Female Hormones Flashcards
What are the main functions of the ovaries?
- Oogenesis, or the production of female gametes during the fetal period
- Maturation of the oocyte when it is ready for fertilization
- ovulation of the mature oocyte
- production of the female sex steroid hormones, estrogen and progesterone, and the peptide hormones inhibin and activin
Give an overview of the products of oogenesis
Oogenesis begins during embryonic development as diploid oogonia (46,2N) that undergo many mitoses so that females are typically born with 2-4 million diploid primary oocytes (46, 4N) (no new oocytes are procued after birth). These primary oocytes are arrested in prophase of meiosis I (and 99.99% of which undergo degeneration) until ovulation occurs and meiosis I completes to produce haploid secondary oocytes (23, 2N), which again arrest in metaphase. Meiosis II is completed at fertilization (or the 2ndary ooccytes degenerate) to produce an haploid ovum (23, N)
When does the follicular phase of human oocyte maturation occur?
Days 1-14 of a typical cycle (this part can vary in length but the luteal phase is fixed at 14 days)
What are the developmental stages of the follicular phase of human oocyte maturation?
- Primordial follicle
- Primary follicle
- Preantral/early antral follicles
- Mature follicle (1st Meiosis completes)
What is the role of theca cells during oocyte maturation?
providing signal transduction between granulosa cells and oocytes during development by the establishment of a vascular system, providing nutrients, and providing structure and support to the follicle as it matures.
The theca cells are also responsible for the production of androstenedione, and indirectly the production of 17β estradiol, also called E2, by supplying the neighboring granulosa cells with androstenedione that with the help of the enzyme aromatase can be used as a substrate for this type of estradiol. FSH induces the granulosa cells to make aromatase that converts the androgens made by the theca interna into estradiol.
What is the role of granulosa cells during oocyte maturation?
These are the cells directly lining the ovarian follicle and have a primary function of hormone production (estrogen, progesterone, inhibin, and activin)
These proliferate with oocyte maturation
What happens on Day 14 of the menstrual cycle?
Ovulation- a mature secondary oocyte (23,2N) is released from the follicle to the ovarian surface as meiosis I is completed
What occurs during days 14-25 of the menstrual cycle?
The luteal phase, which occurs post-ovulation, and is marked by the formation of the corpus luteum (which regresses after 10 days- days 25-28- if no fertilization occurs)
What hormones does the corpus luteum secrete?
progesterone!! (the elevation of progesterone is indicative of ovulation), and some estrogen, inhibin, and activin
What is the main source of the cholesterol needed to make steroid hormones?
LDL from the liver
What are the female sex steroid hormones?
- Estrogens (17B-estradiol (E2), Estrone (E1), and Estriol (E3))
- Progesterone
What are estrone and estriol?
Estrone is a weak estrogen and a precursor of E2, while Estriol (E3) is even weaker than E1 and is a metabolite of E2.
17B-Estradiol is the major estrogen in the body
What organs make 17B-Estradiol?
Ovaries (directly produce 17B-estradiol),
Adrenal glands, placenta,
adipose tissue (contains aromatase to convert testosterone and androstenedione)
What cells in the ovaries produce progesterone?
- theca cells
- corpus luteum (after ovulation)
When do theca cells produce progesterone?
during the follicular phase and up to ovulation
When does the corpus luteum produce progesterone?
This is the main source of progesterone- post-ovulation
How is progesterone produced in the ovary theca cells?
LH from the anterior pituitary stimulates cholesterol desmolase (CYP11A1) stored in the mitcohondria of the theca cells to produce pregnenolone from cholesterol, which is then transformed to progesterone via 3B-HSD.
NOTE: LH also inhibits 17a-hydroxylase (inhibits conversion of pregnenolone to 17-hydroxypregnenlone)
at high levels to shut down production of testosterone and 17B-estradiol
How is 17B-Estradiol made (1 of 2)?
1) Cholesterol is converted to pregnenolone via cholesterol desmolase via LH infuence
2) Pregnenolone is converted to 17-Hydroxypregnenolone via 17a-hydroxylase
3) 17-Hydroxypregnenolone is converted to DHEA via 17,20-lyase
4) DHEA is converted to Androstenedione via 3B-HSD
All in the theca cells