Ovirakenne

Ovirakenne is a Finnish term that translates to "egg structure" and is used in biology to describe the architecture of eggs (ova) as they occur across different organisms. The concept encompasses the cellular and extracellular components surrounding the embryo, as well as the physical shells or envelopes that protect and regulate exchange with the environment.

In vertebrate eggs, key elements typically include the yolk, which provides nutrients; the vitelline or zona pellucida envelope that surrounds the oocyte; the plasma membrane; and the perivitelline space between the envelope and the oolemma. Many eggs also possess outer coverings such as a calcified shell in birds and most reptiles, with associated shell membranes, pores, and specialized structures like the micropyle for sperm entry. Additional membranes of the developing embryo, such as the amnion, chorion, and allantois, form during embryogenesis but are part of the extraembryonic apparatus rather than the egg capsule itself.

In invertebrates, eggs are often surrounded by a chorion or gelatinous layers, with species-specific adaptations that affect fertilization, gas exchange, and desiccation resistance. Techniques used to study ovirakenne include light microscopy, scanning and transmission electron microscopy, and histological sectioning.

Significance: understanding ovirakenne contributes to reproductive biology, developmental timing, and evolutionary biology, and informs applied fields such as aviculture, fisheries, and conservation.