Reproduction Flashcards
GnRH, FSH, LH
GnRH: stimulates release of FSH & LH
FSH: initiates follicular growth (development of graafian follicle), stimulates secretion of estrogens by developing follicles
LH: stimulates further development of ovarian follicles, triggers ovulation, stimulates secretion of estrogens/progesterone/relaxin/inhibin by corpus luteum
Estrogen, Progesterone, Relaxin, Inhibin
Estrogen: promote proliferation and development/maintenance of female reproductive structures, secondary sex characteristics
Progesterone: cooperates w estrogens to prepare and maintain endometrium (thickening) for implantation, prepare mammary glands for milk production
Relaxin: produced by corpus luteum to relax uterus by inhibiting contractions of myometrium (for baby delivery), increases flexibility of pubic symphysis
Inhibin: inhibits secretion of FSH and LH
Estrogen Function
Help develop & maintain both the reproductive system and female characteristics (breasts and pubic hair)
• 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
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 fallopian tubes
• Promotes development of lobules and alveoli of breasts to proliferate, enlarge and become secretory in nature
Theca & 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 → testosterone
2. Most testosterone is converted by aromatase (under stim of FSH)→ estradiol (major estrogen)
Aromatase inhibitors: class of drugs used in treatment of breast cancer by reducing estrogen level
Estrogen Biosynthesis
Estrogens and other steroid hormones are derived from cholesterol ☞ pregnenolone
Conversion of pregnenolone=17α- hydroxypregnenolone and DHEA
Conversion of progesterone= 17α- hydroxy-progesterone and androstenedione (a precursor to testosterone)
Androstenedione released into blood by theca cells
Conversion of androstenedione=estrone (E1) (a weak estrogen) requires aromatase
Liver converts estrogens to less potent form (estriol) to be excreted in the urine
4 major estrogens
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
Follicular phase: time b/w first day of period and ovulation
- GnRH secreted in pulses by hypothalamus
- Malnutrition/stress inhibit release of GnRH
- Photoperiods (in animals) control GnRH release
- Kisspeptin neurons in human forebrain stim hypothalamic cells to release GnRH - Ant. pituitary gland secrete FSH/LH
- FSH stim maturation of follicle
- Follicular cells produce and secrete estrogens –cause uterine lining to thicken
- Estrogen secreted by follicles affect ant pituitary and hypothalamus
- During early part of follicular phase: blood estrogen low–exerts neg feedback (LH/FSH low)
- When conc high, increase secretion of LH/FSH (pos feedback)
- 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
o At early stage, they do NOT have LH receptors
o Later (in mature follicle) they produce receptors in their cell membrane
Luteal Phase
Luteal phase: time b/w ovulation and b/f menstruation
- 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, corpus luteum 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
Last events of Reproductive Cycle (after luteal phase)
- If egg cell not fertilized, 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
Phases of Uterine Cycle (3)
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 w follicular phase in ovary
3) Secretory phase (days 14-28): endometrium ready to accept implantation of embryo – overlaps w 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 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 female reproductive system go into capacitation (a change undergone by sperm in female reproductive tract that enables them to penetrate and fertilize an egg)
• If female mate w more than one male in brief period of time– sperm competition occur
oIn species with female insemination by multiple males, males tend to have large testes = larger number of sperms
Stages of Fertilization
• Sperm penetrates corona radiata (follicular cells) of ovum
• Sperm penetrates zona pellucida (transparent layer of pr) of ovum
- Undergoes acrosomal rxn which releases enzymes to allow sperm to cut through
• Sperm head attaches to plasma membrane of ovum
- Izumo1 on sperm head bind w Juno in oocyte cell membrane
• 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