Mod 4. L28 Flashcards
Reproduction in animals 2
Roogenesis (and the 3 related cycles)
most species = females producee their lifetime supply of gametes early in life and only develop them when needed later in life
3 inter-related cycles
1) Ovarian cycle
2) Uterine cycle
3) Hormonal cycle
Ovarian cycle
cycle that includes:
- the development of an ovarian follicle
- rupture of the follicle
- discharge of the ovum
- formation and regression of a corpus luteum
follicle
oocyte + various cell types (follicular cells)
Follicle-stimulating hormone (FSH). [oovogenesis]
released by anterioir pituitary
induces ripening of follicles
promotes production of estrogen
Theca cells
synthesize : androstenedione and testosterone
LH stimulation contributes to this process
Granulosa cells
convert androstenedione and testosterone to estrogen (estradiol)
stimulated by FSH
Uterine cycle (in humans)
what happens in the uterus in conjunction with ovarian cycle
tissue lining the uterus builds and, under the influence of progesterone and estrogen, forms a special tissue called endometrium
if the ovum is not fertilized and implanted into endometrium = progesterone and estrogen production stops
endometrium degenerates
endometrium
tissue lining the uterus built under progesteron and estrogen influence
follicular phase
FSH ->development of follicles
->promotes estrogen production ->stimulates endometrium development
near the end:
estrogen stimulates LH and FSH (positive feedback)
-> LH and FSH surge
->ovulation!
FSH and LH [oovogenesis]
secreted by anterior pituitary gland
synthesis and release of estrogen in ovaries
(also progesteron and testosterione)
NEGATIVE feedback loop
(progesterone and testosteron inhibit LH and FSH)
near ovulation time:
estrogen promotes LH release
causes LH and FSH surge (Positive feedback)
Ovulation
Caused by LH and FSH surge
release of the ovum from the follicle
development of the corpus luteum
Luteal phase
corpus luteum synthesizes progesterone and estrogen
->further stimulate endometrium development (preparation for pregnancy)
if no fertilize-> endometrium sloughs off and cycle repeats
social suppression of reproduction (females)
environmental stimuli and physiological condition could act at various levels of the reprouctive axis in females to modulate the timing of reproductive cycles
use of GnRH (Gonadotropin-releasing hormones)
gonadotropin-releasing hormone (GnRH)
synthesized by specialized neurons in hypothalamus
carried into anterior pituitary gland (LH and FSH)
where it binds to receptors that synthesize LH and FSH
endocrine disruptors
anthropogenic compounds that interfere with endogenous hormone function
can mimic or block effect of sex steroid hormones
