| major calices | The primary subdivisions of the renal pelvis, usually two or three in number. Synonym: calices renales majores. (05 Mar 2000) |
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| major connector | A plate or bar (lingual bar, palatal bar) used for the purpose of uniting partial denture bases. (05 Mar 2000) |
| major depression | A clinical syndrome that includes a persistent sad mood or loss of interest in activities that persists for at least 2 weeks in the absence of external precipitants. This should not be confused with a grief reaction (death of loved one). Features may include change in eating habits, insomnia, early morning wakening, lack of interest, depressed mood, fatigue and suicidal thoughts. (27 Sep 1997) |
| major duodenal papilla | Point of opening of the common bile duct and pancreatic duct into the duodenum; it is located posteriorly in the descending part of the duodenum. Synonym: papilla duodeni major, bile papilla, papilla of Vater, Santorini's major caruncle. (05 Mar 2000) |
| major epilepsy | tonic-clonic seizure |
| major fissure | The deep fissure in each lung that runs obliquely downward and forward. It divides the upper and lower lobes of the left lung and separates the upper and middle lobes from the lower lobe of the right lung. Synonym: fissura obliqua pulmonis, major fissure, oblique fissure. (05 Mar 2000) |
| major forceps | Occipital radiation of the corpus callosum; that part of the fibre radiation of the corpus callosum which bends sharply backward into the occipital lobe of the cerebrum. Synonym: forceps major, forceps posterior, occipital part of corpus callosum, pars occipitalis corporis callosi. (05 Mar 2000) |
| major general | An officer of the army holding a rank next above that of brigadier general and next below that of lieutenant general, and who usually commands a division or a corps. Source: Websters Dictionary (01 Mar 1998) |
| major groove | In a detailed analysis of DNA structure, there are two types of grooves that can be seen; the major groove has the nitrogen and oxygen atoms of the base pairs pointing inward toward the helical axis, while in the minor groove, the nitrogen and oxygen atoms point outwards; important because the major groove is more dependent on base composition and may be the site for protein recognition of specific DNA sequences or regions. (05 Mar 2000) |
| major hippocampus | <anatomy> Area of mammallian brain and an important preparation for the study of synaptic plasticity. The hippocampus has been known since the 1950s to be important for long term memory storage in humans and other mammals, it is essential for initial storing of long-term memory for a period of days to weeks before the memory trace is consolidated elsewhere. Also the site of long-term synaptic plasticity: see long-term potentiation, which is exhibited by defined synaptic pathways in the hippocampus. (18 Nov 1997) |
| major histocompatabilty complex | <immunology> A cluster of genes on chromosome 6 concerned with antigen production and critical to transplantation. The MHC includes the human leukocyte antigen (HLA) genes. (12 Dec 1998) |
| major histocompatibility antigen | <immunology> A set of plasmalemmal glycoprotein antigens involved in rapid (e.g. 7 days in the mouse) graft rejection and other immune phenomena. The minor histocompatibility antigens are involved in much slower rejection phenomena. The major antigens show remarkable polymorphism and occur as Class I and Class II types in mammals, birds may have a Class III molecule as well. See: histocompatibility antigens, MHC restriction. (18 Nov 1997) |
| major histocompatibility complex | The set of gene loci specifying major histocompatibility antigens, for example HLA in man, H 2 in mice, RLA in rabbits, RT 1 in rats, DLA in dogs, SLA in pigs, etc. Acronym: MHC (18 Nov 1997) |
| major hypnosis | A state of extreme suggestibility in hypnosis in which the subject is insensible to all outside impressions except the commands of the hypnotist. (05 Mar 2000) |
| major hysteria | A syndrome, now rarely seen, described by Charcot and characterised by a first stage of aura, a second stage of epileptoid convulsions, a third stage of tonic and clonic spasms, a fourth stage of dramatic behaviour, and a fifth stage of delirium; the entire attack may last from a few minutes to half an hour. Sometimes used as a synonym for hysteroepilepsy. (05 Mar 2000) |