Homeostasis Health Dictionary

This is a genetically controlled type of cell death. There is an orchestrated collapse of a cell (see CELLS), typi?ed by destruction of the cell’s membrane; shrinkage of the cell with condensation of CHROMATIN; and fragmentation of DNA. The dead cell is then engulfed by adjacent cells. This process occurs without evidence of the in?ammation normally associated with a cell’s destruction by infection or disease.

Apoptosis, ?rst identi?ed in 1972, is involved in biological activities including embryonic development, ageing and many diseases. Its importance to the body’s many physiological and pathological processes has only fairly recently been understood, and research into apoptosis is proceeding apace.

In adults, around 10 billion cells die each day

– a ?gure which balances the number of cells arising from the body’s stem-cell populations (see STEM CELL). Thus, the body’s normal HOMEOSTASIS is regulated by apoptosis. As a person ages, apoptopic responses to cell DNA damage may be less e?ectively controlled and so result in more widespread cell destruction, which could be a factor in the onset of degenerative diseases. If, however, apoptopic responses become less sensitive, this might contribute to the uncontrolled multiplication of cells that is typical of cancers. Many diseases are now associated with changed cell survival: AIDS (see AIDS/HIV); ALZHEIMER’S DISEASE and PARKINSONISM; ischaemic damage after coronary thrombosis (see HEART, DISEASES OF) and STROKE; thyroid diseases (see THYROID GLAND, DISEASES OF); and AUTOIMMUNE DISORDERS. Some cancers, autoimmune disorders and viral infections are associated with reduced or inhibited apoptosis. Anticancer drugs, GAMMA RAYS and ULTRAVIOLET RAYS (UVR) initiate apoptosis. Other drugs – for example, NONSTEROIDAL ANTI-INFLAMMATORY DRUGS (NSAIDS) – alter the process of apoptosis. Research is in train to harness new knowledge about apoptosis for the development of new treatments and modi?cations of existing ones for serious disorders such as cancer and degenerative nervous diseases.... apoptosis

The brain and spinal cord together form the central nervous sytem (CNS). Twelve cranial nerves leave each side of the brain (see NERVES, below) and 31 spinal nerves from each side of the cord: together these nerves form the peripheral nervous system. Complex chains of nerves lying within the chest and abdomen, and acting largely independently of the peripheral system, though linked with it, comprise the AUTONOMIC NERVOUS SYSTEM and govern the activities of the VISCERA.

The control centre of the whole nervous system is the brain, which is located in the skull or cranium. As well as controlling the nervous system it is the organ of thought, speech and emotion. The central nervous system controls the body’s essential functions such as breathing, body temperature (see HOMEOSTASIS) and the heartbeat. The body’s various sensations, including sight, hearing, touch, pain, positioning and taste, are communicated to the CNS by nerves distributed throughout the relevant tissues. The information is then sorted and interpreted by specialised areas in the brain. In response these initiate and coordinate the motor output, triggering such ‘voluntary’ activities as movement, speech, eating and swallowing. Other activities – for example, breathing, digestion, heart contractions, maintenance of BLOOD PRESSURE, and ?ltration of waste products from blood passing through the kidneys – are subject to involuntary control via the autonomic system. There is, however, some overlap between voluntary and involuntary controls.... brain

Convulsion occurring in a child aged six months to six years with a high temperature in which the limbs twitch; he or she may lose consciousness. The condition is common, with one child in 20 suffering from it. It is a result of immature homeostatic control (see HOMEOSTASIS) and is not usually serious, occurring generally during an infection such as measles or tonsillitis. The brain and nervous system are normal in most cases. Treatment is tepid sponging and attention to the underlying cause, with the child placed in the recovery position. It is important to rule out more serious illness, such as MENINGITIS, if the child seems particularly ill.... febrile convulsion

These are ‘chemical messengers’ that are dispersed by the blood and act on target organs to produce effects distant from their point of release. The main organs involved in hormone production are the PITUITARY GLAND, PANCREAS, ovary (see OVARIES), testis (see TESTICLE), THYROID GLAND, and ADRENAL GLANDS. The release of many hormones is, ultimately, under the control of the central nervous system via a series of inhibiting and releasing factors from the HYPOTHALAMUS. Hormones are involved in maintaining homeostasis: for example, insulin regulates the concentration of glucose in the blood. They also participate in growth and maturation: for example, growth hormone promotes growth and helps to regulate fat, carbohydrate, and protein metabolism; and the sex hormones promote sexual maturation and reproduction. (See also ENDOCRINE GLANDS.)... hormones

The sum total of changes in an organism in order to achieve a balance (homeostasis). Catabolic burns up, anabolic stores and builds up; the sum of their work is metabolism.... metabolism

Groups of neurons (see NEURON(E)), usually sited in the HYPOTHALAMUS and the BRAIN stem, that are the control centres for various essential body functions. Examples are: blood pressure, breathing, heart rate and temperature control. The centres are part of the body’s re?ex adjustments to the outside world and its internal environment and are essential in maintaining HOMEOSTASIS.... vital centres

fibroblast growth factor 23: a hormone that is central to phosphate homeostasis. It is synthesized by osteoblasts and osteoclasts in response to high phosphate intake, hyperphosphataemia, or an increase in serum *calcitriol concentration. It inhibits phosphate reabsorption by the proximal tubule of the kidney and stimulates 24-hydroxylase, the enzyme that converts calcitriol and its precursor, 25-hydroxy vitamin D, into inactive metabolites. It may also have a negative effect on parathyroid hormone synthesis.... fgf23

Body temperature is the result of a balance of heat-generating forces, chie?y METABOLISM and muscular activity, and heat-loss, mainly from blood circulation through and evaporation from the skin and lungs. The physiological process of homeostasis – a neurological and hormonal feedback mechanism – maintains the healthy person’s body at the correct temperature. Disturbance of temperature, as in disease, may be caused by impairment of any of these bodily functions, or by malfunction of the controlling centre in the brain.

In humans the ‘normal’ temperature is around 37 °C (98·4 °F). It may rise as high as 43 °C or fall to 32 °C in various conditions, but the risk to life is only serious above 41 °C or below 35 °C.

Fall in temperature may accompany major loss of blood, starvation, and the state of collapse (see SHOCK) which may occur in severe FEVER and other acute conditions. Certain chronic diseases, notably hypothyroidism (see THYROID GLAND, DISEASES OF), are generally accompanied by a subnormal temperature. Increased temperature is a characteristic of many acute diseases, particularly infections; indeed, many diseases have a characteristic pattern that enables a provisional diagnosis to be made or acts as a warning of possible complications. In most cases the temperature gradually abates as the patient recovers, but in others, such as PNEUMONIA and TYPHUS FEVER, the untreated disease ends rapidly by a CRISIS in which the temperature falls, perspiration breaks out, the pulse rate falls, and breathing becomes quieter. This crisis is often preceded by an increase in symptoms, including an epicritical rise in temperature.

Body temperature is usually measured on the Celsius scale, on a thermometer reading from 35 °C to 43·3 °C. Measurement may be taken in the mouth (under the tongue), in the armpit, the external ear canal or (occasionally in infants) in the rectum. (See also THERMOMETER.)

Treatment Abnormally low temperatures may be treated by application of external heat, or reduction of heat loss from the body surface. High temperature may be treated in various ways, apart from the primary treatment of the underlying condition. Treatment of hyperthermia or hypothermia should ensure a gradual return to normal temperature (see ANTIPYRETICS.... temperature