phase

[fāz]

1. one of the aspects or stages through which a varying entity may pass.

2. In physical chemistry, any physically or chemically distinct, homogeneous, and mechanically separable part of a system.

phase 0 in cardiac physiology, the phase representing the upstroke of the action potential, in which rapid depolarization occurs after the cell reaches or is driven to threshold potential. It is the result of the opening of fast sodium channels and calcium channels.

phase 1 in cardiac physiology, the initial rapid repolarization phase of the action potential, caused by the closure of the fast sodium channels and an exodus of potassium from the cell.

phase 2 in cardiac physiology, the phase representing the plateau of the action potential, which contributes to the refractory period of the heart; there is a slow entry of calcium into the cell. It is the result of a balance between inward and outward currents and is particularly long in Purkinje and ventricular cells.

phase 3 in cardiac physiology, the terminal rapid repolarization phase of the action potential; it begins with the closing of the slow channels, resulting in an exodus of potassium from the cell and the activation of the sodium-potassium pump. The result is reestablishment of the normal resting potential.

phase 4 in cardiac physiology, the phase representing electrical diastole, i.e. the time between action potentials. It is the resting phase of the electrical cardiac cycle and is steadily maintained in nonpacemaker cells. In pacemaker cells, the membrane potential is normally reduced slowly until threshold potential is reached; if there is an outside stimulus, it may be driven down more rapidly.

continuous phase in a heterogeneous system, the component in which the disperse phase is distributed, corresponding to the solvent in a true solution. See also colloid.

disperse phase the discontinuous portion of a heterogeneous system, corresponding to the solute in a true solution.

G₁ phase a part of the cell cycle during interphase, lasting from the end of cell division (the M phase) until the start of DNA synthesis (the S phase).

G₂ phase a relatively quiescent part of the cell cycle during interphase, lasting from the end of DNA synthesis (the S phase) until the start of cell division (the M phase).

M phase the part of the cell cycle during which mitosis occurs; subdivided into prophase, metaphase, anaphase, and telophase.

S phase a part of the cell cycle near the end of interphase, during which DNA is synthesized; it comes between the G₁ and G₂ phases.

syn·the·sis pe·ri·od

the period of the cell cycle when there is synthesis of DNA and histone; it occurs between the gap₁ and gap₂ periods.

Synonym(s): S phase

Farlex Partner Medical Dictionary © Farlex 2012

S phase

The phase of the mitotic cycle during which DNA synthesis occurs.

Patient discussion about S phase

Q. What is the second phase of alcohol rehab? I guess the first one is well known... admitting you are addicted, but then what?

A. anybody??? advises about the second phase of rehab??

Q. what is the window phase for HIV?

A. The 'window' period for HIV infection describes the strong immune defense that reduces the number of viral particles in the blood stream, marking the start of the infection's clinical latency stage. Clinical latency can vary between two weeks and 20 years. During this early phase of infection, HIV is active within lymphoid organs, where large amounts of virus become trapped in the follicular dendritic cells. The surrounding tissues that are rich in CD4+ T cells may also become infected, and viral particles accumulate both in infected cells and as free virus. Individuals who are in this phase are still infectious.

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