MNSR 44 - Hormones of the Gonads, Oestrus and Menstrual Cycles Flashcards
what do gonads produce
produce different types of hormones and gametes
the sex hormones are all -1. __ based 2.___
- cholesterol
2. steroids
how many carbon atoms does cholesterol have
27 carbon atoms
production of steroid from cholesterol
removes 6 terminal carbons -> 21 carbon intermediate called pregnenolone
pregnenolone converted into active sex steroids
3 types of carbon sex steroids
- The C-21 Steroids: Progestogens, Cortisol, Aldosterone
- The C-19 Steroids: Androgens
- The C-18 Steroids: Estrogens
androgens
hormones released from testes
where is 95% of circulating testosterone produced
in leydig cells
At puberty, under the influence of 1. ___, the 2. ___
begin to secrete 3.___ and continue to do so during
reproductive life though reaching a peak at about 4.___ years
- pituitary LH
- interstitial cells
- testosterone
- 20
function of testosterone
- Maintenance of the male ducts and glands
- Stimulate and support spermatogenesis
- Induce and maintain the male secondary sexual characteristics
- Anabolic effects - muscle build-up, nitrogen retention, male shape
- During fetal life from the 7th week small quantities are produced by the testes which differentiate male ducts and organs.
menstrual cycle
phenomenon of blood loss as a result of degradation of endometrium where the ovum is not fertilised only found in higher primates
how do mammals not experience blood loss at the end of the oestrous cycle
most mammals reabsorb the endometrial lining and do
not experience a loss of blood at the end of the oestrous cycle
what cells does follicle stimulating hormone stimulate
sertoli cell
what is the FSH promoting when stimulating sertoili cells
promotes spermatogenesis
and induce secretion of androgen binding protein (concentrates testosterone in seminiferous tubules)
What is the physiological response and result when hypothalamus secretes gonadotrophin-releasing hormone
Increase secretion of FSH and decrease secretion of LH in anterior pituitary
Stimulates spermatogenesis and inhibin secretion to provide negative feedback to stop FSH secretion
Decrease of LH increases release of testosterone in leydig cells which provides negative feedback for LH and stops LH secretion and testosterone is released in blood stream
2 groups that the hormones released from ovaries fall in
estrogens and progestagens
what hormones control estrogens and progestagens
FSH and LH
3 significant estrogens
Eestradiol-17
Estriol
Estrone
Estradiol-17
most active and abundant in women
produced by granulosa cells in developing ovarian follicle
Estriol
produced in large amounts by placenta in pregnant women
Estrone
main estrogen for post-menopausal women
produced in peripheral tissue esp. adipose tissue
androstenedione can be converted estrone with the help of what enzyme
aromatase
testosterone can be converted to estradiol with the help of what enzyme
aromatase
estrogen function
maintenance of female ducts - inc. division of vaginal epithelium and uterine endometrium
induce and maintain female secondary sexual characteristics
other physiological effects - bone density, liver, cardiac and cognitive function
name the most active progestogen hormone
progesterone
where and when is progesterone secreted
secreted by cells of corpus luteum and placenta during pregnancy
progesterone function
prepare uterine endometrium for implantation
stimulate growth of secretory alveoli in mammary glands for milk production but inhibit lactation during pregnancy
reduce uterine smooth muscle sensitivity to oxytocin
oestrous cycle
period in time in which female will become sexually receptive to male within the same frame as ovulation this is controlled by endocrine system
oestrus
drive to mate
anoestrus
will not mate
polyoestrous
mammals that display a succession of oestrous cycles e.g. domesticated animals and rodents
monoestrous
only breed at a certain time of the year e.g. carnivores
monthly menstrual fluid loss
50-100ml
follicular phase of menstrual cycle
follicle develops
controlled by estrogen under control of FSH and LH
Ends at ovulation
Luteal phase of menstrual cycle
begins after ovulation
corpus luteum develops from ovarian follicle and secretes progesterone
phase ends when drop in progesterone trigger menstruation and begin next cycle
endocrinology of follicular phase
- before menstruation - high levels of estrogen and progesterone from corpus luteum suppress prod. FSH and LH
- Break down of corpus luteum - drop in progesterone and estradiol-17 - triggers menstruation and stops negative feedback of FSH and LH
- Hypothalamus release Gonadotrophin-Releasing Hormone (GnRH) and FSH and LH from anterior pituitary gland are released and 6-12 primary follicles in ovaries enlarge into secondary follicles
- LH and FSH induce secondary follicles to secrete estradiol-17
- Estrogen trigger regrowth of endometrial lining
- Estrogen inhibits GnRH, causing FSH and LH levels to drop
- Reduced FSH and LH cause most follicles to die
Endocrinology of ovulation
- peak of LH cause lutenization of membrana granulosa cells of follicle becoming corpus luteum
- body grows for 7-8 days after ovulation producing large quantities of progesterone and estradiol-17 -> inhibit the hypothalamus and pituitary gland LH and FSH
- High levels of progesterone during luteal phase of cycle cause endometrium to further proliferate
- if fertilisation doesn’t occur corpus luteum regresses by day 26 of cycle
- leads to drop in progesterone and estradiol-17 - causes constriction in spiral arteries in endometrium and breaks down
- Drop in progesterone and estrogen stops negative inhibition of FSH and LH from hypothalamus and anterior pituitary - rise start next cycle,
endocrinology of pregnancy
- if fertilization occurs blastocyst is implanted on endometrial wall for 6-7 days
- must maintain corpus luteum until placenta over 6th week
- Blastocyst secretes Human Chronic Gonadotrohpin (HCG) - maintains corpus luteum and steady increase estrogen and progesterone
- After 60 days HCG levels drop to low levels for rest of pregnancy by estrogen and progesterone levels remain high as they are now produced by placenta reach 10X and 200X those of luteal phase
- Human Placental Lactogen (HPL) is release has growth hormone and prolactin like properties
- Labour occurs contraction of smooth muscles of myometrium at ~280 days/9 months
