Repro 3.1 Puberty and Menopause Flashcards
When are primary sexual characteristics established?
Before birth
When do male and female reproductive systems become active?
Puberty
When do male hormone levels change?
First few months of life
At what age do girls and boys reach puberty?
Girls - 8-13
Boys - 9-14
From where are sex steroids secreted?
Adrenal glands and gonads
Why do boys grow taller?
Growth spurt starts later so they have grown more before it starts and grow at a faster rate during the growth spurt and it is also slightly longer (10cm/year as opposed to 9cm/year in girls)
What terminates the growth spurt?
Epiphyseal fusion - adult height virtually set
What controls the development of secondary sexual characteristics in girls?
Gonadal oestrogens influence breast development and female genital development
Androgens from adrenals control the development of pubic and axillary hair
What controls the development of secondary sexual characteristics in boys?
Testicular androgens control the development of genitalia and body hair and deepening of the voice
What is the name for the onset of a girls first menstrual bleed?
Menarche
NB. This does not indicate the onset of full fertility
What is the equivalent event for boys to menarche in girls?
Nocturnal erection and first ejaculation (more difficult o monitor)
NB. This does not indicate the onset of full fertility
Describe the hormonal changes in a girl until menarche.
Plasma levels of FSH and LH rise gradually from about 7 years of age to reach adult levels at of soon after menarche.
Plasma oestrogen levels rise steadily until at the beginning of menstrual cycles regular cyclical rises and falls are associated with the ovarian cycle
Weak androgens are secreted from adrenal glands
Describe the hormonal changes in boys from birth to adult level.
FSH and LH rise later than girls to reach adult levels around 16 years of age. This is associated with a steady rise in testosterone levels
Weak androgens are secreted from adrenal glands
What changes in the body signal the onset of puberty?
The brain initiates pulsatile GnRH secretion. This does not seem to depend on any signal from the gonads
What are the 2 theories explaining the onset of puberty?
Decreasing hypothalamic sensitivity to feedback -> Increased GnRH secretion
Hypothalamic mechanisms mature and steadily secrete more GnRH under other influences
Why has the onset of puberty become steadily earlier in the last 150 years in western society?
The main determining factor for onset of puberty is weight. Increased average body mass has decreased the age at which the onset of puberty occurs
Approximately what is the body weight at menarche?
47kg