Endo 5 Flashcards
(36 cards)
What are the functions of ovaries?
1-Production of mature eggs
2-Production of steroid hormones made in follicle
What is the fundamental reproductive unit of the ovaries? What are they made of?
Primordial follicles: Oocytes are surrounded by a single layer of granuolsa cells.
Explain the initation of the growth of the primordial follicle.
Primordial becomes a primary follicle, (an unknown initiating event) Once growth is initiated, gonadatropins (FSH and LH) and steroid hormones control the growth until the follicle ovulates or degenerates.
Explain the steps of development of the oocytes.
1-Enlargment and differentiation
2-Granulosa divide and make 2 or more layers to form a primary follicle (influenced by FSH and estrogen)
3-Primary follicles develop into secondary follicles and express receptors for FSH, estrogen and LH (influenced by FSH and LH)(dab)
4-Granulosa elaborate follicular fluid to become preovulatory follicles (influenced by FSH and LH)
What is special about the hormones responsible for oocytes development?
The estrogen produced by granulosa cells is important for the expression of LH and FSH receptors, which drive the cells’ development.
What are the two events that can follow follicular development?
1-Follicular atresia
2-Ovulation
What is follicular atresia?
When a secondary follicle degenerates and doesn’t reach reproduction during a reprodructive cycle.
What is ovulation (mechanism isn’t understood)?
One follicle ovulates into each reproductive cycle.
What major event happens during lutheinization?
The follicle is ruptured and becomes the Corpus Luteum
What is the function of the Corpus Luteum?
It produces progesterone and estrogen for a few days after ovulation but stops if there is no implantation. The hormones induce thickening of the endomitral wall
What happens to the corpus luteum after implantation?
It becomes the corpus luteum of pregnancy. It continues to synthesise progesterone and estrogen to make a proper endocrine environment for the maintenance of pregnancy until it can be made by the placenta
What happens to the corpus luteum if there is no implantation?
The corpus luteum will stop producing hormones (decreased LH by prostaglandin will stop steroidogenesis). The decrease of plasma progesterone and estrogen may trigger the next reproductive cycle
When does menses (bleeding) begin?
When estrodiol and progesterone are very low in circulation, there is a increased pituitary FSH secretion (lack of -ve feedback loop) which initiates a new follicular development
What is the potential (science isn’t sure) cause of FSH increase at the same time as LH increase?
There is a decrease in inhibin, which inhibits the secretion of FSH
Explain the follicular phase
FSH
LH
Estrogen
Progesterone
-VE feedback: Low estrogen & progesterone → GnRH release → FSH secretion → Follicles grow → secrete estrogen → Estrogen inhibits FSH
FSH ↑ : Stimulates follicle growth.
LH (low, then ↑ gradually): Helps follicle mature.
Estrogen ↑ (from developing follicle): Thickens endometrium and -ve feedback on FSH and LH While making more receptors to increase sensitivity
Progesterone (low) : No corpus luteum yet.
Explain the ovulation phase
FSH
LH
Estrogen
Progesterone
High estrogen for ~48 hours → switches to +ve feedback on hypothalamus & pituitary → massive LH surge.
LH surge → follicle rupture → ovulation.
LH surge ↑↑: Triggers ovulation.
FSH ↑ slightly: Assists ovulation.
Estrogen peaks: Switches to positive feedback
Progesterone (still low)
Explain the luteal phase
FSH
LH
Estrogen
Progesterone
Corpus luteum forms after ovulation → secretes progesterone & estrogen → inhibits FSH & LH (negative feedback).
LH & FSH ↓: Suppressed by progesterone & estrogen.
Estrogen: Maintains endometrium. (thickening)
Progesterone ↑: Prepares uterus (specialization)
Explain the menstruation phase
FSH
LH
Estrogen
Progesterone
No fertilisation → corpus luteum degenerates → progesterone & estrogen drop –> endometrium degenerates (bleeding)
Low hormones remove inhibition on GnRH → FSH rises → new cycle begins.
Progesterone & Estrogen ↓↓↓: Corpus luteum degenerates.
FSH: Stimulates new follicle growth.
LH remains low until next ovulation.
What kind of feedback does estradiol have when it is in moderate concentrations
There is a negative feedback on FSH release
LH synthesis is increased in the pituitary as well as the sensitivity to GnRH in the pituitary. BUT estradiol inhibits LH release, so it accumulates
What kind of feedback does estradiol have when it is in high concentrations? why does the concentration increase?
Developing follicle increases concentration
The new concentration stimulates LH release (surge), which also causes the follicle to rupture
DRAW THE FEEDBACK LOOPS of steroid hormones and gonadotropin hormones
SLIDE 9
How do oral contraceptives work?
Pills contain E and P to suppress the release of LH and FSH from the pituitary and prevent ovarian follicles from maturing and getting ovulated
Explain the steps necessary to have fertilisation and implantation
- Unfertilized egg taken by the fimbria of the fallopian tube to be propelled towards the lumen of the uterus
- If spermatozoa deposits in vagina, it can travel as far as the fallopian tubes to fertilise the egg
- The egg starts dividing to become a blastocyte during it’s transport into the uterine lumen
What happens to the blastocytes after implantation?
It differentiates into a trophoblast (placenta) and the inner cell mass (embryo). Trophoblast invades the uterine mucosa to imbed the developing embryo in the endometrium.
