Hormonal changes in puberty

Although the outward physical changes associated with puberty tend to become more obvious after the age of 11, the blood levels of the hormones that drive these changes begin to increase from about the age of 7 to 8 years old.

The initial change occurs in a group of steroid hormones, called androgens, that are produced by the adrenal glands in the abdomen. These adrenal androgens are also key to the commencement of secondary sexual characteristic development in both girls and boys.

The hormonal cascade that triggers puberty starts in the hypothalamus of the brain. This releases a hormone called gonadotrophin releasing hormone, or GNRH, and as puberty begins the pattern of release of this hormone changes dramatically. GNRH acts on the pituitary gland, a pea-shaped gland at the base of the brain, causing an increase in the release of two hormones called follicle stimulating hormone (FSH) and luteinizing hormone (LH). These stimulate the growth and function of the ovaries in girls and testes in boys.

In girls FSH acts on the ovaries and is responsible for the development of the follicles which contains the developing eggs, or ova. As these follicles mature they produce the sex steroid, oestrogen. Luteinizing hormone (LH) is responsible for release of the ovum from the ovary and also for progesterone production. In boys follicle stimulating hormone (FSH) encourages the growth of seminiferous tubules, which produce sperm through the process of spermatogenesis, whilst luteinizing hormone (LH) stimulates other cells within the testes that produce the male sex steroid, testosterone.