1. Human Body Systems and Homeostasis
Chapter 8.1
McGraw-Hill Ryerson
Biology 12 (2011)

2. Homeostasis
Maintenance of a relatively stable internal, fluid environment (internal milieu) despite a changing external environment
Critical for survival since proteins, enzymes, etc, require optimal conditions for operation
Temperature
37oC (98.6oF)
Blood pH
7.35
Blood sugar level
0.1%

3. Homeostasis
Example:
Blood glucose levels rise after a meal thus endocrine system works to lower it to normal
Blood glucose levels fall during a fast thus endocrine system works to raise it to normal by resorting to glycogen supply in the liver

4. Homeostatic Control Systems
Homeostasis relies on a feedback system: cycle of events in which a variable* is monitored assessed and adjusted
3 main components of feedback system
A sensor -> senses state of system
A control centre-> receives incoming info about system and decides what the next steps should be
A regulator or effector -> carries out the appropriate next step to keep system at homeostasis
*Variable can be tempearture, blood pH, blood glucose level, etc.

5. Positive Feedback System
A mechanism by which an output is enhanced
Contractions in childbirth: contractions stimulate oxytocin which stimulates more muscle contractions
Negative feedback mechanism consists of reducing the output or activity of any organ or system back to it's normal range of functioning.
Blood vessels can sense resistance of blood flow against the walls when blood pressure increases. The blood vessels act as the receptors and they relay this message to the brain. The brain then sends a message to the heart and blood vessels, both are the effectors. The heart rate would decrease as the blood vessels increase in diameter. This change would result in the blood pressure to fall back to its normal range. The opposite would happen when blood pressure decreases.

6. Positive Feedback System
What positive feedback actually does is push the variable even further away from the normal
The system is pushed to the extreme until the ordeal is over
Positive feedback is not very commonly seen
Negative feedback systems are much more common in organisms
Negative feedback mechanism consists of reducing the output or activity of any organ or system back to it's normal range of functioning.
Blood vessels can sense resistance of blood flow against the walls when blood pressure increases. The blood vessels act as the receptors and they relay this message to the brain. The brain then sends a message to the heart and blood vessels, both are the effectors. The heart rate would decrease as the blood vessels increase in diameter. This change would result in the blood pressure to fall back to its normal range. The opposite would happen when blood pressure decreases.

7. Negative Feedback System
a mechanism by which an output is diminished
The system resists change thus will initiate a response to bring it back to normal range
Negative feedback loops require a Receptor, A Control Center, and Effectors
Negative feedback mechanism consists of reducing the output or activity of any organ or system back to it's normal range of functioning.
Blood vessels can sense resistance of blood flow against the walls when blood pressure increases. The blood vessels act as the receptors and they relay this message to the brain. The brain then sends a message to the heart and blood vessels, both are the effectors. The heart rate would decrease as the blood vessels increase in diameter. This change would result in the blood pressure to fall back to its normal range. The opposite would happen when blood pressure decreases.

8. Negative Feedback System

9. Negative Feedback System
Blood vessels have receptors which can measure the resistance of blood flow against vessel walls
The brain (control center) receives info about change in body’s internal conditions, sends out signals via nerves
Effectors - the muscles, organs, and other structures that receive signals from the control center and respond to correct the deviation.
Sweating when hot
Shivering when cold
Negative feedback mechanism consists of reducing the output or activity of any organ or system back to it's normal range of functioning.
Blood vessels can sense resistance of blood flow against the walls when blood pressure increases. The blood vessels act as the receptors and they relay this message to the brain. The brain then sends a message to the heart and blood vessels, both are the effectors. The heart rate would decrease as the blood vessels increase in diameter. This change would result in the blood pressure to fall back to its normal range. The opposite would happen when blood pressure decreases.

11. Homework
Pg. 348 #1, 2, 7, 8, 9