The Endocrine System

The Endocrine system (along with the nervous system) controls and regulates the complex activities of the body. The Endocrine system regulates the activities of the body by secreting complex chemical substances (hormones) into the blood stream. These secretions come from a variety of glands which control various organs of the body. The key functions are:

1. To regulate the metabolic functions of the body.

2. To regulate the rate of chemical reactions in various cells.

3. To influence the ability of substances to transport themselves through cell membranes.

 

About Hormones

Hormones

are secreted from the glands of the endocrine system, they are specific in that each hormone causes a response in a specific target organ or group of cells, rather than on the body as a whole. Exocrine hormones are secreted via a duct into the blood and usually effect a distant organ or tissue. Endocrine hormones are secreted within the tissue (rather than via a duct) and enter the blood stream via capillaries.

Hormones can be grouped into three main types:

1.      amines, these are simple molecules

2.      proteins and peptides which are made from chains of amino acids

3.      steroids which are derived from cholesterol.

Glands

discharge hormones directly into the bloodstream. They have built in feedback mechanisms that maintain a proper balance of hormones, and prevent excess hormone secretion. Low concentrations of a hormone will often trigger the gland to secrete. Once the concentrations of the hormone in the blood rise this may cause the gland to stop secreting, until once again hormone concentrations fall. This feedback mechanism (which is characteristic of most glands) causes a cycle of hormone secretions.

Disposal of waste.

Once hormones have served their function on their target organs/tissues they are destroyed. They are either destroyed by the liver or the actual tissues of the target organs. They are then removed by the kidneys.

The Pituitary Gland

This is known as the "master gland" because it exerts control over all of the other glands of the endocrine system. Despite its importance the pituitary gland is no larger than a small pea. The Pituitary gland is made up of two separate glands: the Anterior lobe which is an outgrowth of the pharynx, and the Posterior lobe which is an outgrowth of the brain composed of neural (nerve) tissue.

The Anterior Lobe of the pituitary plays the 'master' role secreting six major hormones that affect most of the body, including the other Endocrine glands: