S3.1 Puberty & The HPG Axis

Question 1

Define puberty

Answer 1

A stage of human development when sexual maturation and growth are completed and result in ability to reproduce.

Question 2

What are the phases of puberty?

Answer 2

Accelerated somatic growth - longer and faster in boys hence they’re taller
Maturation of primary sexual characteristics - gonads and genitals
Appearance of secondary sexual characteristics - pubic hair, breast Menstruation and spermatogenesis

Question 3

What is the critical weight for puberty to occur?

Answer 3

47kg, any less puberty shall stop

Question 4

What is the age and first sign of puberty in girls?

Answer 4

9-13 years

Breast bud development

Question 5

What is the age and first sign of puberty in boys?

Answer 5

10-14 years

Genital development

Question 6

How do we monitor puberty development?

Answer 6

Tanner scale

Question 7

Describe the mechanism underlying such changes at puberty

Answer 7

Gradual activation of GnRH, increased frequency and amplitude of LH pulses

Question 8

Describe the HPG axis in the male

Answer 8

Hypothalamus GnRH which acts on the AP to release LH and FSH.
These then act on the testis, LH acts on leydig cells producing testosterone, FSH acts on serotoli cells producing inhibin

Question 9

Describe the HPG axis in the female

Answer 9

Hypothalamus GnRH which acts on the AP to release LH and FSH.
In girls they act on the ovaries, FSH acts on granulosa cells producing oestrogen, LH acts on theca cells forming progesterone and inhibin.

Question 11

Describe feedback mechanisms in the HPG axis

Answer 11

Testosterone and moderate oestrogen cause negative feedback by decreasing GnRH secretion.
High oestrogen causes positive feedback as it increases GnRH, this leads to an LH surge (as FSH still inhibited by inhibin).
Progesterone causes negative feedback.
Inhibin causes negative feedback decreasing FSH secretion.

Question 12

What is the role of lepton?

Answer 12

Reproductive dysfunction associated with leptin deficiency. The fat levels of leptin tell the hypothalamus if there is enough body mass for puberty.

Question 13

Describe the hypothalamic hormone characteristics

Answer 13

Hormones are:
Secreted in pulses
Act on specific receptors
Transduce signals via second messengers

Question 14

Would you expect a girl to be shorter or taller as an adult because of precocious puberty?

Answer 14

Taller, more time for growth to occur, and later closing of epiphiseal plate

Question 15

Delayed puberty can present with amenorrhoea. What may be the cause if:

1. LH and FSH are normal
2. LH and FSH are low?

Answer 15

1. Blockage in the cervix

2. Low GnRH or underweight

Question 16

Describe the presentation of turners syndrome in a girl

Answer 16

45X
Low oestrogen
Amenorrhoea 
Delayed puberty
Osteoporosis

Question 17

Describe the presentation of klinefelters syndrome in a boy

Answer 17

47XXY
Primary sexual characteristics are testis due to the SRY region on Y chromosome, but secondary sexual characteristics will be large breasts and wide hips

Question 18

What is precocious puberty?

Answer 18

Puberty at an early age (8-9), possibly caused by tumours of the pineal gland.