Human Endocrine System | Biology for Grade 10 PDF Download

Hormones and Nerves

• A hormone is a chemical substance, produced by a gland and carried in the bloodstream, which alters the activity of specific target organs. An example of this is the release of the hormone adrenaline, which is released by the adrenal gland. One of its target organs is the heart, where it increases the heart rate.
• Once a hormone has been used, it is destroyed by the liver.
• Hormones can control the body, and the effects are much slower than the nervous system, but they last for longer.
  
  Contraceptive pills contain hormones to reduce the chances of becoming pregnant
• There are important differences between nervous and hormonal control.
  

Master Gland

The pituitary gland in the brain is known as a 'master gland'. It secretes several hormones into the blood in response to the body's condition, such as blood water levels. These hormones can also act on other glands to stimulate the release of different types of hormones and bring about effects.

Different Hormones

The body produces a range of different chemical hormones that travel in the bloodstream and affect a number of different organs or cells in the body. The diagram below shows this in detail.

Important hormones released into the bloodstream include ADH (anti-diuretic hormone), adrenaline and insulin.