(1) Hormonal Regulation of the Menstrual Cycle
What happens to the corpus luteum if fertilisation does not occur?
- CL degenerates spontaneously - Progesterone falls - Uterus loses its endocrine support - Menstruation - FSH & LH get to work again on the follicles
What happens to the corpus luteum if fertilisation does occur?
- CL maintained by hCG from the chorion - Becomes the Corpus Luteum of Pregnancy - Maintains uterine lining until placenta takes over as main producer of progesterone at 3 months
What happens during follicular phase?
-Growth of egg cell and surrounding follicular cells -Lasts about 14 days -high ESTROGEN output from day 7-14
What happens during Luteal phase?
-Post-ovulation period when corpus luteum active -also lasts about 14 days -high PROGESTERONE output from day 15-24
What happens during follicular phase? (in depth)
0-10 DAYS. Hypothalamus produces GnRH, which stimulates the Anterior pituitary to produce FSH and LH. LH and FSH stimulate the developing follicle in the ovaries to produce low levels of oestrogen. The ovaries then produce the hormone inhibin which inhibits (negative feedback) the anterior pituitary to produce FSH and LH, as well as the hypothalamus to produce GnRH.
What happens during the late Follicular phase? (in depth)
10 - 15 DAYS. Hypothalamus produces GnRH, which stimulates the Anterior pituitary to produce FSH and LH. LH and FSH stimulate the mature follicle (Graafian follicle). Then high levels of oestrogen are produced from mature follicle. When the amount of oestrogen changes in our system, the way it acts on the hypothalamus and anterior pituitary also changes. Instead of inhibiting the production of the relative hormones from these glands, instead it stimulates them to produce their hormones. It turns from negative feedback to positive feedback. So there is even more FSH and LH production. So it causes LH surge, we want this because LH surge is responsible for the production of ovum from the graafian follicle. We dont need the FSH peak, but it is a result of the LH peak because of positive feedback. However, the FSH peak is smaller because the ovaries produce inhibin which inhibits the production of FSh from the anterior pituitary but it doesn't inhibit the production of LH in this instance.
What happens during the Luteal Phase? (in depth)
15 - 28 DAYS. Hypothalamus produces GnRH, which stimulates the Anterior pituitary to produce FSH and LH. LH and FSH stimulate the Ovary to produce corpus luteum which stimulates the production of High Levels of progesterone. When there are high levels of progesterone, it has an affect on the endometrium of the nucleus. It makes sure that the endometrium is favourable for implantation of a fertilised egg. The high levels of progesterone inhibit the hypothalamus and anterior pituitary from producing their hormones, but the moderate level of oestrogen stimulate the hypothalamus and anterior pituitary from producing their hormones. However, the inhibition of the high levels of progesterone causing negative feedback dominate and keeps LH and FSH down.
On average how long is the menstrual cycle?
28 days
What is GnRH and what does it do?
Gonadotropin Releasing Hormone: increases FSH and LH
What is hCG?
Human Chorionic Gonadotropin A hormone found in the urine of women only when they're pregnant
What is HPG axis?
Hypothalamus-pituitary-gonad axis, the negative feedback loop that regulates sex-hormone production.
Where are the hypothalamus and pituitary gland located?
In the central nervous system - in the brain
What is the lining of the internal layer of the female reproductive system called? and what is the outer layer called? Which one is responsible for the changes in the uterus during menstruation?
Inner = Endometrium. Outer = Myometrium. Endometrium is the one that is responsible for the changes in the uterus during menstruation.
How are ovarian follicles arranged in the ovary?
Like lots of small sacks (the ovarian follicles) inside one large sack (the ovary)
What is the first 5-7 days of the menstrual cycle called? and what does it do?
Menstrual Flow and i think it cleanses uterus and vagina
What do ovarian follicles contain?
Oocytes and cells that produce oestrogen and progesterone
What do LH and FSH stimulate?
Ovarian Follicles and Corpus Luteum. These structures are stimulated to produce oestrogen and progesterone
What is more more complex, Regulation of hormone secretion by testes or ovaries? why?
Ovaries. Because, unlike testes, the ovaries involves both negative and positive controls
Development of ovarian follicles (image) - but learn
Primary follicles are sometimes called preantal follicle. Secondary follicles are sometimes called Antral follicles. Also use Graafian follicle instead of vesicular follicles. Each step the cell grows in size.
When does GnRH secretion begin? and where from?
Puberty from the hypothalamus
What is the corpus luteum? (with image)
a hormone-secreting structure that develops in an ovary after an ovum has been discharged but degenerates after a few days unless pregnancy has begun.
What happens during ovulation?
egg is released from ovaries
What are the three phases of the ovarian cycle?
follicular phase, ovulation, luteal phase
What happens during proliferative phase?
functional layer rebuilds
menstrual cycle (image)
look at a few different images similar to cross reference
What are the phases of the uterine cycle?
menstrual phase, proliferative phase, secretory phase. These are what happens to the endometrium of the uterus.
What is the sequence of hormones for the Control of Ovarian Function? (image)
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female reproductive organs (image)
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What happens during menstrual phase?
shedding of the endometrium
What happens during secretory phase?
the endometrium prepares for implantation