Unit 3 - Endocrine System

Endocrine System

Uses chemicals (hormones) to communicate.

Needs interstitial fluid and/or bloodstream for the transmition of signals and requires receptors for signal recognition.

Slow response time, longer action duration.

Endocrine System Function

Regulation of growth and development.

Maintenance of the optimum internal environment to sustain optimal body function.

Initiating and maintaining the reproductive system.

Hormone

A chemical signal produced by a cell, tissue, or organ.

Released into the blood and transported to other organs through blood circulation.

Able to produce a specific response in target organ at a very low concentration.

Can be classified according to their chemical composition and physical properties.

Endocrine (Distant Tissues)

Chemical signals produced by cells and released into blood circulation. Chemical signals bind to distant target cells to exert the action.

Paracrine (Neigbouring Tissues)

Chemical signals produced by cells and released into extracellular space.

Chemical signals bind to neigbouring cells in the same organ.

Autocrine (Same Cell)

Chemical signals produced by cells and released into extracellular space.

Chemical signals bind to neigbouring cells in the same cell.

Hormone Destruction

Hormones in the bloodstream are generally degraded by enzymes in the liver and kidneys.

Hormone Transport

Steroid Hormone: lipophilic and can easily diffuse acorss surface membrane of its target.

Water-Soluble Hormone: circulate in a “free form”, dissolved in plasma.

Lipid-Soluble Hormone: bound to transport proteins synthesized in the liver.

Hormone Responsiveness

Depends on: binding of the signal to the target’s receptors and signal transduction pathways (receptors on outer plasma membrane = faster, on membrane of the nucleus = slower).

Endocrine Secretion Control

Tropic hormone controls secretion of another endocrine gland to produce hormone.

Hypothalamic Region - tropic signals from CNS.

Anterior Pituitary Region - tropic signals from hypothalamic.

Endocrine Gland - tropic signals from anterior tropic hormones.

Endocrine Interactions

Synergism - combined effect is greater than the sum of individual effects.

Permissiveness - need second hormone to get full effect.

Antagonism - one substance opposes the action of another.