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Medical Dictionary     B
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  • B
    As a subscript, refers to blood. Abbreviation for bis [L.], twice; barn.
  • B bile
    bile from the gallbladder.
  • B cell
    β cell of pancreas or of anterior lobe of hypophysis;

    Alternate names: B lymphocyte

  • B cell receptors
    a complex comprising a membrane-bound immunoglobulin molecule and two associated signal-transducing α and β chains.
  • B cells

    B cells: A type of white blood cell and, more particularly, a key kind of lymphocyte. Many B cells mature into plasma cells, which produce antibodies (proteins) necessary to fight off infections (bacteria, viruses, etc.), while other B cells mature into memory B cells. All of the plasma cells descended from a single B cell produce the same antibody which is directed against the antigen that stimulated it to mature. The same principle holds with memory B cells. Thus, all of the plasma cells and memory cells "remember" the stimulus that led to their formation. The maturation of B cells in birds takes place in an organ called the bursa of Fabricus. Hence, the B (from bursa). B cells in mammals, including humans, mature largely in the bone marrow. So the B is again pertinent.

  • B chain
    the longer polypeptide component of insulin containing 30 amino acyl residues, beginning with a phenylalanyl residue (NH2-terminus); insulin consists of a B chain linked to an A chain by two disulfide bonds; the amino acid composition of the B chain is a function of species; the light chain of an immunoglobulin.
  • B fibers
    myelinated fibers autonomic nerves, with a diameter of 2 mcm or less, conducting at a rate of 3–15 meters per second.
  • B lymphocyte
    an immunologically important lymphocyte that is not thymus dependent, is short-lived, and resembles the bursa-derived lymphocyte of birds in that it is responsible for the production of immunoglobulins; it is the precursor of the plasma cell and expresses surface immunoglobulins (SIGS) but does not release them. It does not play a direct role in cell-mediated immunity. B lymphocyte can be characterized immunophenotypically by CD19 surface markers.

    Alternate names: B cell2

    See Also: T lymphocyte

  • B variant GM2-gangliosidosis

    B variant GM2-gangliosidosis: This disorder known as Tay-Sachs disease (TSD) is concisely defined by OMIM (Online Mendelian Inheritance in Man) as �an autosomal recessive, progressive neurodegenerative disorder, which in the classic infantile form, is usually fatal by age 2 or 3 years, results from deficiency of the enzyme hexosaminidase A. � �Autosomal� points to the gene for TSD residing on a nonsex (autosomal) chromosome (namely, chromosome15q23-q24). �Recessive� indicates a person with 2 copies of the gene has TSD whereas someone with 1 copy is a carrier in normal health. TSD worsens, with time, as the central nervous system progressively deteriorates. The �classic� (�textbook�) type of TSD has its insidious onset in infancy. The child with TSD usually develops normally for the first few months of life. An exaggerated startle reaction may first be noted. Head control is lost by 6-8 months of age. The infant cannot roll over or sit up. Spasticity and rigidity develop. Excessive drooling and convulsions become evident. Blindness and head enlargement set in by the second year. �Fatal by age 2 or 3 years� today would be modified to �fatal by age 5.� After age 2, total constant nursing care is needed. Death is due usually to cachexia (wasting away) or aspiration pneumonia initiated by food going down �the wrong way� into the lungs. TSD is due to deficiency of an enzyme (a protein needed to catalyze a specific chemical reaction within the body). Lack of the enzyme which results in failure to process a lipid (a fat) which accumulates and is deposited in the brain and other tissues, to their detriment. The enzyme is called hexosaminidase-A (hex-A) and the lipid that is deposited is called GM2-ganglioside. TSD is a model of a fatal metabolic disease that occurs primarily within a well- defined subpopulation. It is one of several genetic diseases found more often in persons of Jewish origin. (Other Jewish genetic diseases include Gaucher disease, Niemann-Pick disease, Bloom syndrome, and factor XI defiency). The frequency of TSD is much higher in Ashkenazi Jews (of European origin) than in other groups of Jews. (In the U.S., 95% of Jews are Ashkenazi and are at risk for TSD). TSD occurs more rarely, in non-Jews. Knowledge of the biochemical basis TSD has permitted screening programs for carrier detection and prenatal diagnosis of TSD. There are forms of TSD with somewhat more hex-A and hence later onset, termed juvenile TSD and adult TSH. Alternative names for TSD itself are amaurotic familial idiocy (outdated), hexosaminidase A deficiency, hex-A deficiency. TSD is named for the English physician Waren Tay (1843-1927) and the New York neurologist Bernard (Barney) Sachs (1858-1944). Tay in 1881 studied an infant with progressive neurological impairment and described �symmetrical changes in the yellow spot in each eye�, the �cherry-red spots� characteristic of TSD. Sachs saw a child In 1887 and the child�s sister in 1898 with the cherry-red spots and �arrested cerebral development� and in 1910 he demonstrated the presence of accumulated lipid in the brain and retina.

