aztreonam - An antibiotic used to treat some types of meningitis and infections by certain types of bacteria, including PSEUDOMONAS.
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azoospermia
azoospermia - The absence of sperm from semen, causing infertility in males. Azoospermia may be caused by a disorder present at birth or that develops later in life or after vasectomy.
Congenital azoospermia may be due to a chromosomal abnormality such as Klinefelter’s syndrome; failure of the testes to descend into the scrotum; absence of the vasa deferentia (ducts that carry sperm from the testes to the seminal vesicles); or cystic fibrosis.
In some males, azoospermia may be the result of hormonal disorders affecting the onset of puberty. Another cause is blockage of the vasa deferentia, which may follow a sexually transmitted infection, tuberculosis, or surgery on the groin. Azoospermia can also be the result of damage to the testes.
This can follow radiotherapy, treatment with certain drugs, and prolonged exposure to heat, or the effects of occupational exposure to toxic chemicals. If the cause is treatable, sperm production may restart. However, in some cases, the testes will have been permanently damaged.
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Congenital azoospermia may be due to a chromosomal abnormality such as Klinefelter’s syndrome; failure of the testes to descend into the scrotum; absence of the vasa deferentia (ducts that carry sperm from the testes to the seminal vesicles); or cystic fibrosis.
In some males, azoospermia may be the result of hormonal disorders affecting the onset of puberty. Another cause is blockage of the vasa deferentia, which may follow a sexually transmitted infection, tuberculosis, or surgery on the groin. Azoospermia can also be the result of damage to the testes.
This can follow radiotherapy, treatment with certain drugs, and prolonged exposure to heat, or the effects of occupational exposure to toxic chemicals. If the cause is treatable, sperm production may restart. However, in some cases, the testes will have been permanently damaged.
azithromycin
azithromycin - A macrolide antibiotic drug used to treat infections of the skin, chest, throat, and ears. Azithromycin is also used to treat genital infections due to chlamydia (see chlamydial infections).
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azathioprine
azathioprine - An immunosuppressant drug used to treat severe rheumatoid arthritis and other autoimmune disorders. It is also used to prevent organ rejection after transplant surgery. Increased susceptibility to infection is a side effect.
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avulsed tooth
avulsed tooth - A tooth that has become completely dislodged from its socket following an injury. If the tooth is kept moist, and treatment is sought immediately, reimplantation may be possible (see reimplantation, dental).
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aviation medicine
aviation medicine - The medical speciality concerned with the physiological effects of air travel and with the causes and treatment of medical problems that may occur during a flight.
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aversion therapy
aversion therapy - An outdated form of behaviour therapy in which unpleasant stimuli, such as electric shocks, are administered at the same time as an unwanted behaviour in an attempt to alter behavioural patterns.
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avascular necrosis
avascular necrosis - The death of cells in body tissue caused by damage to blood vessels supplying the area.
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autosuggestion
autosuggestion - Putting oneself into a receptive hypnotic-like state as a means of stimulating the body’s ability to heal itself. For example, in one method used to control anxiety symptoms, people are taught muscular relaxation (biofeedback) techniques and learn to summon up calming imagery or pleasant thoughts.
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autonomic nervous system
autonomic nervous system - The part of the nervous system that controls the involuntary activities of a variety of body tissues. The autonomic nervous system is divided into the sympathetic and parasympathetic nervous systems.
The sympathetic nervous system comprises 2 chains of nerves that pass from the spinal cord throughout the body tissues. Into these tissues, the nerve endings release the neurotransmitters adrenaline (epinephrine) and noradrenaline (norepinephrine).
The system also stimulates adrenaline release from the adrenal glands. In general, the actions of the sympathetic nervous system heighten activity in the body, quickening the heartbeat and breathing rate, widening blood vessels, and inducing sweating.
The parasympathetic nervous system is composed of a chain of nerves that passes from the brain and another that leaves the lower spinal cord. The nerves are distributed to the same tissues that are supplied by the sympathetic nerves.
