Repro Flashcards
Describe oogenesis
- The formation of gametes in the ovaries.
- Starts in utero, in developing fetus
- Primordial germ cells migrate from the yolk sac to the ovaries where they differentiate into oogonia
What are Oogonia?
What is a germ cell
- Diploid stem cells that divide mitotically to produce millions of germ cells
- Cell containing half the number of chromosomes of a somatic cell and able to unite with one from the opposite sex to form a new individual; a gamete.
What happens to oogonia produced in early fetal development before birth
- most degenerate and die
- few develop into primary oocytes (immature egg) before birth
- these enter first phase of mitotic division Prophase 1
- Don’t complete this until after puberty
- These can be found in primordial follicles
- female germ cells produce a primordial germ cell (PGC), which then undergoes mitosis–> oogonia –> oogenisis –> primary oocytes –> prophase
Development of what 2 things occurs at the same time?
- follicle
2. gamete
What happens at puberty?
- Several primordial follicles will be stimulated each month
- Follicles develop from primary to sec to tertiary follicle
- Oocytes develop from primary to secondary
What happens at point of ovulation?
- Tertiary follicle ruptures to expel secondary oocyte into pelvic cavity, normally to be swept into fallopian tube
- At ovulation secondary oocyte will complete meiosis 1
What is Corpus Luteum?
- In ovary the mature tertiary follicle (Graafian) becomes CL
- It is formed in an ovary at the site of a follicle, or sac, that has matured and released its egg
- Temporary structure essential for establishing and maintaining pregnancy in females as secretes progesterone
- if sec oocyte not fertilised CL stops secreting progesterone and degenerates into corpus albicans
What does the pituitary gland look like?
- Cherry red circle ventral aspect of brain
2. Protrusion off the bottom of the hypothalamus at base of brain
Outline the development of the pituitary
- Comprises 3 different structures: Anterior pituitary, intermediate lobe, Posterior pituitary
- AP and IL derived from upgrowth extension endoderm of buccal cavity
- PP derived from neural ectoderm, downgrowth extension of hypothalamus
- Pituitary is 2 fused glands
- IL developmentally is same as AP but is distinct anatomic area with distinct function. Releases MSH (melanin, skin pigment produced)
Posterior pituitary does not …….
NOT sysnthesise anything
It releases substances that are synthesised in neuroendocrine cells in the hypothalamus
What do neuro endocrine cells in the hypothalamus do to the anterior pituitary
- act on AP, which releases tropic hormones = released into general circulation into another endocrine gland = amplify signal
What hormones does the anterior pituitary secrete?
FLAT PIG
1. FSH = follicle stimulating hormone (testes and ovary)
2. LH = (T and O) = leutinising hormone. triggers ovulation and development of the corpus luteum
3. ACTH = Adreno corteco tropic hormone
4. TSH = thyroid stimulating hormone
5. GH = growth hormone
6. Prolactin (mammary gladns)
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Exception of prolactin, everything else affects another endocrine gladn
Difference between long adn short feedback
- Short = hormones act back into system nearest to them e.g. release of pituitary hormone affects hypothalamus
Where is ADH synthesised?
HYPOTHALAMUS
What day is day 0 and why?
- the first day of menstrus
2. straight forward reference point
With regards to ovulation what hormones are we talking about and where from?
- GnRH from hypothalamus
- FSH and LH from AP
- Ostrogens and progesterone and inhibin from ovary
What does GnRH cause
- release of FSH and LH from pituitary whihc affects gonads
- FSH stimulates the growth and recruitment of immature ovarian follicles
- LH = variety - productions of precursors of oestrogen, stimulates maturation of ovarian follicles, triggers ovulation and development of the corpus luteum
What role does hypothalamus have on AP
- regulated output from AP
2. BRAIN CONTROLS REPRODUCTION
If there was a graph showing peaks of GnRH production, where would the peaks of LH and FSH be?
- FSH peak little behind GnRH and little lower
- LH on/ little behind FSH peak and huge peak
LH and FSH released from pituitary at same time but FSH = longer half life therefore diff shape
Talk through from hypothalamus to the 3 hormones released
- hypothalamus secretes GnRH
- AP secretes FSH and LH
- FSH acts of developing follicles, releasing inhibin and oestrogen
- LH acts of corpus luteum releasing progesterone AND on dev follicles releasing inhibin and oestrogen
What type of endocrone gland are both follicles and corpus luteum
- TRANSIENT (come and go away)
2. So ovary (apart from housing female gamete) is a collection of transient endocrine glands
What negative feedback effects does progesterone, inhibin and oestrogen have?
- Progesterone ALWAYS neg feedback = inhibits GnRH release and LH
- Inhibin neg feedback on FSH
- Oestrogen usually neg feedback on LH and GnRH and FSH
What is the follicular phase?
- first 2 weeks of human menstral = follicles developing before ovulate
What is the end of the follicular phase?
- positive feedback
- oestrogen starts producing more GnRH = more LH, FSH inhibited by inhibin
- more and more LH = inc maturation of follicle and inc precursors of oestrogen = more and more = positive feedback
- this continues until LH surge = ovulation
Important changes in hormones to remmeber
- LH surge JUST before ovulation always as it causes it
- first half of cycle = inc oestrogen as this drives LH surge, peak close and before LH surge
- same peak of oestrogen = little peak in FSH as huge inc in GnRH
- ## Progesterone rise AFTER ovulationThis occurs due to neg and pos feedback occurring at pituitary and hypothalamus
