Medical Dictionary

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meroanencephaly (mer′o-an-en-sef′a-le)
A type of anencephaly in which the brain and cranium are present in rudimentary form. [mero- + G. an- priv. + enkephalos, brain]

merocrine (mer′o-krin, -krin, -kren)
See m. gland. [mero- + G. krino, to separate]

merodiastolic (mer′o-di-a-stol′ik)
Partially diastolic; relating to a part of the diastole of the heart. [mero- + diastole]

merogastrula (mer′o-gas′troo-la)
The gastrula of a meroblastic ovum.

merogenesis (mer-o-jen′e-sis)
1. Reproduction by segmentation. 2. Cleavage of an ovum. [mero- + G. genesis, origin]

merogenetic, merogenic (mer-o-je-net′ik, -o-jen′ik)
Relating to merogenesis.

merogony (me-rog′o-ne)
1. The incomplete development of an ovum that has been disorganized. 2. A form of asexual schizogony, typical of sporozoan protozoa, in which the nucleus divides several times before the cytoplasm divides; the schizont divides to form merozoites in this asexual phase of the life cycle. [mero- + G. gone, generation]

meromelia (mer-o-me′le-a)
Partial absence of a free limb (exclusive of girdle); e.g., hemimelia, phocomelia. [mero- + G. melos, a limb]

meromicrosomia (mer′o-mi′kro-so′me-a)
Abnormal smallness of some portion of the body; local dwarfism. [mero- + G. mikros, small, + soma, body]

meromyosin (mer-o-mi′o-sin)
A subunit of the tryptic digestion of myosin; two types are produced, H-m. and L-m.. H-m., heavy-m. one of the relatively heavy products (mol. wt. about 350,000) of the action of trypsin on myosin; it carries the ATPase activity of myosin. L-m., light-m. the relatively low molecular weight product (mol. wt. about 120,000) of the tryptic digestion of myosin.

meront (mer′ont)
A stage in the life cycle of sporozoans in which multiple asexual fission (schizogony) occurs, resulting in production of merozoites. SEE ALSO: schizont.

merorachischisis, merorrhachischisis (mer′o-ra-kis′ki-sis)
Fissure of a portion of the spinal cord. SYN: rachischisis partialis. [mero- + G. rhachis, spine, + schisis, fissure]

merosmia (me-roz′me-a)
A condition in which the perception of certain odors is wanting; analogous to color blindness. [mero- + G. osme, smell]

merosporangium (mer′o-spor-ran′-je-um)
A cylindrical small sporangium containing few spores and found in certain Zygomycetes. [G. meros, part, + sporangium]

merosystolic (mer′o-sis-tol′ik)
Partially systolic; relating to a portion of the systole of the heart. [mero- + systole]

merotomy (me-rot′o-me)
The procedure of cutting into parts, as the cutting of a cell into separate parts to study their capacity for survival and development. [mero- + G. tome, incision]

merozoite (mer-o-zo′it)
The motile infective stage of sporozoan protozoa that results from schizogony or a similar type of asexual reproduction; e.g., endodyogeny or endopolygeny. Merozoites form at the surface of schizonts, blastophores, or invaginations into schizonts, and are responsible for the vast reproductive powers of sporozoan parasites; this is seen in human malaria, where the cyclic production of merozoites produces the typical fever and chill syndrome. SYN: endodyocyte (2) . [mero- + G. zoon, animal]

merozygote (me-ro-zi′got)
In microbial genetics, an organism that, in addition to its own original genome (endogenote), contains a fragment (exogenote) of a genome from another organism; the relatively small size of the exogenote permits a diploid condition for only a limited region of the endogenote. [mero- + zygotos, yoked]

merphalan (mer′fa-lan)
The racemic mixture of melphalan and medphalan; an antineoplastic agent. SYN: sarcolysine.

MERRF
Acronym for myoclonic epilepsy with ragged red fiber myopathy. One of the mitochondrial disorders, this condition is caused by a point mutation of the mitochondria genome locus 8344, where transfer RNA is coded.

Merrifield
R. Bruce, U.S. biochemist and Nobel laureate, *1921. See M. synthesis.

Merrifield knife
See under knife.

Merritt
Katharine K., U.S. pediatrician, *1886. See Kasabach-M. syndrome.

mersalyl (mer′sa-lil)
Sodium salt of (3-hydroxymercuric-2-methoxypropyl)salicylamide-O-acetic acid; a mercurial diuretic. SYN: mercuramide. m. acid a mixture of o-carboxymethylsalicyl-(3-hydroxymercuric-2-methoxypropyl)amide and its anhydrides; same use as m.. m. theophylline m. plus theophylline added to inhibit decomposition of m..

Méry
Jean, French anatomist, 1645–1722. See M. gland.

