Puberty and the Menopause Flashcards
What is puberty?
Primary sexual characteristics are established before birth but reproductive system is inactive.
Puberty is when the reproductive system becomes active
Give an overview of puberty in girls.
Normally at age 8-13
Breast bud (thelarche) Pubic hair growth begins (adrenarche) Growth spurt Onset of menstrual cycles (menarche) Pubic hair adult Breasts adult
Give an overview of puberty in boys
Normally age 9-14
Genital development begins Pubic hair growth Spermatogenesis begins Growth spurt Genitalia adult Pubic hair adult
Describe the growth spurt
Occurs in both sexes
Earlier and shorter in girls
Men become larger because the growth spurt is longer and slightly faster
Ended in both sexes by epiphyseal fusion
How does hormonal control play a part in puberty?
Most parts of the reproductive system can work before the normal age of puberty - precocious puberty
But they don’t because hormone levels are low
Due to low GnRH secretion
Give an overview of the hypothalamic-pituitary-gonadal axis.
Hypothalamus secretes GnRH
GnRH acts on the Anterior Pituitary
Anterior Pituitary secretes FSH & LH
FSH & LH act on the Gonads which then does two things
The Gonads secrete Gonadal Steroids
And the Gonads secrete Gonadal Hormones which have some feedback (positive and negative) on the Anterior Pituitary and Hypothalamus.
Give an overview of the female hypothalamic-pituitary-gonadal axis.
Follicles only partly developed - secrete very little steroid or inhibin
Oestrogen and Progesterone levels low
Little inhibition at Hypothalamus or Pituitary - FSH rises
Oestrogen levels rise
Inhibin levels rise - selective inhibition of FSH
Oestrogen exerts positive feedback at Hypothalamus and Pituitary
LH levels rise
Precise timing of LH surge - ovulation affected by environment
Corpus luteum forms
Secretes Progesterone and Oestrogen
Maintains inhibition of FSH
Progesterone also stops positive feedback and inhibits LH
Death of corpus luteum
Leads to rapid fall in steroid levels
Relieves inhibition of FSH
How is puberty initiated?
The onset of puberty is associated with a steady rise in FSH & LH secretions
Due to a rise in GnRH secretion
Puberty is initiated by the brain
How is Pubic and axillary hair controlled?
Depends on androgens in both sexes
- Testosterone in boys
- From adrenals in girls
How is breast development controlled?
By oestrogens
Testosterone can be converted to oestrogen
How is the growth spurt controlled?
Depends on growth hormone and steroids in both sexes
Oestrogen closes epiphyses earlier in girls
How is genital development controlled in boys?
By testosterone
How is the timing of puberty’s beginning controlled?
Controlled by the brain
Could be reduction in sensitivity to negative feedback by steroids
Or (more likely) “maturation” of central mechanisms
Body weight is the most important factor
When a fractional weight of a persons projected weight is achieved, puberty occurs
In girls, on average critical weight is 47kg for menarche
There is some involvement of the pineal gland (detects light) so might be related to season
Pineal tumours can affect puberty in humans
What is precocious puberty?
Signs of puberty before age of 8
Majority are an unknown cause
Can be due to:
- Neurological - early stimulation of central maturation
>Pineal tumours
>Meningitis
- Uncontrolled gonadotrophin or steroid secretion
- Hormone secreting tumours
What is the period of the end of the female reproductive life called?
The climacteric
- Pre-menopause
- Menopause
- Post menopause
