Reproduction, Menstrual cycle and Spermatogenesis Flashcards
What three stages make up the menstrual cycle?
Follicular
Ovulation
Luteal
Which of the three phases have a constant duration and what is it?
Luteal phase
Lasts for 14 days
Which is the variable stage and by how much does it deviate?
Follicular
14 +/- 7 days
Which cells does LH bind to?
Theca cells
What does LH stand for?
Luteinizing hormone
What does the binding of LH trigger?
The release of androgens
Activation of progesterone
What does FSH stand for?
Follicle stimulating hormone
What does FSH bind to?
The granulosa cells surrounding the oocyte
What does the binding of FSH do?
Causes the conversion of androgens to oestrogen
Switches on the expression of LH receptors
What is a follicle?
An oocyte surrounded by follicular (granulosa) cells
What does FSH do to the follicle?
Causes growth in the granulosa cells, NOT the oocyte
When does the FSH and LH surge occur?
Usually day 14
Which hormone FSH or LH precedes the other?
FSH is first as it triggers LH receptor expression
When is the peak of LH usually recorded?
24-36 hours pre ovulation
Folliculogenesis
Creation of the follicles
How many follicles does a female foetus have?
7 million
By birth how many follicles does a female have?
2 million
BY puberty how many follicles does a female have?
0.5 million
During the early stages of follicular growth it is driven by gonadotrophin. True/False
False
Early stages is independent of gonadotrophins
When do follicles become dependant on gonadotrophins
When they reach a certain size
For a follicle to continue to grow what must occur?
It must become dependent on gonadotrophins during the FSH LH surge otherwise the follicles are lost.
If the follicle becoming dependent on gonadotrophins coincides with the FSH LH surge what happens next?
A number of follicles continue to develop, however only one (dominant) is used for ovulation.
What is the trigger behind the formation of the corpus luteum?
LH switching on progesterone production
How does progesterone cause the creation corpus luteus?
Triggers a proteolytic enzyme to break down follicular cells exposing the oocyte
What happens to the follicle cells surrounding the oocyte?
They are converted into luteal cells
What do luteal cells do?
They increase the amount of progesterone released
How else does LH cause an increase in progesterone levels?
It triggers angiogenesis, increases the blood flow to the area and in turn the amount of cholesterol.
Why is cholesterol important?
It is the building block of progesterone
If there is successful implantation of a fertilised egg what hormonal changes occur?
LH is reduced in favour of hCG
Why is hCG produced?
Acts in the same way as LH but has a longer half life
List some functions of oestrogen
Increases the thickness of the vaginal wall Regulates LH surge Reduces vaginal pH Increases Vaginal Lactic acid Decreased cervical mucous viscosity
By reducing vaginal pH and cervical mucous viscosity what does oestrogen do?
Creates an environment to better facilitate sperm penetration
List some function of progesterone
Maintains vaginal wall thickness
Relaxes myometrium
Taking into account the function of progesterone what may a reduction in progesterone towards the end of pregnancy result in?
Contraction of the myometrium, pushing the baby out.
What hormone is released by both genders from the the hypothalamus?
GnRH
In what pattern is GnRH released from the hypothalamus?
Released in a pulsatile manner
Why is the pattern of GnRH release important and more so in which gender?
Especially important in women
The frequency of pulses determines which hormone LH or FSH will be released predominantly.
Which hormone favours an increased frequency of GnRH release?
LH
Which hormone favours a decreased frequency of GnRH release?
FSH
What hormone causes an increased frequency in GnRH release?
Oestrogen
Which hormone causes a decreased frequency in GnRH release?
Progesterone
Which hormone exhibits both positive and negative feedback on the gonadal axis?
Estrogen
When levels surpass a set point oestrogen exhibits a positive feedback affect.
When oestrogen exerts a positive feedback affect, what happens?
LH and FSH surge
Formation of the corpus luteum
Progesterone release
What is the effect of progesterone on LH and FSH?
Exerts only negative feedback reducing levels
What does oestrogen do to LH and FSH levels?
Reduced FSH
Increased LH
In a male what does FSH do?
Causes testes to produce sperm
In a male what does LH do?
Causes testes to secrete testosterone
In regards to the gonadal axis what does testosterone exert?
Only negative feedback
Where does spermatogenesis occur?
Within the testes
How many sperm are produced each heart beat
1,000
What cells does FSH bind to?
Binds to Sertoli cells
Upon Sertoli cells being bound to by FSH what occurs?
Triggers the stem cells to differentiate into spermatoza
What cells are stimulated by LH
Leydig cells
What is the function of leydig cells?
Secrete testosterone into the blood and the testes
What happens to most the testosterone released by leading cells?
90% is taken up by sertoli cells
What two functions does testosterone have within the testes?
Maintains blood testes barrier
Stimulates the release of mature sperm cells
