HPG axis 2

Question 1

what do gonads produce?

Answer 1

mature gametes

Question 2

what do testes produces?

Answer 2

spermatozoa

Question 3

what do ovaries produce?

Answer 3

oocytes

Question 4

what is puberty?

Answer 4

the transition from a non-reproductive to a reproductive state

• breast development in females, increased testicular volume in males.
• secondary characteristics develop
• profound physiological changes

Question 5

do both secondary and primary sexual characteristics develop in puberty?

Answer 5

no, primary are present at birth

Question 6

what are the 2 endocrine events of puberty?

Answer 6

adrenarche and gonadarche

Question 7

what is adrenarche?

Answer 7

change in adrenal androgen secretion due to cellular remodelling of adrenal gland

• secretion of DHEA and DHEAS from the zona retucularis
• no known trigger

Question 8

what is pubarche?

Answer 8

the result of adrenarche

-appearance of pubic / axillary hair resulting from adrenal androgen secretion

Question 9

what is pubarche associated with?

Answer 9

acne, due to increased sebum production

Question 10

when does gonadarche occur?

Answer 10

Several years after adrenarche (typically ~11 yrs of age)

Question 11

what is gonadarche?

Answer 11

• Reactivation of hypothalamic GnRH

- Activation of gonadal steroid production production of viable gametes and ability to reproduce

Question 12

when does GnRH secretion occur in puberty?

Answer 12

• Pulsatile GnRH secretion in foetus until 1-2 years postnatally when ceases
• GnRH neurones ‘restrained’ during postnatal period, 10 years or more
• Re-activation at ~11 years
• At puberty a gradual rise in pulsatile release of GnRH

Question 13

there is a nocturnal rise in which hormone?

Answer 13

GnRH

Question 14

what happens with anorexia nervosa or intensive physical training?

Answer 14

• Reduced response to GnRH
• ↓gonadotrophin levels
• Amenorrhea
• Restored when nourished / exercise stopped

Question 15

what is required for menarche (first occurrence of menstruation)?

Answer 15

a certain fat body weight

Question 16

types of KISS1R mutations?

Answer 16

inactivating and activating mutations

Question 17

what do inactivating mutations of KISS1R cause?

Answer 17

• Hypogonadism
• Failure to enter puberty
• Hypogonadotrophic hypogonadism

Question 18

Hypogonadotrophic hypogonadism

Answer 18

No GnRH being released, so no LH or FSH aren’t being released, resulting in a hypogonadotrophic status. No positive drive to testis or ovary to produce follicles or mature sperm.

Question 19

what do activating mutations of KISS1R cause?

Answer 19

overactive receptor that acts in the absence of a ligand

-precocious puberty (puberty occurs early)

Question 20

what do ghrelin and leptin regulate?

Answer 20

kisspeptin production

Question 21

what is consonance?

Answer 21

• smooth ordered progression of changes

- puberty follows specific order of changes, individual will always follow this pattern regardless of how long it takes

Question 22

physical changes in girls during puberty

Answer 22

• Breasts enlarge
• Pubic/axillary hair
• Uterus enlarges, secretions in response to E2
• Uterine tubes
• Vagina
• Cervical changes
• Height
• Body shape
• HPG axis, increase in ovarian size and follicular growth
• Menarche
• Fertility

Question 23

physical changes in boys during puberty

Answer 23

• External genitalia, increase in testicular volume, growth of penis, scrotum, scrotal skin changes
• Vas deferens, lumen increases
• Seminal vesicles & prostate
• Facial/body hair
• Pubic / axillary hair
• Larynx, androgens enlarge larynx, Adams apple, voice deepens
• Height
• Body shape
• Onset of fertility

Question 24

what is the Adams apple?

Answer 24

projection of thyroid cartilage

Question 25

what does testosterone from Leydig cells stimulate in puberty?

Answer 25

stimulates meiosis & spermatogenesis in Sertoli cells

Question 26

are boys fertile at the beginning of puberty?

Answer 26

yes

Question 27

what is involved in a growth spurt?

Answer 27

a complex interaction between growth hormone and oestrogen | -earlier in girls

Question 28

what effect does oestrogen have on epiphyseal growth?

Answer 28

a biphasic effect - Low levels = linear growth & bone maturation - High levels = epiphyseal fusion

Question 29

Psychological changes in puberty?

Answer 29

1. Increasing need for independence 2. Increasing sexual awareness/interest 3. Development of sexual personality

Question 30

precocious puberty

Answer 30

Development of any secondary sexual characteristic before the age of 8 in girls and 9-10 in boys

Question 31

premature activation of HPG axis

Answer 31

1. Gonadotrophin-dependent precocious puberty – consonance - Excess GnRH secretion - idiopathic or secondary - Excess gonadotrophin secretion - pituitary tumour 2. Gonadotrophin-independent precocious puberty - loss of consonance - Testotoxicosis - activating mutation of LH receptor - Sex steroid secreting tumour or exogenous steroids

Question 32

what is the most common gonadotrophin independent precocious puberty?

Answer 32

McCune Albright syndrome

Question 33

what is McCune Albright syndrome?

Answer 33

café au lait skin pigmentation - g alpha s subunit mutation, activates LH and FSH pathways - GNAS1 gene mutations - also side effects because of other hormone pathways being activated

Question 34

what is pubertal delay?

Answer 34

-absence of secondary sexual maturation by 13yrs in girls or 14yrs in boys OR -absence of menarche by 18yrs

Question 35

give 3 reasons for delayed HPG axis activation?

Answer 35

1. Constitutional delay affecting both growth and puberty. Approx. 90% of all pubertal delay cases. ~10X more common in boys secondary to chronic illness e.g., diabetes, cystic fibrosis. 2. Hypogonadotrophic hypogonadism (low LH and FSH) Kallman’s syndrome (X-linked KAL1 gene, impaired GnRH migration), Other mutations causing defects in GnRH production 3. Hypergonadotrophic hypogonadism (high LH and FSH) Gonadal dysgenesis and low sex steroid levels: gonadal dysgenesis with normal karyotype, viral e.g. mumps

Question 36

kleinfelters syndrome genotype

Answer 36

XXY

Question 37

turners syndrome genotype

Answer 37

XO - ovarian streak (underdeveloped) - being shorter than normal