Human body cholesterol

As we have seen in this chapter steroids have a number of functions in human physiology Cholesterol is a component part of cell mem branes and is found in large amounts in the brain Derivatives of cholic acid assist the digestion of fats in the small intestine Cortisone and its derivatives are involved in maintaining the electrolyte balance in body fluids The sex hormones responsible for mascu line and feminine characteristics as well as numerous aspects of pregnancy from conception to birth are steroids... 

Diseases. Liquid crystals have been impHcated in a number of disease conditions in the human body. A complex cholesterol—phosphoHpid—Hpoprotein Hquid crystal phase has been identified in the initiation and maintenance of atheromatous deposits on the aortic intima in dissected human and rabbit arteries (40). The paracrystalHne nature of this precursor to plaque buildup with the resultant loss of arterial elasticity... 

Pectin, the substance that makes jellies and jams so jelly-like, can help lower blood cholesterol levels by forcing the body to make more bile acids. Pectin is a type of fiber, and like most fiber, pectin cannot be digested by the human body. Instead, the fiber moves slowly through the small intestines. When pectin encounters sugar and acid, its molecules trap water within its long chains, turning into a gel-like mass. This gel traps and eventually eliminates bile acids from the gut. When this happens, the body must make more bile acids, reducing the amount of cholesterol in the blood. 

Nutritional understanding of the effect of fats in the diet has made considerable progress.26-30 It was understood that saturated fats (see Chapter 3, Section 3.8) were the least beneficial as they raised serum cholesterol. High serum cholesterol is now associated with heart attacks and strokes. There was for this reason pressure over the cholesterol content of foods. This pressure has now been relieved since it appears that dietary cholesterol is not a particularly serious issue. The human body makes cholesterol, so dietary cholesterol does not necessarily affect serum cholesterol level as dietary intake can be compensated for by reduced cholesterol synthesis. 

The spread mixed lipid monolayer studies provide information about the packing and orientation of such molecules at the water interface. These interfacial characteristics affect many other systems. For instance, mixed surfactants are used in froth flotation. The monolayer surface pressure of a pure surfactant is measured after the injection of the second surfactant. From the change in n, the interaction mechanism can be measured. The monolayer method has also been used as a model biological membrane system. In the latter BLM, lipids are found to be mixed with other lipidlike molecules (such as cholesterol). Hence, mixed monolayers of lipids + cholesterol have been found to provide much useful information on BLM. The most important BLM and temperature melting phenomena is the human body temperature regulation. Normal body temperature is 37°C (98°F), at which all BLM function efficiently. 

In the human body choline is needed for the synthesis of phospholipids in cell membranes, methyl metabolism, transmembrane signaling and lipid cholesterol transport and metabolism [169]. It is transported into mammalian cells by a high-affinity sodium-dependent transport system. Intracellular choline is metabolized to phosphorylcholine, the reaction being catalyzed by the enzyme choline... 

Estradiol, testosterone, and progesterone are the principal sex hormones from the estrogen, androgen, and progestin gronps, respectively. These hormones are synthesized in the human body starting with cholesterol. 

Cholesterol is a soft waxy substance that is a steroidal alcohol or sterol. It is the most abundant steroid in the human body and is a component of every cell. Cholesterol is essential to life and most animals and many plants contain this compound. Cholesterol biosynthesis occurs primarily in the liver, but it may be produced in other organs. A number of other substances are synthesized from cholesterol including vitamin D, steroid hormones (including the sex hormones), and bile salts. Cholesterol resides mainly in cell membranes. 

A very similar reaction is catalyzed by 3-hydroxy-3-methylglutaryl-CoA lyase (HMG-CoA lyase), which functions in the formation of acetoacetate in the human body (Eq. 17-5, step c) and also in the catabolism of leucine (Fig. 24-18)182183 and in the synthesis of 3-hydroxy-3-methyIgIutaryI-CoA, the presursor of cholesterol (Eq. 17-5, step fr)183a... 

