S4 Puberty And HPG axis

Question 1

What is adrenarche?

Answer 1

Maturation and increased activity of the adrenal glands prior to puberty

Question 2

What is gonadarche?

Answer 2

Activation of reproductive glands by the pituitary hormones FSH and LH

Question 3

What is thelarche

Answer 3

The onset of breast development occurring near the beginning of puberty in girls

Question 4

What is pubarche?

Answer 4

Onset of the growth of public hair

Question 5

What is menarche?

Answer 5

The onset of mensuration at puberty

Question 6

What is seen during puberty?

Answer 6

Accelerated somatic growth
Maturation of primary sexual characteristics (gonads and genitals)
Appearance of secondary sexual characteristics (pubic and axillary hair, female breast development, male voice changes)
Menstruation and spermatogenesis begin

Question 7

What factors are important in the timing of puberty?

Answer 7

• environmental factors
• the pineal gland > disorders of this can cause early onset puberty (evidence shaky)
• body weight (in girls mostly), nutrition and leptin (released from adipose tissue)
• economic/social factors MAY effect (stress)
• genetics

Question 8

What are sexual maturity ratings (SMR) based on?

Answer 8

Also called a Tanner scale

• based on pubic hair and breasts (female)
• pubic hair and genitalia size (testes. Males)

Scale rating from 1-5

Question 9

Average range of puberty in girls

Answer 9

8-13

Question 10

Average age of puberty males

Answer 10

9-14 yrs

Starts with genital development (testes size inc)

Question 11

Accelerated somatic growth is dependent on?

Answer 11

Growth hormone
IGF 1 (insulin growth factor)- monitor of general growth activity. Greatest peak at puberty.
Sex steroids

(In both sexes)

Question 12

What ends the accelerated somatic growth

Answer 12

Fusion of growth plates at the end of long bones- epiphyseal fusion
> oestrogen closes epiphytes earlier in girls

Question 13

Hypothalamus pituitary unit regulates the function of?

Answer 13

Thyroid ( hypothalamic pituitary thyroid axis HPT)
Adrenal (hypothalamic pituitary adrenal axis HPA)
Reproductive glands ( HPX)

also regulates

• somatic growth
• lactation
• milk secretion
• water metabolism

Question 14

where is GnRH produced? where’s its receptor?

function?

Answer 14

gonadotrophin releasing hormone:

hypothalamus
receptor in anterior pituitary (travels via hypophysial portal system)

• regulates puberty onset, sexual development and ovulatory cyclin females.

Question 15

describer how GnRH is reread during puberty

Answer 15

as low frequency pulses during the night but after maturation of synaptic connections, it matches the adult pattern

Question 16

why is it important that release of GnRH is pulsate?

Answer 16

released in bursts so that the receptors don’t develop an insensitivity if exposed to high levels of the hormone for long periods > desensitise HPG pathway >infertility

Question 17

what is adenohypophysis and neurohypophysis

Answer 17

anterior pituitary
posterior pituitary

hypophysis= pituitary

Question 18

GnRH stimulates pituitary to release ?

Answer 18

follicle- stimulating hormone (FSH)
luteinizing hormone (LH)

Question 19

high levels of LH and FSH initiate?

Answer 19

gonadal development

Question 20

level of testosterone in boys is increased when?

Answer 20

Mornings

because the sleep related LH increase which stimulates a nocturnal rise of T

Question 21

Males: LH stimulates?

Answer 21

Leydig cells in testis > to produce testosterone

*negative feedback on anterior pituitary and hypothalamus

Question 22

Males: FSH stimulates?

Answer 22

Sertoli cells (responsible for spermatogenesis)
> inhibin released

*negative feedback on anterior pituitary n possibly hypothalamus

Question 23

role of the testes

Answer 23

• contains seminiferous tubules
• interstitial tissue contains Leydig cells
  > produce testosterone

Question 24

role of sertoli cells

Answer 24

• provide nutrition and hormonal support to germ cells allowing sperm formation
• sensitive to FSH (inc sperm production)
• secrete inhibin

Question 25

Females: FSH stimulates?

Answer 25

granulosa cells
> which converts androgens to oestrogen
> follicular development
> releases inhibin. inhibits FSH only

Question 26

Females: LH stimulates?

Answer 26

theca interna cells
> releases androgens
> LH surge required for ovulation
> maintains corpus luteum after ovulation

Question 27

oestrogen effect on GnRH secretion

Answer 27

relatively low concentrations- reduce secretion (-ve feedback)

high concentrations - promote secretion (+ve feedback)

Question 28

effect of progesterone?

Answer 28

‘buffer oestrogen actions’

• increases inhibitory effects of moderate oestrogen
• prevents positive feedback of high oestrogen > so we only have 1 cycle every 28 days

Question 29

differencer in oestrogen and progesterone effect on GnRH

Answer 29

oestrogen reduces GnRH conc per pulse

progesterone FREQUENCY of pulses

Question 30

effect of growth hormone from pituitary?

Answer 30

• inc TSH (thyroid)
• inc metabolic rate
• promotes tissue growth
• inc androgens> retention of minerals in body to support bone and muscle growth

Question 31

role of leptin?

Answer 31

signals info about energy stores to CNS
> regulating neuroendocrine function
> reproductive dysfunction associated with leptin deficiency
> accelerate onset of reproductive function

• can regulate GnRH levels

Question 32

what is central precocious puberty? causes?

Answer 32

early onset puberty with ELEVATED GnRH levels

• idiopathic
• CNS leisions
• rare pituitary gonadotrophin secreting tumours
• obesity related due to inc leptin in obesity

Question 33

what is peripheral precocious puberty? causes?

Answer 33

early onset puberty WITHOUT elevated GnRH

• due to inc androgen production
• ovarian cyst
• congenital adrenal hyperplasia
• primary hypothyroidism
• obesity related due to inc insulin resistance in obesity

Question 34

define delayed onset of puberty age. causes?

Answer 34

absent or incomplete development of secondary sex characteristics by the age of 14 in boys or 13 in girls.

• growth delay > not pathological. may be inherited
• malnutrition
• chronic illnesses e.g. hypothyroidism/ inflammatory bowel disease
• hypogonadism

Question 35

most parts of reproductive system can work before normal age of puberty - why don’t they?

Answer 35

hormones levels low

> due to low GnRH secretion

Question 36

hormone levels associated with onset of puberty?

Answer 36

nocturnal GnRH pulsatility precedes phenotypic changes by several years
- steady rise in FSH and LH secretion