Disorders and deficiencies

Most people go through life in general good health, suffering occasionally from temporary acute disorders, which are more inconvenient than threatening. The common cold is a typical example of an infectious illness that is a great nuisance, but not permanently debilitating.

The human body is, however, susceptible to a wide variety of more serious chronic disorders and diseases, which include hereditary conditions; defects present at birth; disorders caused by dietary defects; disorders that affect one or other of the body systems; neoplasms, whether benign tumors or malignant cancers; conditions that affect the brain or nervous system (or both); psychosomatic disorders mental disturbances that produce the physical symptoms of illness; and complaints associated with occupation, environment, and the body’s natural degeneration.

Each part of the body is susceptible to its own set of characteristic disorders, and there are other conditions that affect the body as a whole. The chief categories are infections (which often cause inflammation of a tissue or organ); traumas, which usually result from injury; tumors and other abnormal growths; autoimmune diseases; deficiency diseases; and degenerative disorders, generally resulting from the process of aging. Disorders that affect the whole body include, as well as generalized infections, those involving the skin, the skeleton, the circulation, the lymphatic system, and the peripheral nervous system. Certain glandular disorders, particularly those involving hormones, may also have a profound effect on the whole of the body. The illustration indicates some of the disorders that can affect the various parts of the body.

Hereditary disorders

Some disorders may be inherited from one or both parents and may affect a child directly. In other cases, an inherited disorder may not be apparent for one or more generations. Severe hereditary disorders include hemophilia (in which a person’s blood fails to clot, resulting in excessive bleeding from even minor injuries), and sickle-cell anemia (in which a person is anemic because of abnormally-shaped red blood cells). Color blindness is an example of a less serious inherited disorder. Certain hereditary disorders such as hemophilia, like some birth defects (for example, Down syndrome), can be detected during pregnancy by amniocentesis. Many inherited diseases can be linked to abnormalities in the number or type of chromosomes.

Other birth defects

Some defects are not inherited but acquired while the fetus is in the uterus. Faults in normal physical development may cause such disorders as cleft palate, harelip, spina bifida, hydrocephalus (water on the brain), and congenital heart abnormalities. Faults in the chromosome distribution can lead to Down syndrome, in which the child has an abnormal number of chromosomes.
Other disorders appear as a result of abnormal circumstances during pregnancy. For instance, a baby may be born deaf, or with cataracts in the eyes, or even with heart disease, if its mother contracted rubella (German measles) during the first three months of pregnancy. Also, certain drugs taken by a pregnant woman may cause abnormalities in her child. Damage to the baby may also be caused during complicated births. For example, if the fetus does not receive sufficient oxygen during the birthing process, brain damage (cerebral palsy) or even death might result.

Dietary defects and deficiencies

The necessity for a normal, well-balanced diet is well known, and generally the body compensates for variations, losses, and temporary excesses in diet. At its simplest, this is illustrated by the body’s desire for liquids (thirst) after an insufficient intake of fluids or after eating salty food. But certain disorders are actually aggravated by a normal diet. Celiac disease makes the intestines react to the protein called gluten (an ingredient of wheat flour) in such a way that normal absorption of other nutrients is prevented. A gluten-free diet is usually prescribed in order to relieve the symptoms and prevent further deficiency disorders from developing. Phenylketonuria (PKU) is a hereditary deficiency disorder in which enzymes that normally break down the amino acid phenylalanine are absent, so that this substance (which occurs in many foods) accumulates in the blood and damages the brain, causing symptoms that range from irritability to convulsions. In most countries, babies are tested at birth for this deficiency, which can be corrected by adjusting the baby’s diet.

Malnutrition, resulting from a diet that lacks essential vitamins or minerals, is responsible for diseases such as rickets, scurvy, and beriberi. Severe malnutrition in children up to the age of eighteen months causes an irreversible reduction in intellectual ability. Overindulgence can also lead to problems. For instance, a diet rich in sugar may lead to obesity and aggravate diabetes, and diets rich in animal fats contribute to heart disease and disorders of the circulatory system.
Some foods that have no ill effect on most people cause abnormal allergic reactions in others. The reaction can vary from a temporary rash or digestive disturbance to water-filled blisters over most of the body.

Atmospheric pollution is an environmental hazard that may cause respiratory disorders or severely aggravate existing ones. Sulfurous gases from incompletely burned or “dirty” fuels, for example, are a particular risk for people who suffer from asthma or bronchitis.

System failure

Occasionally, one of the body’s systems fails completely. Disease or damage to the kidneys may lead to kidney failure, which can be fatal if both kidneys are affected and the condition is untreated. Cardiac failure may cause the heart to stop pumping blood around the body, and unless the heart is restarted quickly this will result in death. The term cardiac failure also describes partial failure of the heart, which results in an accumulation of blood in various organs because circulation is impaired. Liver and lungs may be damaged by disease or toxic substances, and this damage may also be fatal.

The body’s systems are finely balanced, and although some effect usually occurs if a system is only partly faulty, nevertheless the body has a remarkable capacity to cope with and even compensate for partial failure of its systems.

Old age is associated with general slow degeneration and gradually decreasing efficiency of all the body’s systems. The lungs, heart, liver, kidneys, and brain all work less well, and the senses tend to deteriorate. Sight and hearing in particular are liable to suffer quite rapid decline in older people; this probably contributes more than anything else to the problems of aging.

