Repro7 - Puberty and the HPG Axis

Question 1

5 features of secondary sexual characteristics in females

Age
3 Stages
Scale

Answer 1

1. ) Age - appear between 9-13 years (puberty)
2. ) Thelarche - stage where male and female breasts becomes distinct (breast buds form)
3. ) Adrenarche - early stage in maturation
   - growth spurt, pubic hair growth
4. ) Menarche Cycles - menstrual cycle begins
   - breasts and pubic hair fully grow and mature
5. ) Tanner Scale - scale of physical development
   - 5 stages using breast size and pubic hair growth

Question 2

5 features of secondary sexual characteristics in males

Age
3 Stages
Scale

Answer 2

1. ) Age - appear between 10-14 years
2. ) Genital Development
3. ) Spermatogenesis and Pubic Hair Growth
4. ) Growth Spurt
   - also, genitalia and pubic hair fully grow and mature
5. ) Tanner Scale - scale of physical development
   - 5 stages using penis size, pubic hair growth, and scrotum growth

Question 3

3 features of accelerated somatic growth in males and females

Answer 3

1.) Hormone Dependent - depends on GH, IGF-1 and sex steroids in both sexes

2. ) Larger Males - starts later in males but the growth spurt is longer and slightly faster
   - genital development in boys depends on testosterone
3. ) 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)

Question 4

4 features of the HPG (hypothalamus-pituitary-gonadal) axis

Sequence
GnRH Release
Puberty Onset

Answer 4

1.) Sequence - Hypothalamus (GnRH) –> Anterior Pituitary (LH + FSH) –> Gonads (androgens + oestrogen)

2. ) 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
3. ) 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

Question 5

3 features/structures relating to male androgen production

Seminiferous Tubules
Leydig Cells
Sertoli Cells

Answer 5

1. ) Seminiferous Tubules (ST) - spermatogenesis occurs
   - ST need functioning leydig cells
2. ) Leydig Cells - produces majority of testosterone
   - stimulated by LH
   - production is affected by circadian rhythm (highest in early morning) and environmental stimuli
3. ) Sertoli Cells - provides nutrition and hormonal support for sperm
   - stimulated by FSH
   - can secrete inhibin, producing -ve feedback on AP

Question 6

6 features of female androgen production

2 Stimulatory Hormones
2 Types of Cells
3 Sex Steroids and their effect on HPG axis

Answer 6

1.) FSH and LH - bind to G(as)PCRs to activate AC

2. ) Granulosa Cells - stimulated by FSH, LH and androgens produced by the theca interna cells
   - produce oestrogen, progesterone, and inhibin
3. ) Theca Interna Cells - stimulated by LH
   - produce progesterone and androgens
4. ) 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
5. ) 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)

Question 7

4 features of leptin

Type of Hormone
Function
Type of Release
Relation with HPG Axis

Answer 7

1. ) Hormone Type - adipocyte-derived protein hormone
2. ) Function - signals info about energy stores to CNS
3. ) Pulsatile Release - associated with variations in LH
4. ) 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