Endocrine System

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.

Functions of Endocrine Glands

The endocrine glands include the hypothalamus, pituitary, thyroid, parathyroid, adrenal, thymus, and pancreas.

Functions of Endocrine GlandsThe pituitary gland communicates with the hypothalamus to

control many body activities.

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

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.

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.

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.

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.

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.