hypostasis

1. Formation of a sediment at the bottom of a liquid. 2. SYN: hypostatic congestion. 3. The phenomenon whereby the phenotype that would ordinarily be manifested at one locus is obscured by the genotype at another epistatic locus; e.g., in humans, the phenotype for the ABO blood group locus can be expressed only in the presence of its precursor, H substance. The Bombay factor in the homozygous state blocks H formation and obscures the ABO phenotype. [G. hypo-stasis, a standing under, sediment]

- postmortem h. SYN: postmortem livedo.

- pulmonary h. hydrostatic congestion of the lung.

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hy·pos·ta·sis hī-'päs-tə-səs n, pl -ta·ses -.sēz

1) the settling of blood in relatively lower parts of an organ or the body due to impaired or absent circulation <the face was discolored by postmortem \hypostasis>

2) failure of a gene to produce its usual effect when coupled with another gene that is epistatic toward it

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n.

accumulation of fluid or blood in a dependent part of the body, under the influence of gravity, in cases of poor circulation. Hypostatic congestion of the lung bases may be seen in debilitated patients who are confined to bed. It predisposes to pneumonia (hypostatic pneumonia) but it may be prevented by careful nursing and physiotherapy. A similar condition affects the dependent parts of the body after death.

• hypostatic adj.

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hy·pos·ta·sis (hi-posґtə-sis) [hypo- + stasis] poor or stagnant circulation of the blood in a dependent part of the body or organ, as in venous insufficiency.