Reproductive Physiology Flashcards
What are the key reproductive hormones?
GnRH, LH, FSH, oestrogen, progesterone, testosterone
What are the two gonadotropic hormones secreted by the pituitary gland?
Follicle stimulating hormone (FSH), luteinizing hormone (LH)
What is the function of FSH?
Males = causes testes to produce sperm Female = causes growth of ovarian follicles and causes ovary to secrete oestrogen
What is the role of LH?
Males = causes testes to secrete testosterone Females = causes ovulation and cause progesterone production by the corpus luteum
What is GnRH responsible for?
The release of FSH and LH from the anterior pituitary
What is GnRH?
Neuropeptide hormone synthesised and released from GnRH neurone within the hypothalamus
How is GnRH secreted in males?
Secreted in pulses at a constant rate
How is GnRH secrete in females?
Frequency of pulses varies during menstrual cycle = pulses every 1-2hrs during early follicular phase, less frequent in late follicular phase and decreases again to every 4hrs during luteal phase
What do high frequency GnRH pulses cause?
Stimulate LH pulses
What do low frequency GnRH pulses cause?
Stimulate FSH release
How can oestrogen affect GnRH pulsatility?
Oestrogen concentrations above a certain threshold will increase GnRH pulsatility driving the release of LH
What affect does increasing the progesterone concentration have on GnRH pulsatility?
Reduced the frequency of GnRH pulses
What is appropriate modulation of LH pulse frequency essential for?
Pubertal maturation and reproductive function
What is the onset of pubertal growth associated with?
Steady acceleration in GnRH pulsatility = peak at night (in boys this diurnal rhythm results in peak testosterone in the early morning causing erections)
What is activation of the GnRH a central mechanism of?
Delayed puberty = manifest in girls as no puberty by 15, manifests in boys as no sign of testicular development by age 14
What are some reproductive disorders associated with abnormalities of GnRH pulse frequency?
Hypothalamic amenorrhoea, anovulation
What hormones regulate GnRH pulsatility?
Oestrogen and progesterone
Which neurone regulate GnRH?
Kisspeptin neurons = GnRH producing Britons don’t have receptors for oestrogen and progesterone
What are the phases of the menstrual cycle?
Follicular (proliferative) phase = variable, typically 14 days +/- 7 days
Luteal (secretory) phase = more constant
What is the follicular phase of menstruation characterised by?
Follicular growth
What does FSH stimulate in the menstrual cycle?
Growth of ovarian follicles = associated with an increase in oestrogen levels
What does rising oestrogen levels do during the menstrual cycle?
Exert a negative feedback regulation (at level of hypothalamus and pituitary) to temporarily lower FSH levels
What happens once oestrogen reaches a certain level during the menstrual cycle?
Exerts a positive feedback regulation resulting in an increase in FSH levels and the LH surge
What does the LH surge cause in menstruation?
Eventually leads to ovulation and regulated the formation of the corpus luteum and progesterone production and secretion
How does increasing progesterone levels in menstruation decrease LH secretion?
By influencing GnRH
What does a follicle consist of?
An oocyte surrounded by follicular cells (granulosa and theca cells)
What does follicular growth entail?
An increase in the number of follicular cells and accumulation of follicular fluid = causes an increase in the diameter and overall size of the follicle
What changes occur in the endometrium during menstruation?
Thickens under influence from oestrogen and becomes a secretory tissue under the influence of progesterone
What do the early stages of folliculogenesis occur independent of?
Gonadotrophins
When does a follicle become gonadotrophin-dependent?
Once it reaches a certain size = 2-5mm diameter
What happens if the follicle becoming gonadotrophin-dependent doesn’t coincide with rise in FSH during early follicular phase?
Follicle is lost
What is the dominant follicle?
Follicle selected for
the ovulation
What causes the number of follicles to continue to grow during folliculogenesis?
FSH = totally FSH dependent and if removed, the follicle will be lost
What cause FSH levels to drop initially during folliculogenesis?
Rising oestrogen levels (associated with follicle growth) = occurs due to negative feedback at HPA axis
What follicle is able to survive the drop on FSH levels?
Likely to have the most FSH receptors and the highest vascularity
What can be used to predict the timing of ovulation within a cycle?
The LH surge = surge preceded ovulation by 34-36hrs
What threshold of oestrogen is needed for the LH surge to occur?
200pg/ml needed to increase GnRH pulsatility and hence LH surge
What happens to progesterone levels during the LH surge?
They increase
Why is it crucial for progesterone levels to rise for ovulation?
Progesterone stimulates expression of enzyme that help breakdown of the follicular wall leading to the release of the oocyte
What is the formation of the corpus luteum influenced by?
LH
What do luteal cells of the corpus luteum form from?
Granulosa and theca cells
Why do progesterone levels increase during the formation of the corpus luteum?
LH stimulates angiogenesis = ensures efficient delivery of cholesterol
LH stimulates enzymes involved in conversion of cholesterol to progesterone
What are the functions of oestrogen?
Increases thickness of vaginal wall, regulates the LH surge, reduces vaginal pH through increase in lactic acid production, decreases viscosity of cervical mucus to facilitate sperm penetration
What kind of roles does progesterone have?
Pro-gestation = maintains pregnancy
What are the functions of progesterone?
Maintains thickness of endometrium
Responsible for infertile thick mucus = prevent sperm transport and help prevent infection
Relaxes the myometrium = functional progesterone withdraws thought to regulate birth
What is the process of making sperm called?
Spermatogenesis =!occurs within testes, entire process takes 70 days
What controls spermatogenesis?
Endocrine hormones = LH, FSH, testosterone
When does spermatogenesis begin?
At puberty and occurs for 60 years or more
What properties does sperm need to have?
Must be motile to
successfully traverse the female reproductive tract
How are the testicles organised?
Extratubular compartment = interstitial and intravascular component
Intratubular compartment = Sertoli cells and germ cells (different stages of development)
What are the endocrine and paracrine factors that influence spermatogenesis?
Endocrine = LH and FSH Paracrine = testosterone and inhibin
How much of the testosterone from the circulation do Sertoli cells take in?
90% = testosterone in testes in 25-125 fold greater than in serum
What is the role of testosterone during spermatogenesis?
Maintains integrity of blood-testes barrier, release of mature spermatozoa from Sertoli cells by influencing peritubular myoid cells
What roles does dihydrotestosterone play in males?
Enlargement of male sex organs, secondary sexual characteristics, anabolism
What do Sertoli cells in the seminiferous tubule secrete?
Androgen binding globulin (ABG) and the inhibin
What factors stimulate spermatogenesis?
FSH together with testosterone
What effect does inhibin have on FSH?
Decreases FSH secretion
What stimulates testosterone secretion?
LH
What does testosterone decrease the secretion of?
Release of GnRH and LH
