1. Chapter 7: Maintaining an Internal Balance
Unit 3: Homeostasis
Chapter 7: Maintaining an Internal Balance

2. What is Homeostasis?
The body’s attempt to adjust to a fluctuating external environment.
Body maintains a constant balance or steady state.
The system of balance requires: constant monitoring and feedback about body conditions.

3. Homeostatic Control Systems
The system has three functional components:
A monitor
A coordinating center
A regulator

4. What are the functions? 1. Monitor
Section 7.1: Pages
What are the functions?
1. Monitor
Located in the organs and signals a coordinating center when it detects an organ is working outside its normal limit
2. Coordinating Center
Relays information to the corresponding regulator
3. Regulator
Works to restore the normal balance

5. An Example: When you exercise…
Section 7.1: Pages
An Example: When you exercise…
Carbon dioxide levels increase and
Chemical receptors in the brain are stimulated  Monitor
Nerve cells from the brain relay the message via impulses to the organ  Coordinating Center
Muscles increase the depth and rate of breathing which flushes the excess carbon dioxide  Regulator

6. Homeostasis is often referred to as dynamic equilibrium.
Section 7.1: Pages
Homeostasis is often referred to as dynamic equilibrium.
The homeostatic mechanism ensures that all body systems function within a tolerable range.
This includes monitoring and regulating fluctuations in blood glucose, body temperature, blood pressure and blood pH.

7. Section 7.1: Pages

8. Section 7.1: Pages
Feedback Loops
There are two types of feedback systems that exists within the body: a) Negative Feedback System – mechanism that makes adjustments to bring body back to acceptable range b) Positive Feedback – mechanism that perpetuates the system and moves the controlled variable even further away from its steady state Think… (-) = resisting change or compensating (+) = reinforcing the change

9. Section 7.1: Pages
Negative Feedback System Suppose you like your house a certain temperature…

10. Positive Feedback System: The Birthing Process
Section 7.1: Pages
Positive Feedback System: The Birthing Process
Decrease in progesterone
Initiates contractions
Contractions release the hormone oxytocin
This release strengthens contractions
Contractions keep building

11. Section 7.2: Pages
Thermoregulation

12. Ectotherms Endotherms
Section 7.2: Pages
Thermoregulation: This describes the body’s ability to maintain a temperature range where cells can function
Ectotherms
Endotherms
Ectotherms depend on air temperature to regulate metabolic rate  activity is partially dependant on environment
Ectotherms – most fish, amphibians, and reptiles
Endotherms maintain a constant body temperature regardless of the surrounding temperature
They increase cellular respiration to compensate for heat loss
Endotherms – mammals and birds

13. Section 7.2: Pages
The Hypothalamus
It is the region of the vertebrate brain that is responsible for numerous nerve and hormone functions
The “thermostat”
An example of the coordinating center in the homeostatic control system.

14. How to deal with stress: the hot and cold kind

15. How to deal with stress:

16. Section 7.2: Pages
Quick Review:

17. The Importance of Excreting Wastes
Section 7.3: Pages
The Importance of Excreting Wastes

18. Section 7.3: Pages
Getting Rid of Wastes
Average Canadian consumes more protein than is required to maintain tissues and promote cell growth
Excess protein  Converted into carbohydrates
The proteins contain nitrogen which has two hydrogens attached = toxic

19. Section 7.3: Pages
Deamination
AMINO ACID

20. Deamination: Flushing it Out
Section 7.3: Pages
Deamination: Flushing it Out
There are three types of waste products: ammonia, urea and uric acid.
Deamination of amino acids results in NH3 (a toxic, water-soluble gas)
Ammonia plus carbon dioxide results in  urea which is 100,000 times less toxic than ammonia
An additional waste product results from the breakdown of nucleic acids, such as DNA  uric acid

21. Section 7.3: Pages
Water Balance
The kidney helps maintain water balance when water is lost due to urine, perspiration, increased physical activity and exhaled air
They are also responsible for filtering wastes from the blood.

22. Excretion for the Simple and Complex
Section 7.3: Pages
Excretion for the Simple and Complex
In unicellular and primitive multicellular organisms, wastes are expelled directly into the environment and carried away by water
How do primitive organisms maintain fluid retention?
The contractile vacuole maintains osmostic balance by pumping water out of the cell

23. Excretion for the Multicellular
Section 7.3: Pages
Excretion for the Multicellular
Triple-layered organisms such as insects, worms and mammals, cannot directly expel wastes because:
- not every cell interacts with the environment
- not every cell is designed to remove wastes (cell specialization)
Resolution?
- wastes are transported to cells that are capable of excretion and removed or stored by the excretory system

24. Any Questions?