Reproductive Endocrinology Flashcards
Cell division
Chromosomes replicate and create identical copies
Mitosis
2 daughter cells receive identical genetic material to parent cell
Meiosis
4 daughter cells; haploid; different genetic information/non-identical cells
Sex vs gender vs gender identity
Media mistakenly uses these somewhat interchangeably
Sex = reproductive category
Gender = societal role
Gender identity = sense of inner self
SRY gene
Gene present on Y chromosome that produces the sex-determining region of Y protein
Genetic sex
XX or XY
Gonadal sex
Gonads develop into testes or ovaries
Phenotypic sex
Reproductive tract and external genitalia
Gonads between sexes
Gonads automatically develop into ovaries, or DIFFERENTIATE into testes
Alpha-5 reductase deficiency
This enzyme usually converts testosterone into DHT, which is required for the development of male external genitalia
This deficiency means testes will be formed internally but no external genitalia will develop so the person will be genetically male and phenotypically female
Androgen Insensitivity Syndrome
Genetically male but outwardly female genitalia
Y chromosome differentiates gonads into androgen-[rpducing testes but other tissues are non-responsive to DHT and continue along the (default) female path
Outwardly female but internal testes instead of ovaries, and no womb
Spermatogenesis
Begins at puberty and continues until ~70 years
It’s an ~64 day process
3 main phases
3 main phases of spermatogenesis
1st = mitotic division – produces large numbers of cells, whilst nuclear division is complete cytoplasmic division is incomplete (resting primary spermatocytes)
2nd = division produces genetic diversity and halves chromosome number - meiosis
3rd – cytodifferentiation packages the chromosomes for effective delivery to the oocyte
Role of the sertoli cells
Protective barrier between seminiferous tubules and general circulation
Maintain stable conditions in lumen
Protection from immune system
Produce fluid in lumen & regulate composition
Site of action for control of spermatogenesis by testosterone and FSH.
Provide nourishment for sperm for development.
Engulf cytoplasm extruded from spermatids during remodelling
Secrete inhibin -ve feedback of FSH release.
Spermatogenesis is controlled by what hormones?
GnRH
Follicle Stimulating Hormone (FSH)
Luteinising hormone (LH)
Inhibin
Testosterone
Where are the hormones that control spermatogenesis from?
Hypothalamus
Anterior pituitary
Testes
Role of testosterone
Promotes spermatogenesis
Male secondary sex characteristics
Maintains accessory glands and organs in reproductive system
Stimulates muscle and bone growth
Drives and maintains sexual behaviours
Negative feedback loop to hypothalamus
Oogenesis
Formation of oocytes (gametes) in the ovaries (inside follicles)
Process starts in the foetus and then stops until puberty, when it restarts until around 50/51 (essentially til menopause)
Part of the monthly ovarian cycle
Oogenesis - pre-birth
Primordial germ cells migrate from the yolk sac to the ovaries and differentiate into oogonia
Oogonia are diploid stem cells that divide mitotically to produce millions of germ cells called primary oocytes (2n)
Primary oocytes begin meiosis I, until prophase 1 and remain at this stage until puberty
They are found within primordial follicles within ovaries (the fundamental functional unit of the ovary)
Oogenesis - at puberty
Several primordial follicles are stimulated each month.
Maturing oocytes within these maturing follicles complete Meiosis I to bring about one 2o oocyte (haploid 1n) within a 2o follicle (mature Graafian follicle) and finally a pre-ovulatory follicle at the point of ovulation.
2o oocyte is released (at ovulation) in metaphase of Meiosis II
If fertilisation occurs, the 2o oocyte is a mature ovum
What happens to follicles if oocyte is fertilised?
Oogenesis and follicular development
Separate but interrelated events
Post-ovulation, in the ovary:
The mature Graafian follicle has become a corpus luteum
Temporary structure BUT essential to establish and maintain pregnancy
After approx. 14 days, if the 2o oocyte is not fertilized, the corpus luteum undergoes luteolysis; it degenerates into a mass of fibrous scar tissue (corpus albicans).
Phases of the ovarian cycle
Follicular
Luteal
Follicular phase
Primary follicle develops into theca then antrum, moving towards ovulation.
Hormone levels show FSH is higher than LH as it’s competing to develop follicles. LH is very steady up until positive feedback and a sudden spike called the LH surge, which is needed for the release of an egg
Luteal phase
Corpus luteum forms and matures and the corpus albicans
Hormones both at their lowest stage of the cycle
The uterine (menstrual) cycle - hormones
As follicles develop oestrogen and inhibin increase
Progesterone really peaks in the second part of the cycle
The uterine (menstrual) cycle - occurring in the uterus
Lining is shed
Proliferative phase
Secretory phase
Follicular phase - brain
Hypothalamus releases GnRH, which activates anterior pituitary
FSH and LH released and act on ovaries -> oestrogen, with a positive feedback loop until a threshold is reached and a negative feedback loop replaces it
**Negative feedback back to hypothalamus and stuff
**related to inhibin but check on the pathway/explanation
LH surge
**
Luteal phase (post-ovulation) in the brain
Positive oestrogen feedback loop and negative progesterone feedback loop (I think **)
Late luteal phase - if no fertilisation
Corpus luteum degenerates and 12 days post-ovulation it becomes non-functional
Progesterone and oestrogen levels fall markedly
Blood supply to endometrial functional layer is restricted, endometrial tissues deteriorate resulting in menstruation
BUT…Drop in oestrogen and progesterone levels stimulate GnRH release, stimulating FSH and LH release and the next cycle begins….
Application of reproductive physiology - contraceptive pills
Combined oral contraceptive pill contains 3 hormones: oestrogen and progesterone. Giving these both at the same time every day prevents the LH surge, so no ovulation, so no pregnancy.
No menstrual bleeding/lining shedding due to progesterone
Stopping taking the pill can cause a withdrawal bleed, where any lining of the the womb is suddenly shed
Application of reproductive physiology - trying to conceive
Ovulation tests can check for LH or oestrogen
