1. Endocrine System

2. Principal characteristics of the endocrine system  Made up of endocrine glands that release chemical messengers called HORMONES right into the bloodstream  Allow for the maintenance of the internal environment in the body, or internal homeostasis  Allow the regulation of growth and development of an organism.

3. Functions of Endocrine Glands  The endocrine glands include the hypothalamus, pituitary, thyroid, parathyroid, adrenal, thymus, and pancreas.

4. Functions of Endocrine Glands The pituitary gland communicates with the hypothalamus to control many body activities.

5. What Are Hormones? Hormones are chemical substances created by the body that control numerous body functions. They actually act as "messengers" to coordinate functions of various body parts. Most hormones are proteins consisting of amino acid chains. Functions controlled by hormones include: activities of entire organs growth and development Reproduction sexual characteristics usage and storage of energy levels of fluid, salt and sugar in the blood

6. Endocrine system maintains HOMEOSTASIS The word homeostasis means “the maintenance of stable internal conditions in an organism”. Example: Blood sugar is too high, and the pancreas makes more insulin to reduce the level of insulin. Blood sugar goes down. When it is low enough, the production ceases. Insulin will be produced again when blood sugar again increases.

7. Negative Feedback Through negative feedback, when the amount of a particular hormone in the blood reaches a certain level, the endocrine system sends signals that stop the release of that hormone.

8. The Nervous System is different from the Endocrine System The nervous system exerts point- to-point control through nerves, similar to sending messages by conventional telephone. Nervous control is electrical in nature and fast.

9. Hormones travel via the bloodstream to target cells The endocrine system broadcasts its hormonal messages to essentially all cells by secretion into blood and fluid that surrounds cells. Like a radio broadcast, it requires a receiver to get the message - in the case of endocrine messages, cells must bear a receptor for the hormone being broadcast in order to respond.

10. A cell is a target because is has a specific receptor for the hormone Most hormones circulate in blood, coming into contact with essentially all cells. However, a given hormone usually affects only a limited number of cells, which are called target cells. A target cell responds to a hormone because it bears receptors for the hormone.