reproduction Flashcards
(31 cards)
what are the key reproductive hormones
- GnRH
- LH
- FSH
- oestrogen
- progesterone
- testosterone
what does FSH cause to happen
- causes testes to produce sperm
- causes growth of ovarian follicles
- causes ovary to secrete oestrogen
what does LH do
- causes testes to secrete testosterone
- causes ovulation
- causes progesterone production by the corpus luteum
what is GnRH responsible for the release of
release of FSH and LH from anterior pituitary
how is GnRH secreted
In males GnRH is secreted in pulses at a constant frequency whereas in females the frequency of the pulses varies during the menstrual cycle
what do high frequency GnRH pulses stimulate
LH pulses
what do low frequency pulses stimulate
FSH release
what hormone reduced frequency of GnRH pulses
increase in progesterone concentrations
how long is the follicular phase of the menstrual cycle
typically 14 days +/- 7
what happens after FSH stimulates growth of ovarian follicles
- Rising oestrogen levels in turn exert negative feedback regulation (level of hypothalamus and pituitary) to lower FSH levels (temporarily)
- Once oestrogen reaches a certain concentration it exerts positive feedback regulation resulting in an increase in FSH levels and the LH ‘surge’
what does the LH surge lead to
- LH surge eventually leads to ovulation and regulates the formation of the corpus luteum and progesterone production and secretion
- Increasing progesterone decrease LH secretion by influencing GnRH pulsatility
what does a follicle consist of
an oocyte surrounded by follicular cells
what happens in the ovary and endometrium during the 28 days
- growth entails an increase in the number of follicular cells and accumulation of follicular fluid
- both resulting in an increase in the diameter and overall size of follicle
- endometrium thickens under the influence of oestrogen
- becomes a secretory tissue under the influence of progesterone
what happens in folliculogenesis
- once a follicle reaches a certain size it becomes gonadotrophic dependent
- only one follicle is secreted
why does only one follicle get released
because with rising oestrogen levels, FSH levels initially decrease so only one follicle able to cope with this fall in FSH
how is the corpus luteum made
- Occurs under the influence of LH
- Granulosa and theca cells transform to luteal cells
- Increase in progesterone production
- LH stimulates angiogenesis (ensures efficient delivery of cholesterol (substrate for progesterone synthesis))
- LH stimulates enzymes involved in conversion of cholesterol to progesterone
what are the functions of oestrogen
- increase in thickness of the vaginal wall
- regulate LH surge
- reduce vaginal pH through an increase in lactic acid production
- decrease viscosity of cervical mucous to facilitate sperm penetration
how does progesterone maintain pregnancy
- maintains thickness of endometrium
- responsible for infertile mucus
- relaxes the myometrium
how does sperm transport through the cervix
sperm enter the cervical canal rapidly where they encounter cervical mucus
what is the sperms ability to penetrate the mucus regulated by
- Thickness of the mucus- Hydration of cervical mucus under hormonal control
- Motility of the sperm- Only progressively motile sperm are able to pass through. Poorly motile cells get stuck
- Interaction with reactive oxygen species (produced by leukocytes that have infiltrated the cervical mucus)
- Interaction with mucins (see De Jonge diagram)
features of spermatogenesis
- Occurs within the testes
- Under endocrine control (LH, FSH and testosterone)
- Entire spermatogenic process takes 70 days
- Estimates suggest that humans produce as many as 1,000 sperms for every heartbeat
- Begins at puberty for and occurs for 60 years or more
- Sperm need to be motile to successfully traverse the female reproductive tract
what are the two compartments of the testicles
- extratubular compartment
- intratubular compartement
what is most of the testosterone released taken up by
sertoli cells
what does testosterone do in spermatogenesis
- maintains integrity of blood-testes barrier
- release of mature spermatozoa from sertoli cells by influencing peritubular myoid cells
