Puberty and the HPG axis

How do we measure physical development in children?

Tanner scale

When does puberty start for boys and girls?

Tanner scale 2

boys: Enlargement of testis & scrotum

girls: Thelarche (Breast budding)

How can diet affect puberty?

malnourishment: not enough fat → low leptin levels → puberty is slower/ doesn’t start

over nourishment: high fat → high leptin → puberty slows down

** both can also affect fertility

What is the endocrine hallmark of puberty?

Release of luteinizing hormone (LH) and follicle-stimulating hormone (FSH)

What gene codes for gonadotropin releasing hormone?

GNRH1 (chromosome 8)

Where is gonadotropin-releasing hormone released from, how frequently, and where does it go to?

secreted from the hypothalamus in pulses (in puberty its secreted in nocturnal pulses)

secreted in the hypophysial portal bloodstream to the anterior pituitary gland

Who starts puberty earlier and who’s puberty lasts longer and why?

girls go through puberty first (usually have a growth spurt earlier)

boys puberty lasts longer as oestrogen closes the epiphysis earlier and testosterone supports longer growth period for men 

What effect does LH and FSH have on men?

LH → Leydig cells (testis) to secrete testosterone
FSH → Sertoli cells (testis) to stimulate spermatogenesis and gonadal growth

When is testosterone highest?

in the morning

follows a circadian rhythm 

where are Sertoli cells found and what are their function?

located in the seminiferous tubules 

nourish and support the formation of the spermatozoa

What effect does LH and FSH have on women?

LH → Theca cells to produce estradiol
FSH → Granulosa cells to stimulate gametogenesis and gonadal growth

Function of theca cells

Synthesise androgens
production of androstenedione and 17β estradiol

How do Granulosa cells respond to FSH

Convert androgens (coming from the theca cells) to estradiol
after ovulation they turn into granulosa lutein cells that produce progesterone

What can cause early puberty and why is it bad?

Overweight and obesity might be the underlying causes of premature puberty

Risk of premature epiphyseal fusion

What can cause Hirsutism and menstrual abnormalities?

Polycystic ovary syndrome