  • B wave
    the initial positive deflection in the electroretinogram, possibly arising from the inner nuclear layer of the retina.
  • Bárány caloric test
    a test for vestibular function, made by irrigating the external auditory canal with cool and warm water; this thermal stimulation of the vestibular apparatus results in nystagmus and past-pointing; in vestibular disease, the response may be reduced or absent.

    Alternate names: caloric test, nystagmus test

  • Bárány sign
    in cases of ear disease, in which the vestibule is healthy, injection into the external auditory canal of water below the body temperature will cause rotatory nystagmus toward the opposite side; when the injected fluid is above the body temperature the nystagmus will be toward the injected side; if the labyrinth is diseased or nonfunctional there may be diminished or absent nystagmus.
  • Béclard hernia
    a hernia through the opening for the saphenous vein.
  • Béclard triangle
    area bounded by the posterior border of the hyoglossus muscle, the posterior belly of the digastric, and the greater horn of the hyoid bone.
  • Békésy audiometer
    an automatic audiometer in which the test tone sweeps the frequency range while the patient controls intensity by pressing a button when the tone is heard and releases when tone cannot be heard; may be operated either at a fixed frequency or at steadily changing frequencies.

    Alternate names: automatic audiometer

  • Békésy audiometry
    audiometry in which the subject controls increases and decreases in intensity at a fixed frequency or, more unusually, as the frequency of the stimulus is gradually changed so that the subject traces back and forth across the threshold of hearing.

    Alternate names: automatic audiometry

  • Bérard aneurysm
    an arteriovenous aneurysm in the tissues outside the injured vein.
  • Béraud valve
    a small fold in the interior of the lacrimal sac at its junction with the lacrimal duct.

    Alternate names: Krause valve

  • Böök syndrome
    premolar aplasia, hyperhidrosis, and premature canities; autosomal dominant trait.
  • Bödecker index
    a modification of the DMF caries index.
  • Börjeson-Forssman-Lehmann syndrome
    a condition characterized by mental deficiency, epilepsy, hypogonadism, hypometabolism, obesity, large ears, and narrow palpebral fissures; X-linked recessive inheritance.
  • Böttcher cells
    cells of the basilar membrane of the cochlea.
  • Böttcher crystals
    small crystals observed microscopically in prostatic fluid that is treated with a drop or two of 1% solution of ammonium phosphate.
  • Böttcher ganglion
    ganglion on the cochlear nerve in the internal acoustic meatus.
  • Büchner extract
    a cell-free extract of yeast, such as was prepared by Eduard and Hans Büchner who observed it to catalyze alcoholic fermentation; this observation essentially eliminated “vitalism” as being responsible for biologic chemical reactions and initiated the beginnings of modern biochemistry (enzymology).
  • Büchner funnel
    a porcelain funnel that contains a perforated porcelain plate upon which filter paper can be laid.
  • Bürger-Grütz disease
    obsolete term for idiopathic hyperlipemia.
  • Bürow triangle
    a wedge of skin and subcutaneous fat excised, usually at the end of a closed wound and created by flap transfer or advancement, so that a smooth repair can be obtained.
  • B-cell coreceptor
    a complex of three proteins associated with the B-cell receptor (CR2, CD19, and TAPA-1).
  • B-cell differentiation/growth factors
    various substances, usually obtained from the supernatant of T-cell cultures, such as interleukins-4, -5, and -6. These substances are necessary for B-cell growth, maturation, and differentiation into plasma cells or B-memory cells.
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