Gametogenesis Flashcards
What is the magnitude of epigenetic changes in oocytes from their initial creation until fertilisation?
- After creation, there is a trend of demethylation
- Following this, around the time of birth, increases
- In the early stages of embryonic development, some methylation can decrease, before beginning denovo in the new embryo
Which cells migrate do the primitive gonad during development? Which gene determines what forms there?
- Primordial germ cells migrate to primitive gonad
- If SRY gene present (from Y chromosome), this causes testis to form
Oocytes are frozen at two places of the cell cycle before fertilisation. Which parts, and when? Do all oocytes fo this?
- Arrested at prophase 1 from birth til puberty
- Arrested at metaphase 2 from ovulation to fertilisation
Not all oocytes make it this far. Only those chosen as primary follicles get to M2, and only fertilised get to the full oocyte.
How long does spermatogenesis take?
63-72 days
What is the function of sertoli cells? Which hormones are required for spermatogenesis?
- Sertoli cells support spermatogenesis/add structure to the seminiferous tubules
- Spermatogenesis is dependent on androgens (DHT and Testosterone)
A sperm undergoes all normal maturations in the epididymis, and waits 24 hours. Is it now as ready as ever for fertilisation?
- No
- Needs to undergo capacitation, which can only occur in the female reproductive tract
Describe the process by which ovarian follicles can produce estrogen. What hormones does this process depend on?
- LH stimulates theca interna cells (theca=case)
- They synthesise androgens, which cross basement membrane and cause granulosa cells to produce estrogen
- Estrogen production is FSH dependent
Which weird hormonal feedback change causes ovulation?
- At the end of the follicular phase, estrogen begins to exert a positive feedback loop on GnRH
- GnRH surges in response to flywheel, causing LH to surge, which causes ovulation
(It’s like the increased granulosa cells stress the hypothalamus, until it finally gets disciplined as succumbs to positive change)
What is the role of the polar bodies in oocyte development? Why are they so small?
- They contain the discared genetic material from meiosis
- They’re small to ensure all cyotplasmic/cellular components are given to the oocyte
What happens to FSH levels during menopause? Why?
- During menopause, estrogen production from follicles decreases, removing negative feedback from GnRH
- This increases the production of FSH
What is the main reason why the rate of nonviable foetuses increases in women as age increases (but before menopause)?
- Increased risk of aneuploidy (wrong chromosome number)
- Leads to increased rate of miscarriage
