Ovarian function Flashcards
when does the PGCs first become visible?
- first become visible after 3 weeks in the epithelium of yolk sac
- expand by mitosis and migrate to the genital rides during weeks 3-7
- remain indifferent until week 6-7
what occurs during week 7?
- > absence of SRY expression female gonads develop
- further dev is dependent on normal germ cells (XX)
- not dependent on endocrine activity
what is the prime function of the ovaries ?
- production of oocytes
- produce hormones which regulate the whole process
what are primordial germ cells?
- earliest form of recognisable germinal cell
- capable of infinite mitosis
- migrate to genital ridge –> week 6/7 embryo development
briefly outline the life of the human egg
PGC (migration to genital ridge)–> oogonium (during embryogenesis) –> primary oocyte arrested at prophase 1 –> ovulation–> secondary oocyte arrested at metaphase 2 (+ polar body) –> fertilisation –> 1 haploid ovum + 3 polar bodies
list the 2 types of somatic follicular cells
- granulose cells -> epithelia, these produce oestrogens and progestagens
- theca cells (stromal) produce androgens and progestogens
what is a primordial follicle ?
- a primary oocyte surrounded by a single layer of flattened granulosa cells
when does folliculogenesis occur ?
- during puberty
- growth of the oocyte and production of proteins needed for maturation and development post fertilisation
what is atresia?
- degeneration and resorption of follicles before they have reached maturity
- very few oocytes and follicles survive ovulation
- majority eliminated before birth
what are the signs of apoptosis in Graafian follicles `?
- Pyknosis and fragmentation of chromosomes and also wrinkling of nuclear envelope of oocyte
what happens to the pre-antral follicle?
- granulosa become cuboidal
- the theca and ZP start to become visible
what is the role of the zona pellucida ?
- contains many holes to allow for communication with granulosa cells
- is a glycoprotein layer composed of 4 main ZP proteins
- ## granulosa cell processes traverse ZP and contact the oocyte –> essential for egg nutrition
why are the cumulus cells important?
- involved in protection of the early embryo
what happens at the secondary follicle ?
- G cells proliferate and become 3/6 layers deep secreting follicular fluid in the process
- theca forms 2 distinct layers (Interna + externa)
what happens at the tertiary follicle ?
- G cells continually secrete follicular fluid
- oocyte surrounded by granulosa cells attached by cumulus oophorus
- 1 dominant follicle secreted per menstrual cycle
list the order of stages that occur during folliculogenesis
primordial follicle growth–> primary(pre-antral) –> secondary (early antral) –> tertiary (pre- ovulatory)
what is the action of FSH on the ovaries?
- stimulates development of follicles
- secretion of estradiol and ovulation
what is the action of LH on the ovaries?
- stimulates follicle maturation and dev of corpus luteum
- secretion of estradiol and ovulation
what is the role of 17b estradiol during puberty and menstrual cycle ?
- growth of body + sex organs (p)
- development of secondary sexual characteristics (P)
- follicle maturation (M)
- preparation/ thickening of endometrium for pregnancy (M)
- thinning of cervical mucus (M)
what roles does progesterone elicit ?
- at the uterus it completes the preparation of endometrium for Pregnancy
- at the breasts it stimulates development of mammary glands
what occurs during the follicular phase?
- follicular maturation
- endometrial proliferation
- oocyte release
what occurs during the luteal phase ?
- involves corpus lute
- endometrium is now prepared for blastocyst implantation
what stage signifies no pregnancy ?
menses
the menstrual cycle is?
- oocyte maturation followed by endometrial growth
- follicular phase then the luteal phase
- cyclical process with different levels of hormone production signifying each stage
what is the 2 cell hypothesis ?
- occurs during follicular phase (neg feedback)
- LH stimulates theca cells to produce androgens –> these androgens enter the neighbouring granulosa cells
FSH stimulates granulosa cells (via aromatase) to convert androgen to oestrogen (oestradiol) –> helps thicken the endometrium and thins cervical mucus
- LH stimulates theca cells to produce androgens –> these androgens enter the neighbouring granulosa cells
what occurs during the pre-ovulatory phase?
- stimulation of ovulation
- switching to +ve feedback by FSH/LH
- Dominant follicle has the highest FSH receptor density
- Granulosa cells in the dominant follicle express LH receptors
- High levels of oestrogen at mid cycle stimulate the hypothalamus to release GnRH –> +ve feedback
- Causes a surge in LH and FSH spike from the AG
when do you see a surge in LH and FSH levels?
during the pre-ovulatory phase of the menstrual cycle
what happens during the ovulation process ?
- changes in the follicle
- one dominant follicle secreted by ovaries
- Increase in the number of granulosa cells and the accumulation of follicular fluid
- Cumulus oophorus loosens
- Follicle wall weakens
- Proteases are produced
- Increased osmotic pressure
- Stigma forms —> all attribute to the process of ovulation
LH and FSH levels fal
what occurs during the luteal phase (post ovulatory)?
- formation of the corpus lute um stimulated by large surge in LH
- fibrin clot forms in ruptured follicle
what Is the role of LH in the luteal phase?
LH helps maintain the corpus luteum
LH and FSH stimulate progesterone and oestrogen production
Increased progesterone and oestrogen maintain the endometrium
This limits the dev of a new follice
what is luteolysis?
- 12 days post ovulation
- occurs if there is no hCG secreted by an implanting blastocyst -> corpus luteum degenerates forming the corpus albicans
what happens to estrogen and progesterone levels during luteolysis?
- levels fall removing the negative feedback on APG so the cycle can recommence -> cyclical process
what happens if pregnancy occurs?
- developing embryo produces hCG –> acts like LH to maintain the corpus luteum
what occurs at 6-7 weeks?
the placenta takes over production of progesterone
