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