A chronically ill person usually needs a prolonged course of treatment, sometimes involving a long stay in a hospital. The aim is to support the patient so that he or she can live at home and lead as normal a life as possible.

Causes of disease

Some diseases and disorders seem to occur without obvious cause, as with some cancers and other growths and with many of the disorders that affect the nervous system. Many conditions, however, are brought about by specific identifiable circumstances.

Certain lifestyles give rise to particular hazards, and some occupations are associated with specific diseases. For example, cardiovascular disorders are particularly prevalent in sedentary workers who are also subject to stress; and respiratory diseases such as asbestosis, bagassosis, or silicosis, are likely to affect the lungs of those who work in conditions in which large quantities of certain types of dust are inhaled.

There are some disorders that may occur at particular stages of life; for instance, one type of leukemia is more common in children and young adults than in older people, and gallstones are particularly likely to affect middle-aged people. Other conditions, such as allergies and chilblains, can occur at any age.

External factors

Excessive use of alcohol or tobacco, abuse of drugs, stress, obesity, and poor diet can all cause or aggravate certain disorders. For instance, smoking is associated with bronchitis and lung cancer. Women who smoke or drink during pregnancy also risk causing significant harm to the child in their womb. Stress is strongly associated with cardiovascular disease. Lack of exercise, especially in combination with a sedentary occupation, has been associated with obesity and circulatory disorders, and especially with cardiovascular disease.

Rickets is a deficiency disease caused by a lack or insufficiency of vitamin D. The vitamin is supplied in sufficient quantities in a balanced diet containing such foods as eggs and fish; it is also formed in the skin on exposure to sunlight. Its deficiency affects calcium metabolism and results in deformed bones in children.
In adults, vitamin D deficiency causes osteomalacia, which is also characterized by a softening of the bones.


New growths of normal or abnormal body tissue are known medically as neoplasms. They can take many forms some are harmless; some cause discomfort, irritation, or pain; and some are potentially fatal. Examples of harmless (benign) growths are common warts, moles, and fatty growths known as lipomas. Growths capable of causing pain or difficulty include fibroids (fibrous lumps in the uterus), and polyps in the nose, rectum, or cervix.

Malignant growths of excess tissue are called cancers. Such growths can be found in almost any part of the body, including the brain, lungs, breasts, uterus, bones, kidneys, mouth, stomach, liver, and colon. Cancerous cells multiply abnormally fast and starve surrounding tissue of nutrients. If the malignant growth is confined to only one accessible area, it can often be removed by surgery or destroyed by radiation or chemotherapy. Once cancerous cells have entered the bloodstream or lymphatic system, however, they may spread to almost any part of the body. If this happens, it is very difficult to cure the disease. Some cancers are caused by known cancerproducing agents (carcinogens) such as tobacco smoke, ultraviolet rays, and X rays. Other cancers have been linked to certain inherited predispositions.

Hemophilia is a comparatively rare but serious inherited disorder. People with the condition lack an essential clotting factor in their blood, and, as a result, bleed excessively from even a minor cut or bruise. Most hemophiliacs are males; they inherit the disorder from their mothers, who are carriers but do not themselves suffer from the disease. However, as the diagram shows, it is possible for a girl to be a hemophiliac if her father has the disease and her mother is a carrier.

Neurological conditions

The brain and nervous system are also subject to various disorders. The brain is the most complex organ of the body and is directly or indirectly involved in all bodily functions. If something goes wrong with the brain’s functioning, for example as a result of epilepsy, injury to its tissues, a brain tumor, a stroke, or encephalitis (inflammation of the brain), the results can be far-reaching and sometimes unpredictable.

Diseases can also attack the nerve pathways. One of the best known, and most serious, examples is multiple sclerosis. In this disorder, the cause of which is unknown, the protective cells around the nerves of the brain and spinal cord are damaged, causing a variety of symptoms that may become progressively more severe and can eventually lead to disability.

Untreated cancer can spread from the primary site by the process of metastasis. The diagram (left) indicates how breast cancer can progress first to the lymph nodes and then to the bones, from which it moves to the liver and finally the lungs.

Psychological and similar disorders

The mind can affect the body, and many physical disorders are thought to be caused or aggravated by emotional disturbances. Stress is perhaps the most common of such causes, and can be a significant factor in disorders such as indigestion, headaches, palpitations, high blood pressure, heart disease, and diabetes. It may aggravate disorders like asthma, eczema, psoriasis, excessive sweating, and migraine. Combined with emotional difficulties, stress can lead to such severe conditions as anxiety or panic attacks, alcoholism, drug dependence, and anorexia nervosa.

Sexual difficulties may result from emotional problems, perhaps related to irrational guilt or fear or to feelings of inadequacy, or they may be a result of stress. The most common physical symptoms associated with sexual difficulties of this sort are inability to achieve an erection or experience orgasm.

Reassurance and psychotherapy may be needed to resolve psychologically based physical problems the physical symptoms are unlikely to disappear unless the underlying emotional problem is dealt with.

Curvature of the spine in the elderly may result from osteoporosis, a degenerative disorder in which a gradual loss of calcium causes porosity of the bones. The vertebrae, in particular, may become deformed and compressed, leading to a stiff neck and a characteristic stoop, which in turn affects the way the person walks.