The Reproduction and Sex Steroid Axis Flashcards
hypothalamic-pituitary-ovarian axis
cholesterol is converted to pregnelone which is converted to progesterone which is converted to androstenedione which is converted to estradiol
activin
- has a negative affect on the conversion of cholesterol to pregnelone
- has a positive affect on the conversion of androstendion to estradiol
inhibin
- has a positive affect on the conversion of cholesterol to pregnelone
- has a negative affect on the conversion of androstenedione to estradiol
gonadotropin releasing hormone is secreted by
the arcuate nucleus of the hypothalamus
GnRH is a
- deca peptide hormone
- there are 3 types; GnRH 1, GnRH 2, GnRH 3
- GnRH 1 is the type involved with reproduction
GnRH is released in a
pulsatile manner and has a half life of 2-4 minutes
FSH
- has a half life of several hours
- is responsible for the recruitment of the dominant follicle, the growth of granulose cells and the activation of aromatase
LH
- acts on the theca cells to produce androstenedione
oestrogen acts
synergistically with FSH and induces FSH and LH receptors
inhibin
- negative feedback affect on the secretion of FSH by the pituitary but enhances LH induced androstenedione production
activin
stimulates FSH induces oestrogen production
organisation of the testis
- tubular components= sertoli cells and germ cells
- interstitial components= leydig cells and capillaries
hypothalamus secretes
GnRH which acts on the anterior pituitary to secrete LH and FSH
- Lh acts on the LEYDIG cells to produce testosterone
- FSH acts on the SERTOLI CELLS resultinng in the production of testosterone binding globulin and inhibin
dihydrotestosterone causes
enlargement of male sex organs and secondary sex characteristics
why are egg cells larger than sperm
they carry cytoplasm and organelles necessary for cell division which allows cell growth to being
fertilisation occurs in
the ampulla of the fallopian tubes
pre-fertilisation events
- thinning of the cervical mucous
- muscular contractions of the uterus and fallopian tubes
- fimbriae comes into contact with the ovary and peristaltic movements brings it to the ampulla
capactiation
sperm cannot fertilise the egg unless capacitation has taken place in the female genital tract, capacitation is the functional maturation of the spermatozoon, the area of the acrosomal cap is altered so that the acrosome reaction is possible, capacitation causes there seem to become hyper-active
the sperm must penetrate
the corona radiate to reach the outer layer of the egg the bona pallucis, they then attach to specific sperm receptors on the surface which trigger there acrosomes to release digestive enzymes enabling the sprem to burrow into the zona pellucida, the first sperm to do so causes fertilisation and the seprm attaches to the egg cell membrane and there outer membranes fuse
preventing polyspermy
the egg releases chemicals which pushes sperm away from the egg and the bona pellucid hardens riveting further sperm from entering
