Flashcards in Hypothalamic - Pituitary - Gonadal Axis II Deck (51)
What is puberty the transition from and to?
→ Non reproductive to reproductive state
What are the 4 main things that happen during puberty?
→Breast development in females and increased testicular volume in males.
→Secondary characteristics develop
→Profound physiological changes
→Profound psychological changes
What is gonadarche characterized by?
→ An increase in GnRH ( measured through FSH and LH)
What does an increase in LH result in?
→ Secondary sex characteristics
Why does adrenarche occur?
→ Increase in adrenal androgen secretion due to cellular remodelling of adrenal cortex.
What are the adrenal androgens?
→Dehydro-epiandrosterone sulphate (DHEAS)
Where are the adrenal androgens secreted from?
→ The zona reticularis (cortex)
What is pubarche the result of?
What appears during pubarche and why?
→Appearance of pubic/axillary hair resulting from adrenal androgen secretion
What is pubarche associated with?
→ an increase in sebum production which leads to acne
What is acne caused by?
→ Infection and abnormal keratinization
When is puberty considered precocious?
→ 8 years old in girls
→ 9 years in boys
When does gonadarche happen?
→ several years after adrenarche
What happens during gonadarche?
→ Reactivation of hypothalamic GnRH
What is the HPG axis required for?
→ male differentiation during fetal development
When are the GnRH neurons not restrained anymore?
→ until gonadarche
What does the activation of gonadal steroid production cause?
→ The production of viable gametes and the ability to reproduce
What hormones does the hypothalamus produce?
→ Gonadotrophin releasing hormone
What hormones does the pituitary release?
→ Gonadotrophin hormones
What is GnRH secreted and synthesized by?
→ Specialist hypothalamic centres (arcuate nucleus)
When is the HPG axis activated?
→ at the 16th week of gestation
When does pulsatile GnRH secretion continue in the fetus until?
→ 1-2 years postnatally
Around what age are GnRH neurons reactivated?
→ age 11
What is a good measure of GnRH?
→ LH mimics exactly what GnRH does
Why is GnRH difficult to measure?
→ It is only released in the hypothalamus
What stimulates the onset of puberty?
→ environmental and genetic factors
→ body fat and nutrition
What is the Frisch et al. body fat hypothesis?
→ A certain body fat % is required for menarche 17% and to maintain female reproductive ability
What happens as a result of anorexia?
→ Reduced response to GnRH
→ Decreased gonadotrophin levels
What happens if someone has an inactivating mutation of the KISS1R gene?
→ Failure to enter puberty
→ Hypogonadotrophic hypogonadism
What happens if there is an activating mutation of KISS1R?
→ Precocious puberty
What is consonance?
→ A smooth ordered progression of changes
What are the physical changes in girls during puberty?
→ Breasts enlarge
→ Pubic/axillary hair
→ Uterus enlarges
→ Cytology changes
→ Increase in height
→ Body shape
What changes occur in girls due to the activation of the HPG axis?
→ Increase in ovarian size and follicular growth
Why is menarche not equated with the onset of fertility?
→ 80% of menstrual cycles in the first year are anovulatory
What are the physical changes in boys during puberty?
→ External genitalia grow
→ Facial/ body hair
→ Pubic/axillary hair
→ Vas deferens lumen increases
What stimulates spermatogenesis and how?
→ Testosterone from Leydig cells stimulate meiosis and spermatogenesis in Sertoli cells
What changes the larynx in males and how?
→ Androgens lead to an enlarged larynx
→ Voice deepens
What is the growth spurt due to?
→ Interaction between growth hormone and estrogen
What is the biphasic response (growth spurt)?
→ Low levels of estrogen → linear growth and bone maturation
→ High levels of estrogen → Epiphyseal fusion
What do androgens do at the pilosebaceous units?
→ Increase sebum production
How does beard formation occur?
→ at the vellus pilosebaceous unit there is differentiation
→ Terminal pilosebaceous unit formation
What are pubic and axillary pilosebaceous units called?
→ APO pilosebaceous units
What are the 3 psychological changes in puberty?
→ Need for independence
→ Increasing sexual awareness/interest
→ Development of sexual personality
What are the three disorders when there is premature activation of the HPG axis?
→ Gonadotrophin dependent precocious puberty
→ Gonadotrophin independent precocious puberty
→ Mc Cune Albright syndrome
What are the features of gonadotrophin dependent precocious puberty?
→ Excess GnRH secretion
→ Excess gonadotrophin secretion → pituitary tumor
What are the features of gonadotrophin independent precocious puberty?
→ Testotoxicosis - activating mutation of LH receptor
→ Sex steroid secreting tumor or exogenous steroids
What are the features of McCune albright syndrome?
→ Cafe au lait skin pigmentation
→ Autonomous endocrine function
→ Hyperactivation of adenylate cyclase mediated signalling
What classes as pubertal delay?
→ Absence of secondary sexual maturation by 13 in girls
→ Absence of menarche by 18
→ Absence of secondary sexual maturation by 18 boys
What is constitutional delay?
→ Affects both growth and puberty
→ 90% of all pubertal delay cases
What is an example of hypogonadotrophic hypogonadiam?
→ Kallmans syndrome (impaired GnRH migration)