Sexual Development

The foetal gonad is initially bipotential and undifferentiated.

– In males, the SRY gene on the Y chromosome is responsible for the differentiation of the gonad into a testis

– This leads to the production of testosterone and its metabolite dihydrotestosterone which causes development of male genitalia

– In the absence of SRY, the gonads become ovaries and the genitalia female

During puberty, the hypothalamus produces pulsatile secretions of GnRH.

– This stimulates the anterior pituitary to produce LH and FSH which act on the gonads:

Testes:

– LH acts on Leydig cells –> produces testosterone

– FSH acts on Sertoli cells –> produces sperm

Ovaries:

– LH acts on theca cells –> produces progesterone ad androstenedione

– FSH acts on granulosa cells –> convert androstenedione to oestrogen 

Pubertal Development:

Puberty is caused by activation of the HPG axis, resulting in increased sex hormone production which drives the development of primary and secondary sexual characteristics:

Primary sexual characteristics:

This mainly refers to the genitals (directly involved in sexual reproduction)

Secondary sexual characteristics:

This refers to any sex-specific characteristics not directly involved in sexual reproduction (e.g. breasts, hair)

These sexual characteristics share similar features in both sexes, but differ in which order they occur:

Females:

– First sign is development of the breasts (maybe asymmetrical)

– This is followed by growth and maturation of external genitalia and internal reproductive organs

– Females have then their growth phase with increases in height and widening of the pelvis

– One of the latest stages in menarche (first period) and the initiation of having regular menstrual cycles

– During this time, they will also have pubic hair growth, lowering of the voice and increase in sweat/sebaceous glands

Males:

– The first sign is growth of the testicles

– After this, boys have a significant growth spurt, with increase in height

– They will have increase muscular development and sweat/sebaceous gland proliferation

– The voice will also become lower.