puberty

definition of puberty

immature individual acquires the physical and behavioral attributes which all him or her to reproduce

GnRH axis

• hypothalamus produces gonadotrophin releasing hormone

• acts on GPCR receptor of gonadotrophins present in anterior pituitary

• stimulates release of LH and FSH

• acts on gonads

• produces gametes and sex steroids : testosterone, progesterone and oestrogen

GnRH

• simple hormone 

• released from hypothalamus

• analogues both agonists and antagonists to be used for treatment to reproductive problems 

prepuberty control 

• few GnRH pulses, less gonadotrophins, less FSH and LH

• dampened down by CNS 

• operative and sensitive feedback from sex steroids 

initiation of puberty

• mechanism of release of dampening from CNS

• dec sensitivity of feedback as LH and FSH increase

• rise during night initially

• circadian rhythm lost as puberty progresses

does FSH and LH require gonadotrophs to rise in puberty

no

adrenarche

• contribution of adrenal glands to puberty

• androstenedione and dehydroepiandrosterone androgens (DHEA)

• converted to testosterone and dihydrotestosterone in peripheral tissues

• inc hair growth, oily skin, acne

what is testosterone and dihydrotestosterone responsible for

• pubic and axillary hair growth

• axillary sebaceous glands

puberty in males

• growth of testes 

• inc mass of seminiferous tubules 

• pubic hair development

• all controlled by testosterone 

tanner scale for male puberty

1. no pubic hair

2. hair at base of penis

3. hair spread and coarser, testes and penis growth

4. more hair, enlargement of penis and testes

5. adult appearance achieved

secondary sexual characteristics seen in males

increased laryngeal size

deepening of the voice

increased bone mass

increased mass & strength of skeletal muscle

thickened skin i

ncreased &thickened hair on trunk, axillae & face

puberty in males vs females

• females occurs earlier and has faster progression than in males

what is pubic hair development controlled by

testosterone

secondary sexual characteristics in females

keratization of vaginal mucosa

enlargement of labia minora and majora

uterine enlargement

increased fat deposition in hips & thighs

all stimulated by estrogen

menarche

first menstrual period

around 13 

growth hormone secretion interaction with puberty

• androgens and oestrogens increase GH secretion

• pulsatile

• IGF-1 levels also rise

rate of growth for girls compared to boys

• starts 2 years earlier in girls

• and slower rate

what can cause the epiphyseal to close in puberty?

sex steroids - oestrogen

leptin

• hormone product of ob gene

• expressed in adipose tissue

• increased at start of puberty

k/o leptin mice effect

• low Gn levels

• underdeveloped gonads

is leptin receptor expressed by GnRH neurons

• no 

• so kisspeptin is needed for mediation 

what is kisspeptin produced by?

• CNS (hypothalamus, predominantly infundibular nucleus)

• Periphery (gonads, GI tract, placenta)

where does kisspeptin act? and effect?

• acts at a GPCR – GPR54

• GPR54 is expressed by GnRH neurones

• kisspeptin-1 activation of GPR54 stimulates GnRH release

effect of mutation to GPR54

• delayed puberty

• k/o animals fail to attain puberty

kisspeptin interaction with leptin?

leptin receptor is expressed by Kiss1 neurones