Lipids are hydrocarbons that are found in living systems in the environment. The main classes of lipids are triglycerides, waxes, steroids, phospholipids, gylcolipids, and sphingolipids (Glanze). The simplest lipid, which makes up the backbone of all of these, is the fatty acid (see page 2). The main characteristics that separate the different kinds of lipids are the derivatives, such as acids, alcohols, amines, amino alcohols, and aldehydes, found on the end of the hydrocarbons and their solubility in water. Most lipids are nonpolar and there for are not soluble in water but instead in fat solvents such as ether, chloroform, and benzene. From these two basic distinctions, there are dozens of possible lipids that can be formed in nature and synthetically (Cooper).
Triglycerides are compounds consisting of a fatty acid (oleic, palmitic, or stearic) and a glycerol (See page 2). Triglycerides make up most animal and vegetable and are the principal lipids in the blood where they circulate, bound to proteins, forming high- and low-density lipo-proteins; examples of which are lard and butter. This type of lipid is not soluble in water, but is soluble in substances like ether and benzene. Glycerol is an alcohol and is soluble in ethyl alcohol and water. The other main component in is the fatty acid. Fatty acids are any of several organic acids that are unsaturated molecules and cannot be produced by the body. Therefore, fatty acids have to be ingested in an animal s diet (Cooper).
Waxes are fatty esters of long-chain alcohols (See page 3). Theses can be derived from insects, such as beeswax, plants, or petroleum products. There are four main uses for waxes in society. There is a bone wax that is a nontoxic, biocompatible wax used during surgery to plug up cavities in cranial bones and other bones to control bleeding. Because waxes are insoluble in water, they are very useful for the use on humans. Another form of wax is the casting wax with is a mixture of several waxes that can be carved or formed into shapes to be cast in metal. Carnauba wax is used for the general care of cars and used in products like chewing gum. The last use of wax is in dentistry. With the combination of waxes for their specific properties, they can be used in dental procedures (Glanze).
Steroids , or sterol, are a group of substances related to fats. They are alcohols with a cyclic nucleus and are found free or esterified with fatty acids (See page 3). They are found in animals (zoosterols) and in plants (phytosterois). They are generally colorless, crystalline compounds, and soluble in certain organic solvents. The two forms of sterols are cholesterol and ergosterol(Thomas).
The most common steroid is cholesterol. Cholesterol is a fat-soluble crystalline steroid alcohol found in animal fats and oil, and egg yolk, and widely distributed in the body, especially in the bile, blood, brain tissue, liver, kidneys, adrenal glands, and myelin sheaths or nerve fibers(Hole). It helps the absorption and transport of fatty acids and acts as the precursor for the synthesis of vitamin D at the surface of the skin as well as for the synthesis of various other steroid hormones. Among these are cortisol, cortisone, and aldosterone in the adrenal glands and of the sex hormones progesterone, estrogen, and testosterone. Cholesterol is found almost exclusively in foods of animal origin and is continuously synthesized in the body, mainly the liver and the adrenal cortex(Cooper).
Phospholipids are one of a class of compounds, widely found in living cells, containing phosphoric acid, fatty acids, and a nitrogen base (See page 4). The most important kind of phospholipids is lecithin(Marieb). Lecithin is a lipid most common in animals and plants. Lecithins are found in the liver, nerve tissue, semen, and in smaller amounts in bile and blood. They are essential for the metabolism is fats and are used in the processing of foods, pharmaceutical products, cosmetics, and inks. Rich sources of these are found in soybeans, egg yolks, and corn(Glanze).
Glycolipids are compounds that consists of a lipid and a carbohydrate, usually galactose, found primarily in the tissue of the nervous system, especially the myelin sheath and the ganglion cells (See page 3). The most important of these lipids are the cerebrosides. The glycolipids are found in the brain and other tissue of the nervous system, especially the myelin sheath(Thomas).
Sphingolipids are compounds that consist of a lipid and a sphingosine (See page 4). It is found in high concentrations in the brain and other tissues of the nervous system, especially membranes. The most important of these lipids is the sphingomyelin. This is a group of lipids containing phosphorus. It occurs primarily in the tissue of the nervous system, generally in membranes, and in the lipids in the blood. Another type of sphingolipid is cerebroside, which is also a glycolipid(Cooper).
