Reproduction: Physiology and Biochemistry Flashcards
Key Reproductive hormones (6)
GnRH (gonadotrophin releasing hormone) LH (luteinizing hormone) FSH (follicle stimulating hormone) Oestrogen Progesterone Testosterone
Gonadotropic Hormones (2) released by pituitary gland
Follicle Stimulating Hormone
Luteinizing Hormone
Follicle Stimulating Hormone role
male: causes testes to produce sperm (spermatogenesis)
Female: causes growth of ovarian follicles (oogenesis) and causes ovary to secrete oestrogen
Luteinizing Hormone role
male: causes testes to release testosterone
Female: causes ovulation and it causes progesterone production by the corpus luteum (progesterone produced from cholesterol)
Gonadotrophin Releasing Hormone (GnRH) role
Responsible for the release of LH and FSH from the anterior pituitary
Its a neuropeptide hormone synthesised and released from GnRH neurons within hypothalamus
GnRH release
Released in a pulsatile manner
Males: secreted in pulses at constant frequency
Females: frequency of pulses varies during menstrual cycle
High frequency GnRH pulses
Stimulates LH release
Low frequency GnRh pulses
FSH release
Effect of oestrogen on GnRH pulsatility
Oestrogen concentration above a certain threshold will increase pulsatility
- drive release of LH
Effect of progesterone on GnRH pulsatility
Progesterone increase reduces pulsatility
- drive release of FSH
Pubertal maturation on GnRH pulsatility
Onset of pubertal maturation results in a steady acceleration in GnRH pulsatility
Activation of GnRH pulse frequency in central mechanism associated with delayed puberty
GnRH regulation
Regulated by kisspeptin
GnRh neurons do not contain a receptor for oestrogen or progesterone
Oestrogen and progesterone influence kisspeptin neurons that then subsequently release GnRH neurons.
menstrual cycle phases
Follicular Phase
- proliferative phase
- variable
- typically 14 days +/- 7 days
- Characterised by follicular growth
Ovulation
Luteal Phase
- secretory phase
- Constant at 14 days
Menstrual Cycle - stages
FSH stimulates growth of ovarian follicles (associated with increased oestrogen)
Rising oestrogen levels exert a negative feedback regulation to lower FSH levels.
Once oestrogen reaches a certain concentration it exerts a positive feedback regulation
- Increase FSH levels
- Increase LH (LH surge)
LH surge eventually leads to ovulation and regulates formation of corpus luteum and progesterone production and secretion
Increasing progesterone decrease LH secretion by influencing GnRH pulsatility
Follicle
Consists of an oocyte surrounded by follicular cells (granuloma and theca)
Follicle Growth
Increase in number of follicular cells
Accumulation of follicular fluid
–> Increase in diameter and overall size of follicle
(Oocyte remains dormant)
Oestrogen impact on endometrium
Endometrium thickens
Progesterone impact on endometrium
Endometrium becomes a secretory tissue
Follicluogenesis
Early stages of growth occur independently of gonadotrophin
Once follicle reaches certain size (2-5mm in diameter) it becomes gonadotrophin dependent
Number of follicles will continue to grow under influence of FSh but only 1 will be selected for ovulation
Totally dependent on FSH levels (if removed follicles are lost)
Theca cell
LH hormones cause theca cells to convert cholesterol to androgens
Granuloma cell
FSH hormones cause granuloma cells to convert androgen to oestrogen (requires aromatase)
LH surge
LH surge precedes ovulation by 34-36 hours
LH surge requirements
Threshold of oestrogen (200pg/ml) us required for an increase in GnRH pulsatility and therefore LH surge
LH surge and progesterone
Increase LH levels leads to increase in progesterone levels
Crucial for ovulation as progesterone stimulates expression of enzymes that help breakdown follicular wall to release oocyte.
