Copy of `Dorland's Medical Dictionary`

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Dorland's Medical Dictionary Category: Health and Medicine > Medical Dictionary Date & country: 31/12/2010, USA Words: 39128

megakaryocytosis
(meg″ә-kar″e-o-si-to´sis) the presence of megakaryocytes in the blood or of excessive numbers in the bone marrow, as in polycythemia vera.

megalencephaly
(meg″әl-әn-sef´ә-le) macrencephalia; hypertrophy of the brain.

megaloblast
(meg´ә-lo-blast″) a large, nucleated immature progenitor of an abnormal erythrocytic series, an abnormal counterpart to the normoblast; megaloblasts are present in the blood in certain anemias. adj., megaloblas´tic., adj.

megaloblastic anemia
any of various anemias characterized by the presence of megaloblasts in the bone marrow or blood; the most common type is pernicious anemia.

megalocephaly
(meg″ә-lo-sef´ә-le) macrocephaly. adj., megalocephal´ic., adj.

megalocheiria
(meg″ә-lo-ki´re-ә) abnormal largeness of the hands.

megalocornea
(meg″ә-lo-kor´ne-ә) a developmental anomaly of the cornea, which is of abnormal size at birth and continues to grow, sometimes reaching a diameter of 14 or 15 mm in the adult.

megalocystis
(meg″ә-lo-sis´tis) megacystis.

megalocyte
(meg´ә-lo-sīt″) macrocyte.

megalocytic anemia
macrocytic anemia.

megalodactyly
(meg″ә-lo-dak´tә-le) excessive size of the fingers or toes; called also macrodactyly.

megaloesophagus
(meg″ә-lo-ә-sof´ә-gәs) megaesophagus.

megalomania
(meg″ә-lo-ma´ne-ә) a mental state characterized by delusions of exaggerated personal importance, wealth, power, or goodness. adj., megaloma´niac., adj.

megalomelia
(meg″ә-lo-me´le-ә) macromelia.

megalonychia
(meg″ә-lo-nik´e-ә) macronychia.

megalopenis
(meg″ә-lo-pe´nis) macropenis.

megalophthalmos
(meg″ә-lof-thal´mos) macrophthalmia.

megalopodia
(meg″ә-lo-po´de-ә) abnormal largeness of the feet; called also macropodia.

megaloureter
(meg″ә-lo″u-re´tәr) megaureter.

megarectum
(meg″ә-rek´tәm) megacolon confined to the rectum.

megaspore mother cell
any of the diploid cells developed in the megasporangium of plants which divide by meiosis to produce four haploid daughter cells (megaspores), usually only one of which survives to become a megagametophyte, or female gametophyte.

megaureter
(meg″ә-u-re´tәr) congenital dilatation of the ureter; it may be either a primary condition or secondary to something else. Called also megaloureter.

megaureter-megacystis syndrome
megacystis-megaureter syndrome.

megavitamin
(meg´ә-vi″tә-min) a term denoting massive doses of vitamins far exceeding the recommended daily allowances.

megavolt
(MV) (meg´ә-vōlt″) one million (106) volts.

megavoltage
(meg´ә-vōl″tәj) in radiation therapy, voltage greater than 1 megavolt, as contrasted to orthovoltage and supervoltage.

megestrol
(mĕ-jes´trōl) a synthetic progestational agent administered orally as an antineoplastic agent for palliative treatment of recurrent, inoperable, or metastatic carcinoma of the breast or endometrium and for the treatment of anorexia, cachexia, and weight loss in patients with cancer or acquired immunodeficiency...

meglumine
(meg´loo-mēn) a crystalline base used in preparing salts of certain acids for use as diagnostic radiopaque media. Meglumine diatrizoate is used in angiocardiography and excretory urography; meglumine iodipamide is used in cholecystography; and meglumine iothalamate is used in cerebral angiography, excretory u...

megohm
(meg´ōm) one million (106) ohms.

megophthalmos
(meg″of-thal´mos) hydrophthalmos.

MEGX test
monoethylglycinexylidide test.

meibomian cyst
chalazion.

meibomian glands
sebaceous follicles between the cartilage and conjunctiva of the eyelids. Called also tarsal glands.

Meige disease
(māzh) lymphedema praecox.

Meige syndrome
(māzh) focal dystonia of facial and oromandibular muscles with blepharospasm, grimacing mouth movements, and protrusion of the tongue, usually occurring in older women. Called also Brueghel syndrome.

Meigs syndrome
(megz) Meigs-Salmon syndrome ascites and hydrothorax associated with ovarian fibroma or other pelvic tumor.

