N   

Nausea  /nô'zè×æ,nô'zhæ/,     a sensation leading to the urge to vomit. Common causes are motion sicknesses, early pregnancy, intense pain, emotional stress, gallbladder disease, food poisoning, and various infections. -nauseate, v., nauseous, adj.

Necropsy       See 1898autopsy.autopsy  /ô'topsè/     an examination after death that is done to determine the cause of death. Also called necropsy, thanotopsy.

Necrosis  /nekrò'sis/     local tissue death that occurs in groups of cells because of disease or injury. In coagulation necrosis, blood clots block the flow of blood, keeping blood from nearby tissue. In gangrenous necrosis, lack of blood combined with bacterial decay causes rotting of tissue. See also 7892gangrene.

Nephritis  /nefrí'tis/     any disease of the kidney marked by swelling and abnormal function. Kinds of nephritis include acute nephritis, glomerulonephritis, hereditary nephritis, interstitial nephritis, parenchymatous nephritis, suppurative nephritis.

Nephron  /nef'ron/     a filtering unit of the kidney, resembling a tiny funnel with a long stem and two twisted tubes. Each kidney contains about 1.25 million nephrons. Each nephron is made up of a renal corpuscle containing a ball of blood vessels (glomerulus) surrounded by a Bowman's capsule and several long tubes. Urine is formed in the renal corpuscles and in the tubes by filtering, reabsorption, and release. The collecting tubes carry the urine to the kidney pelvis and the ureters. Also called nephrone /nef'ròn/.

Neonatal       the period of time covering the first 28 days after birth.

Neoplasia  /nè'òplà'zhæ/     the new and abnormal development of cells that may be harmless (benign) or cancerous (malignant). -neo-plastic, adj.

Neurasthenia  /nõr'æsthè'nè×æ/     1. a condition of nervous exhaustion and physical tiredness that often follows depression. 2. a stage in the recovery from schizophrenia in which the patient is listless and apparently unable to cope with routine activities and relationships. -neurasthenic, adj.

Neurogen  /nõr'æjæn/     a substance within the early growing embryo that stimulates the making of the neural plate, which leads to the growth of the tissue of the nervous system.

Neurotic       1. referring to neurosis or to a neu-rotic disorder. 2. one who is afflicted with a neurosis. 3. informal. an emotionally unstable person.

Neutralization       the interaction between an acid and a base that makes a solution that is neither acidic nor basic. The usual products of neutralization are a salt and water.

Nightmare       a dream occurring during rapid eye movement (REM) sleep that brings out feelings of strong, inescapable fear, terror, distress, or extreme anxiety, usually awakening the sleeper. Compare 13236pavor nocturnus, 15926sleep terror disorder.

Noma  /nò'mæ/     a sudden ulcer disease of the mucous membranes of the mouth or genitals. The condition is most often seen in children with poor nutrition and cleanliness. There is rapid and painless breakdown of bone and soft tissue along with a bad odor. Bacteria may be involved. Healing eventually occurs but often with disfiguring defects. Also called gangrenous stomatitis.

Nostrils (anterior nares)compression       the act of applying pressure to an area of the body. A tumor or bleeding may cause compression of brain tissue, for example.

Notch       a gap or a depression in a bone or other organ, as the sciatic notch, a groove in the hipbone.

Noxious  /nok'shæs/     something that is harmful, causes injury, or endangers health.

Nucleic acid    /nöklè'ik/     a chemical compound involved in making and storing energy, and carrying hereditary characteristics. Kinds of nucleic acid are deoxyribonucleic acid, ribonucleic acid. See also 12401nucleotide.medulla  /mædul'æ/     pl. medullas, medullae, 1. the most inner part of a structure or organ, as the adrenal medulla, or inner part of the adrenal gland.

Nullipara  /nælip'æræ/, pl.nulliparae,     a woman who has not given birth to a living infant. The term "para 0" means nulliparity. Compare 11726multipara, 14125primipara.-nulliparity, n., nulliparous, adj

Nutrient       a substance that provides nourishment and aids in the growth and development of the body.

Nversion       1. an abnormal state in which an organ is turned inside out, as a uterine inversion. 2. a chromosomal defect in which two or more parts of a chromosome break off and separate. They rejoin the chromosome in the wrong order.

Nymphomania       a psychosexual disorder of women marked by an excessive desire for sexual satisfaction, often due to an unconscious conflict, as a desire to disprove lesbianism or frigidity. See also 14373psychosexual disorder.

Nystagmus      /nístag'mæs/     involuntary, rhythmic movements of the eyes back and forth, up and down, around, or mixed. Jerking nystagmus, marked by faster movements in one direction than in the opposite direction, is the most common. Pendular nystagmus has eye movements that are about equal in both directions. Jerking nystagmus occurs normally when a person watches a moving object. It may be a sign of barbiturate overdose or of another disorder. A disorder of the inner ear may cause rolling eye movements and is usually seen with dizziness and nausea. Other causes are various diseases of the retina of the eye and multiple sclerosis. Miners, after many years of working in darkness, may have eye movements that are very quick, increase on upward gaze, and are often linked to dizziness, head trembling, and sensitivity to light.