Download The Endocrine System

The Endocrine System
The Endocrine system is made up of glands that release their products into the
bloodstream. Their products deliver messages throughout the body. (like broadcasting via
radio)
Hormones:
 The “chemicals” released from glands to carry messages
 They are releases in one part of the body and travel through the bloodstream to
affect the activities of cells in other parts of the body
 Hormones do this by binding to specific chemical receptors on “target cells”
 In general the body’s response to hormones is slow and long-lasting. It can ranges
from several minutes to several hours or even days
 There are two types of hormones: steroid hormones and non-steroid hormones
 Steroid hormones:
-Are produced from a lipid called cholesterol
-Because they are lipids they can cross the cell membrane easily and pass
directly into the cytoplasm and nucleus to deliver their message


Non-steroid (protein) hormones:
-are usually protein molecules
-they can not pass through the cell membrane
-the non-steroid hormone binds to receptors on the cell membrane and this
promote an enzyme inside the cell to activate a secondary messenger to
relay the message
Prostaglandins –a hormone-like substance produced by all cells except red blood
cells. They are names from the prostrate gland where they were first discovered.
They are modified fatty acids that generally affect only nearby cells and tissue.
Some prostaglandins cause smooth muscle to contract (uterus, bronchioles and blood
vessels). Others may cause the sensation of pain (Headaches – caused by these
hormones can be relieved by taking aspirin which inhibits their production)
Glands:
 An organ that produces and releases a substance, or secretion
 Exocrine glands release their secretions , through tube-like structures called
ducts, directly to the organ that uses them (glands that release sweat, tears and
digestive juices)
 Endocrine glands release their secretions (hormones) directly into the bloodstream
 See worksheet on Endocrine glands for overview
The Master Gland: Pituitary Gland
See worksheet and answers
Hypothalamus:
See worksheet and answer
Endocrine Glands: (see handout given in class)
Thyroid Gland:
Parathyroid Glands
Adrenal Glands
Pancreas
Reproductive Glands
Control of the Endocrine System
 Like most systems in the human body, the endocrine system is regulated by
feedback mechanisms that function to maintain homeostasis.
 Feedback inhibition occurs when an increase in any substance “feeds back” to inhibit
the process that produces the substance in the first place.
 Example 1 (controlling metabolism)
Thyroid gland produces thyroxin which affects the activity of cells
throughout the body increasing their rate of metabolism. Remember that the activity of
the thyroid gland is controlled by the hypothalamus and the anterior pituitary gland.
When the hypothalamus senses that the thyroxin levels in the blood are low, it secretes
TRH which stimulates the anterior pituitary gland to release TSH (thyroid stimulating
hormone) which stimulates the release of thyroxin by the thyroid gland. High levels of
thyroxin in the blood inhibit TRH and TSH, which stops the release of additional
thyroxin. Temperature changes can also trigger the hypothalamus. If the core body
temperature drops the hypothalamus produces extra TRH which in turn stimulated more
TSH and additional thyroxin is produced causing metabolism to increase as well as the
body temperature
Example 2 (maintaining water balance)
When you exercise strenuously you lose water as you sweat. If the water
loss continued your body would soon become dehydrated. This doesn’t generally happen
thanks to ADH and the kidneys. When cells in the hypothalamus detect a decrease in
the concentration of water in the blood it stimulated the pituitary gland to release ADH
(antidiuretic hormone) which heads to the kidneys signaling them to decrease their
absorption of water from the blood. Later you experience a sensation of thirst and you
take a drink to restore water loss. Now the hypothalamus notes that the water
concentration in the blood is fine and stops the release of ADH. The kidneys begin their
water re-absorption again.
