Cholesterol is a lipid and a sterol with a structure comprising of four connected hydrocarbon rings, a hydrocarbon tail, and a hydroxyl group. Its molecular formula is C27H45OH. The hydroxyl group (OH) in the cholesterol molecule is polar making it water soluble. On the other hand, the ring region and tail of the structure are made up of carbon and hydrogen atoms which make them non-polar. This means that they are insoluble in water but can dissolve in organic substances such as fats and oils ("Chemical and Physical Properties of Cholesterol", n.d.). Most animal membranes contain cholesterol in varying amounts except for intracellular and prokaryotic membranes. In humans, about 80 percent of cholesterol is made in the liver while the remaining 20 percent is obtained from daily diet (Kamps, n.d). The structure and properties of cholesterol make it an important component in the human body when in moderate amounts but risky in high amounts.
Moderate amounts of cholesterol in the human body serve a variety of important functions. First, cholesterol is important in producing certain hormones in the body. Some of these hormones include estrogen, testosterone, cortisone, and aldosterone. In turn, these hormones control various body functions (Tabas, 2002). Secondly, it assists the liver in the production of bile acids which are crucial in the digestion process and absorption of vitamin A, D, E, and K since they are fat soluble (Tabas, 2002). Thirdly, cholesterol is an important component in the formation of the myelin sheath. The myelin sheath insulates the axon in the nerve cells from electrical activity. This enhances the functions of the nervous system circuitry (Tabas, 2002). Lastly, cholesterol assists the cell membrane to be more rigid while at the same time ensuring its fluidity. The extra rigidity of cholesterol makes the membrane stronger, therefore, making it difficult for small molecules to pass through it (Tabas, 2002). Despite the rigidity, cholesterol creates some extra space between neighboring lipids hence allowing them to move easily throughout the cell membrane.
Despite the importance of cholesterol to the human body, having excess amounts of certain types of cholesterol poses a health risk of cardiovascular diseases. Since cholesterol is insoluble in blood, it must be carried through the bloodstream by substances known as lipoproteins, which are made of lipids and proteins. The two kinds of lipoproteins that transport cholesterol are high-density lipoprotein (HDL) and low-density lipoprotein (LDL) (Barter et al., 2007). HDL is considered to be good cholesterol since it is protective. On the other hand, LDL is considered to be bad cholesterol since too much of it in the system is unhealthy.
Despite both HDL and LDL containing lipids and proteins, the relative composition of each constituent varies. About 20 percent of the weight composition of HDL particles is cholesterol while 50 percent is protein (Kamps, n.d.). LDL particles, on the other hand, consist of 50 percent cholesterol and 25 percent protein by weight (Kamps, n.d.). Since protein has a higher density than fat, HDL particles are denser than LDL particles hence their names. Apart from the composition of protein and cholesterol, the other difference between HDL and LDL particles is in terms of the different types of protein in their structures. While HDL particles mostly contain A-I and A-II proteins, LDL particles contain B-100 proteins (Barter et al., 2007). These proteins are the ones that determine the functions that the lipoproteins perform.
Both high-density and low-density lipoproteins carry cholesterol throughout the blood. However, the difference is that they transport cholesterol to different body parts. The primary carriers of cholesterol are low-density lipoproteins which transport cholesterol throughout the bodys cells (Kamps, n.d.). As a result, the particles can result in a buildup of cholesterol in the arteries which makes them less flexible. On the other hand, high-density lipoproteins transport cholesterol from the heart and other organs of the body and bring them back to the liver which breaks them down and passed from the body (Kamps, n.d.).
High levels of LPD cholesterol increase the risks for cardiovascular disease. Cell surfaces contain special receptors that bind LDL particles. Inadequate LDL-receptors may result in a reduction of cholesterol uptake (Durstine et al., 2001). Therefore, they will remain in the bloodstream and raise blood levels. Excess LDL in the bloodstream can clog the inner walls of arteries that transport blood to the brain and heart. The blockage may result in various cardiovascular diseases such as arteriosclerosis, hypertension, and stroke. The high levels are also linked to diabetes (Leon & Sanchez, 2001). On the other hand, high levels of high-density lipoproteins are beneficial to the health of an individual because they remove excess cholesterol in the blood and deliver it to the liver which may either excrete or re-utilize them, therefore preventing clogging of the arteries.
