The Endocrine system works in conjuction with the nervous system to coordinates and direct the activities of the bodies cells. The endocrine system acts much more slowly than the nervous system and carries out its duties through hormones, which are chemical messengers secreted into the blood to be transported through the body to reac h their target organs.  Hormones have a variety of different effects, their major functions are  to control :

• reproduction
• growth and development
• mobilizing body defenses against stressors
• maintaining homeostasis  ( like electrolyte, water, and nutrient balance)

The endocrine system is responsible for regulating processes that go on for long periods and in some cases continuously.
In comparison to other organ systmes throughout the body, the organs of the endocrine system are relatively small.
Interesting fact:  To make one kilogram  of hormone-producing tissue, you would need to obtain all of the endrocrine glands from about 8 adults. Most other organ systems are for the most part  structurally continuous ( like the digestive system's organs are all in contact with each other in a tract that runs from the mouth to the rectum, The brain, nerves, and spinal cord are all connected, etc...) . The endocrine system, on the otherhand has bits and pieces spread throughout the body. Most of these organs are isolated from one another. 

The Endocrine System  and Hormone Function  

Objectives:

• Define hormone and target organ.
• Describe how hormones bring about their effects in the body.
• Explain how various endocrine glands are stimulated to release their hormonal products.
• Define negative feedback, and describe its role in regulating blood levels of various hormones.

Marieb - pages 300-303

The Chemistry of Hormones

Hormones - chemical substances that re secreted by cells into extracellular fluid  and regulate the metabolic processes of other cells in the body. The word hormone  comes from a greek word meaning  " to arouse"

Hormones may be classified as

• amino-acid based molecules ( proteins, peptides, and amines)
• steroids -  (cholesterol based) included are
• sex hormones
• hormones of the adrenal cortex
• prostaglandins - (p. 321)  local hormones made from highly active lipids  found in the cells plasma membrane

Mechanisms of Hormone Action

Bloodborne hormones circulate to all organs of the body, a given hormone only effects certain tissue cells or organs.a These cells that a hormone affects are called target cells. Hormones only bind to cells with specific protein receptors  on the plasma membrane  or inside the cell, to which the hormone may attach.  Once this binding has taken place, the hormone is then able to influence the workings of the cell.  Hormones alter cellular activity by increasing or decreasing normal metabolic processes. This typically causes one of the following to occur:

• Changes in  plasma membrane permeability or electrical state.
• Synthesis of proteins or certain regulatory molecules, such as enzymes, inside the cell.
• Activation or deactivation of enzymes.
• Stimulation of mitosis. 

There are typically two mechanims by which hormones trigger changes in the cell  (see pages 294-296, Hole's)  

• Steroid Hormone Action (this includes thyroid hormone)   

• see page 294 (hole's) figure 11.2
• page 301 (marieb) figure 9.1
• tutorial here
• Image here

Steroid hormones are molecules of complex rings of carbon. they are lipid soluble and therefore can diffuse through the cell membrane much more easily than amino-acid based hormones. Once inside the target cell the steroid hormone may then bind with protein receptors that are specific to that hormone. This hormone-protein complex will then bind within the nucleus of the cell to a particular segment of DNA. Once bound it will activated specific genes with will then be transcribed into messenger RNA. This will instruc the cell to manufacture specific proteins.

• Nonsteroid Hormone Action

• see page 295 (hole's) figure 11.3
• page 301 (marieb) figure 9.1
• Tutorial here 

Nonsterois hormones are amines, peptides, and  proteins. These hormones must usually combine with receptors located on the membrane of the target cell, due to the fact that they can not pass through the phospholipid bilayer of the cell.

Control of Hormone Release

The Major Endocrine Organs

• Andrenal
• Hypothalmus
• Pancreas (Islets of Langerhans)
• Parathyroid
• Pineal
• Pituitary
• Thyroid
• Gonads
• Testes (males)
• Ovaries (females)

Adrenal Gland

These two bean shaped glands curve over the tops of the kidneys. They are composed of a glandular tissue (the cortex) and neural tissue (medulla).


this section under construction.......

Table 9.1  Major Endocrine Glands and Some of Their Hormones
Gland	Hormone	Chemical class	Representative  Actions	Regulated by
Pineal Body	Melatonin	Amine	Involved in Biological Rythyms	Light / Dark Cycles
Hypothalmus
Pituitary Posterior Lobe	Oxytocin	Peptide	Stimulates contraction of the uterus and the milk "let-down" reflex	Nervous System (hypothalmus) in response to uterine strecthing and/or suckling of a baby
	Antiduiretic hormone (ADH)	Peptide	Promotes retention of water in the kidneys	Hypothalmus in response to water and/ or salt imbalance
Pituitary Anterior Lobe	Growth hormone (GH)	Protein	Stimulates growth (especially of bones and muscles) and metabolism	Hypothalamic releasing and inhibiting hormone
	Prolactin (PRL)	Protein	stimulates milk production	Hypothalmic hormones
	Follicle-Stimulating Hormone (FSH)	Protein	Stimulates production of ova and sperm	Hypothalmic hormones
	Luteininzing Hormone (LH) - may be called interstitial cell stimulating hormone (ISCH), bu personally i think that is way too long	Protein	Stimulates ovaries and testes	Hypothalmic hormones
	Thyroid-stimulating Hormone (TSH)	Protein	Stimulates thyroid gland	Thyroxine in blood; hypothalmic hormones
	Adrenocorticotropic hormone (ACTH)	Protein	Stimulates adrenal cortex to secrete glucocorticoids	Glucocorticoids; hypothalmic hormones
Thyroid Gland	Thyroxine (T4)	Amine	Stimulates Metabolism	TSH
	Triiodothyronine (T3)	Amine	Stimulates Metabolism	TSH