| first arch syndrome | <syndrome> Generic term including syndrome's of malformations involving derivatives of the first branchial arch, with or without associated malformations; includes mandibulofacial dysostosis, micrognathia with peromelia, otomandibular dystosis, acrofacial dysostosis, and others. (05 Mar 2000) |
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| first-class | Of the best class; of the highest rank; in the first division; of the best quality; first-rate; as, a first-class telescope. First-class car or First-class railway carriage, any passenger car of the highest regular class, and intended for passengers who pay the highest regular rate; distinguished from a second-class car. Source: Websters Dictionary (01 Mar 1998) |
| first cranial nerve | Collective term denoting the numerous olfactory filaments: slender fascicles each composed of the thin, unmyelinated axons of 8 to 12 of the bipolar olfactory receptor cells in the olfactory portion of the nasal mucosa; the olfactory filaments pass through the cribriform plate of the ethmoid bone and enter the olfactory bulb, where they terminate in synaptic contact with mitral cells, tufted cells, and granule cells. See: olfactory tract. Synonym: nervi olfactorii, fila olfactoria, first cranial nerve, nerve of smell, olfactory fila. (05 Mar 2000) |
| first cuneiform bone | The largest of the three cuneiform bones, the medial bone of the distal row of the tarsus, articulating with the intermediate cuneiform, navicular, and first and second metatarsal bones. Synonym: os cuneiforme mediale, first cuneiform bone, wedge bone. (05 Mar 2000) |
| first degree A-V block | See: atrioventricular block. (05 Mar 2000) |
| first degree burn | A burn involving only the epidermis and causing erythema and oedema without vesiculation. Synonym: superficial burn. (05 Mar 2000) |
| first dentition | A tooth of the first set of teeth, comprising 20 in all, that erupts between the mean ages of 6 and 28 months of life. Synonym: dens deciduus, baby tooth, deciduous dentition, dens lacteus, first dentition, milk tooth, primary dentition, primary tooth, temporary tooth. (05 Mar 2000) |
| first duodenal sphincter | The sphincter supposedly located at the level of the aboral extremity of the duodenal bulb. (05 Mar 2000) |
| first finger | The first digit on the radial side of the hand. Synonym: digitus primus, pollex, first finger. Origin: A.S. Thuma (05 Mar 2000) |
| first heart sound | Occurs with ventricular systole and is mainly produced by closure of the atrioventricular valves. (05 Mar 2000) |
| first law of thermodynamics | This law, derived from the principle of conservation of energy, is expressed as E = Q - W, where E is the internal change in energy, Q is the heat the environment transfers into the system, and W is the work the system does. In other words, it means that: The internal energy in a system isolated from other systems remains constant The change in the internal energy of a system that is not isolated is equal to the energy that crosses its boundariesinto or out of other systemsIt can be further extrapolated to mean that despite all the processesgoing on in the universe, the total energy contained in the universeremains constant. (09 Oct 1997) |
| first meiotic division | The first of two consecutive divisions of the nucleus of an eukaryotic cell during the process of meiosis. It includes the following stages of meiosis: prophase I, metaphase I, anaphase I, and telophase I. (09 Oct 1997) |
| first molar | First permanent molar, sixth permanent tooth or fourth deciduous tooth in the maxilla and mandible on either side of the midsagittal plane of the head following the arch form. (05 Mar 2000) |
| first-order kinetics | A term describing the reaction rate of a chemical reaction in which the rate is proportional to the concentration (in moles) of only one of the reactants. Such a reaction might have an equation like rate = k[A], where k is the reaction rate constant and [A] is the concentration of a reactant A. (09 Oct 1997) |
| first-order reaction | A reaction the rate of which is proportional to the concentration of the single substance undergoing change; radioactive decay is a first-order process, defined by the equation -(dN/dt)=kN, where N is the number of atoms subject to decay (reaction), t is time, and k is the first-order decay (reaction) constant, i.e., the fraction of all atoms decaying per unit of time. See: decay constant, order. (05 Mar 2000) |