hardening of the arteries caused by cholesterol plaque deposits. It can occur in the coronary arteries, the carotid arteries, the aorta, and the leg arteries. Healthy arteries are flexible, strong, and elastic. The inner layer, the tunica interna, is smooth, enabling blood to flow freely. As a person ages, the arteries normally become thicker and less elastic, and their calcium content increases. This natural ' hardening' process occurs throughout the artery system.
Atherosclerosis, by contrast, affects only the larger arteries. As the plaque builds up, the inner layers of the artery walls become thick and irregular. Fat, cholesterol, and other materials accumulate in certain areas. This gradual build-up over a long period of time reduced the circulation of blood and increases the risk of heart attack, stroke, and other serious arterial diseases. A person having atherosclerosis will often experience symptoms of angina, stroke, and claudication. All of the symptoms are caused by insufficient blood flow due to atherosclerosis. Initially, the deposits of fat-containing cells that lead to atherosclerosis are only slight streaks, and are called fatty streaks. As the fatty streaks enlarge, they invade the deeper layers of the artery walls, causing scarring and calcium deposits. Large deposits are called athermas or plaques. The plaques calcify into a chalky substance. The plaque consists of a firm shell that contains calcium with areas of fatty material, and a centre consisting of soft cholesterol. As the plaque deposits grow the cardiac muscle beyond the blockage becomes deprived of blood, a condition known as myocardial ischemia. The healthy elastic wall of the artery changes into dead and unresponsive scar tissue. If insufficient blood flow continues, the cardiac muscle dies, causing myocardial infarction. As the degeneration of the endothelial lining of the arteries continues, the lining may be damaged. Blood platelets stick to the site of injury, and a chemical signal is activated that promotes an influx of cholesterol.
The symptoms of atherosclerosis develop slowly as the development of the occlusion of the arteries progresses. Symptoms include angina, stroke, and claudication. The specific symptoms depend on which artery or arteries are occluded. If the leg arteries are affected, symptoms usually include numbness, fatigue, or pain in the leg. Occlusion of the coronary arteries may lead to angina or even a heart attack. When atherosclerosis occurs in the coronary arteries, it can lead to myocardial ischemia, an insufficient flow of blood to the heart. If the duration of ischemia is brief, the damage is reversible. However, if the duration of ischemia is longer than 40 to 60 minutes, irreversible damage may occur, and the parts of the heart muscle deprived of blood become permanently damaged, leading to myocardial infarction. Other commonly affected large arteries include the carotid arteries and the abdominal aorta. Initially, the symptoms of atherosclerosis are more likely to occur during exercise or strenuous activity than at rest. The symptoms develop during exercise because the arteries cannot supply the muscles with enough oxygen and nutrients. This process results in the build-up of by-products in the muscle that cannot be removed efficiently because of the occluded blood flow. This build-up of waste products, such as lactic acid, causes pain. It is similar to the build-up of lactic acid in muscles due to overexertion. As the narrowing of the arteries increases, the symptoms become prevalent with less and less exertion. The symptoms generally disappear after a few minutes of rest. However, the occlusion can be so severe that even the resting muscle does not get enough blood flow and the symptoms may be experienced even when sitting still.
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Cholesterol is a steroid alcohol present in animal cells and body fluids.
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The endoplasmic reticulum (cytoskeleton) forms a network of membranous tubes and flattened sacs within a cell and is distributed throughout the cell, predominantly between the plasma membrane and the membrane that encircles the nucleus. Endoplasmic reticulum networks may be loosely organized of tightly packed. The membranes that form the interrelated channels may appear smooth, while others appear rough. The rough-surfaced membranes are dotted with ribosomes that form granules on the outer surfaces and are the site of protein synthesis. The ribosomes on the rough surface deposit the newly formed proteins into the lumen, or inner space, of the endoplasmic reticulum. The endoplasmic reticulum segregates the proteins into those that will be needed in the cytoplasm and those that will be transported to the other organelles or secreted from the cell.
The smooth endoplasmic reticulum has no ribosomes and is, instead, a site of lipid synthesis. The endoplasmic reticulum appears to serve several functions. Its membranes provide an increase in surface area where chemical reactions can occur. The channels of the reticulum provide both storage space for products synthesized by the cell and transportation routes through which material can travel through other parts of the cell. The endoplasmic reticulum is also the cell's membrane factory. Phospholipids and cholesterol, the main components of membranes throughout the cell, are synthesized in the smooth portion of the endoplasmic reticulum. These compounds form the coating of protein filled sacs, called vesicles, that break off from the endoplasmic reticulum, migrate to another organelle, fuse with it, and then deposit the protein cargo. Most of the proteins leaving the endoplasmic reticulum are still not mature and undergo further processing in another organelle, the Golgi apparatus, before they are ready to perform their functions within or outside the cell.
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The gall bladder serves the function of concentrating and storing bile, produced in dilute form by the liver, and secreting the bile through the cystic ducts into the duodenum where it can help in digestion. The gall bladder itself is a blue-green organ, about eight centimeters long, located on the underside of the liver. Bile is composed of cholesterol, bile salts, and bile pigment. The gall bladder is not critical to the survival of the human, and may be removed without severely adverse effects. The crystallization of the bile salts in the gall bladder gives rise to gallstones, which often requires surgical correction.
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Hyperlipidaemia is an abnormally high level of lipids, particularly cholesterol, in the blood, predisposing to atherosclerosis and other arterial diseases.
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The sebaceous glands lie just below the skin adjacent to the hair follicles and connected by a short duct. They secretes sebum into the hair follicles, providing a lubricant for the hair and skin. Sebum is a semifluid substance composed of waxes, fatty acids, cholesterol, and debris from skin cells. By coating the hair and the dead keratin cells of the stratum corneum, sebum sequesters moisture, keeping hair glossy and skin pliable. Sebum is important for many other reasons. It contains a precursor to vitamin D that produces the mature vitamin when struck by the ultraviolet rays of the sun. It also kills certain forms of harmful bacteria.
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The tunica interna, is a thin layer only a few cells thick of a vein and artery. It is sometimes referred to as the intima membrane. It is this layer that gives smoothness to the lining of the vessel, enhancing blood flow. It is through this tunica interna that nutrients reach the deeper parts of the media. With the passage of time the tunica interna of major arteries become coated with atheromatous plaques. These plaque deposits vary in size and shape. At a relatively early stage, these plaques consist of little lumps or nodules of scar tissue in the tunica interna. In the centre of each nodule is a small cavity containing a yellowish, soft material known as cholesterol. Over time, the nodules may enlarge and protrude into the artery increasing the risk of total blockage of the vital artery (thrombosis). Atheromatous deposits also weaken the walls of the arteries causing them to bulge (aneurysm) and eventually rupture.
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