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 duringembryonic development asdiploidoogonia (46,2N)that undergo many mitoses so thatfemales are typically born with 2-4 million diploidprimary oocytes (46, 4N)(no new oocytes are procued after birth). These primary oocytes are arrested in prophase of meiosis I (and99.99% of which undergo degeneration) until ovulation occurs and meiosis I completes to produce haploidsecondary oocytes (23, 2N), which again arrest in metaphase. Meiosis II is completed at fertilization (or the 2ndary ooccytes degenerate) to produce an haploidovum (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 follicle2. Primary follicle3. Preantral/early antral follicles4. Mature follicle (1st Meiosis completes)
What is the role of theca cells during oocyte maturation?
providing signal transduction betweengranulosa cellsandoocytesduring 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 ofandrostenedione, and indirectly the production of 17βestradiol, also called E2, by supplying the neighboringgranulosa cellswithandrostenedionethat with the help of the enzymearomatasecan be used as a substrate for this type ofestradiol. 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- amature 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 doesthe 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 infuence2) Pregnenolone is converted to 17-Hydroxypregnenolone via 17a-hydroxylase3) 17-Hydroxypregnenolone is converted to DHEA via 17,20-lyase4) DHEA is converted to Androstenedione via 3B-HSDAll in the theca cells
What things can happen to androstenedione?
It can be converted to testosterone by diffusing into granulosa cells and via 17B-HSD orit can be converted to estrone in the theca cells via aromatase
How istestosterone converted to 17B-estradiol in the ovaries?
Via aromatase under positive influence of FSH from the anterior pituitary
Estrogen production is age-dependent. Give a brief outline of the levels of estrogen in the body at various points in life.
Estrogen production starts at an early embryonic age (8-12 weeks) and is thought to be very important in the development of internal female organs. By birth estrogen levels fall significantly until about 2-3 mo of age when a transient “minipuberty” occurs which is thought to stimulate brain development. Levels then drop again to near zero until puberty, where they remain high until about 45 yers of age, which sees a progressive decreased in estrogen secretion by the ovaries and a small compensation by the adipose tissues
Describe the Hypothalamic-Pituitary-Gonadal Axis
The Hypothalamus produces pulsatileGnRH which promotes secretion of LH and FSH from the anterior pituitary to act on the ovaries to produce testosterone, estrogen, progesterone, activin, and inhibin
Describe what is happening in this graph
During childhood, levels of FSH and LH are very low until puberty which is met with a 5-10x increase in the gonadotropins. During menopause, the decreased producton of estrogen produces a lack of negative feedback on the production of FSH and LH and their levels surge up to 10x where they remain high into the 60s until slowly decreasing until death
How do the LOW levels of estradiol affect production of FSH, LH, and GnRH during the early and middle follicular phase of ovulation?
Low levels of estradiol inhibit production of GnRH and mainly LH from the anterior pituitary, whereas inhibin production during this phase from the ovaries inhibits FSH
