Some History on Secretin and Other Hormones

"hormones play a vital role in our lives.  They are the regulators of the metabolic processes.  Hormones were first recognized in 1902 by William Bayliss and Ernest Starling who discovered the substance secretin.  Secretin is produced in the small intestine.  From there, it travels through the blood stream to the pancreas, where it stimulates the secretion of pancreatic substances.

Bayliss and Starling soon realized that secretin was only one of a class of substances that originated in specific organs of the body and traveled to other remote organs of the body to do their work.  They names these substances hormones, from the Greek hormon, meaning "to stir up".

Many hormones are also peptides, with as many as 150 amino acids, or more, combined to provide the unique characteristics of each type of hormone./  Some hormones are very specific in their activity.  When hormones are released into the blood stream, they act on remote cells, throughout the body, they are uniquely designed for, like a key in a lock.  Some hormones limit their effects to specific body tissues.  Others act in a more general manner, stimulating responses throughout the body.  They also interact with each other, regulating their own production and output by a complex and very sensitive feedback system.

Hormonal function begins in the portion of the brain called the Hypothalamus, the region that regulates growth and the metabolic process.  At the base of this region is the pituitary gland, often referred to as the master gland because of its influence on the rest of the body's regulators.  The pituitary is the dominant gland of the endocrine system.

Hormones released from the pituitary gland act on other target glands including the thyroid, the adrenals, and the male and female sex glands.  The pituitary hormones act as messengers to these target glands, providing instructions for the release of specific hormones.  The pituitary responds to the results of its own stimulus on these target glands by sensing the presence of the new hormones in circulation and boosting its own production when the target glands are not producing adequately, or reducing its production when their output is adequate.

This glandular feedback system acts very much like the thermostat in a build's heating and cooking system.  When a room cools off, the thermostat signals the heater to turn on and raises the temperature.  When the temperature reaches an adequate level, the thermostat signals the heater to turn off.  When the pituitary hormones stimulate a target gland, the target steps up productions of its own hormones which stimulate a response in other tissue cells.  The rising level of these hormones in the circulatory system provides feedback signals to the hypothalamus and pituitary gland, stimulating a reduction in the production of pituitary hormones, which in turn reduces the stimulation of the target gland, shutting off production of its own hormones.

It is to the cell that all this activity is targeted.  Whether bone, muscles, nerve, skin, or the component of a specific organ, it is at the level of the cell that all action and reaction begins.  Homeostasis is the body wide effort that balances these complex relationships"

 This information was found at the following web site:

www.synapse-project.com/synacademy/courses/masterkey/hormones.htm