Meigs test
(for fat in milk) to 10 mL of milk in a special apparatus add 20 mL of water, 20 mL of ethyl ether, and shake. Then add 20 mL of 95 per cent alcohol. Remove the ethereal layer, evaporate, and weigh.

meiosis
(mi-o´sis) the process of cell division by which reproductive cells (gametes) are formed. There are two successive divisions, meiosis I and meiosis II, in which four daughter cells are formed, each with the haploid number of chromosomes (23 in humans). As in mitosis, meiosis I and II are each divided into four phases: p...

Meirowsky phenomenon
darkening of existing melanin, perhaps by oxidation, beginning within seconds and complete within minutes to a few hours after exposure to ultraviolet radiation of longer wavelengths; it is particularly noticeable in light-skinned individuals (see tan).

melalgia
(mәl-al´jә) pain in the limbs.

melancholia
(mel″an-ko´le-ә) former name for depression; now used particularly to refer to major depressive disorder. adj., melanchol´ic., adj.

melaniferous
(mel″ә-nif´әr-әs) containing melanin or other black pigment.

melanin
(mel´ә-nin) any of several closely related dark, sulfur-containing pigments normally found in the hair, skin, ciliary body, choroid of the eye, pigment layer of the retina, and certain nerve cells. They occur abnormally in the tumors known as melanomas and may be excreted in the urine when such tumors are present ...

melanin test
see Thormählen test.

melanism
(mel´ә-niz″әm) melanosis.

melanoameloblastoma
(mel″ә-no″ә-mel″o-blas-to´mә) melanotic neuroectodermal tumor.

melanoblast
(mel´ә-no-blast″) (mә-lan´o-blast) a cell that originates in the neural crest and develops into a melanocyte.

melanocyte
(mel´ә-no-sīt) (mә-lan´o-sīt) a type of dendritic clear cell of the stratum basale of the epidermis; it synthesizes tyrosinase and has melanosomes that produce melanin and can later be transferred from melanocytes to keratinocytes. adj., melanocyt´ic., adj.

melanocyte system
pigmentary system.

melanocyte-stimulating hormone
(MSH) melanophore-stimulating hormone(MSH) an anterior pituitary hormone that influences formation or deposition of melanin in the body and pigmentation of the skin.

melanocytic nevus
any of numerous acquired or inherited skin lesions composed of nests of nevus cells (altered melanocytes); they usually present as tan to deep brown small macules or papules with well-defined, rounded borders, although the clinical appearance is variable. There are three principal types, based on the histologic pattern and loca...

melanocytoma
(mel″ә-no″si-to´mә) a neoplasm or hamartoma composed of melanocytes.

melanoderma
(mel″ә-no-dur´mә) abnormally increased melanin in the skin, woth production of hyperpigmented patches; it is due either to increased production by melanocytes that are normally present or to an increase in absolute numbers of melanocytes.

melanodermatitis
(mel″ә-no-dur″mә-ti´tis) dermatitis with a deposit of melanin in the skin.

melanogen
(mә-lan´o-jәn) a colorless chromogen, convertible into melanin, which may occur in the urine in certain diseases.

melanogenesis
(mel″ә-no-jen´ә-sis) the production of melanin.

melanoid
(mel´ә-noid″) resembling melanin. a substance resembling melanin.

melanoleukoderma
(mel″ә-no-loo″ko-dur´mә) a mottled appearance of the skin. melanoleukoderma colli a mottled appearance of the skin of the neck and adjacent regions, a rare manifestation of syphilis.

melanoma
(mel″ә-no´mә) a tumor arising from the melanocytic system of the skin and other organs. malignant melanoma.

melanomatosis
(mel″ә-no″mә-to´sis) the formation of melanomas throughout the body.

melanonychia
(mel″ә-no-nik´e-ә) blackening of the nails by melanin pigmentation.

melanophage
(mel´ә-no-fāj″) a histiocyte laden with phagocytosed melanin.

melanoplakia
(mel″ә-no-pla´ke-ә) pigmented patches on the mucous membrane of the mouth.

melanosis
(mel″ә-no´sis) disordered melanin production, with darkening of the skin; called also melanism. a disorder of pigment metabolism. melanosis coli brown or black discoloration of the mucosa of the colon due to pigment from cathartics that has leaked into the lamina...

melanosome
(mel´ә-no-sōm″) any of the granules that contain melanin. The melanin is synthesized within melanocytes; then the melanosomes are transferred to keratinocytes.

melanotic
(mel″ә-not´ik) characterized by the presence of melanin; pertaining to melanosis.

melanotic carcinoma
malignant melanoma.

melanotic neuroectodermal tumor
a benign, rapidly growing, dark-colored tumor of the jaw or occasionally some other site, almost always seen in infants; called also melanoameloblastoma.

melanuria
(mel″ә-nu´re-ә) the discharge of darkly stained urine.

melarsoprol
(mә-lahr´so-prol) an antiprotozoal agent effective against trypanosomes.

