Εndocrinology is the study of the endocrine system of glands, the regulatory substances (hormones) they produce and disorders of the system.
The endocrine system is a very complex, delicately balanced arrangement of ‘hormonal’ feedback loops designed to co-ordinate many bodily functions and ensuring they work normally.
The system uses many different hormones as ‘messenger’ signals. These are produced by a number of different endocrine glands that include the adrenal glands, sex glands (ovaries in women and testes in men), pancreas, parathyroid, pituitary gland and thyroid.
The hormones produced by these glands are secreted directly into the blood stream from within the gland where they are transported throughout the body for action on a wide range of target organs and systems.
The pituitary gland and hypothalamus
The pituitary gland, located on the underside of the brain, was once thought to be the ‘master’ gland being responsible for producing seven hormones regulating various bodily activities including growth and reproduction.
Although an important endocrine gland, hormone production by the pituitary gland is itself regulated by a small area of the brain called the hypothalamus, an area that provides an important link between the nervous and endocrine systems.
The hypothalamus produces nine different hormones, which (through the response of the pituitary gland) help regulate virtually all aspects of growth, development and metabolism.
Growth hormone
Growth hormone is one of the main hormones produced by the pituitary gland, and is a crucial factor in promoting normal growth and development in the body. Its action determines how the body is built, how it functions, and in particular the way bones develop.
Growth hormone is released in a cycle of short bursts throughout the day, roughly once every four hours, though about 70 per cent of the total growth hormone is secreted during the early hours of sleep particularly during dreaming.
Once sufficient growth hormone has been released, the increased concentration in the blood feeds back to the hypothalamus and a second hormone, called somatostatin (also known as GH-inhibiting factor), is released telling the pituitary gland to stop secreting growth hormone for the moment.
Role of growth hormone in growth
During childhood and puberty growth hormone secretion is at its highest causing bone cells to multiply by acting on ‘growth plates’ at the end of each tubular bone. It is the increase in the length of the long bones in the body that causes the body to grow taller and overall growth causes the skeleton to take on an adult shape.
After growth is complete, the growth plates of the long bones fuse together and close preventing further lengthening, and the secretion of growth hormone gradually falls to the much lower levels typical of adulthood.
Disorders of the endocrine system
The feedback mechanism of the endocrine system is designed to prevent overproduction (hypersecretion) or underproduction (hyposecretion) of any given hormone. However in some disease conditions there is an imbalance in the regulation.
The under- or overproduction of hormones from the pituitary gland cause several problems. Imbalance in the production of growth hormone affects the natural growth of children. Any shortfall in the production of growth hormone during childhood and puberty will affect the height and development of a child, and once the growth plates of the long bones have closed, growth hormone is unable to have any further effect on the height of an individual.