3. Puberty

Question 1

what is the normal age of onset of puberty in males and females

Answer 1

females = 8-13 yrs
males = 9-14 yrs

Question 2

list the 4 stages of female dev and their approximate age of onset

Answer 2

1. breast bud growth (TELARCHE): 8-11 yrs
2. pubic hair growth (ADRENARCHE): 11-12 yrs
3. growth spurt
4. menstrual cycle (MENARCHE): <16 yrs

Question 3

list the 5 stages of male dev.

Answer 3

1. testicular volume increase
2. genitalia size increase
3. pubic hair growth
4. spermatogenesis
5. growth spurt

Question 4

what measurement is used to assess puberty dev. and what characteristics does it look at in males and females

Answer 4

Tanner scale

• females: breast size + pubic hair growth
• males: testicular volume + pubic hair growth

Question 5

which hormones are responsible for onset of puberty in males and females

Answer 5

• females: oestrogen and testosterone

- males: testosterone

Question 6

describe the occurence of accelerated somatic growth in males and females during puberty, inc. hormones involved

Answer 6

Depends on GH and sex steroids:

• females: earlier and shorter
• males: later, longer and slightly faster

Question 7

why is accelerated somatic growth faster in females than males

Answer 7

epiphyseal fusion (i.e. end of somatic growth) depends on oestrogen

Question 8

describe the general hormonal changes seen in puberty

Answer 8

1. gradual activation of GnRH - pulsatile release…
2. increased frequency and amplitude of LH pulses…
3. gonadotrophins stimulate secretion of oestrogens and androgens

+ extragonadal hormonal changes, e.g. increased IGF-1 and adrenal steroids

Question 9

why is it important than GnRH release be pulsatile

Answer 9

if GnRH Rs continuously exposed to GnRH, they become desensitised… stop FSH and LH production… stops gonadal steroids production

Question 10

what is the role of GHRH and GH in puberty

Answer 10

Mediate accelerated somatic growth:

1. Hypothalamus releases GHRH…
2. stimulates AP somatotropes to release GH…
3. GH stimulates growth spurt:
   - increased TSH
   - increased IGF-1 (from liver)
   - increased metabolic rate and tissue growth
   - increased androgens (mineral retention in body to support bone and muscle growth)

Question 11

describe the role of the HPG axis in puberty

Answer 11

Sexual development

1. Hypothalamus releases GnRH (pulsatile release)…
2. stimulates AP gonadotrophs to release LH and FSH:
   - nocturnal pulsatile release pre-puberty (9-12 yrs)
   - steady increase in release with puberty onset
3. stimulates androgen and oestrogen production from gonads

Question 12

why is body mass one of the key factors in female onset of puberty, and what is the effect of significant weight loss on the reproductive cycle

Answer 12

• Leptin release from adipose tissue signals attainment of critical weight (47kg)
• Pulsatile release stimulates hypothalamic KISS neurones… GnRH release
• Significant weight loss causes cessation of reproductive cycle = SECONDARY AMENORRHEA

Question 13

what is the effect of LH in males and females

Answer 13

• males: stimulates testes Leydig cells to produce testosterone from cholesterol
• females:
  i) stimulates ovarian Theca cells to produce androgens and progesterone
  ii) triggers ovulation

Question 14

what is the effect of FSH in males and females

Answer 14

• males: stimulates Sertoli cells to increase spermatogenesis (provide nutrition and hormonal support to germ cells)
• females:
  i) stimulates Granulosa cells to produce oestrogen and progesterone
  ii) triggers ovulation
  iii) inhibin secretion

Question 15

what is the role of inhibin

Answer 15

negative feedback:

i. inhibits FSH release from AP
ii. small inhibitory effect on LH

Question 16

what is the role of oestrogen and progesterone on the HPG axis

Answer 16

oestrogen:
- moderate titres: negative feedback -
decrease GnRH release (per pulse) from hypothalamus
- high titres: positive feedback - increase GnRH release from hypothalamus… LH surge

progesterone: decreases frequency of GnRH pulses from hypothalamus:
- increases inhibitory effects of moderate Oe
- prevents positive feedback of high Oe… no LH surge