Repro7 - Puberty and the HPG Axis Flashcards
5 features of secondary sexual characteristics in females
Age
3 Stages
Scale
- ) Age - appear between 9-13 years (puberty)
- ) Thelarche - stage where male and female breasts becomes distinct (breast buds form)
- ) Adrenarche - early stage in maturation
- growth spurt, pubic hair growth - ) Menarche Cycles - menstrual cycle begins
- breasts and pubic hair fully grow and mature - ) Tanner Scale - scale of physical development
- 5 stages using breast size and pubic hair growth
5 features of secondary sexual characteristics in males
Age
3 Stages
Scale
- ) Age - appear between 10-14 years
- ) Genital Development
- ) Spermatogenesis and Pubic Hair Growth
- ) Growth Spurt
- also, genitalia and pubic hair fully grow and mature - ) Tanner Scale - scale of physical development
- 5 stages using penis size, pubic hair growth, and scrotum growth
3 features of accelerated somatic growth in males and females
1.) Hormone Dependent - depends on GH, IGF-1 and sex steroids in both sexes
- ) Larger Males - starts later in males but the growth spurt is longer and slightly faster
- genital development in boys depends on testosterone - ) Epiphyseal Fusion - determines the end of accelerated somatic growth and depends on oestrogen
- oestrogen closes epiphyses earlier in girls
- males have less oestrogen so closes later in boys
- males can testosterone –> oestrogen (aromatisation)
4 features of the HPG (hypothalamus-pituitary-gonadal) axis
Sequence
GnRH Release
Puberty Onset
1.) Sequence - Hypothalamus (GnRH) –> Anterior Pituitary (LH + FSH) –> Gonads (androgens + oestrogen)
- ) Nocturnal GnRH - causes LH secretions at night which precedes phenotypic changes (e.g. breast buds/testicular enlargement) by several years
- amount of sleep is directed related to LH release which can cause early pubertal changes - ) Pulsatile GnRH Release - released every 1-3 hours
- if GnRH receptors are exposed to continuous presence of GnRH, they become desensitised, stopping FSH and LH production –> stopping gonadal steroid production
- GnRH agonist can be used as a contraceptive
4.) Onset of Puberty - associated with steady rise in FSH/LH secretion
3 features/structures relating to male androgen production
Seminiferous Tubules
Leydig Cells
Sertoli Cells
- ) Seminiferous Tubules (ST) - spermatogenesis occurs
- ST need functioning leydig cells - ) Leydig Cells - produces majority of testosterone
- stimulated by LH
- production is affected by circadian rhythm (highest in early morning) and environmental stimuli - ) Sertoli Cells - provides nutrition and hormonal support for sperm
- stimulated by FSH
- can secrete inhibin, producing -ve feedback on AP
6 features of female androgen production
2 Stimulatory Hormones
2 Types of Cells
3 Sex Steroids and their effect on HPG axis
1.) FSH and LH - bind to G(as)PCRs to activate AC
- ) Granulosa Cells - stimulated by FSH, LH and androgens produced by the theca interna cells
- produce oestrogen, progesterone, and inhibin - ) Theca Interna Cells - stimulated by LH
- produce progesterone and androgens - ) Oestrogen - produces +ve and -ve FB on GnRH
- moderate/small levels promotes -ve feedback
- high levels promote GnRH leading to an LH surge
- it affects the amount of GnRH per pulse - ) Progesterone - inhibits oestrogen
- increases -ve feedback of moderate oestrogen
- prevents +ve feedback of high oestrogen
- it reduces the frequency of GnRH pulses
6.) Inhibin - inhibits secretion of FSH (-ve FB on AP)
4 features of leptin
Type of Hormone
Function
Type of Release
Relation with HPG Axis
- ) Hormone Type - adipocyte-derived protein hormone
- ) Function - signals info about energy stores to CNS
- ) Pulsatile Release - associated with variations in LH
- ) Regulate GnRH Levels - secretion may be influenced by gonadal steroids but it’s independent of LH control
- can accelerate the onset of reproductive function, whilst deficiency can lead to reproductive dysfunction