Perivitelline

Perivitelline refers to the region surrounding an oocyte or embryo that lies between the plasma membrane of the cell (the oolemma) and the enclosing enveloping layers, such as the vitelline membrane, zona pellucida, or later eggshell structures, depending on the species. The term is most commonly used in reference to the perivitelline space, the fluid-filled gap between the oolemma and the surrounding protective envelope.

Anatomy and variation: In mammals, the perivitelline space is the small cavity between the oocyte plasma membrane and the zona pellucida. In many invertebrates and egg-laying species, the analogous region lies between the oolemma and the vitelline membrane or other early eggshell layers, such as the vitelline envelope and chorion.

Function: The perivitelline space accommodates cellular structures such as polar bodies during meiosis and provides a compartment that participates in fertilization. After sperm entry, cortical granules release enzymes into the perivitelline space, which modify the surrounding envelope and contribute to the block to polyspermy. It also serves as a microenvironment for sperm–egg interactions and early zygote formation before pronuclei migrate into the ooplasm.

Clinical and research relevance: In assisted reproduction, the size and integrity of the perivitelline space can be considered in oocyte quality assessments and fertilization outcomes. Abnormalities in its size or composition may influence fertilization success and early embryo development. The perivitelline concept is also used in comparative reproductive biology to study egg activation and early development across species.

See also: Zona pellucida, Vitelline membrane, Oolemma, Cortical reaction, Polyspermy block.