Session 3 - puberty Flashcards
what is puberty
A stage of human development when sexual maturation and growth are
completed and result in ability to reproduce
– Morphological physiological and behavioural development and development of secondary sexual characteristics
why can a tumour in the pineal gland cause early onset of puberty (pernicous puberty)
ANSWER LATER
what is the current average age of menarche
13 years
what is thought to be the critical weight that girls have to reach before starting their periods
47kg
periods can stop if you ball below this
body weight is thought to be the most important factors
leptins may be involved in signalling to show that there is enough fatty deposits to sustain another life
both boys and girls have oestrogen and testosterone
what keeps free testosterone levels lower in girls
testosterone binding proteins
and what age do girls commence puberty
9-13 years
- breast bud development (thelarche)
- pubic hair growth (adrenarche)
what causes the growth of pubic hair in males and females
response to testosterone
what is thelarche
is the onset of female breast development
what is adrenarche
when the adrenal cortex secretes increased levels of androgens such as DHEA and DHEAS, but without increased cortisol levels.
causes pubic hair growth, onset of growth spurt and onset of mestrual cycles (menarche)
what is the role of oestrogen in a growth spurt
Oestrogen important in maintaining bone mass and
closing epiphysial growth plates in males and females.
Females enter and leave the growth spurt face earlier so tend to be shorter
what is aromatase
an enzyme found in fatty tissues that converts testosterone to oestrogen
at what age do boys go through puberty
10-14
what happens to boys during puberty
pubic hair growth
spermatogenesis
growth spurt
genital development (testosterone)
what is a growth spurt
accelerated somatic growth which occurs in both boys and girls
it depends on growth hormone and sex steroids in both sexes
earlier and shorter in girls
men larger becaucse growth spurt longer and slightly faster
ended in both sexes by epiphyseal fusion
oestrogen causes the epiphyses to close earlier in girls
what causes the onset of puberty
Hormonal changes precede physical changes
Increased stimulation of hypothalamo-pituitary-gonadal axis
– gradual activation of the GnRH
– increases frequency and amplitude of LH pulses.
– gonadotropins stimulate secretion of sexual steroids
(oestrogenes and androgenes)
– extragonadal hormonal changes (elevation of IGF-I, and adrenal steroids)
what happens in GNRH is blocked
Lack of gonadotrophin synthesis and secretion and reproductive development occurs if GnRH is blocked
what are the characteristics of hormones released from the hypothalamus
• Secretion in pulses tied to internal biological clock
– Synchronized external signals i.e. by light
• Act on specific membrane receptors
• Transduce signals via second messengers
• Stimulate release of stored pituitary hormones
• Stimulate synthesis of pituitary hormones
• Stimulates hyperplasia and hypertophy of target cells
• Regulates its own receptor
when GnRH is released from the hypothalamus it stimulates the anterior pituitary to produce which two hormones
Stimulates the anterior pituitary gland gonadotrophs to secrete two
gonadotropic hormones:
– (1) luteinizing hormone (LH)
– (2) follicle-stimulating hormone(FSH).
– Gonadotrophs make up 5-10% total Anterior pituitary cells
– Gonadotrophs produce both LH and FSH
• In the absence of GnRH gonadotrophs secret little or no FSH LH
what is the role of leptin in the onset of puberty
• Leptin is an adipocyte-derived protein hormone
• Signals information about energy stores to CNS
• important role in regulating
neuroendocrine function.
– reproductive dysfunction
associated with leptin deficiency
– leptin can accelerate the onset of reproductive function
• Leptin has pulsatile release pattern significantly associated with the variations in LH.
• leptin can regulate GnRH levels, and its secretion may, in turn, be influenced by gonadal steroids but
appears to be independent of LH control
what is the hormonal change underlying a growth spurt
GH secretion from pituitary • Increases TSH • increases metabolic rate • promotes tissue growth • ↑ androgens = retention of minerals in body to support bone and muscle growth • = Growth spurt
how does GnRH cause the secretion of FSH and LH
One releasing hormone – GnRH 10 amino acid peptide • GnRH release is pulsatile – Every 1-3 hrs – Intensity of GnRH stimulus is affected by • Frequency of release • Intensity of release – GnRH travels to pituitary in hypophysial portal system • Anterior pituitary: connected to the hypothalamus by the superior hypophyseal artery • The anterior pituitary produces FSH, LH & Prolactin most significant for reproduction
how do hormones change as children get older
- in young children, LH and FSH levels insufficient to initiate gonadal function
- between 9-12 yrs., blood levels of LH, FSH increase
- amplitude of pulses increases, especially during sleep
- high levels of LH, FSH initiate gonadal development
which cells produce testosterone
• LH stimulates Leydig cells in testis
• Produce Steroid hormone ( from cholesterol ) Testosterone
• Greatest amount produced from testis
• Once production starts in the medium long term testosterone levels
remain constant
When are testosterone levels highest
early in the morning
what are sertoli cells
– provide nutrition and hormonal support to germ cells allowing sperm formation
– Sensitive to FSH (increase sperm production)
– Secreted inhibin (-) feedback on anterior pituitary FSH
what are the actions of FSH and LH
• Act primarily on gonads via Gα s PCR →adenylate cyclase • Female: Target cells Ovarian granulose cells, Theca interna, – Stimulate sex hormone synthesis (steroidgenesis) • ( i.e. oestrogen, progesterone, inhibin) – Control gamete production (folliculogenesis and ovulation)
Which cells respond to FSH
granulosa
Which cells respond to LH
theca
what feedback do we get if we have moderate levels of oestrogen
Moderate titres of oestrogen reduce GnRH secretion
• Negative feedback
what feedback do we get if have high levels of oestrogen alone
– High titres of oestrogen alone promote GnRH secretion
• Positive feedback
• LH ‘surge’
what happens to the levels of FSH and LH if we give oestrogen and progesterone
– Progesterone increases inhibitory effects of moderate oestrogen
– Progesterone prevents positive feedback of high oestrogen
• No LH surge
– Oestrogen reduces GnRH per pulse, progesterone frequency of pulses
how the pill works
whcih cells secrete inhibin
granulosa cells of corpus luteum
what does inhibin do
Inhibits the secretion of FSH
Has a small inhibitory effect on LH
