oocyte

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oocyte

physiology

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Last updated

July 1, 2026

Quick Summary

Oogenesis is the process by which a primary egg cell, or ovum, matures into a mature ovum capable of fertilization. This process begins before a female is born, with all the egg cells she will ever have already present in her ovaries. These immature cells, called primary ova, remain dormant until ovulation, when one is released from the ovary.1

Upon release, the egg undergoes cell division, forming a larger secondary ovum and a smaller polar body. The secondary ovum then travels to the fallopian tubes, where it can be fertilized by a sperm cell. If fertilization does not occur within 24 hours, the ovum degenerates. The ovary itself is the female reproductive organ that produces eggs and essential reproductive hormones. It contains immature eggs within follicles, which mature and are released through ovulation, controlled by hormones from the pituitary gland.23

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animal development
Preparatory events
…or egg), derived from an oocyte (immature egg), and the male sex cell (spermatozoon or sperm), derived from a spermatocyte. Eggs are produced in ovaries; sperm, in testes. Both the egg and the sperm contribute to the development of the new individual; each providing one set of genes, thereby restoring…
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…or egg), derived from an oocyte (immature egg), and the male sex cell (spermatozoon or sperm), derived from a spermatocyte. Eggs are produced in ovaries; sperm, in testes. Both the egg and the sperm contribute to the development of the new individual; each providing one set of genes, thereby restoring…
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human reproductive system
Ovarian structure
…contains a primitive ovum, or oocyte, and each is covered by a single layer of flattened cells. As many as 700,000 primary follicles are contained in the two ovaries of a young female. Most of these degenerate before or after puberty.
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…contains a primitive ovum, or oocyte, and each is covered by a single layer of flattened cells. As many as 700,000 primary follicles are contained in the two ovaries of a young female. Most of these degenerate before or after puberty.
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insect
Reproductive system
…of undifferentiated cells that form oocytes, nurse cells, and follicular cells. The nurse cells provide nourishment for the oocytes during the early stages of their growth; follicular cells, which invest the enlarging oocyte as a continuous epithelium, provide the materials for yolk formation and, in the final stages, lay down…
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…of undifferentiated cells that form oocytes, nurse cells, and follicular cells. The nurse cells provide nourishment for the oocytes during the early stages of their growth; follicular cells, which invest the enlarging oocyte as a continuous epithelium, provide the materials for yolk formation and, in the final stages, lay down…
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animal reproductive system
Ovaries
…ovarian follicle consists of an oocyte, or immature egg, surrounded by an epithelium, the cells of which are referred to variously as follicular, nurse, or granulosa cells. In cyclostomes, teleosts, and amphibians, the epithelium is one layer thick. In the hagfish and those vertebrates in which the oocyte receives heavy…
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…ovarian follicle consists of an oocyte, or immature egg, surrounded by an epithelium, the cells of which are referred to variously as follicular, nurse, or granulosa cells. In cyclostomes, teleosts, and amphibians, the epithelium is one layer thick. In the hagfish and those vertebrates in which the oocyte receives heavy…
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