5.What and where are the hypothalamus and the pituitary gland ?

The hypothalamus and pituitary gland are essential for normal sexual development. These tiny glands are located within, but not actually part of the brain, as shown in Figure 3. 

 Location of the hypothalamus and pituitary gland.

Location of the hypothalamus and pituitary gland.

 

The hypothalamus (item 1) is walnut sized gland and is regarded as the master or controlling gland which takes in information from all around the body and controls the levels of hormones released from the other endocrine glands under its control.

The pea-sized pituitary gland (item 3) is connected to the hypothalamus by a tiny structure called the pituitary stalk (item 2) containing a rich network of tiny blood vessels or capillaries. It is through this network of blood vessels that GnRH travels in order to stimulate the pituitary into releasing its hormones, LH and FSH. Since GnRH is not released into the general blood circulation it is impossible to measure GnRH levels in the normal way by means of a blood sample taken from a vein.

Located very near the hypothalamus and pituitary are the two olfactory bulbs.(item 4). These are involved in the ability to smell and relay signals from the nose to the brain. These bulbs are missing or are markedly reduced in size in people with Kallmann syndrome which results in the absence of the sense of smell (anosmia).

The hypothalamus and pituitary work as a team to control the function of endocrine glands around the body. With regard to Kallmann syndrome it is the hypothalamic-pituitary-gonadal pathway which is of most interest.

In Figure 4, the hypothalamic hormone, GnRH,  targets the pituitary gland. As the name suggests GnRH causes the release of the gonadotropins LH and FSH from the pituitary gland.

The FSH and LH then travel in the peripheral blood stream to the testes or the ovaries.

Under the influence of LH and FSH the testes release testosterone and produce sperm and the ovaries release oestrogen and progesterone as well as causing the maturation and release of the eggs already located inside the ovaries. The levels of these hormones normally act in a feedback manner back onto the hypothalamus to ensure the only the correct amount of hormone is released at the correct time.

 The normal hypothalamic - pituitary - gonadal pathway.

The normal hypothalamic - pituitary - gonadal pathway.