Cholesterol serves two important functions in the body. First, it is a minor component of cell membranes, where it helps to keep the membranes fluid. Second, it serves as the body s starting material for the synthesis of all other steroids, including the sex hormones. Although news reports sometimes make cholesterol sound dangerous, there would be no life without it. The human body obtains its cholesterol both by synthesis in the liver and by ingestion of food. Even on a strict no-cholesterol diet, an adult is able to synthesize approximately 800 mg per day. 

Cholesterol is a vital component of the human body. It stabilizes cell membranes and is the precursor of bile acids, vitamin D, and steroid hormones. The body s cells can synthesize cholesterol when needed, but excess cholesterol cannot be broken down and must be excreted from the body through the bile into the small intestine. When imbalances occur, cholesterol can accumulate in the gallbladder promoting gallstone formation. Cholesterol accumulation in the bloodstream (hypercholesterolemia) can cause atherosclerotic plaques to form within artery walls. 

Oxysterols are defined as oxygenated derivatives of cholest-5-en-3(3-ol (cholesterol) (Figure 18.1) or precursors of CHOL that may be formed directly by autoxidation or by the action of a specific monooxygenase, or that may be secondary to enzymatic or nonenzymatic lipid peroxidation (Guardiola et al., 1996 Schroepfer, 2000 Bjorkhem and Diczfalusy, 2002). These OS may be formed in the human body by endogenous free-radical attack on CHOL or by enzymatic processes, mainly in the biosynthesis of bile acids and steroid hormones. In addition, OS may be formed exogenously by autoxidation of CHOL in foods. The nomenclature and abbreviations of OS are presented in Table 18.1. It should be emphasized at this point that the OS that occur in... 

A [ 1,7]H shift occurs in the final stages of the human body s synthesis of vitamin D from cholesterol. Here is the last step of the biosynthesis. 

It is known that apoE plays an important role in the distribution and metabolism of cholesterol and triglycerides within many organs and cell types in the human body (Mahley et al., 2006). The apoE polymorphism is unique to humans and has been... 

Just as all animal tissues and foods contain cholesterol, which is needed for life itself, all plants have phytosterols, plant sterols. The molecular structures of cholesterol and phytosterols are virtually identical (see the illustration). Because they are so similar, the human body cannot tell the difference. 

Archeological evidence shows that pahn oil has been consumed by humans for more than 5000 years (145). Its digestion and absorption rates in the human body are in excess of 97%, which is very similar to other common edible oils and fats. In many communities pahn oil is an important source of dietary energy and provides sufficient quantities of the essential fatty acid, linoleic acid (18 2, n-6) for normal healthy metabolic functions. Like all other edible oils of vegetable origin, palm oil is considered cholesterol free. 

Phytosterols are found in most common vegetable oils. For example, soybean oil, one of the most commonly consumed oils, is reported to contain approximately 0.36% sterols and 0.124% tocopherols (15). The effect of phytosterols on the reduction of serum cholesterol has been attributed to the possible inhibition of intestinal reabsorption of circulating cholesterol. The saturated version of sterols, stanols, is reported to be more readily metbolized, and this has led to the development of nutritional supplements and it is used commercially in food products such as margarines. The main stanol reported for this application is sitostanol, a saturated derivative of sitosterol. Sterol and cholesterol are used by the human body to synthesize important hormones such testosterone and progesterone, which are used also in many pharmaceutical applications. 

Cholesterol is a solid alcohol the average human body contains about 200 g distributed in brain, spinal cord, and nerve tissue and occasionally clogging the arteries and the gall bladder (see Chapter 22 for background and procedure for isolating cholesterol from human gallstones). 

The human body tunts over about 800 mg of cholesterol per day. Most of this turnover (synthesis, degradation, or loss from the body) inv olves bile salts. More specifically, about 400 mg cholesterol is used to manufacture new bile salts to replace those that have been lost in the feces. About 80 mg cholesterol is lost through the skin about 50 mg is used for synthesis of steroid hormones. Cholestyramine can stimulate the loss of much more than the equivalent of 400 mg, and can produce clinically significant decreases in serum cholesterol Cholestyramine alone does not drastically lower serum cholesterol, because the liver senses any depletion and responds by increasing its rate of cholesterol biosynthesis. However, use of the drug in combination with other drugs that Inhibit... 

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