The high levels of LDL cholesterol may be as a result of risk factors that can either be modifiable and non-modifiable. The major non-modifiable factor is genetics since high LDL levels can be inherited. On the other hand, the two major modifiable risk factors are diet and exercise (Leon & Sanchez, 2001). Eating foods from diets that contain too many saturated fats such as fatty meat, chocolates, cream, cheese, and deep-fried and processed foods can lead to high levels of LDL. Other foods such as avocados, peanuts, cashew nuts, and spreads containing canola, peanut, and olive oil contain monounsaturated fats which assist in lowering the amount of LBD in the bloodstream. Another type of fat known as polyunsaturated fats assists in keeping the heart healthy and in reducing triglycerides fat in the blood. Apart from diet, research has also shown that moderate exercise can reduce LDL levels in the bloodstream. Moderate exercise can increase the size of LDL particles hence minimizing the risk of cardiovascular diseases. This is because smaller LDL particles are the ones that are associated with cardiovascular diseases. Other studies have shown that moderate exercise can enhance transport of LDL cholesterol to the liver which will excrete or reutilize them (Durstine et al., 2001). Clearly, diet and exercise play a critical role in controlling the amount of cholesterol in human bodies.
When the levels of cholesterol in the blood are high, an individual has the option of choosing various classes of drugs to lower blood cholesterol. Some of the classes of cholesterol reduction drugs include statins, ezetimibe, orlistat, and niacin ("Cholesterol Medications", 2016). Statins work by limiting cholesterol biosynthesis. Ezetimibe, on the other hand, inhibits the intestines from absorbing cholesterol and related substances. Similarly, orlistat inhibits cholesterol absorption but by reducing the secretion of pancreatic and gastrointestinal lipase. Finally, niacin works by inhibiting the breakdown of fats hence resulting in a decrease in free fatty acids and consequently secretion of LDL by the liver.
Cholesterol can be both beneficial and detrimental to the human body. At moderate levels, cholesterol is an important substance for the normal functioning of the body. However, if the levels are too high, then it becomes a danger and may out one at risk of various cardiovascular diseases. The two risk factors of high cholesterol levels in the bloodstream are diet and exercise. Though there are various classes of drugs that can be used to lower blood cholesterol levels, limiting certain diets and performing regular exercise are the most effective ways of reducing the risk of having high cholesterol.
Barter, P., Gotto, A. M., LaRosa, J. C., Maroni, J., Szarek, M., Grundy, S. M., ... & Fruchart, J. C. (2007). HDL cholesterol, very low levels of LDL cholesterol, and cardiovascular events. New England Journal of Medicine, 357(13), 1301-1310.
Chemical and Physical Properties of Cholesterol. Scienceofcooking.com. Retrieved 25 October 2016, from http://www.scienceofcooking.com/cholesterol.htmCholesterol Medications. (2016). Heart.org. Retrieved 25 October 2016, from http://www.heart.org/HEARTORG/Conditions/Cholesterol/PreventionTreatmentofHighCholesterol/Cholesterol-Medications_UCM_305632_Article.jspKamps, A. How Do LDL and HDL Differ Structurally and Functionally?. Healthyeating.sfgate.com. Retrieved 25 October 2016, from http://healthyeating.sfgate.com/ldl-hdl-differ-structurally-functionally-2003.htmlLeon, A. S., & Sanchez, O. A. (2001). Response of blood lipids to exercise training alone or combined with dietary intervention. Medicine and science in sports and exercise, 33(6; SUPP), S502-S515.
Tabas, I. (2002). Cholesterol in health and disease. The Journal of clinical investigation, 110(5), 583-590.
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