The Reproduction and Sex Steroid Axis

Question 1

hypothalamic-pituitary-ovarian axis

Answer 1

cholesterol is converted to pregnelone which is converted to progesterone which is converted to androstenedione which is converted to estradiol

Question 2

activin

Answer 2

• has a negative affect on the conversion of cholesterol to pregnelone
• has a positive affect on the conversion of androstendion to estradiol

Question 3

inhibin

Answer 3

• has a positive affect on the conversion of cholesterol to pregnelone
• has a negative affect on the conversion of androstenedione to estradiol

Question 4

gonadotropin releasing hormone is secreted by

Answer 4

the arcuate nucleus of the hypothalamus

Question 5

GnRH is a

Answer 5

• deca peptide hormone
• there are 3 types; GnRH 1, GnRH 2, GnRH 3
• GnRH 1 is the type involved with reproduction

Question 6

GnRH is released in a

Answer 6

pulsatile manner and has a half life of 2-4 minutes

Question 7

FSH

Answer 7

• 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

Question 8

LH

Answer 8

• acts on the theca cells to produce androstenedione

Question 9

oestrogen acts

Answer 9

synergistically with FSH and induces FSH and LH receptors

Question 10

inhibin

Answer 10

• negative feedback affect on the secretion of FSH by the pituitary but enhances LH induced androstenedione production

Question 11

activin

Answer 11

stimulates FSH induces oestrogen production

Question 12

organisation of the testis

Answer 12

• tubular components= sertoli cells and germ cells
• interstitial components= leydig cells and capillaries

Question 13

hypothalamus secretes

Answer 13

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

Question 14

dihydrotestosterone causes

Answer 14

enlargement of male sex organs and secondary sex characteristics

Question 15

why are egg cells larger than sperm

Answer 15

they carry cytoplasm and organelles necessary for cell division which allows cell growth to being

Question 16

fertilisation occurs in

Answer 16

the ampulla of the fallopian tubes

Question 17

pre-fertilisation events

Answer 17

• 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

Question 18

capactiation

Answer 18

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

Question 19

the sperm must penetrate

Answer 19

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

Question 20

preventing polyspermy

Answer 20

the egg releases chemicals which pushes sperm away from the egg and the bona pellucid hardens riveting further sperm from entering