The Endocrine System
Maintaining Homeostasis
The Endocrine System
•	Function: Maintains homeostasis using hormones.
•	An endocrine (ductless) gland secretes its products (hormones) directly into the blood stream.
•	Hormones are slow working but long lasting. 
•	Hormones can only affect specific target cells. 
•	What do we call glands that release their products through ducts to the outside of the body or into body cavities?
•	Exocrine glands Examples: Sweat, tears, & digestive juices

II. Endocrine Gland Types & Functions
A. Pituitary – Secretes 9 hormones that directly regulate many body functions, & controls the actions of several other endocrine glands.
	** The pituitary gland is controlled by the hypothalamus

•	Hypothalamus – Produces hormones that control the pituitary gland, & makes hormones stored in the pituitary gland.
•	Thyroid – Regulates the body’s metabolism using a hormone called thyroxine.
•	Too much thyroxine = hyperthyroidism and too little = hypothyroidism
•	What might the symptoms of each be?
•	Parathyroid – Releases parathyroid hormone which acts to maintain homeostasis of the calcium levels in the blood and bones.
•	Adrenal – Release epinephrine & norepinephrine which help the body respond to stress (flight or fight response).
•	Pancreas – produces insulin & glucagon which regulate the level of glucose in the blood.
•	Ovary – produces estrogen and progesterone. These produce primary and secondary sex characteristics and regulate the menstrual cycle and pregnancy.
•	Testis – produces testosterone for sperm production and primary and secondary sex characteristics.

III. How do hormones work?
•	There are two types of hormones:
•	Steroid hormones 
	1. Can cross the cell membrane directly into the cytoplasm and nucleus. 
2. The hormone binds to a receptor protein inside the cell.
3. This hormone-receptor complex activates genes.
4. These genes code for proteins that carry out the actions associated with the hormone.
5. Estrogen, progesterone and testosterone are examples.
C. Nonsteroid hormones – Cannot pass through the cell membrane.
•	The hormone (first messenger) binds to a receptor on the cell membrane.
•	This activates an enzyme on the inner surface of the cell membrane.
•	The enzyme converts ATP into cyclic AMP (the second messenger).
•	The second messenger activates or inhibits  enzymes.
•	These produce the hormones effects.
•	Human growth hormone and insulin