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
Morula, Blastocyst, Trophoblast cells
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 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
HCG (Human chorionic gonadotropin) function
- Prevents degeneration of corpus luteum
- Corpus luteum continues to secrete progesterone and estrogens until placenta matures
- Prevents menses
- Levels rise over first 2 months of pregnancy, then drop sharply
Placental Hormones & Roles
Between 2nd-3rd month, levels of estrogens and progesterone (produced by placenta) rise and remain high throughout pregnancy =Inhibit menses
During first part of pregnancy, HCG secreted by chorion contributes to:
• formation of placenta
• sustains life of corpus luteum→ secretes estrogen and progesterone into the blood
In later pregnancy, placenta becomes principal source of estrogen and progesterone
Somatomammotropin
Blocks maternal insulin leading to an increase in maternal blood glucose levels (ensure adequate fetal nutrition)
Develops maternal breasts
Embryonic Period vs Fetal Period
Embryonic Period (Weeks 3-8 (first trimester)): Most critical period –Differentiation of all major systems occurs during this time
Development during Embryonic Period: Heart, Main blood vessels, GI tract with very large liver, Lungs with branching bronchioles, Cerebral cortex, meninges, ventricles, CSF, Spinal cord, Ossification in occipital bone, mandible and humerus, Eye and internal ear beginning to develop, Testes/ovaries and sexless external genitals
Fetal Period (Week 9-42 (birth)): By week 9, all body systems are present in some form
Birth
Accomplished by coordination of uterine myometrium (smooth muscles)
Oxytocin released into posterior pit
Increase blood oxytocin conc
Oxytocin stim myometrial smooth muscle to contract
Smooth muscle secrete prostaglandin to also stim contraction=strengthening contractions
Force fetus against cervix, cervix widen, fetus born
Mammary Glands
- Each breast has one pigmented projection (nipple) that has a series of closely spaced openings (lactiferous ducts)
- Circular pigmented area = areola–contains modified sebaceous glands (secrete oily fluid that lubricates nipple, and volatile compounds serve as olfactory stim for newborn)
- Breasts attached to fascia by suspensory ligaments–become loose w age/excessive strain
Within each breast is a mammary gland
- consists of 15-20 lobes separated by various amounts of adipose tissue
- each lobe contains smaller compartments called lobules composed of a grape-like cluster of glands (alveoli)
Lactation
Synthesis, secretion and ejection of milk
• Milk production (produced in alveoli) stim by prolactin; ejection by oxytocin
• Suckling stim secretion of prolactin and oxytocin by pituitary gland
• Other neural signals (infant’s cry) can stim oxytocin (but not prolactin) secretion and promote milk ejection
