Hormones: Complex molecules produced by the body which act as chemical messengers to the body's cells. They are made by the endocrine glands of various organs, including the pituitary gland, parthyroid gland, thyroid gland, pancreas, hypothalamus, adrenal glands, stomach, small intestine, and gonads (males). These proteins, in response to the proper signal, are secreted and then exert influence on they are carried through the bloodstream to exert influence of target tissues, which may be a great distance away. They act by chemically stimulating a cell to increase or decrease its functional activity or to increase or decrease the secretion of another hormone.

The word hormone derives from the Greek hormon which means "to urge on". Hormon is in turn derived from horme, meaning "impulse" or "impetus".

Hormones can be either protein or amino-acid based or cholesterol derived steroids. Through hormones, one part of the body communicates with another, but through the use of chemical signals instead of nerve impulses.

Hormones, once secreted and released into the circulation, only interact with cells that have specific receptors. Therefore, only those cells will respond to the hormone. A hormone may only communicate with one type of tissue, because only one type has the specific receptors, or it may communicated with several different tissues possessing these receptors. Some hormones bind to receptors on the plasma membrane which corresponds to a specific intracellular event, such as a reduction or rise in the levels of a certain compound within the cell. Other hormones, such as steroid hormones, bind to receptors within the cytoplasm or nucleus which then binds to a gene promoter or to DNA, causing a gene to turn on, or to initiate the transcription process of a protein.

Some examples of protein hormones are insulin, glucagon, adrenalin, and growth hormone. Some examples of steroid hormones are testosterone, estrogen, and cortisol. The following table gives some examples of the hormones secreted by particular glands and the functions of those hormones. Note that the list of hormones for each particular gland is not exhaustive.

Gland Hormone Main Activity
Pituitary (Anterior Lobe) Growth Hormone (IGH or hGH), somatotrophic hormone Increase and regulates tissue growth by stimulating protein synthesis and fat utilization
Prolactin Increase milk production during lactation
Pituitary (Middle Lobe) Melonocyte-stimulating hormone (MSH) increases skin pigmentation
Pituitary (Posterior Lobe) Vasopressin (ADH) Raises blood pressure, promotes the reabsorption of water in kidney tubules
Thyroid Thyroxinie (T4) regulates body metabolism and growth and development
Adrenal medula Epinephrine (adrenalin) increases heart rate and stroke volume, increases blood glucose release from liver into blood
Adrenal Cortex Cortisol (glucocorticoid) increases glucose release into blood by gluconogenesis, aiding in fat, protein, and carbohydrate metabolism, suppresses immune system
Pancreas Insulin increases glucose uptake by fat cells and skeletal muscle and lowers blood sugar, increases processing of fat, glycogen production, and storage, increases amino acid uptake and protein production

This page created 16 Nov 2011 22:40
Last updated 01 Mar 2016 20:12

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