Problems with the Immune System

Not all "nonself' markers are harmful. Sometimes the body cannot distinguish between harmful and harmless "nonself markers. For example, it may fail to recognize certain pollens as harmless. Reactions called allergies then occur. Although most allergic reactions are not medically serious, some can be life-threatening. One example is the violent immune response some people have to bee venom.

The body occasionally fails to recognize some body cells as "self and attacks them as antigens. Such misdirected attacks occur in autoimmune diseases. Rheumatoid arthritis is an auto­immune disease affecting joint tissue.

The body may also lose its ability to attack invading micro­organisms and diseased cells. This condition is called immune deficiency. In its most severe form, immune deficiency is al­most always fatal. Its victims suffer from repeated infections and illnesses. Occasionally the deficiency is genetic and is pres­ent at birth. More often it develops later in life. AIDS (acquired immune deficiency syndrome) is an example of the latter. AIDS is caused by the human immunodeficiency virus (HIV). The virus kills T lymphocytes, destroying the body's immune system. Rejection of transplanted organs and tissues is also caused by the body's immune system. Transplanted organs are recog­nized only as "nonself." Previously, drugs were used to sup­press a patient's entire defense system to prevent rejection. The patient then became vulnerable to all diseases. Cyclosporine, a recently developed drug, suppresses transplant rejection but does not disrupt other immune functions.


Nutrition and digestion


The human body is a marvelous, complex machine. Like many machines, it needs fuel in order to operate. Food is that fuel. However, food is very different from all other types of fuel. In addition to providing energy, food also supplies almost all of the materials required for the growth, maintenance, and repair of the human machine - the body.

Actually, energy and building materials exist in food only in potential form. The body cannot directly use food in either its raw or cooked state. Your body cannot take a steak and attach it to your biceps to give you a stronger muscle. Your body must change the food you eat in usable form.


Food and Nutrition

When you sit down to a meal, you immediately notice the appearance, aroma, and taste of foods. The most important thing about the food, however, is whether it provides the proper nutrients, the substances needed for the body growth and maintanence. Your daily diet should include the proper amounts of carbohydrates, fats, proteins, vitamins, minerals, and water. All the nutrients required for the functioning of the body can be obtained by drinking water and eating the proper amount of food from four basic food groups. These group are the milk group, the meat group, the fruit and vegetable group, and the grain and grain products group.



Proteins are the major building blocks of body tissue. The body requires proteins for growth and tissue repair. Proteins called enzymes act as catalysts in chemical reactions in the body. The body can even use proteins to supple energy if its supplies of carbohydrates and fats have been used up.

Proteins consist of long chains of molecules called aminoacids. The body requires 20 kinds of amino acids, which are divided into two groups based on dietary requirements. The nonessential amino acids are those that the body can synthesize from other amino acids. The essential amino acids must be obtained directly from food and so are required in the diet. There are 12 nonessential and 8 essential amino acids. The essential amino acids must be obtained directly from food and so are required in the diet. There are 12 nonessential and 8 essential amino acids.

Complete proteins contain the 8 essential amino acids. From these, the body can synthesize the 12 nonessential amino acids. Meat, eggs, and dairy products contain complete proteins. Incomplete proteins do not all essential amino acids. Most plant proteins are incomplete. However, a diet that combines plant proteins can provide all the essential amino acids.


Carbohydrates supply most of the body’s energy needs. The simplest form of carbohydrate is a monosaccharide, or a simple sugar molecule. Glucose,fructose,dextrose,and galactose are monosaccharides. They exist in such foods as fruits, honey,syrups, artichokes, and onions. Disaccharides, or double sugars, consist of two monosaccharides. Disaccharides include sucrose, or cane sugar; and lactose, which is found in milk.

Complex carbohydrates called polysaccharides consist of many simple sugar molecules. Starches and cellulose are two important polysaccharides. Starches are found in cereal grain and such vegetables as potatoes, beans, and corn. Cellulose is present in all plant tissues but cannot be digested by human beings. However, cellulose provides the body with fiber, which aids digestion by stimulating the muscles of the digestive tract.



Fats are highly concentrated sources of energy. They provide twice as much energy per gram as do carbohydrates are not available for energy. Fats also form part of cell membranes and organelles. Thus, they are a structural material of the body.

Fats exist in two forms-saturated and unsaturated. Both forms consist of hydrogen,carbon, and oxygen atoms. In saturated fat, all the carbon atoms are joined by single bonds, and so the molecules contain the maximum number of hydrogen atoms. It is saturated with hydrogen. An unsaturated fat has at least one double bond between carbon atoms. For every double bond, two hydrogen atoms are missing. A molecule with two or more double bonds is called polyunsaturated. Animal fats are saturated fats. Butter, lard, and other saturated fats are solids at room temperature. Plant oils are unsaturated fats. Corn oil, olive oil, sunflower oil, and other unsaturated fats.



Vitamins are organic substances that act as coenzymes-that is, they assist enzymes during chemical reactions. Although vitamins do not provide energy, they are necessary for normal growth and body activity. Vitamins are classified as either fat-soluble or water-soluble. Fat-soluble vitamins-vitamins A,D,E and K-are stored in the body’s fatty tissue. Water-soluble vitamins-all the B vitamins and vitamin C-can be dissolved in water but cannot be stored in the body. They must be obtained directly from food.

Excessive amounts of vitamins A and D may cause disorders of the bones and other body tissues. Vitamin deficiencies cause many types of disorders. A well-balanced diet provides the proper amounts of all the necessary vitamins daily.


Minerals are inorganic substance that form an important part of living tissue. Like vitamins, minerals do not supply energy but help regulate body functions. Teeth and bones require calcium and phosphorous. Iron is the central atom in the oxygen-carrying molecules of the blood. Magnesium, calcium, and zinc help regulate nerve and muscle function.


About two-thirds of the body’s weight is water, most of it in the cytoplasm of cells. Blood plasma, tissue fluids, and body cavities contain the remainder. Water is required for many body functions. Most chemical reactions in the body can take place only in a water solution. Water carries nutrients to the blood plasma and into body cells. Water also forms the major part of urine and sweat, which help rid the body of wastes.


The energy value of food is commonly measured in Calories. One Calorie is the amount of heat energy needed to raise the temperature of one kilogram of water 1C. The energy potential of food and the daily energy requirements of individuals are stated in Calories. A teenage boy needs about 3,000 Calories daily, and a teenage girl about 2,000.


Table 6.2

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