Gonadal steroidogenesis Flashcards
Where are the two areas in the body that steroid hormones are produced from cholesterol?
Adrenal glands and gonads
What is the HPG axis?
Hypothalamic-pituitary-gonadal axis
Hypothalamus secretes Gonadotropin-releasing hormone (GnRH) which stimulates the pituitary to release LH and FSH
This causes the testis to produce testosterone and the ovaries to produce estrogen and progesterone
How the HPG axis activity change throughout the individuals life?
What is testosterone required for?
Testosterone is required for spermatogenesis (sperm production) and important for development of primary and secondary sexual characteristics, increasing libido and increasing bone and muscle growth
What are leydig and Sertoli cells?
Leydig cells= produce testosterone
Sertoli cells= produce sperm
Both present in testis
What is the feedback pathway in the HPG axis for males?
What do sertoli cells get stimulated by, and what do they produce?
Stimulated by FSH to produce inhibin and activin which have both negative and positive feedback loops
Also produce sperm
What stimulates leydig cells, and what do they produce?
LH stimulates leydig cells to produce testosterone
How do the testosterone levels affect what the Sertoli cells produce?
Raised testosterone levels= increases inhibin, low testosterone levels= activin
What is a oocyte?
In the ovaries, there are follicles each containing an egg- known as a oocyte.
A single oocyte will be released from the dominant (largest) follicle during each menstrual cycle
What cells are within follicles?
Theca cells
Granulosa cells
What does FSH act on and what are the effects? (female)
FHS acts on granulosa cells to produce estradiol which stimulates preovulatory growth and granulosa cells also produce inhibins- only negatively feedback onto FSH
What is the feedback and forward pathways of the HPG axis in females?
How do the levels of estradiol change in the follicle as it matures?
As follicle grows, level of estradiol increased.
Once follicle has grown and ready to rupture, is secreting high levels of estradiol.
What are the feedback pathways of estradiol?
Moderate levels= negative feedback
High levels (in the absence of progesterone)= positive feedback, causing LH to be released and the LH spike causes egg to be released
What does LH act upon? (female)
LH surge when estradiol levels rise causes egg to be released
LH binds to corpus luteum and acts on theca cells to produce androgens and progesterone
What happens to androgens released by the corpus luteum?
converted to estradiol in granulosa cells
What type of feedback does high estradiol with progesterone give?
Negative feedback
When are hormones important for male development?
Hormones needed for development of testicular and reproductive systems in foetal life
Also important in puberty spermatogenesis and sperm production/ erectile function
What is needed for creation of testis and mascualisation of the foetus?
X,Y chromosomes result in the formation of testis
Testosterone needed in the mascuilisation of the foetus
How does regression of the female reproductive tract occur in male foetuses?
Anti-mullerian hormone (AMH) is produced by testicular sertoli cells and induces regression of mullein ducts
How does the amount of testosterone produced relate to the phenotype of geniltalia produced?
What enzyme converts testosterone to dihydrotestosterone?
5-alpha reductase
What receptor do testosterone and dihydrotestosterone act through?
Androgen receptor