Session 4: Puberty Flashcards
Define primary sexual characteristics.
Sexual characteristics already present at birth. Anatomy of the internal and external genitalia.
Define secondary sexual characteristics.
Develop after puberty; Pubic hair Breasts Genital development or enlargement Menstruation
Explain the sequence of events of puberty in girls.
Usually between 9-13 yrs of age. Thelarche -> Pubic hair growth -> Adrenarche Growth spurt -> Menarche -> Pubic hair adult -> Breast development
What is thelarche?
The breast bud development
What is the first sign of puberty in girls?
Usually the thelarche.
What is the pubic hair growth stimulated by in girls?
Testosterone
What is the pubic hair growth stimulated by in boys?
Testosterone
What is the growth spurt dependent on? (In both sexes)
Depends on growth hormone + IGF-1 and also sex steroids and also oestrogen.
What makes the growth spurt end?
Epiphyseal plate fusion.
Explain how oestrogen is important in growth spurt.
Oestrogen causes the epiphyseal plates to close earlier. This is the case in both boys and girls.
In boys testosterone can convert to oestrogen.
Explain how the growth spurt differ in boys and girls.
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.
What determines the genital development in boys?
Testosterone.
Explain the sequence of events of puberty in boys.
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
Complications of precocious puberty.
Can lead to levels of oestrogen rising earlier and result in a shorter stature.
Important factors for start of puberty.
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)
What is the crucial axis responsible for puberty?
The HPG axis
What is the typical first sign of puberty in boys?
Testes enlargement
What is puberty initiated by?
The hypothalamus in the brain. Mainly nocturnal pulsatile GnRH secretion steadily increasing levels of LH.
Does the nocturnal GnRH pulsatility start with puberty?
No, it can precede the physical appearances by years.
What is the onset of puberty associated with?
A steady rise in LH and FSH secretions.
Most parts of the reproductive can work before puberty begins.
Why does it not?
Because the hormone levels are too low and GnRH therefore is too low.
Explain the action of GnRH.
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.
Six peptide hormones of the anterior pituitary gland.
Prolactin
TSH
FSH and LH
GH
ACTH
When do the amplitude of pulses of FSH and LH increase in children aged 9-12 yrs?
During sleep
What will the increasing levels of FSH and LH cause?
Initiation of gonadal development
Explain the effect of LH in boys.
LH stimulates leydig cells.
Leydig cells produce testosterone from cholesterol
What external factors affect androgen production?
Circadian rhythm (highest in the morning)
Environmental stimuli
Where can the leydig cells be found?
In the interstitium of the seminiferous tubules.
The seminiferous tubules are lined by a complex epithelium made up by two kinds of cells.
Which?
Sertoli cells (supporting) and germ cells (spermatogenic)
What does FSH act on?
Sertoli cells
Explain the function of sertoli cells.
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.
What does FSH and LH act on in females?
FSH act on granulosa cells
LH act on theca interna
Function of inhibin.
Inhibit FSH and only LH in small amounts.
Effects of small levels of oestrogen on the hypothalamus.
Inhibits the production of GnRH by negative feedback.
Effects of higher lvls of oestrogen on the hypothalamus.
Positive feedback promoting the production of GnRH.
This leads to a surge in LH.
However not as big of a surge to FSH.
Why is the surge in FSH not as big as LH?
Because of the presence of inhibin.
What is inhibin secreted by in females?
Granulosa cells of the corpus luteum.
Effect of progesterone on oestrogen.
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.
What is the consequence of the effect progesterone has on oestrogen?
There will be no further surge in LH and LH levels decline.
Give an example of a contraceptive preventing ovulation.
Progesterone in order to prevent the initial LH surge causing ovulation.
Explain the function of Leptin in puberty.
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.
