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
- 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
- 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
- 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.