MELAS syndrome
mitochondrial encephalopathy, lactic acidosis, and stroke-like episodes; a familial type of mitochondrial encephalopathy, of maternal (mitochondrial) inheritance.

melasma
(mә-laz´mә) melanosis with sharply demarcated blotchy, brown macules usually in a symmetric distribution over the cheeks and forehead and sometimes on the upper lip and neck. It is most often seen in women during pregnancy (melasma gravidarum or “mask of pregnancy”), at menopause, and while takin...

melatonin
(mel″ә-to´nin) an indoleamine hormone synthesized and released by the pineal body during the hours of darkness; it may have a role in the control of the regulation of gonadotropin release.

Meleda disease
(mel´ә-dah) mal de Meleda.

melena
(mә-le´nә) darkening of the feces by blood pigments.

Meleney ulcer
a variety of progressive synergistic gangrene associated with formation of burrowing cutaneous fissures and sinus tracts that open at distant sites. Called also burrowing phagedenic ulcer and undermining burrowing ulcer. progressive synergistic gangrene.

melioidosis
(me″le-oi-do´sis) a glanderslike disease of rodents, caused by Pseudomonas pseudomallei and occasionally transmitted to humans; it is most commonly seen in China and Southeast Asia. Two forms are noted in humans: the acute form is characterized by pulmonary, liver, and spleen involvement with septicemia; and the c...

melituria
(mel″ĭ-tu´re-ә) sugar in the urine; specific types are named for the sugar in question, such as fructosuria, galactosuria, glycosuria, and lactosuria.

Melkersson syndrome
(mel´kәr-son) Melkersson-Rosenthal syndrome (mel´kәr-son ro´zen-tahl) an autosomal dominant condition usually beginning in childhood or adolescence, characterized chiefly by chronic noninflammatory facial swelling, usually confined to the lips in the form of granulomatous cheilitis, with recu...

Meller operation
an operation for excision of the tear sac.

Melnick-Fraser syndrome
(mel´nik fra´zәr) branchio-oto-renal syndrome.

melon seed body
any of a class of small fibrous masses sometimes occurring in the joints and in cysts of the tendon sheaths.

meloplasty
(mel´o-plas″te) plastic surgery of the cheek.

melorheostosis
(mel″o-re″os-to´sis) a form of osteosclerosis, with linear tracks extending through the long bones.

melotia
(mә-lo´shә) congenital displacement of the auricle of the ear onto the cheek.

meloxicam
(mә-lok´sĭ-kam) a nonsteroidal antiinflammatory drug used in the treatment of osteoarthritis; administered orally.

melphalan
(mel´fә-lan) a cytotoxic alkylating agent derived from nitrogen mustard, used as an antineoplastic agent, primarily for treatment of multiple myeloma; administered orally or intravenously.

melting point
(mp) the minimum temperature at which a solid begins to liquefy; see also freezing point.

mem retinoscopy
a type of dynamic retinoscopy in which the fixation target is a series of letters on the retinoscope, or a card with letters at a normal reading distance.

member
(mem´bәr) a distinct part of the body. limb.

membra
(mem´brә) plural of membrum.

membrana
(mem-bra´nә) Latin word meaning membrane; a term used in anatomy.

membrane
(mem´brān) a thin layer of tissue that covers a surface, lines a cavity, or divides a space or organ. adj., mem´branous., adj.

membrane attack complex
(MAC) C5b,6,7,8,9, the five-molecule complex that is the cytolytic agent of the complement system.

membrane bone
membranous bone.

membrane cofactor protein
(MCP) an inhibitor of complement activation found in most blood cells, endothelial and epithelial cells, and fibroblasts.o

membrane of round window
secondary tympanic membrane.

membrane potential
the electric potential that exists on the two sides of a membrane or across the wall of a cell. Called also transmembrane potential.

membrane protein
one found in association with the cell membrane, either attached to (peripheral or extrinsic) or inserted in (integral or intrinsic) the membrane; possible roles include enzyme, receptor for a hormone or other molecule, and mediator of active or passive transport of lipid-insoluble substances across the membrane. See Plat...

membrane receptor
a receptor located on or in the membrane of a cell. Called also cell-surface receptor.