In the body, fats are the most concentrated source of energy(Marieb). They contain very little water, and the energy given off form the catabolism of fats is approximately twice that gained form either glucose (the most simple sugar) or protein breakdown. The primary fat is triglyceride, an ester of three fatty acids and a glycerol. This substance is not digested in the stomach and passes into the duodenum (the first part of the small intestine, between the stomach and the jejunum), where it causes the release of enterogastrone, a hormone that reduces stomach motility. The amount of fat in ones diet regulates the rate at which entergastrone is released into the intestinal tract. Fat, together with other partially digested foods, cause the release of hormones, secretin, pancreozymin, and cholecystokinin from the wall of the duodenum into the bloodstream. Secretin causes the secretion of an alkaline pancreatic juice that is rich in bicarbonate ions, while pancreozymin causes secretion of pancreatic enzymes. One of these enzymes, lipase, is important in the digestion of fat. Cholecystokinin, which is a protein substance chemically inseparable from pancreozymin, stimulates the gallbladder to release bile into the duodenum. Bile is secreted by the liver and concentrated in the gallbladder and contains two bile salts, both derived from cholesterol: taurocholic and glycocholic acids. These act as detergents by emulsifying the triglycerides in the intestinal tract, making the fats more vulnerable to attack by pancreatic lipase. In this reaction, which works best in the alkaline solution provided by the pancreatic juice, each triglyceride is split into three fatty acid chains, forming monoglycerides. The fatty acids pass across the membranes of the intestinal lining cells. Enzymes in these membranes split monoglycerides to glycerol and fatty acid, but triglycerides are reformed within the lining cells from glycerol and those fatty acids with a medium-chain fatty acids are absorbed directly into the bloodstream once they pass through the intestinal lining. The triglycerides formed in the lining cells pass into the intestinal lymphatic system as lipoproteins called chylomicrons. The thoracic duct, the main lymphatic channel, carries the chylomicrons to the great veins. Here they enter the circulatory system and can be taken up and metabolized into the tissue(Marieb).
During meal consumption, excesses in fats cells are stored in tissue called adipose tissue. This is found beneath the skin, between muscle fibers, around organs and their supporting structures, and around joints. When fats are absorbed, they are absorbed in excess and stored in the vacuoles as fatty acids. The fat stored in these vacuoles are a source of energy between meals. These fatty acids are broken down between meals through oxidation of the fatty acids(Cooper).
During the oxidation of fatty acids, or Beta-oxidation, the mitochondria, in a cell, breaks down the fatty acids into two carbon acetic acid fragments and reduced coenzymes. Each acetic acid molecule is then fused to one coenzyme, forming acetyl CoA. The Acetyl CoA molecule is then picked up by an oxaloacetic acid and enters the aerobic pathways to be completely oxidized to carbon dioxide and water. The Acetyl CoA molecule is by far one of the most important molecules in the body. This molecule is the starting molecule in a process called the Krebs Cycle. This cycle, which takes place in mitochondrial matrix, is the reaction that creates ATP and other intermediate molecules. These molecules are vital for certain metabolic pathways including amino acid synthesis and tricarboxylic acid cycle. ATP is the molecule that is broken down in cells to produce energy used to function(Marieb).
Another important aspect of lipids is their use in the cell membrane of cells. The fundamental building blocks of all cell membranes are phospholipids, consisting of two hydrophobic fatty acid chains linked to a phosphate-containing hydrophilic head. Because the fatty acid tail is poorly soluble in water, phospholipids form bilayers in aqueous solutions. They form a membrane that consists of the tails being buried in the interior of the membrane and the polar heads, on both sides, in contact with the water. This membrane formed by the formation of these fatty acids if called a phospholipid bilayer and makes up the basic structure of all biological membranes in nature(Cooper).
Lipids play an important part in our society. A lack of or excess in lipids may lead to may disease in the body. In a human diet, the increase of cholesterol can lead to many disorders such as atherosclerosis. This leads to four primary changes(Phipps). First: there is injury to the intimal cell wall causing increased cell permeability. Second: an accumulation of smooth muscle cells and lipids that produce a fatty streak. Third: there is a formation of plaque from lipids on the arterial walls. Four: Development of a complicated lesion from calcified fibrous plaque. These effects cause insufficient blood flow to the tissues, producing ischemia. Ischemia is a decrease in the blood supply to a body organ or part. It is often marked by pain and organ dysfunction. Other effects of the four changes is a diminished or absent pulse. There is also an interference with nutrients arriving to the tissue, leading to ischemic ulcers and changes in the skin. As the tissue is insufficiently receiving blood, the skin that is not getting blood rots and forms ischemic ulcers. The changes seen in the skin are the discoloration incurred from the rotting of the skin. First the skin turns red, then mushy, then an open sore appears and then rots down to the bone(Phipps).
