L44 Endocrine Control of Reproduction Flashcards
Where is gonadotropin-releasing hormone (GnRH) produced and what does it do?
Produced in median eminence of hypothalamus.
Stimulate secretion of gonadotropins (LH and FSH) from anterior pituitary.
Why is GnRH released in pulses (pulsatile secretion)?
Gonadotropin (LH/FSH) levels are replenished in the pituitary gland between GnRH pulses.
It is very important for the hypothalamus to secrete GnRH in pulses. What happens if too much GnRH is produced?
Gonadotropin levels (LH and FSH) in the pituitary will be depleted and insufficient to produce their desired effect.
It is very important for the hypothalamus to secrete GnRH in pulses. What happens if too little GnRH is produced?
Leads to inadequate gonadotropin (LH/FSH) production & deficiency.
Where does follicle-stimulating hormone take effect?
Sertoli cells
Affects production of Androgen Binding Protein (transports testosterone in blood) and directly affects germ cells.
Causes follicle growth and follicular secretion of oestradiol and inhibin (-ve feedback).
Where does leutenising hormone take effect?
Leydig cells, which then produce testosterone.
LH initiates meiosis I to produce secondary oocyte and first polar body.
LH stimulates testosterone production in leydig cells. What does testosterone do?
Stimulate germ cells
Affects bone, skin, hair, and the accessory sex organs (post-puberty)
Converted to dihydrotestosterone (DHT), which affects prostate; and oestradiol, which is important in epiphyseal closure and the reproductive system
How is FSH production regulated?
- GnRH
- Negative feedback: inhibin (Sertoli cells)
- Positive feedback: activin and follistatin
How is LH production regulated?
- GnRH
- Negative feedback: testosterone
What are the 4 phases of the ovarian cycle?
- follicular phase
- ovulatory phase
- luteal phase
- menstruation
Which phase of the ovarian cycle is the longest?
Follicular phase (10-16 days)
or
luteal phase (14 days)
Which phase of the ovarian cycle is the shortest?
Ovulatory phase (36 hours)
What are the 2 main steroids involved in regulation of the ovarian cycle?
Oestradiol and progesterone
What is the relationship between levels of FSH and levels of oestradiol?
FSH levels drop as levels of oestradiol increase.
What happens during the luteal phase of the ovarian cycle?
Empty tertiary follicle collapses - granulosa cells invade and luteinise to form ‘corpus luteum’ (an endocrine structure).
Towards end of luteal phase, macrophages destroy corpus luteum and the endometrium begins to disintegrate (menstruation).
FSH rises again as negative feedback is lost.
