1. Endocrine System
Chapter 34

2. Hormones
A hormone is a chemical signal that is secreted into the circulatory system and communicates regulatory messages within the body.
Hormones may reach all parts of the body, but only certain types of cells, target cells, are equipped to respond.

3. Systems of Internal Communication
Animals have two systems of internal communication and regulation:
The nervous system
The endocrine system

4. Systems of Internal Communication
The nervous system conveys high-speed electrical signals along specialized cells called neurons.
The endocrine system, made up of endocrine glands, secretes hormones that coordinate slower but longer-acting responses to stimuli.
These 2 systems work in together in maintaining homeostasis.
Example: The endocrine system is all about hormones and growth, the nervous system signals to the glands that there is a need for a hormone.

5. Hormones Advantages of using chemical messengers:
Chemical molecules can spread to all tissues through the blood.
Chemical signals can persist longer than electrical ones.
Many different kinds of chemicals can act as hormones; different hormones can target different tissues.
Each gland can secrete more than 1 type of hormone
Ex. Pituitary gland secretes 9 different hormones including GH (growth hormone), oxytocin, TSH (thyroid)

6. Glands Many hormones are secreted by ductless endocrine glands.
Obtain raw materials from and secrete hormones directly into the bloodstream.
Example: pituitary
Exocrine glands have ducts for discharging secretions onto a free surface.
Sweat glands, salivary glands, enzyme-secreting glands in the digestive tract.

7. Control Pathways and Feedback Loops
A common feature of control pathways is a feedback loop connecting the response to the initial stimulus.
Feedback inhibition: an increase in a substance causes the production of that substance to decrease.

8. The Pancreas
The pancreas is located behind the stomach and is connected to the small intestine by a small tube.
It secretes digestive enzymes into the digestive tract (exocrine function).
Endocrine function – production of insulin and glucagon.

9. Glucose Homeostasis Insulin removes glucose from the blood.
The islets of Langerhans:
-Beta cells in the
pancreas secrete insulin
and glucagon. (regulate
blood sugar
Insulin removes glucose
from the blood.
Glucagon returns
glucose to the blood.

10. Diabetes Mellitus Endocrine disorder
Body fails to produce or properly respond to insulin
Type I: develops before age 15, immune system kills beta cells, little/no secretion of insulin
Type II: after age 40, produce low to normal amts of insulin. Body does not respond to the hormone. Can be caused by obesity

11. Sex hormones
Puberty: rapid growth and development, occurs between ages 9-15
Female reproductive hormone, estrogen: responsible for, breast development, and widening hips
Male reproductive hormone, testosterone: responsible for facial hair, increased muscle development and deepening of the voice.