Hypothalamic-Pituitary Axis and The Menstrual Cycle Flashcards
What 2 hormones are secreted from the anterior pituitary gland in this axis?
LH and FSH
How are LH and FSH secreted? In response to what?
In pulses, in response to GnRH from the hypothalamus
What 2 hormones exert negative feedback on LH secretion and have multiple peripheral effects?
Testosterone and oestrogen
What exerts negative feedback on FSH secretion?
Inhibin
What is the function of LH in males? Where does it exert its action?
Production of testosterone from the Leydig cells of the testes
What type of receptor does testosterone act on?
Nuclear androgen receptors
What are the roles of testosterone once it has bound to its receptor?
Male secondary sex characteristics, anabolism, maintenance of libido, aids spermatogenesis
Testosterone circulates, mainly bound to what?
Sex-hormone binding globulin
Testosterone feeds back to inhibit secretion of what?
GnRH and LH
Where does FSH act in males?
Sertoli cells (spermatogenic) in the seminiferous tubules
What is the action of FSH at the Sertoli cells?
To produce mature sperm and produce inhibins A and B
What is the function of inhibin?
Feeds back to the anterior pituitary to decrease FSH production
What peptide counteracts inhibin?
Activin
From where exactly in the hypothalamus is GnRH released?
Arcuate nucleus
Describe the production of GnRH from the hypothalamus in an adult female?
A menstrual cycle of 28 days upon the activity of GnRH. Pulses are released at about 2 hour intervals.
Where does LH act in a female?
Theca cells
Where does FSH act in a female?
Granulosa cells
What is the function of LH in a female?
Stimulates ovarian androgen production (at the theca cells)
What has to occur for ovarian androgen production to occur?
ATP - cAMP
What are the 3 functions of FSH in a female?
Stimulate follicular development and activity of aromatase. Also stimulates release of inhibin from ovarian stromal cells.
What is aromatase?
An enzyme required to convert androgens to oestrogens
What must occur for aromatase to be produced?
ATP - cAMP
What hormone and enzyme mix to produce oestrogen?
Aromatase and androgen
What chemical is the basis needed to produce oestrogen?
Cholesterol
What is cholesterol converted to in the cycle to produce oestrogen?
Pregnenolone and then progesterone
What exhibits a) positive feedback and b) negative feedback, on the change from pregnenolone to progesterone?
a) Inhibin (+), b) Activin (-)
What is progesterone converted into which can finally be converted to oestrogen?
Androstenedione
What exerts positive feedback on the conversion of androstenedione to oestrogen?
Activin
When in the menstrual cycle does ovulation usually occur?
Day 14
The follicular stage of the menstrual cycle begins when oestrogen levels are?
Low
What stimulates the follicle to develop in the follicular stage of the menstrual cycle?
FSH
What happens to the granulosa cells around the egg in the follicular stage of the menstrual cycle?
They enlarge, releasing oestrogen
What does the increased oestrogen by the end of the follicular stage of the menstrual cycle do?
Causes thickening of the uterine lining
What hormone level peaks at the beginning of the follicular stage of the menstrual cycle?
FSH
What happens to oestrogen levels in the follicular stage of the menstrual cycle?
They start low and are raised at the end
What is the relative concentration of progesterone throughout the follicular stage of the menstrual cycle?
Low
When does ovulation occur?
At the peak of follicular growth, in response to an LH surge
What happens after the LH peak in the ovulation stage of the menstrual cycle?
The oocyte is released into the ampulla of the fallopian tube
What hormone has a large peak at the beginning of ovulation?
LH
What hormone has a small peak at the beginning of ovulation?
FSH
In the luteal phase of the menstrual cycle, why are the remaining granulosa cells around the egg yellow?
They absorb a lot of keratin
What are the remaining granulosa cells known as in the luteal phase?
Corpus luteum
What hormone does the corpus luteum secrete?
Progesterone
When is there a peak of oestrogen in the luteal phase?
First 1/3rd of the phase
What is the major hormone of the luteal phase?
Progesterone
What hormones are responsible for endometrial proliferation in preparation for implantation?
Oestrogen initially and then progesterone
If implantation does not occur, what happens to the corpus luteum?
It regresses, so progesterone and inhibin levels fall so that the endometrium is shed
What hormones are increased again if no pregnancy occurs at the end of a menstrual cycle?
GnRH and FSH
What hormone will be produced at the end of the menstrual cycle if a pregnancy has occurred?
HCG
How is the ovary attached to the pelvic side wall?
Infundibulopelvic ligament
What are the two parts of an ovary? Which contains the follicles?
Outer cortex and inner medulla, the cortex contains the follicles
What components make up the uterus?
Body of the uterus and cervix
Oestrogen acts synergistically with what other hormone?
FSH
Where can oestrogen be synthesised?
Ovaries, but also adrenal glands, fat and bone
What are both inhibin and activin and where are they found?
Peptides in follicular fluid
