Module 2
1. Module 2
1.11. Page 9
Module 2—The Endocrine System
Lesson Summary
In this lesson you investigated the following focusing question:
- How is the endocrine system organized, and how do its parts communicate with each other and with various parts of the body?
To answer this question, the major glands of the endocrine system, including the hypothalamus-pituitary complex, the thyroid gland, the parathyroid glands, the adrenal glands, and the islet cells of the pancreas, were introduced and studied. These glands secrete hormones, which have unique effects on the body by interacting with target cells. Some of these hormones work opposite each other and are called antagonistic hormones. Other hormones, called tropic hormones, target other endocrine glands, causing them to secrete more hormones. Levels of hormonal secretions are regulated by negative feedback mechanisms. Negative feedback tends to stabilize a system because the response compensates for the change in the internal environment. This leads to the re-establishment of homeostasis. Reinforcing the change in the internal environment leads to instability and an imbalance or deviation from homeostasis called positive feedback. It is rarely beneficial in the body.
As a review of the concepts of this lesson, you may wish to view all of “The Hypothalamus and Pituitary: The Master Complex.”
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Lesson Glossary
Consult the glossary in the textbook for other definitions that you may need to complete your work.
antagonistic hormones: two hormones that produce opposite effects
endocrine gland: a cell, tissue, or organ that produces secretions that are released directly into the bloodstream; a ductless gland; for example, the thyroid gland
exocrine gland: a cell, tissue, or organ that produces secretions that are released through ducts or channels; for example, a sweat gland
gonadotropic hormones: hormones that affect the reproductive organs; also called the gonads
hormone: a circulating chemical messenger that is produced by specialized cells, circulated in the bloodstream, and co-ordinates the various parts of the body by interacting with target cells
lipid-soluble hormone: a hormone that is chemically identified as a lipid or steroid, such as testosterone, estrogen, progesterone, or cortisol
negative feedback: a mechanism where deviation from the optimum state causes a return to the optimum state; acts to eliminate any deviation from optimal conditions and leads to stability
positive feedback: a mechanism where movement away from the optimum state causes further deviation from the optimum state; usually leads to instability and is tolerated by the body only for a short time
set point (set value): ideal or optimum conditions
target cells: cells with specialized receptor structures
When stimulated, these receptor structures cause a response in the target cells.
tropic hormone: a hormone that has another endocrine gland as its target cell
water-soluble hormone: a hormone that is chemically identified as being either an amino acid or a protein, such as epinephrine, human growth hormone, thyroxine, insulin, and glucagon