Ovarian cycle

Question 1

What is the purpose of the ovarian cycle - x2 physiological roles?

Answer 1

-Transport spermatozoa & fertilization - during oestrogen dominant part of cycle (follicular phase)

-Support implantation & subsequent development of embryo - during progesterone dominant part of cycle (luteal phase)

Question 2

Give the stages of follicular development.

Answer 2

Pre/early-antral (takes 77-85 days) = gonadotropin-independent:
-Granulosa cells proliferate
-Oocyte increases in size & symp activity
-Oocyte secretes zona pellucida
-Cytoplasmic processes between granulosa cells & oocyte
-Theca cell layers develop along w/ blood supply

Antral (takes 8-12 days)= gonadotropin-dependent:
-Granulosa cells secrete follicular fluid which gathers in antrum -> increasing follicular size
-Symp activity maintained in oocyte
-Morphological changes occur in follicle

Pre-ovulatory (takes 30-36 hrs) = LH & progesterone dependent
-Cytoplasmic processes withdrawn
-Oocyte synthesises cortical granules
-Rapid antral fluid vol expansion
-LH-stimulated progesterone secretion by granulosa cells
-Hormone stimulated protease activity

Question 3

What are the 2 types of follicular cells?

Answer 3

-Granulosa cells
-Theca cells

Question 4

Facts about granulosa cells:
-Where arise from?
-Function?

Answer 4

-Arise from mesenchymal cells that condense around oogonium
-Nutritional support for oocyte
-FSH-stimulated oestrogen production via aromatization of androgens made by theca cells

Question 5

Facts about theca cells:
-Where arise from?
-Function?

Answer 5

-Arise from ovarian stroma that surround primary follicles
-LH-stimulated production of androgens from circulating cholesterol
-Poor synthesis of oestrogens

Question 6

What is primary hypogonadism/hypergonadotrophic hypogonadism?

Answer 6

-Gonads (testes & ovaries) - produce low levels of sex hormones due to a disruption of HPG axis

-Hypothalamus secretes GnRH - pituitary gland stimulating secretion of FSH & LH into bloodstream
-FSH & LH then stimulate gonads to produce oestrogen & progesterone (female) or testosterone (male)

-Congenital causes = genetic disorders: Klinefelter syndrome & Turner syndrome

-Causes decrease/absence of sex hormones - so is NO -ve feedback on HPG axis
–> so get overproduction of LH & FSH (=gonadotropins)

*Klinefelter syndrome = in males - who are XXY - testes become fibrotic - no germ cells - can’t make testosterone = lots of LH & FSH:
-Testes cannot respond to LH & FSH
-LH & FSH involved in testosterone production
–> so testosterone not produced
-No testosterone means high LH & FSH levels cannot be inhibited - as testosterone is insufficient to inhibit this

Involves:
-Seminiferous tubule dysgenesis
-Failure of spermatogenesis
-Leydig cell hyperplasia

*Turner’s syndrome = in females - who are X - so have absence of one X chromosome -> so ovaries become fibrotic - no eggs, can’t make oestrogen -> make lots of LH & FSH

Question 7

What is secondary hypogonadism/hypogonadotrophic hypogonadism?

Answer 7

-Low levels of LH & FSH
-Can occur due to hypothalamus OR pituitary gland dysfunction
–> leading to impaired GnRH or gonadotropin (LH & FSH) secretion.

-Congenital causes:

Kallmann syndrome = genetic condition - inability to make GnRH (due to defective migration of GnRH cells) - so no LH & FSH & low/no testosterone & low/no oestrogen
-Both m & f = delayed epiphyseal plate closure
Males = low sperm count/infertile, small testes, micropenis, anosmia (defective formation of olfactory bulb), delayed or absent puberty
Females = amenorrhea - so can’t reproduce, incomplete breast growth, failure of secondary sexual development, delayed or absent puberty

Panhypopituitarism (involves decrease in all pituitary hormones)
-Short height in childhood - due to growth hormone deficiency
-Children with this deficiency often grow at slow rate

-Problem is in brain (abnormality of hypothalamus or pituitary) - can’t make gonadotropins - so no oestrogen or progesterone made