Female Reproductive Cycle Flashcards
GnRH, FSH, LH
Hormonal Control of Female Reproductive Cycle
GnRH: stim FSH & LH release
FSH: initiates follicular growth (development of graafian follicle), stim estrogens secretion by developing follicles
LH: stim further development of ovarian follicles, triggers ovulation, stim secretion of estrogens/progesterone/relaxin/inhibin by corpus luteum
Estrogen, Progesterone, Relaxin, Inhibin
Hormonal Control of Female Reproductive Cycle
Estrogen: promote proliferation and development/maintenance of female reproductive structures, secondary sex characteristics
Progesterone: cooperates with estrogens to prepare and maintain the endometrium (thickening) for implantation, prepare mammary glands for milk production
Relaxin: produced by corpus luteum to relax the uterus by inhibiting contractions of the myometrium (for baby delivery), increases the flexibility of pubic symphysis
Inhibin: inhibits secretion of FSH and LH
Estrogen Function (Ovarian Sex Hormones)
Help develop & maintain both the reproductive system and female characteristics
Causes cellular proliferation and growth of sex organs
Effects on the breasts
Increases bone growth
Increase in protein & fat deposition
Electrolyte balance
Contributes to cognitive health, bone health, function of cardiovascular system & BP, etc.
Progesterone Function (Ovarian Sex Hormones)
Regulating menstruation and supporting pregnancy in female body
Promotes secretory changes in uterine endometrium
Prepares uterus for implantation of fertilized ovum
Increases secretion by mucosal lining of the fallopian tubes
Promotes development of lobules and alveoli of the breasts to proliferate, enlarge and become secretory in nature
Theca vs Granulosa Cells
Theca cells initiate the steps of generating estradiol
Granulosa cells complete the steps
LH affect Theca cells which convert cholesterol to androstenedione (weak androgen)
Granulosa cells have 2 enzymes: 17 B-hydroxysteroid dehydrogenases & aromatase
1) 17 beta-hydroxysteroid dehydrogenases convert androstenedione to testosterone
2) Most testosterone is converted by aromatase (under stim of FSH) to estradiol
Estrogen Biosynthesis
Estrogens and other steroid hormones are derived from cholesterol –> pregnenolone
Conversion of pregnenolone to 17α- hydroxypregnenolone and DHEA
Conversion of progesterone to 17α- hydroxy-progesterone and androstenedione (a precursor to testosterone)
Androstenedione released into the blood by theca cells
Conversion of androstenedione to estrone requires aromatase
Liver converts estrogens to less potent form (estriol) to be excreted in the urine
Major estrogens (4)
Estrone (E1): predominant circulating estrogen during menopause
Estradiol (E2): most potent and prevalent
Estriol (E3): predominant circulating during pregnancy –release by placenta
Estetrol (E4) only during pregnancy
Follicular phase duration
time b/w first day of period and ovulation
Follicular phase steps
- GnRH secreted in pulses by hypothalamus
- Ant. pituitary gland secrete FSH/LH
- FSH stim maturation of follicle
- Follicular cells produce and secrete estrogens –cause uterine lining to thicken
- During early part of follicular phase: blood estrogen low
- When conc high: increase secretion of LH/FSH
- Estrogen w FSH =proliferation of granulosa cells
- Estrogen stim endometrial cells to produce receptor molecules for progesterone in preparation events that occur after ovulation - Ant. pituitary release surge of LH which stim ovulation
- Granulosa cells of developing follicles change in their ability to respond to LH
- At early stage, they do NOT have LH receptors
- Later (in mature follicle) they produce receptors in their cell membrane
Luteal Phase duration
time b/w ovulation and b/f menstruation
Luteal phase steps
- Follicular cells become corpus luteum cells
In human, corpus luteum function for ~ 10 days then starts to degenerate and stops functioning on day 28
If fertilization occurs, the corpus luteum (corpus luteum of pregnancy) grows further and continue to secrete hormones
- estrogen continue to stim uterine wall development
- progesterone stim uterine lining to become more glandular and vascular
- estrogens and progesterone inhibit secretion of FSH and LH
- Inhibin inhibits secretion of FSH and LH
After Luteal phase
- If egg cell is not fertilized, the corpus luteum degenerates and no longer secretes estrogens and progesterone
- As conc of estrogens and progesterone decline, blood vessels in uterine lining constrict
- Uterine lining sloughs off, producing menstrual flow
- Anterior pituitary is no longer inhibited and again secretes FSH and LH
- The reproductive cycle repeats
3 Phases of Uterine Cycle in Humans
1) Menstrual phase (days 1-4): starts when sloughing occurs (menstruation =day 0)
2) Proliferative phase (days 4-14): endometrium undergoes rapid thickening –occurs simultaneously with follicular phase in ovary
3) Secretory phase (days 14-28): endometrium ready to accept implantation of embryo – overlaps with ovarian luteal phase
Menarche
First occurrence of menstrual bleeding
At puberty, increase in FSH and LH production = onset of first ovarian cycle
Ovulation (day 14)
FSH and LH surge stim ovulation & formation of corpus luteum from cells of the graafian follicle
Ovulation process: discharge of ova and ovules from ovary
At ovulation:
- LH secretion causes oocyte to come out of surface of ovary and enter fallopian tube
- If fertilization occurs, meiosis of secondary oocyte is completed and second polar body is formed
Fertilization
Normally occurs in infundibulum of fallopian tube (usually within 24 hr after ovulation)
A sperm penetrates an ovum to form a zygote
Millions of sperms enter female reproductive system, very few arrive to the oocyte, only one fuses with it
Sperms in the female reproductive system go into capacitation (a change undergone by sperm in female reproductive tract that enables them to penetrate and fertilize an egg)
Stages of Fertilization
Sperm penetrates corona radiata (follicular cells) of the ovum
Sperm penetrates zona pellucida (transparent layer of pr) of the ovum
Sperm head attaches to plasma membrane of ovum
Sperm head enters ovum, tail separates (stays outside ovum)
Ovum reacts:
Zona pellucida hardens and plasma membrane changes = no further sperm entry
Ovum completes second meiotic division, second polar body disintegrates
Ovum nucleus now called female pro-nucleus (haploid)
Sperm head enlarges, becomes male pro-nucleus (haploid)
Nuclei fuse, chromosomes combined -zygote (diploid)
Period of Cleavage
Rapid mitotic divisions without much growth
First cleavage occurs 24 hrs after fertilization
Morula
composed of 16 cells, resembles raspberry
develops by end of day 3
Blastocyst
fluid-like balloon of cells called trophoblasts
develops by end of day 5
Trophoblast cells
become a membrane called the chorion (part of placenta)
secrete placental hormones
Implantation
Occurs ~7 days after ovulation
Trophoblasts grow into endometrial glands
Endometrial cells grow over the point of entry (implantation is complete)
Function of Placenta
Provide diffusion of foodstuffs and oxygen from mother’s blood into fetus’s blood
Diffusion of excretory products from the fetus back into mother
PO2 of mother’s blood is 50 mm Hg whereas mean PO2 of fetal blood is 30 mm Hg = pressure gradient of 20 mm Hg
How does the fetus obtain sufficient oxygen with PO2 of 30 mm Hg?
- Fetal hemoglobin: causes shift to the left of oxygen-hemoglobin dissociation curve, therefore fetal hemoglobin can carry 20-50% more oxygen
- Increased hemoglobin conc of fetal blood
- Bohr effect: hemoglobin can carry more oxygen at low PCO2 than high PCO2
