The word “hormone” comes from Greek meaning “to excite or to set into motion”. Main Function: To release chemicals into the blood to signal other cells to behave in certain ways. It is a slow but widespread form of communication. More free at

Endocrine glands - release hormones into the bloodstream (as opposed to exocrine glands like sweat & digestive glands). Hormones are chemicals released in one part of the body that travel through the bloodstream and affect activities of target cells in other parts of body. consists of:

Endocrine Hormones classified according to their activation site Non-target hormones: affect many cells throughout the body; eg. insulin, epinephrine target hormones: affect specific cells or target tissues; eg. FSH, parathyroid hormone

Chemical Control Systems The endocrine system maintains control over a long duration (nervous system adjusts to short term) So… How does it work? The hypothalamus regulates the pituitary gland through nerve stimulation. It is the pituitary gland that stimulates the glands of the endocrine system to release hormones.

Hormones only affect cells that contain receptors capable of recognizing and interacting with them. There are 2 types (see page 374): o Steroid hormones: fat-soluble molecules made from cholesterol (e.g. male and female sex hormones, cortisol) o Protein hormones: water-soluble molecules derived from amino acids or chains of amino acids (e.g. insulin, growth hormone, thyroxine)

Steroid Hormones Steroid hormones are lipids (and hydrophobic). Because of that, they have no problem interacting with a cell membrane made up largely of phospholipids. Therefore, when a steroid hormone travels through the blood and encounters a cell, it does not have to stop at the cell membrane to try to get in. It simply shoots right through the cell membrane, unencumbered!

Within the nucleus of a cell are steroid receptors. This complex has another binding site in the nucleus. The steroid part can bind to DNA. When the steroid binds to DNA, it stimulates the nucleus to make new proteins off the region of the DNA to which it is attached. hill.com/sites/ /student_view0/chapter10/animation__mechanism_of_steroid_hormone_action__quiz_1_.htmlhighered.mcgraw- hill.com/sites/ /student_view0/chapter10/animation

Protein Hormones A hydrophilic hormone cannot get into a cell, it can only bind to a receptor located on the outside of its target cell's membrane. But, the hormone is bringing a message from your body to that target cell (e.g. the hormone TSH or thyroid-stimulating hormone tells the cells of the thyroid gland that thyroxine needs to be produced) Because the hormone tells the target cell that it needs to carry out some function for the body, it can be referred to as the first messenger.

It is only the "first" messenger, because whatever else it needs for the target cell to do, it cannot make it do that from outside of the target cell. Therefore, a second messenger that is within the target cell must continue to carry the message of the hormone within the cell to get the job done. "cAMP" is the second messenger. It is responsible for continuing the cascade of chemical reactions within the cell to get it to do something new.

Protein Hormone Action

Protein hormone action (continued)

Interaction of Glands The hypothalamus is located in the brain and controls the release of hormones from the pituitary gland. It is an important link between the endocrine and nervous systems. cts/Hypothalamus.gif

The Pituitary Gland The pituitary is a pea sized gland located at the base of the brain. It is connected by a stalk to the hypothalamus. Mainly regulatory hormones are released here. Most control the pituitary gland.

The Pituitary Gland The pituitary controls other endocrine glands and regulates body growth; functions as a control centre, coordinating the endocrine and nervous systems. It produces and stores hormones. Hormones stored in the pituitary gland are secreted when stimulated by the hypothalamus via nerve impulses.

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Pituitary Gland Function: It secretes nine hormones that directly regulate many body functions and controls functions of other glands.

The Posterior Pituitary Lobe No hormones are made here. They are made in the hypothalamus and just released here. Two protein hormones are released from the posterior pituitary lobe ADH (antidiuretic hormone or vasopressin) OT (oxytocin)

Posterior lobe stores and releases hormones which are produced in the hypothalamus

Anterior Pituitary Hormones Growth Hormone (GH): stimulates cells to grow and divide stimulates the production of insulin-like growth factors (produced by liver) which stimulate cell division in the growth plates resulting in elongation of skeleton increases amino acid uptake by cells and protein synthesis inhibits protein degradation increases fat metabolism (changes body – less fat tissue and an increase in protein, and therefore, muscle) Typically, GH is secreted during sleep. GH secretion increases when malnourished

Disorders: Too much growth hormones (GH) in early childhood can result in a condition called gigantism. Too little GH can result in Pituitary Dwarfism.

Questions, p.377 #1-4