Gallstones, or cholelithiasis, are another problem caused by a high amount of cholesterol in the body. The cholesterol forms small crystals in the gall bladder and lodge themselves in the common bile duct, cystic duct, small bile duct, hepatic duct, and the greater duodenal papilla. This causes many different disorders, from pressure and infection of the biliary duct walls to pancreatitis and jaundice. The group most prone to contracting this disorder is females that follow the three F s: fat, fair, and forty. Studies show that the groups most affected by this disorder, in America, are women that are around forty, obese, and have a fair complexion(Phipps).
Another disease attributed to an excess of lipids in the body is artheriosclerosis. This is characterized by a build up of lipids, cholesterol for the most part, on the insides of the arterial walls. The main arteries affected by this are the femoral artery, iliac artery, and popliteal arteries. This build up that is incurred causes a narrowing of the artery, decreasing blood flow and, sometimes, completely obstructing blood flow. This causes a lack of blood to the tissues and eventually leads to the tissue dieing. Ischemic ulcers form because of this lack of nutrition and if the case is severe enough, may lead to gangrene of the limb affected. The limbs affected by this disease are the lower limbs, involving the femoral artery. If the clot, caused by the lipids, isn t treated in time amputation of the limb may occur(Phipps).
The main disease incurred by high lipid content, especially cholesterol, in the body is coronary heart disease. Coronary heart disease (CAD) is the leading cause of death in the industrialized Western world. Each year, an approximate 1 million Americans die of CAD and another 2.5 million are disabled by it(Hole). The main reason for this is the diet of average Americans. In today s society, an average Americans died consists of total and saturated fats, cholesterols and other components such as refined sugar and salt. These components of the average diet are major contributors to heart disease. CAD is characterized by a build up of lipids, mostly cholesterol, on the coronary arteries. This causes a narrowing of the arteries and, if the problem prosists, leads to complete obstruction of the arterial pathway. This causes an imbalance between the myocardial oxygen demand and the myocardial oxygen supply. This imbalance is called coronary atherosclerosis. The combination of the arterial occlusion and coronary atherosclerosis causes one of three things. First: angina pectoris occurs. This is severe pain felt down the inner aspect of the left arm and is usually accompanied by a feeling of suffocation. Second: Acute myodcardial infarction (MI) occurs. This is the complete occlusion of the artery, which results in a MI or a heart attack. Third: Sudden cardiac death occurs. This occurs when the tissue that is being occluded dies. The combination of this and the occlusion of the artery cause the coronary tissue to die. This block, caused by the lipids, causes the left ventricle to be unable to pump the blood through the body. This in turn causes sudden cardiac death(Phipps).
Lipids are one of the most important organic compounds in nature. The basic type of lipid is the fatty acid(Glanze). From this basic fat, all other fats are produced. The other fats produced by different fatty acid formations are triglycerides, phospholipids, waxes, sterols, glycolipids, and sphingolipid. The most common lipid found lipid found in nature is the triglyceride. Triglycerides are then broken down into their most common and important type: the cholesterol. Lipids are most important in nature because they are used in all living organisms. They are used to form the lipid bilayer around cells to protect them. Then they are also used as a major energy supply in the body. The break down on a triglyceride into its fatty acids is the first step in the Krebs Cycle. The Krebs Cycle is responsible for making ATP, the main energy supply in cells. Without the break down of fatty acids into Acetyl CoA, cells wouldn t have the sufficient energy needed to carry out the basic functions of life. But the excess of lipids in one s diet can lead to many problems. These problems range from gall stones and ischemic ulcers to a myodcardial infarction and sudden cardiac death(Phipps). Lipids are one of the most important compounds in nature and without them life wouldn t be able to function as we know it. But, lipids can also lead to some of the devastating diseases in the world.
Glanze, Walter D. Mosby s Medical and Nursing Dictionary. Toronto: The C.V. Mosby Company, 1986.
Phipps, Wilma J. Medical-Surgical Nursing. Toronto: The C.V. Mosby Company, 1991.
Table of Contents
1. Introduction Page 1
2. Triglycerides Page 1
4. Waxes Page 5
5. Steroids Page 5
6. Cholesterol Page 6
7. Phospholipids Page 6
8. Glycolipids Page 7
9. Sphingolipids Page 7
10. Consumption of Lipids Pages 7-9
11. Storage of Lipids Page 9
12. Lipid Oxidation Pages 9-10
13. Lipid Bilayer Page 10
14. Atherosclerosis Page 11
15. Gallstones Page 12
16. Artheriosclerosis Pages 12-13
17. Coronary Heart Disease Pages 13-14
18. Conclusion Pages 14-15