Sex, steroids and NS Flashcards
T/F- Sex chromosomes determine the primary source and type of sex hormones
True
What is the SRY gene?
its a testis determining factor, in other words, a transcription factor that determines developments of male gonadal tissues
what is the common precursor of steroid hormones?
A) progesterone
B) chloestrol
C) aromatase
D) Testosterone
B) cholestro
What is aromatase expression critical for?
determining whether androgen or estrogen is the active factor
what is the basic pathway of the biosynthesis of sex steroids?
Cholesterol–> Progesterone —> Testosterone—-> Either Dihydrotestosterone or estradiol
Sex steroid synthesis by the gonads are driven by which hormones?
Pitutiary hormones (FSH, LH)
Levels and pattern of FSH/LH secretion are determined by?
Hypothalamus
what is hypothalamus activity determined?
circulating hormonal levels and other brain inputs
What are gynadromorphs? what is unique about them
Comprimise a mixture of genetically male and female tissue (some cells are XX and some are XY). Both sides of brain exposed to same hormones, so diff must be due to genes
What are the contributors to sexual dimorphic behaviours?
Sex-specific neurons, and sex-specific of hormone receptors in neurons common to both sexes
What do you mean by discrete pattern of localisation of steroid receptors?
Both sexes have different pattern of receptors, so only a minority of regions become sexually dimorphic.
what is the mechanism of steroid action generally?
1) Steroid (androgen or oestrogen) binds to its specific cytoplasm (AR or ER)
2) Steroid-receptor complex translocates to nucleus to activate specific response elements.
What happens if circulating testosterone hits a cell that expresses aromatase?
testosterone converted to estradiol. Action can then occur via estrogen receptors, androgen receptors or both.
why is estrogen considered a critical masculinising factor in some regions?
in males, neurons that express aromatase see a transient intracellular rise in estrogen as a result of transient rise in testosterone. These neurons also express estrogen receptors, so effects of the rise in E will be mediated by ER’s
Why dont maternal estrogens masculinise the developing nervous system?
maternal estrogens dont affect sexual differentiation of fetal NS as these fetuses express high levels of a-fetoprotein
