3.1: puberty (workbook) Flashcards
when are most primary sexual characteristics developed?
before birth
when do hormonal changes occur in the male?
first few months of life
when do male and female reproductive systems remain inactive until?
puberty
describe the timing of puberty
The timing of puberty varies between the sexes and between individuals
how is the sequence of events in puberty like?
a fixed sequence of events
do girls or boys reach puberty first?
girls
what is the age range of puberty for girls?
8-13 years for girls
what is the age range of puberty for boys?
9-14 years for boys
what are obvious signs of puberty preceded by?
a series of events that depend upon sex steroids secreted from the gonads and adrenal glands
what is the growth spurt?
a marked acceleration of growth in both boys and girls
which gender begins growth spurt first?
girls
what is the velocity of growth spurt in girls?
about 9cm/year in girls
what is the velocity of growth spurt in boys?
about 10cm/year in boys
why do adult males end up larger?
boys grow more before the growth spurt and slightly more during it
what is the growth spurt terminated by?
epiphyseal fusion, at which point adult height is virtually set
what are the main secondary sexual characteristics and what do they develop under?
such as breasts, genitalia and pubic hair
develop under the influence of sex steroids
in the female, what stimulates breasts and female genital development?
gonadal oestrogens (from ovaries) influence breast development and female genital development
what stimulates pubic and axillary hair development in females?
controlled by androgens from the adrenals (adrenal cortex)
what do testicular androgens control in males?
development of genitalia, body hair and deepening of the voice
what is first menstrual bleed in girls called?
menarche
a defining event in puberty for girls
what is the equivalent of menarche in boys?
occurrence of nocturnal erection and the first ejaculation
which is much less easy to monitor
does menarche and nocturnal erection & first ejaculation indicate full fertility?
Neither of the events indicates the onset of full fertility
what happens to plasma levels of FSH and LH in girls (after menarche)?
plasma levels of FSH and LH rise gradually from about 7 years of age to reach adult levels at or soon after menarche
what happens to plasma oestrogen levels in girls?
Plasma oestrogen levels rise steadily, until at the beginning of menstrual cycles regular cyclical rises and falls are associated with the ovarian cycle
what is the anterior pituitary gonadal axis capable of responding to?
stimulation by GnRH long before puberty normally occurs but GnRH secretion is low
what is the anterior pituitary gonadal axis capable of responding to before puberty?
stimulation by GnRH long before puberty normally occurs but GnRH secretion is low
what is the anterior pituitary gonadal axis capable of responding to before puberty?
stimulation by GnRH long before puberty normally occurs but GnRH secretion is low
when does puberty occur?
when the brain initiates pulsatile GnRH secretion
when does puberty occur?
when the brain initiates pulsatile GnRH secretion
what does brain’s pulsatile GnRH secretion depend on?
This does not seem to depend on any signal from the
gonads
how has menarche age changed in girls?
First, puberty has become steadily earlier in western
societies over the past 150 years.
In 1830 girls reached menarche at 17 years of age,
now it occurs at an average, age 13.
how has menarche age changed in girls?
First, puberty has become steadily earlier in western
societies over the past 150 years.
In 1830 girls reached menarche at 17 years of age,
now it occurs at an average, age 13.
The main determining factor influencing puberty?
body weight
what is the body weight at menarche?
about 47kg
what is the body weight at the beginning of growth spurt (in girls)?
30kg
what is the critical weight in boys?
55kg
what may indicate to the hypothalamus the attainment of the initial body weight?
plasma concentration of a fat derived hormone – leptin
in many species (where breeding is seasonal), what is GnRH secretion switched on and off by? reflected in?
by changes in daylight, influencing the pineal gland
and reflected in changes in the secretion of melatonin.
what can precocious and delayed puberty in humans be associated with?
various CNS disorders such as meningitis and tumours
