Lecture 30- Hypothalamic Regulation of Reproductive Function Flashcards
What is the basic hypothalamus- pituitary axis corresponding to changes in the gonads?
Hypothalamus= GnRH
Anterior Pituitary= LH/FSH
Target organ= Gonads which produce testosterone or estrogen (note: there are other hormones produced this just the basic idea)
What two processes do LH and FSH effect in the gonads?
gametogenesis: sperm production in the
testes and ova development in the ovary
steroidogenesis: hormone production
What hormones are produced in the female gonads as opposed to the male gonads?
male: testosterone and inhibin
female: estrogen, progesterone, inhibin
What feature of GnRH neurons means it’s easy for hormones to enter the blood stream to the anterior pituitary?
They are highly fenestrated
How does the release of GnRH hormone differ between male and females?
Pulsatile for males
More of a surge present for females
In the Hypothalamo-Pituitary-Gonadal (HPG) axis what hormones provide feedback to the brain? How is this feedback special?
estrogen, progesterone, testosterone feedback to the hypothalamus
Special as this can either be positive or negative feedback depending on the circumstances
Where in the testes is sperm stored once it is made?
Epididymis
Where does spermatogenesis (the production of sperm) occur in the testes?
Seminiferous tubules
What cell types are there in the seminiferous tubules of the male teste? What are each of their basic roles? What percentage of each cell type is there?
80% = sertoli cells= support cells
20%= leydig cells= testosterone production
Draw the hormone loop/ feedback mechanism invovled in male reproduction….
Answers on slide
What interaction occurs between the Leydig and Sertoli cells/ the processes occurring in each cell….
Leydig cell:
LH binds to a receptor
Causes the production of adenylyl cyclase
This means ATP can be converted to cyclic AMP
PKA is then formed which then enters the nucleus
This allows for new proteins to be synthesized one of which is an enzyme that aids the conversion of cholesterol to testosterone
Sertoli cell:
FSH binds to a receptor
Follows same process as before leading to the production of the protein aromatase
Aromatase converts testosterone (which has come from the Leydig cell) to estradiol
Estradiol then diffuses back across to the Leydig cell to enhance protein production from the nucleus (i.e. enzyme production that promotes conversion to testosterone)
Therefore, in this way both cells support each other and are required cause it’s the interaction that produces testosterone and estradiol.
How do androgen receptors work in the recognition of testosterone i.e. what needs to happen for testosterone to be recognized + have an effect?
-Testosterone is not potent by itself so converted to dihydrotestosterone
via the enzyme 5 alpha reductase
-Dihydrotestosterone has higher infinity to the androgen receptor so have larger effect of testosterone on gene expression
-Enters nucleus results in activation of target genes
Do testosterone levels remain stable throughout the day?
No, they are pulsatile
highest between midnight and noon
How does testosterone secretion differ across a lifetime?
- Large spike after feralization determines the sex of the baby
- There is also a spike right after birth although the reason for this is not well understood
- Spikes at puberty and remains high throughout adulthood
- Declines as get older but never as low as it was before puberty
Describe follicular development in females….
- At birth we have 2 million primordial follicles, most undergo atresia though
- These differentiate to primary follicles, then secondary follicles then to tertiary (Graafian) follicles which are a mature and contain an egg
- Only one of these follicles will be the dominant and enter the ovulatory phase
