Ovarian Function Flashcards
Describe the formation of the female reproductive system pre 7 weeks
Development is indifferent before 7 weeks - same as males
PGCs give rise to the gametes
Appear around week 3 in the epithelium of the yolk sac
Weeks 3-7:
- proliferate by mitosis
- migrate by amoeboid movement to region of dorsal wall that will form the gonads (genital ridges)
- migration is guided by chemotaxis
What determines development post 7 weeks?
no SRY gene –> female gonads develop
Describe the formation of the ovary
- same influences of cells as seen in males
- sex cord cells do not penetrate deeply, closer around oogonia (PGC) –> primordial follicles –> granulosa
- mesonephric cells - vasculature/thecal cells
- there is no endocrine activity during ovarian development in the female foetus
- further developement is dependent on the presence of normal germ cells
What happens to ovaries in turners syndrome?
XO karyotype
normal oocyte developement reuiqres both X chromosomes –> oocyte death
- normal ovary development requires normal germ cells –> ovarian dysgenesis
How are adult ovaries different? x2
produce oocytes
produce hormones
What is the sequence of oogenesis in terms of cell names?
primordial germ cell oogonium primary oocyte secondary oocyte mature/tertiary oocyte
What is the timing of entry into meiosis in males and females?
What is this controlled by?
males = meiosis is initiated post puberty
females = oogonia enter mouses during fatal period -controlled by Stimulated by retinpic act 7 gene (Stra8) retinoic acid
Cytochrome P450 mediated metabolism of RA
IN FEMALES
- during foetal period retinoic acid builds up, activates Stra8 and initiates meiosis
IN MALES
- meiosis isn’t until after puberty so cytochrome P450 metabolises retinioic acid so not enough to activate Stra8 gene
Oogenesis is not continuous.
Describe the two mieotic blocks
Primary oocyte is arrested at Prophase I (in utero)
Secondary oocyte is arrested at Metaphase II (puberty)
Meiosis completed post-fertilisation
Females are born with a finite number of oocytes, why?
all oogonia enter meiosis before birth - no ovarian stem cells
Female germ cells undergo clonal expansion then reduction (atresia?
When are there the most?
Proliferation up to 6 months after conception
Then apoptosis from then til menopause
Also ovulation depletes stores
Meiotic devisions are assymetrical
Describe how
Each meiotic division leads to production of a polar body
- both are relativity small and contain little cytoplasm
- excess genetic material being discarded by the egg
- 1st polar body is released just before ovulation
- presence of 2nd polar body signifies fertilisation and the complete of 2nd meiotic division
What are the two somatic cells in the follicles?
granulosa and theca
What are the stages of follicular development?
primordial follicle
primary follicle
secondary follicle
graafian follicle
Describe the primordial follicle
Primary occyte surrounded by single layer of flattened granulosa (foetus)
From puberty, a few primordial follicles begin to grow each death
- oocyte begins to grow and synthesises proteins needed for oocyte maturation and first few days of development post-fertilisation
- independent of menstrual cycle
Describe the primary follicle
- granulosa cells become cuboidal; theca and zona pellucida become visible
- independent of menstrual cycle
Describe the formation of the zona pellucida
Glycoprotein layer
granulosa cell-processes traverse through into the oocyte
ZP is important for sperm binding, induction of acrosome reaction and protection of the early embryo
Describe the secondary follicle
- granulosa proliferate; theca forms two distinct layers - internal and externa (5-15 follicles per cycle)
- dependent on menstrual cycle
Describe the tertiary follicle
- Granulosa secrete follicular fluid
- oocyte surrounded by laser of corona radiate and on stalk of cumulus cells; only 1 dominant follicle/cycle
- dependent on menstrual cycle
Describe/Draw the fluctuations in hormones during the menstrual cycle
FSH = rises then falls during preovualtory phase, peaks at ovulation then decreases post ovulation LH = low until peak at ovulation Oestrogen = rises pre ovulation, peaks just before LH peak, then decreases post ovulation Progesterone = low until post ovulation where is reins then falls (menses)
Describe extra-ovarian hormonal action (HPGaxis)
From puberty
- hypothalamus =pulsatile GnRH
Anterior pituitary
- FSH - acts on ovary FSHR, stimulates development of follicles
- LH - acts on ovary - LHCGR, stimulates follicle maturation, ovulation and development of corpus luteum
Describe the functions of the ovarian hormones
Progesterone
Oestrogen
Cytokines
Oestrogens
- growth of body and sex organs at puberty
- development of secondary sexual characteristic
- Reproduction: follicle maturation, preparation of endometrium for pregnancy - proliferation
- Thinning of cervical mucus
Progesterone
-produced by corpus lutes
- acts on uterus - completes perparation and maintains endometrium for pregnancy
Numerous Cytokines
What is the two cell hypothesis for oestrogen production?What is the role of LH and FSH
Testoterone is produced by theca cells and diffuses to granulosa where it is converted to oestrogen by aromatase
- LH increases cholesterol uptake by the theca
- FSH increases aromatase activity
What occurs in the follicular/proliferative phase of the menstrual cycle
- hypothalamus secrete GnRH
- a. pituitary secretes FSH
- up to 15 follicles are ‘rescued’
- granulosa and theca cells develop in growing follicle
- produce oestrogen (thickens endometrium/thins cervical mucus)
- oestrogen suppresses FSH production
- granulosa in dominante follicle expresses LHCG receptor
- high levels of oestrogen at mid cycle causes LH surge from a. pituiary
Describe what occurs during ovulation
- Resumption and completion of Meiosis I
- Secondary oocyte entered meiosis II arresting at metaphase
- increase in follicular fluid and number of granulosa
- cumulus oophorus loosens
- follicle wall weakens - MMPs, plasminogen, collagenase, gelatinase
- ovulation - oocyte, ZP, cumulus
- cumulus-oocyte complex picked up by timbre of uterine tube
- 30-36 hours
Describe what happens during the luteal/secretory phase
- corpus luteum formed
- granulation - large lutein cells - progesterone and oestrogen
- theca - many disperse to stromal tissue - small lutein cells - progesterone and androgens - LHCGR
- endometrium becomes secretory
- negative feedback - progesterone and oestrogen, LH/FSH levels low
Describe what happens during pregnancy
- trophoblast cells of embryo produce hCG - binds LHCGR on lutein cells maintains the corpus luteum
- produces progesteron and oestrogen to support pregnancy
- oestrogen/progesterone suppresses ovulation
- 6/40 weeks - placenta takes over and the corpus lute degenerates –> corpus albicans
What is luteolysis?
- around 12 days - if there is not hCG production from an embryo, the corpus luteum degenerates forming the corpus albicans
- progesterone and oestrogen levels fall, removing negative feedback and the cycle recommences
