1. Unit A: Nervous and Endocrine Systems
Chapter 15
Section 15.1
Homeostasis, Hormones and the Endocrine System

2. INTRODUCTION What is the endocrine system? Videos:

3. HOMEOSTASIS
The endocrine system plays a key role in maintaining our body’s homeostasis.
Homeostasis – the maintenance of a constant internal environment despite changes in the environment.
AKA = dynamic equilibrium

4. IDEAL CONDITIONS - 37 ºC - 0.1% blood glucose - blood pH of 7.35
Our body functions best under ideal conditions:
- 37 ºC
- 0.1% blood glucose
- blood pH of 7.35
However, the external environment does not always provide these perfect conditions so our body must make adjustments.
The adjustments are made by the endocrine system.

5. HOMEOSTATIC CONTROL SYSTEMS
All homeostatic control systems have 3 components:
A receptor
A coordination system
An effector

6. Special receptors located in organs of the body signal a coordination center once an organ begins to operate outside its normal limits.
The coordination center relays the information to the appropriate effector.
The effector helps to restore balance.
EX. When carbon dioxide levels increase during exercise, chemoreceptors in the medulla oblongata are stimulated. The brain then sends nerve impulses to the rib muscles and diaphragm to increase breathing movements to expel the excess carbon dioxide.

7. FEEDBACK SYSTEMS
Feedback systems are mechanisms that make adjustments to bring the body back within an acceptable change.
2 types:
Negative Feedback – a mechanism used to restore conditions to their original state.
Positive Feedback – reinforces a change, amplifies an effect in the body.

8. NEGATIVE FEEDBACK SYSTEMS
Most common type of feedback system.
Prevent small changes from becoming large.
Body turns a system on to counteract a change and then the body turns it off when the normal level is reached.

9. EX. of NEGATIVE FEEDBACK
Ex. Body Temperature
- body temperature rises due to exercise
- our body begins sweating to release heat to the environment
- once body temperature is back to normal sweating stops

10. POSITIVE FEEDBACK SYSTEMS
Less common.
Reinforce change.
Accelerates or increases a change.

11. EX. OF POSITIVE FEEDBACK
Ex. Blood Clotting
- cut ourselves
- our body increases the production of enzymes to help stop the bleeding quickly

12. HORMONES
To adjust to changes in the body by way of feedback systems the body commonly uses chemical controls or hormones.
Hormones – chemicals released by cells that affects cells in other parts of the body.
Endocrine hormones – chemicals secreted by endocrine glands directly into the bloodstream.

13. CLASSIFYING HORMONES 2 main ways of classifying hormones:
Based on Activation/Target Sites
Non-target Hormones affect many cells/tissues (ex. insulin)
Target Hormones affect specific cells/tissues (ex. gastrin)

14. 2. Based on Chemical Nature
Water Soluble Hormones – bind to receptors on the cell membrane because they can’t pass through it.
Fat (Lipid) Soluble Hormones – pass through the cell membrane and attaches to a receptor inside the cell.

15. WATER VS. FAT SOLUBLE HORMONES
Water Soluble
Fat/Lipid Soluble

16. ENDOCRINE GLANDS
There are many endocrine glands within our body that are responsible for releasing these hormones that maintain our homeostasis.
The main glands:
- pituitary
- hypothalamus
- thyroid
- parathyroid
- pancreas
- adrenal gland
- female ovaries
- male testes

17. PITUITARY - THE MASTER GLAND
Pituitary gland – found at the base of the brain, together with the hypothalamus, functions to control the entire endocrine system.
Pituitary and Hypothalamus connect the endocrine and nervous systems.
Pituitary gland produces and stores hormones.
Hypothalamus stimulates the release of these hormones by sending nerve impulses or releasing hormones to the pituitary.

18. Releasing hormones – a chemical produced by the hypothalamus that stimulates the anterior pituitary gland to release a stored hormone; also called a releasing factor.
2 lobes of pituitary
Posterior lobe (back) – does not synthesize hormones, it stores and releases hormones that have been made by the hypothalamus.
Anterior lobe (front) – synthesizes, stores and releases it’s own hormones.
Inhibiting factors – chemicals that inhibit the production of a hormone by the anterior pituitary.