alpha (redirected from alpha-blocking agents)

α /α/ (alpha, the first letter of the Greek alphabet) heavy chain of IgA; α chain of hemoglobin.

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alpha /al·pha/ (al´fah) α, the first letter of the Greek alphabet; see also α-.

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al·pha (lf)

n.

1. Symbol The first letter of the Greek alphabet.

2. The first one in a series; the beginning.

3. The first position from a designated carbon atom in an organic molecule at which an atom or radical group may be substituted.

adj.

1. Characterizing the atom or radical group that is closest to the functional group of atoms in an organic molecule.

2. Relating to one of two or more closely related substances, as in stereoisomers.

3. Relating to or characterizing a polypeptide chain that is one of five types of heavy chains present in immunoglobins.

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alpha

[al′fə]

A, α, the first letter of the Greek alphabet. It is commonly used as a scientific notation, denoting the position of an atom in a molecule, identifying a nuclear particle, or designating a particular physiologic rhythm. For example, it is used in chemical nomenclature to distinguish one variation in a chemical compound from others.

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alpha,

n a Greek letter symbolized by α. See also Greek letters.

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alpha

the first letter of the Greek alphabet, A or α; used to denote the first position in a classification system; as, in names of chemical compounds, to distinguish the first in a series of isomers, or to indicate the position of substituent atoms or groups; also used to distinguish types of radioactive decay, brain waves or rhythms, adrenergic receptors, and secretory cells that stain with acid dyes, such as the alpha cells of the pancreas.

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alpha-adrenergic antagonist

see alpha-blocking agents (below).

alpha-blocking agents

a group of drugs that selectively inhibit the activities of alpha receptors in the sympathetic nervous system. As with beta-blocking agents, alpha-adrenergic blocking agents compete with the catecholamines at peripheral autonomic receptor sites. This group includes ergot and its derivatives, and phenotolamine.

alpha brain waves

human brain-wave currents during electroencephalography having a frequency of approximately 8 to 13 hertz (pulsations per second), best seen when patient's eyes are closed and the patient is physically relaxed. See also electroencephalography.

alpha cells

glucagon-producing cells of the pancreas.

alpha-hemolysin

see alpha hemolysis.

alpha hemolysis

see alpha hemolysis.

alpha particles

a type of emission produced by the disintegration of a radioactive substance. The atoms of radioactive elements such as uranium and radium are very unstable; they are continuously breaking apart with explosive violence and emitting particulate and nonparticulate types of radiation. The alpha particles, consisting of two protons and two neutrons, have an electrical charge and form streams of tremendous energy when they are released from the disintegrating atoms. These streams of energy (alpha rays) are used to advantage in the treatment of various malignancies. See also radiation and radiotherapy.

alpha-responsive sympathomimetic drugs

drugs which cause vasoconstriction and maintain correct vascular permeability.

alpha-sheet

α-sheet a common structural feature of many proteins in which a single polypeptide chain turns regularly about itself to make a rigid cylinder in which each peptide bond is regularly hydrogen-bonded to other peptide bonds elsewhere in the chain.

alpha toxin

the toxins of many bacteria are classified as alpha, beta, etc.