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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.