The parasympathetic nerves release the neurotransmitter acetylcholine, which has the opposite effect to adrenaline and noradrenaline. The parasympathetic system is mainly concerned with everyday functions such as digestion and excretion.
The 2 systems act in conjunction and normally balance each other. During exercise or at times of stress, the sympathetic system predominates, however, while during sleep the parasympathetic system exerts more control.
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The sympathetic nervous system comprises 2 chains of nerves that pass from the spinal cord throughout the body tissues. Into these tissues, the nerve endings release the neurotransmitters adrenaline (epinephrine) and noradrenaline (norepinephrine).
The system also stimulates adrenaline release from the adrenal glands. In general, the actions of the sympathetic nervous system heighten activity in the body, quickening the heartbeat and breathing rate, widening blood vessels, and inducing sweating.
The parasympathetic nervous system is composed of a chain of nerves that passes from the brain and another that leaves the lower spinal cord. The nerves are distributed to the same tissues that are supplied by the sympathetic nerves.
The parasympathetic nerves release the neurotransmitter acetylcholine, which has the opposite effect to adrenaline and noradrenaline. The parasympathetic system is mainly concerned with everyday functions such as digestion and excretion.
The 2 systems act in conjunction and normally balance each other. During exercise or at times of stress, the sympathetic system predominates, however, while during sleep the parasympathetic system exerts more control.
automatism
automatism - A state in which behaviour is not controlled by the conscious mind. The individual carries out activities without being aware of doing so, and later has no clear memory of what happened.
Automatism is uncommon and may be a symptom of temporal lobe epilepsy, dissociative disorders, drug or alcohol intoxication, or hypoglycaemia.
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Automatism is uncommon and may be a symptom of temporal lobe epilepsy, dissociative disorders, drug or alcohol intoxication, or hypoglycaemia.
autoimmune disorders
autoimmune disorders - Any of a number of disorders caused by a reaction of the immune system against the body’s own cells and tissues. Bacteria, viruses, and drugs may play a role in initiating an autoimmune disorder, but in most cases the trigger is unknown.
Autoimmune disorders are classified into organ-specific and non-organ-specific types. In organ-specific disorders, the autoimmune process is directed mainly against one organ. Examples include Hashimoto’s thyroiditis (thyroid gland), pernicious anaemia (stomach),
Addison’s disease (adrenal glands), and type 1 diabetes mellitus (pancreas). In non-organ-specific disorders, autoimmune activity is towards a tissue, such as connective tissue, that is widespread in the body. Examples of non-organspecific disorders are systemic lupus erythematosus and rheumatoid arthritis.
Initial treatment for any autoimmune disorder is to reduce the effects of the disease, for example by replacing hormones that are not being produced.
In cases in which the disease is having widespread effects, treatment is also directed at diminishing the activity of the immune system while maintaining the body’s ability to fight disease. Corticosteroid drugs are most commonly used but may be combined with other immunosuppressant drugs.
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Autoimmune disorders are classified into organ-specific and non-organ-specific types. In organ-specific disorders, the autoimmune process is directed mainly against one organ. Examples include Hashimoto’s thyroiditis (thyroid gland), pernicious anaemia (stomach),
Addison’s disease (adrenal glands), and type 1 diabetes mellitus (pancreas). In non-organ-specific disorders, autoimmune activity is towards a tissue, such as connective tissue, that is widespread in the body. Examples of non-organspecific disorders are systemic lupus erythematosus and rheumatoid arthritis.
Initial treatment for any autoimmune disorder is to reduce the effects of the disease, for example by replacing hormones that are not being produced.
In cases in which the disease is having widespread effects, treatment is also directed at diminishing the activity of the immune system while maintaining the body’s ability to fight disease. Corticosteroid drugs are most commonly used but may be combined with other immunosuppressant drugs.
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