This secton deals with various biological aspects which everyone should be aware of like human physiology, hormonal secretion and their functions, the male sex organs and the female sex organs. We have tried to give an accurate picture but in case you need more details, we advise you to pick up a book of biology.
Nobody can will himself to grow or to stop growing; nobody can turn off his digestive system simply by thinking about it; nobody can cause his cells to reproduce themselves simply by concentrating. Yet all of these changes in the body are just as much under the control of the brain as is the conscious decision whether or not to reach out for an extra helping of potatoes.
Instead of being responses to a message sent by the brain along the nerve pathways, these changes and many others are responses to messages delivered in a kind of code by chemicals known as hormones.
These coded signals control the inner rhythms of the body; such as those which take place in a woman's body during menstruation. They are responsible for the bursts of energy produced during emergencies for rapid growth infancy, a slower rate of growth during childhood and the final explosion of growth during adolescence.
Hormones are produced and released in response to instructions from the brain, by various organs and tissues but the chief producers are the endocrine glands. Small and powerful, the endocrines pump their secreted hormones directly into the bloodstream. The blood then carries them to the places where they take effect.
There are six main sets of glands in the endocrine system the pituitary, thyroid, parathyroids, adrenals, islets of Langerhans in the pancreas and gonads (testis in men and ovaries in women). They are ductless glands that secrete their bio-chemical substances called hormone (meaning "I excite"), directly in the blood-stream.
Because of their importance in human sexuality, three glands : pituitary, adrenal and the gonads are important.
The pituitary gland is a small gland - about one-half inch long - weighing less than half a gram and is located in the skull at the base of the brain. Not all hormones secreted by the pituitary have been identified or their action defined, but the best known ones are:
The growth hormone, referred to as HGH (human growth hormone), affects the growth and shaping of the skeleton.