Session 4: Puberty

Question 1

Define primary sexual characteristics.

Answer 1

Sexual characteristics already present at birth. Anatomy of the internal and external genitalia.

Question 2

Define secondary sexual characteristics.

Answer 2

Develop after puberty; Pubic hair Breasts Genital development or enlargement Menstruation

Question 3

Explain the sequence of events of puberty in girls.

Answer 3

Usually between 9-13 yrs of age. Thelarche -> Pubic hair growth -> Adrenarche Growth spurt -> Menarche -> Pubic hair adult -> Breast development

Question 4

What is thelarche?

Answer 4

The breast bud development

Question 5

What is the first sign of puberty in girls?

Answer 5

Usually the thelarche.

Question 6

What is the pubic hair growth stimulated by in girls?

Answer 6

Testosterone

Question 7

What is the pubic hair growth stimulated by in boys?

Answer 7

Testosterone

Question 8

What is the growth spurt dependent on? (In both sexes)

Answer 8

Depends on growth hormone + IGF-1 and also sex steroids and also oestrogen.

Question 9

What makes the growth spurt end?

Answer 9

Epiphyseal plate fusion.

Question 10

Explain how oestrogen is important in growth spurt.

Answer 10

Oestrogen causes the epiphyseal plates to close earlier. This is the case in both boys and girls.

In boys testosterone can convert to oestrogen.

Question 11

Explain how the growth spurt differ in boys and girls.

Answer 11

In girls it starts earlier and its duration is not as long as in boys. This is mainly due to presence and higher levels of oestrogen. In boys it start later, the growth spurt is steeper and it goes on for longer.

Question 12

What determines the genital development in boys?

Answer 12

Testosterone.

Question 13

Explain the sequence of events of puberty in boys.

Answer 13

Age 10-14 yrs.

Genital development where the testes enlarge -> Pubic hair growth -> Spermatogenesis (hard to notice) -> Growth spurt (lower lvls of oestrogen makes this longer in males) -> Genital enlargement due to testosterone -> Pubic hair

Question 14

Complications of precocious puberty.

Answer 14

Can lead to levels of oestrogen rising earlier and result in a shorter stature.

Question 15

Important factors for start of puberty.

Answer 15

Body weight (47 kg in girls) as rapid weight loss can cause the reproductive cycle in girls to cease.

Nutrition (linked to body weight)

Leptins (linked to body weight)

Question 16

What is the crucial axis responsible for puberty?

Answer 16

The HPG axis

Question 17

What is the typical first sign of puberty in boys?

Answer 17

Testes enlargement

Question 18

What is puberty initiated by?

Answer 18

The hypothalamus in the brain. Mainly nocturnal pulsatile GnRH secretion steadily increasing levels of LH.

Question 19

Does the nocturnal GnRH pulsatility start with puberty?

Answer 19

No, it can precede the physical appearances by years.

Question 20

What is the onset of puberty associated with?

Answer 20

A steady rise in LH and FSH secretions.

Question 21

Most parts of the reproductive can work before puberty begins.

Why does it not?

Answer 21

Because the hormone levels are too low and GnRH therefore is too low.

Question 22

Explain the action of GnRH.

Answer 22

The secretions are in pulses and are tied to our internal biological clock.

GnRH is produce in the hypothalamus and is released into the portal system going down into the anterior pituitary (adenohypophysis).

GnRH then stimulates the gonadotrophs to produce FSH and LH.

FSH and LH will be released into the systemic circulation and act on gonads to produce sex hormones.

Question 23

Six peptide hormones of the anterior pituitary gland.

Answer 23

Prolactin

TSH

FSH and LH

GH

ACTH

Question 24

When do the amplitude of pulses of FSH and LH increase in children aged 9-12 yrs?

Answer 24

During sleep

Question 25

What will the increasing levels of FSH and LH cause?

Answer 25

Initiation of gonadal development

Question 26

Explain the effect of LH in boys.

Answer 26

LH stimulates leydig cells. Leydig cells produce testosterone from cholesterol

Question 27

What external factors affect androgen production?

Answer 27

Circadian rhythm (highest in the morning) Environmental stimuli

Question 28

Where can the leydig cells be found?

Answer 28

In the interstitium of the seminiferous tubules.

Question 29

The seminiferous tubules are lined by a complex epithelium made up by two kinds of cells. Which?

Answer 29

Sertoli cells (supporting) and germ cells (spermatogenic)

Question 30

What does FSH act on?

Answer 30

Sertoli cells

Question 31

Explain the function of sertoli cells.

Answer 31

Supporting the germ cells and provide nutrition. Rising FSH levels stimulate the sertoli cells and promote sperm production. Sertoli cells also secrete inhibin to inhibit FSH at the anterior pituitary.

Question 32

What does FSH and LH act on in females?

Answer 32

FSH act on granulosa cells LH act on theca interna

Question 33

Function of inhibin.

Answer 33

Inhibit FSH and only LH in **_small amounts_**.

Question 34

Effects of small levels of oestrogen on the hypothalamus.

Answer 34

Inhibits the production of GnRH by negative feedback.

Question 35

Effects of higher lvls of oestrogen on the hypothalamus.

Answer 35

Positive feedback promoting the production of GnRH. This leads to a surge in LH. However not as big of a surge to FSH.

Question 36

Why is the surge in FSH not as big as LH?

Answer 36

Because of the presence of inhibin.

Question 37

What is inhibin secreted by in females?

Answer 37

Granulosa cells of the corpus luteum.

Question 38

Effect of progesterone on oestrogen.

Answer 38

In moderate to low levels of oestrogen it further enhances the negative feedback of oestrogen on GnRH. In high levels of oestrogen progesterone **_prevents_** the positive feedback of oestrogen on GnRH.

Question 39

What is the consequence of the effect progesterone has on oestrogen?

Answer 39

There will be no further surge in LH and LH levels decline.

Question 40

Give an example of a contraceptive preventing ovulation.

Answer 40

Progesterone in order to prevent the initial LH surge causing ovulation.

Question 41

Explain the function of Leptin in puberty.

Answer 41

Adipocyte-derived protein hormone which signals about energy stores to the CNS. Reproductive dysfunction has been associated with leptin deficiency (meaning underweight). Leptin can also accelerate the onset of reproductive function. Leptin also has a pulsatile pattern which is associated with the levels of LH. Leptin can regulate GnRH levels.