Merzbacher
Ludwig, German physician in Argentina, 1875–1942. See M.-Pelizaeus disease, Pelizaeus-M. disease.

mes-
See meso-.

mesad (me′zad, me′sad)
Passing or extending toward the median plane of the body or of a part. SYN: mesiad. [G. mesos, middle, + L. ad, to]

mesal (me′zal, me′sal)
Rarely used term referring to the median plane of the body or a part. [G. mesos, middle]

mesameboid (mez-a-me′boyd)
Minot′s term for a primitive, “wandering” cell derived from mesoderm, probably a hemocytoblast. [mes- + G. amoibe, change (ameba), + eidos, resemblance]

mesangial (mes-an′je-al)
Referring to the mesangium.

mesangium (mes-an′je-um)
A central part of the renal glomerulus between capillaries; mesangial cells are phagocytic and for the most part separated from capillary lumina by endothelial cells. [mes- + G. angeion, vessel] extraglomerular m. mesangial cells that fill the triangular space between the macula densa and the afferent and efferent arterioles of the juxtaglomerular apparatus. SYN: polkissen of Zimmermann.

mesaortitis (mes-a-or-ti′tis)
Inflammation of the middle or muscular coat of the aorta. [mes- + aortitis]

mesareic, mesaraic (mes-a-ra′ik)
SYN: mesenteric. [G. mesaraion, mesentery, fr. mesos, middle, + araia, flank, belly]

mesarteritis (mes-ar-ter-i′tis)
Inflammation of the middle (muscular) coat of an artery. [mes- + arteritis]

mesaticephalic (me-sat′i-se-fal′ik)
SYN: mesocephalic. [G. mesatos, midmost, + kephale, head]

mesatipellic, mesatipelvic (me-sat′i-pel′ik, -pel′vik)
Denoting an individual with a pelvic index between 90 and 95; the superior strait has a round appearance, with the transverse diameter longer than the anteroposterior by 1 cm or less. [G. mesatos, midmost, + pellis, a bowl (pelvis)]

mesaxon (mez-ak′son, mes-)
The plasma membrane of the neurolemma that is folded in to surround a nerve axon. In electron micrographs this double layer resembles a mesentery in appearance.

mescal buttons (mes′kal)
The dried slices of the cactus Lophophora williamsii containing mescaline and related alkaloids.

mescaline (mes′ka-len)
The most active alkaloid present in the buttons of the mescal cactus, Lophophora williamsii. M. produces psychotomimetic effects similar to those produced by LSD: alteration in mood, changes in perception, reveries, visual hallucinations, delusions, depersonalization, mydriasis, hippus, and increases in body temperature and blood pressure; psychic dependence, tolerance, and cross tolerance to LSD and psilocybin develop; the principal component of peyote.

mesectoderm (mez-ek′to-derm)
1. Cells in the area around the dorsal lip of the blastopore where mesoderm and ectoderm undergo a process of separation. 2. That part of the mesenchyme derived from ectoderm, especially from the neural crest in the cephalic region in very young embryos. SYN: ectomesenchyme. [mes- + ectoderm]

mesencephalic (mez-en′se-fal′ik)
Relating to the mesencephalon.

mesencephalitis (mez′en-sef′a-li′tis)
Inflammation of the midbrain (mesencephalon).

mesencephalon (mez-en-sef′a-lon) [TA]
That part of the brainstem developing from the middle of the three primary cerebral vesicles of the embryo (the caudal of these being the rhombencephalon or hindbrain, the rostral the prosencephalon or forebrain). In the adult, the m. is characterized by the unique conformation of its roof plate, the lamina tecti (tectal plate [TA] or quadrigeminal plate [TAalt]. composed of the bilaterally paired superior and inferior colliculus, and by the massive paired prominence of the crus cerebri at its ventral surface. On transverse section, its patent central canal, the cerebral aqueduct, is surrounded by a prominent ring of gray matter poor in myelinated fibers; the periaqueductal gray is ventrally and laterally adjoined by the myelin-rich mesencephalic tegmentum, and covered dorsally by the mesencephalic tectal plate. Prominent cell groups of the m. include the motor nuclei of the trochlear and oculomotor nerves, the red nucleus, and the substantia nigra. SYN: midbrain vesicle&star, midbrain&star. [mes- + G. enkephalos, brain]

mesencephalotomy (mez′en-sef′a-lot′o-me)
1. The sectioning of any structure in the midbrain, especially of the spinothalamic tracts for the relief of intractable pain or the cerebral peduncle for dyskinesias. 2. A mesencephalic spinothalamic tractotomy. [mesencephalon + G. tome, incision]

mesenchyma (me-seng′ki-ma, me-zeng′)
SYN: mesenchyme.

mesenchymal (me-seng′ki-mal, mez-eng-ki′mal)
Relating to the mesenchyme.

mesenchyme (mez′en-kim)
1. An aggregation of mesenchymal or fibroblastlike cells. 2. Primordial embryonic connective tissue consisting of mesenchymal cells, usually stellate in form, supported in interlaminar jelly. SYN: mesenchyma. [mes- + G. enkyma, infusion] interzonal m. an area of avascular m. between adjacent skeletal elements in the embryo; it denotes the region of future joints. synovial m. vascular m. surrounding the interzonal m.; it develops into the synovial membrane of a joint.

