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Lecture 3

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University of Toronto Mississauga
Daniel Da Silva

Lecture 3- Life and death in the ovary - In females, primary oocytes are arrested in prophase I until puberty. - When the egg gets released during ovulation it is suspended in metaphase II. This is the secondary oocyte. When a sperm fertilizes it, the egg completes meiosis II. - In female embryos, mitotic increase of eggs will continue until about 5 months after conception. By the time the baby is born, mitotic increase of eggs is arrested. Primary oocyte is arrested in meiosis I (prophase I) - Oogonium primary oocyte enters meiosis I but stops at prophase I till puberty primary oocyte completes meiosis I and enters meiosis II (only gets up to metaphase II). It is now a secondary oocyte at puberty, this secondary oocyte is released. If fertilization occurs it will complete meiosis II. - When the sperm penetrates the zona pellucida layer secondary oocyte will complete meiosis II. - *stages of oogenesis? - At puberty, hormones from the hypothalamus stimulate release of FSH and LH from the pituitary glands. FSH helps the eggs mature up to the stage it can be released every 28 days. - In the ovary there is something similar to an endocrine gland which controls the fertilization process corpus luteum. - Granulosa layer protects and preserve the egg until it is released. - Histonine and prostaglandins are released in response to inflammation in the ovaries. This inflammation causes release of an oocyte. - A few eggs will mature each cycle but only the one that’s most matured will be released. - When two eggs are released  can lead to non-identical twins. - Corpus luteum: very important to maintain hormone levels in the ovary. Regulates monthly menstrual cycle. - if there is no fertilization, uterine endometrium is shed. - The first follicles that are formed are called primordial follicles. - Follicular fluid + feca (many layers) - Tertiary follicle is the one that releases the egg. And before the release of the egg it also releases estrogen, which stimulates uterine epithelial cell proliferation. - Corpus luteum releases progesterone. It causes uterine lining maturation which leads to the secretory phase of the uterus. It can then interact with a blastocyst should fertilization occur. - Corpus luteum remains in the ovary during the period that fertilization is possible (1-2 days). Afterwards it degenerates. -
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