| H | Abbreviation or symbol for hyperopia or hyperopic; horizontal; Hauch; Holzknecht unit; henry, unit of electrical inductance; hydrogen; the Fraunhofer line at lambda 3968 due to calcium; histidine; magnetic field strength; heroin. Symbol for enthalpy, heat content, in the equation for free energy. Symbol for hecto-; height; hour. Symbol for Planck's constant; h = h/2π. H+ is the symbol for hydrogen ion, the proton. (05 Mar 2000) |
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| H agglutinin | An agglutinin that is formed as the result of stimulation by, and which reacts with, the thermolabile antigen(s) in the flagella of motile strains of microorganisms. Synonym: flagellar agglutinin. See ABO blood group. (05 Mar 2000) |
| H and D curve | Sensitometric curve of radiographic film, a plot of the film density versus the logarithm of the relative exposure. Synonym: H and D curve, Hunter and Driffield curve. (05 Mar 2000) |
| h antigen | <microbiology> Any bacteria which has a long flagella that is used for movement. The term is used by immunologists and serologists as a form of classification. (09 Oct 1997) |
| h band | <cell biology> The H band is an area within muscle tissue which is light when stained and consists only of myosin fibres (and no actin fibres). The H band is at the centre of each muscle sarcomere. (09 Oct 1997) |
| H chain | <protein> Heavy chain of immunoglobulin, see IgG, IgM, etc. (18 Nov 1997) |
| H colony | <cell culture> A colony of motile organisms forming a thin film of growth. Compare: O colony. Origin: Ger. Hauch, breath (05 Mar 2000) |
| H disk | <cell biology> The H band is an area within muscle tissue which is light when stained and consists only of myosin fibres (and no actin fibres). The H band is at the centre of each muscle sarcomere. (09 Oct 1997) |
| H fields | Three circumscript, myelin-rich regions of the subthalamus known as H fields (from Haubenfelder); 1) field H1, corresponding to the thalamic fasciculus, a horizontal fibre stratum at the junction of the subthalamus and the overlying thalamus, is composed of pallidothalamic and cerebellothalamic fibres (brachium conjunctivum) and is separated by the zona incerta from the more ventrally placed field H2; 2) field H2, formed by the lenticular fasciculus and arching over the dorsal border of the subthalamic nucleus, is composed largely of pallidothalamic fibres; 3) field H3 or prerubral field, is a large field of intermingling gray and white matter immediately rostral to the red nucleus, uniting fields H1 and H2 around the medial margin of the zona incerta; its gray matter forms the prerubral nucleus. See: lenticular loop. Synonym: campi foreli, tegmental fields of Forel. (05 Mar 2000) |
| H gene | In laboratory animals, a gene which can elicit an immune response and thereby cause rejection of a homograft when tissue is transplanted from one individual to another; in humans, histocompatibility gene's control HLA antigens. Synonym: H gene. (05 Mar 2000) |
| H graft | <surgery> A side-to-side shunt between adjacent vessels which utilises a connecting conduit. Synonym: H graft. (05 Mar 2000) |
| H rays | <physics> A stream of hydrogen nuclei; i.e., protons. (05 Mar 2000) |
| H reflex | <clinical sign, neurology> A monosynaptic reflex consistently obtained in normal adults only by stimulating the tibial nerve, generally in the popliteal fossa, while recording from the gastrocnemius-soleus muscle group. It is similar to the Achilles reflex, except the neuromuscular spindles are bypassed; widely used in the EMG laboratory to diagnose S1 radiculopathies and polyneuropathies. (05 Mar 2000) |
| H shunt | <surgery> A side-to-side shunt between adjacent vessels which utilises a connecting conduit. Synonym: H graft. (05 Mar 2000) |
| h strand | <molecular biology> The strand of a double-stranded DNA molecule that is more buoyant than the other and floats at the top of a column when the dsDNA is denatured and put in an equilibrium centrifuge. (09 Oct 1997) |