mesenchymoma (mez′en-ki-mo′ma)
Rarely used term for a neoplasm in which there is a mixture of mesenchymal derivatives, other than fibrous tissue. A benign m. may contain foci of vascular, muscular, adipose, osteoid, osseous, and cartilaginous tissue; such neoplasms are sometimes classed under a compounded name, e.g., angioleiomyolipoma, and the like, but the broader term may be preferred. A malignant m. may also occur as a similar mixture of two or more types of mesenchymal cells that are malignant (other than fibrous tissue cells).

mesenteric (mez-en-ter′ik)
Relating to the mesentery. SYN: mesareic, mesaraic.

mesenteriolum (mez-en-ter-e′o-lum)
A small mesentery, as one of an intestinal diverticulum. SYN: mesoenteriolum. [Mod. L. dim. of mesenterium, mesentery] m. processus vermiformis SYN: mesoappendix.

mesenteriopexy (mes′en-ter-e-o-pek′se)
Fixation or attachment of a torn or incised mesentery. SYN: mesopexy. [mesentery + G. pexis, fixation]

mesenteriorrhaphy (mez′en-ter-e-or′a-fe)
Suture of the mesentery. SYN: mesorrhaphy. [mesentery + G. rhaphe, suture]

mesenteriplication (mez′en-ter-i-pli-ka′shun)
Reducing redundancy of a mesentery by making one or more tucks in it. [mesentery + L. plico, pp. -atus, to fold]

mesenteritis (mez′en-ter-i′tis)
Inflammation of the mesentery.

mesenterium (mez′en-ter′e-um) [TA]
SYN: mesentery, mesentery. [Mod. L.] m. dorsale commune SYN: mesentery (2) .

mesenteron (mez-en′ter-on)
The midportion of the insect alimentary canal and site of digestion; the m. may possess anterior finger-like projections, the gastric ceca, and a tubular anterior midgut, followed posteriorly by the saccular ventriculus, or stomach. [mes- + G. enteron, intestine]

mesentery (mes′en-ter-e) [TA]
1. A double layer of peritoneum attached to the abdominal wall and enclosing in its fold a portion or all of one of the abdominal viscera, conveying to it its vessels and nerves. 2. The fan-shaped fold of peritoneum suspending the greater part of the small intestines (jejunum and ileum) and attaching it to the posterior abdominal wall at the root of the m. (radix mesenterii). SYN: mesenterium dorsale commune, mesostenium. SYN: mesenterium [TA] . [Mod. L. mesenterium, fr. G. mesenterion, fr. G. mesos, middle, + enteron, intestine] m. of appendix SYN: mesoappendix. m. of cecum SYN: mesocecum. m. of lung SYN: mesopneumonium. m. of sigmoid colon See mesocolon. m. of transverse colon See mesocolon. urogenital m. SYN: diaphragmatic ligament of the mesonephros.

meshwork
See network. trabecular m. SYN: trabecular tissue of sclera.

mesiad (me′ze-ad, mes′e-ad)
SYN: mesad.

mesial (me′ze-al, mes′e-al) [TA]
SYN: proximal. [G. mesos, middle]

mesio-
Mesial (especially in dentistry). [G. mesos, middle]

mesiobuccal (me′ze-o-buk′al)
Relating to the mesial and buccal surfaces of a tooth; denoting especially the angle formed by the junction of these two surfaces.

mesiobucco-occlusal (me′ze-o-buk′o-o-kloo′sal)
Relating to the angle formed by the junction of the mesial, buccal, and occlusal surfaces of a bicuspid or molar tooth.

mesiobuccopulpal (me′ze-o-buk′o-pul′pal)
Relating to the angle denoting the junction of mesial, buccal and pulpal surfaces in a tooth cavity preparation.

mesiocervical (me′ze-o-ser′vi-kal)
1. Relating to the line angle of a cavity preparation at the junction of the mesial and cervical walls. 2. Pertaining to the area of a tooth at the junction of the mesial surface and the cervical region.

mesioclusion (me′ze-o-kloo′zhun)
A malocclusion in which the mandibular arch articulates with the maxillary arch in a position mesial to normal; in Angle classification, a Class III malocclusion. SYN: mesial occlusion (2) .

mesiodens (me′ze-o-denz)
A supernumerary tooth located in the midline of the anterior maxillae, between the maxillary central incisor teeth. [mesio- + L. dens, tooth]

mesiodistal (me′ze-o-dis′tal)
Denoting the plane or diameter of a tooth cutting its mesial and distal surfaces.

mesiodistocclusal (MOD) (me′ze-o-dist′o-kloo′sal, -zal)
Denoting three-surface cavity or cavity preparation or restoration (class 2, Black classification) in the premolars (bicuspids) and molars.

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