The Endocrine System - Part 1

The control centers. The endocrine glands secrete chemicals which control the growth and development of the body. These chemicals are secreted into the blood stream and are carried to all parts of the body. Because they are in general circulation, these chemicals, called hormones, can act in areas far from the gland that secreted them. They may even act on several organs at once.

The endocrine glands have a certain similarity to the nervous system because they help to integrate the activities of widely separated organs. Emotional strain, for example, causes one of the endocrines to enlarge and secrete a chemical which speeds up the action of the heart.

 

The master gland. In the base of the skull is a tiny gland called the pituitary, or hypophysis. This gland is called the master gland because it controls growth and the action of the adrenal, thyroid, and male and female glands. Through these glands, it has an enormous effect on the other systems of the body.

The pituitary gland secretes at least eight hormones in order to exercise its control over body functions. Each hormone controls a particular body function. Examine the chart below to see what functions these eight hormones control.

The adrenals. The adrenal glands are two of the glands that are regulated by the pituitary. The adrenals are two glands located above the kidneys. Each adrenal is composed of two parts: an inner part, called the medulla, and an outer layer, called the cortex.

The hormone secreted by the medulla, called epinephrine, is probably the best known hormone in the body. Commonly called adrenalin, this hormone stimulates most of the emergency reactions within the body. It increases the heart beat, releases sugar from the liver into the blood stream, delays fatigue in the skeletal muscles, raises the blood pressure, and performs many other functions.

 

HORMONE	FUNCTION OF HORMONE
A	assists the body in the birth of children
B	prevents excess water loss from the kidneys
C	deepens the pigment of the skin
D	regulates development and function of gonads
E	regulates the activity of the thyroid gland
F	controls the activity of the adrenal cortex
G	regulates the growth of the whole body
H	stimulates the production of milk in mothers

 

In view of these effects you would think that epinephrine is essential to the function of the body. Such is not the case, however. Parts of the autonomic nervous system can control these functions even when the adrenal medulla is removed from the body! It is likely that the medulla serves only to help the autonomic nervous system in times of danger, but that it is not necessary for the body’s functioning.

The adrenal cortex. The adrenal cortex, on the other hand, secretes substances which’ are vital to the body. A person deprived of his adrenal cortex would die within a few days. It is the secretion of the hormone from the adrenal cortex that is controlled by ACTH, a hormone secreted by the pituitary. Scientists are not sure why the cortex is essential, although they have found that cortisone is very useful in alleviating some symptoms of disease.

Related Posts

1. The Endocrine System - Part 2
2. Adolescence and Internal Change
3. The Nervous System
4. The Human Body
5. Heredity and the Growth Spurt