Hypothalamic - Pituitary - Gonadal Axis II

Question 1

What is puberty the transition from and to?

Answer 1

→ Non reproductive to reproductive state

Question 2

What are the 4 main things that happen during puberty?

Answer 2

→Breast development in females and increased testicular volume in males.
→Secondary characteristics develop

→Profound physiological changes
→Profound psychological changes

Question 3

What is gonadarche characterized by?

Answer 3

→ An increase in GnRH ( measured through FSH and LH)

Question 4

What does an increase in LH result in?

Answer 4

→ Secondary sex characteristics

Question 5

Why does adrenarche occur?

Answer 5

→ Increase in adrenal androgen secretion due to cellular remodelling of adrenal cortex.

Question 6

What are the adrenal androgens?

Answer 6

→Dehydro-epiandrosterone (DHEA)

→Dehydro-epiandrosterone sulphate (DHEAS)

Question 7

Where are the adrenal androgens secreted from?

Answer 7

→ The zona reticularis (cortex)

Question 8

What is pubarche the result of?

Answer 8

→ Adrenarche

Question 9

What appears during pubarche and why?

Answer 9

→Appearance of pubic/axillary hair resulting from adrenal androgen secretion

Question 10

What is pubarche associated with?

Answer 10

→ an increase in sebum production which leads to acne

Question 11

What is acne caused by?

Answer 11

→ Infection and abnormal keratinization

Question 12

When is puberty considered precocious?

Answer 12

→ 8 years old in girls

→ 9 years in boys

Question 13

When does gonadarche happen?

Answer 13

→ several years after adrenarche

Question 14

What happens during gonadarche?

Answer 14

→ Reactivation of hypothalamic GnRH

Question 15

What is the HPG axis required for?

Answer 15

→ male differentiation during fetal development

Question 16

When are the GnRH neurons not restrained anymore?

Answer 16

→ until gonadarche

Question 17

What does the activation of gonadal steroid production cause?

Answer 17

→ The production of viable gametes and the ability to reproduce

Question 18

What hormones does the hypothalamus produce?

Answer 18

→ Kisspeptin

→ Gonadotrophin releasing hormone

Question 19

What hormones does the pituitary release?

Answer 19

→ Gonadotrophin hormones

Question 20

What is GnRH secreted and synthesized by?

Answer 20

→ Specialist hypothalamic centres (arcuate nucleus)

Question 21

When is the HPG axis activated?

Answer 21

→ at the 16th week of gestation

Question 22

When does pulsatile GnRH secretion continue in the fetus until?

Answer 22

→ 1-2 years postnatally

Question 23

Around what age are GnRH neurons reactivated?

Answer 23

→ age 11

Question 24

What is a good measure of GnRH?

Answer 24

→ LH mimics exactly what GnRH does

Question 25

Why is GnRH difficult to measure?

Answer 25

→ It is only released in the hypothalamus

Question 26

What stimulates the onset of puberty?

Answer 26

→ environmental and genetic factors | → body fat and nutrition

Question 27

What is the Frisch et al. body fat hypothesis?

Answer 27

→ A certain body fat % is required for menarche 17% and to maintain female reproductive ability

Question 28

What happens as a result of anorexia?

Answer 28

→ Reduced response to GnRH → Decreased gonadotrophin levels → Amenorrhoea

Question 29

What happens if someone has an inactivating mutation of the KISS1R gene?

Answer 29

→ Hypogonadism → Failure to enter puberty → Hypogonadotrophic hypogonadism

Question 30

What happens if there is an activating mutation of KISS1R?

Answer 30

→ Precocious puberty

Question 31

What is consonance?

Answer 31

→ A smooth ordered progression of changes

Question 32

What are the physical changes in girls during puberty?

Answer 32

→ Breasts enlarge → Pubic/axillary hair → Uterus enlarges → Cytology changes → Increase in height → Body shape

Question 33

What changes occur in girls due to the activation of the HPG axis?

Answer 33

→ Increase in ovarian size and follicular growth

Question 34

Why is menarche not equated with the onset of fertility?

Answer 34

→ 80% of menstrual cycles in the first year are anovulatory

Question 35

What are the physical changes in boys during puberty?

Answer 35

→ External genitalia grow → Facial/ body hair → Pubic/axillary hair → Vas deferens lumen increases

Question 36

What stimulates spermatogenesis and how?

Answer 36

→ Testosterone from Leydig cells stimulate meiosis and spermatogenesis in Sertoli cells

Question 37

What changes the larynx in males and how?

Answer 37

→ Androgens lead to an enlarged larynx | → Voice deepens

Question 38

What is the growth spurt due to?

Answer 38

→ Interaction between growth hormone and estrogen

Question 39

What is the biphasic response (growth spurt)?

Answer 39

→ Low levels of estrogen → linear growth and bone maturation | → High levels of estrogen → Epiphyseal fusion

Question 40

What do androgens do at the pilosebaceous units?

Answer 40

→ Increase sebum production

Question 41

How does beard formation occur?

Answer 41

→ at the vellus pilosebaceous unit there is differentiation | → Terminal pilosebaceous unit formation

Question 42

What are pubic and axillary pilosebaceous units called?

Answer 42

→ APO pilosebaceous units

Question 43

What are the 3 psychological changes in puberty?

Answer 43

→ Need for independence → Increasing sexual awareness/interest → Development of sexual personality

Question 44

What are the three disorders when there is premature activation of the HPG axis?

Answer 44

→ Gonadotrophin dependent precocious puberty → Gonadotrophin independent precocious puberty → Mc Cune Albright syndrome

Question 45

What are the features of gonadotrophin dependent precocious puberty?

Answer 45

→ Excess GnRH secretion | → Excess gonadotrophin secretion → pituitary tumor

Question 46

What are the features of gonadotrophin independent precocious puberty?

Answer 46

→ Testotoxicosis - activating mutation of LH receptor | → Sex steroid secreting tumor or exogenous steroids

Question 47

What are the features of McCune albright syndrome?

Answer 47

→ Cafe au lait skin pigmentation → Autonomous endocrine function → Hyperactivation of adenylate cyclase mediated signalling

Question 48

What classes as pubertal delay?

Answer 48

→ Absence of secondary sexual maturation by 13 in girls → Absence of menarche by 18 → Absence of secondary sexual maturation by 18 boys

Question 49

What is constitutional delay?

Answer 49

→ Affects both growth and puberty | → 90% of all pubertal delay cases

Question 50

What is an example of hypogonadotrophic hypogonadiam?

Answer 50

→ Kallmans syndrome (impaired GnRH migration)

Question 51

What is an example of hypergonadotrophic hypogonadism?

Answer 51

→ Gonadal dysgenesis and low sex steroid levels