Mega- Health Dictionary

A greatly enlarged colon that may be present at birth or develop later. It can occur in all age groups and the condition is typi?ed by severe chronic constipation. Megacolon is caused by obstruction of the colon which may be due to faulty innervation, or to psychological factors. Other causes are HIRSCHSPRUNG’S DISEASE or ULCERATIVE COLITIS. In old people the persistent use of powerful laxative drugs may cause the condition.... megacolon

A delusion of grandeur or an insane belief in a person’s own extreme greatness, goodness, or power.... megalomania

A suffix meaning enlargement, as in acromegaly, a condition in which there is enlargement of the skull, jaw, hands, and feet due to excess production of growth hormone.... megaly

Pre?xes denoting largeness.... mega-/megalo

(Greek) In mythology, a Fury Magaere, Magaera, Megaere... megaera

(Welsh) Form of Margaret, meaning “resembling a pearl / the child of light” Maegan, Meg, Magan, Magen, Megin, Maygan, Meagan, Meaghan, Meagin, Meeghan, Meegan, Meghan, Megdn, Meggen, Megen, Meggan, Meggie, Meggy, Meganira, Meighan... megan

An important type of anaemia caused by a deficiency of vitamin B12 or another vitamin, folic acid. Either of these deficiencies seriously interferes with production of red blood cells in the bone marrow. An excess of cells called megaloblasts appears in the marrow. Megaloblasts give rise to enlarged and deformed red blood cells known as macrocytes.

Vitamin B12 is found only in foods of animal origin, such as meat and dairy products. It is absorbed from the small intestine after first combining with intrinsic factor, a chemical produced by the stomach lining. The most common cause of vitamin B12 deficiency is failure of the stomach lining to produce intrinsic factor, usually due to an autoimmune disorder; this is called pernicious anaemia. Total gastrectomy (removal of the stomach) prevents production of intrinsic factor, and removal of part of the small intestine prevents B12 absorption, as does the intestinal disorder Crohn’s disease. In a minority of cases, vitamin B12 deficiency is due to a vegan diet.

Folic acid is found mainly in green vegetables and liver. The usual cause of deficiency is a poor diet. Deficiency can also be caused by anything that interferes with the absorption of folic acid from the small intestine (for example Crohn’s disease or coeliac disease). Folic acid requirements are greater than normal in pregnancy.

Many people with mild megaloblastic anaemia have no symptoms. Others may experience tiredness, headaches, a sore mouth and tongue, and mild jaundice. If B12 deficiency continues for a long time, additional symptoms due to nerve damage, including numbness and tingling in the feet, may develop.

Megaloblastic anaemia is diagnosed by blood tests and a bone marrow biopsy. Megaloblastic anaemia due to poor diet can be remedied with a short course of vitamin B12 injections or folic acid tablets and the introduction of a normal diet. A lifelong course of vitamin B12 injections or folic acid tablets is required if the underlying cause of malabsorption is untreatable.... anaemia, megaloblastic

See anaemia, megaloblastic.... megaloblastic anaemia

n. see macrodontia.... megadontia

n. a cell that gives rise to the platelet-forming cell *megakaryocyte, found in the blood-forming tissue of the bone marrow. It is derived from a *haemopoietic stem cell and matures via an intermediate stage (promegakaryocyte) into a megakaryocyte.... megakaryoblast

n. a cell in the bone marrow that produces *platelets. It is large (35–160 ?m in diameter), with an irregular multilobed nucleus, and with *Romanowsky stains its abundant cytoplasm appears pale blue with fine reddish granules. See also thrombopoiesis.... megakaryocyte

(megalo-) combining form denoting abnormal enlargement. Example: megalomelia (of limbs).... megal

n. an abnormal form of any of the cells that are precursors of red blood cells (see erythroblast). Megaloblasts are unusually large and their nuclei fail to mature in the normal way; they are seen in the bone marrow in certain anaemias (megaloblastic anaemias) due to deficiency of vitamin B12 or folate. —megaloblastic adj.... megaloblast

n. 1. see macrocephaly. 2. overgrowth and distortion of skull bones (see leontiasis).... megalocephaly

n. see macrocyte.... megalocyte

n. gross dilatation of the *ureter. This occurs above the site of a long-standing obstruction in the ureter, which blocks the free flow of urine from the kidney. A common cause of megaureter is reflux of urine from the bladder into the ureters (see vesicoureteric reflux), but some of the most striking examples are found in so-called idiopathic megaureter. In this condition, which may affect one or both ureters, there is a segment of normal ureter of varying length at the extreme lower end of the bladder, above which the ureter is enormously dilated. Both reflux and idiopathic megaureter can be complicated by urinary infection and/or renal impairment. Treatment of megaureter is by corrective surgery if functional obstruction can be demonstrated. Surgery for reflux is normally reserved for children with gross reflux distending the renal pelvis and is usually carried out in the first few months of life.... megaureter