1. Bellwork: What is this lizard doing? Explain why…

2. Homeostasis
Section 28.4

3. What is homeostasis? The maintenance of constant internal conditions
All body systems work together to maintain homeostasis
This makes sense – respiratory and digestive systems would be useless without a circulatory systems
This is just the beginning of homeostasis….

4. Homeostasis and fighting disease
Most environments contain disease-causing micro-organisms or pathogens that may take advantage of steady supplies of oxygen and nutrients intended for body tissues
This has the potential to disrupt homeostasis
Immune systems can distinguish between “self” and “other”. Once an foreign body is detected in an immune system, the body declares war.
This is a common process – every time that the body fights off a cold or any kind of infection
Side effects from the “battle” may be a fever, or other symptoms.

5. How do hormones work?
Hormones are released by endocrine glands, and regulate body activity.
Hormones are transported by the blood stream or body fluids
Hormones can control growth, development, how the body stores energy, or mobilizes it, amount of water in the body, amount of calcium in bones

6. How do animals control their body temperature?
Temperature control is really important, because many body functions are influenced by temperature
Muscles won’t work if they are too cold or too hot!
Body temperature control requires three components
A source of heat
A way to conserve heat
A way to eliminate excess heat
Animals can be Endotherms or Ectotherms

7. What is the difference between an Endotherm and an Ectotherm?
An Ectotherm’s regulation of body temperature depends mostly on it’s relationship to sources of heat outside of the body
Most reptiles, dish and amphibians are ectotherms – absorb or loose heat to the environment
They are characterized by low metabolic rates, so bodies don’t generate too much heat
When muscles are working active heat is easily lost due to low insulation
Sun bather to warm up, stilt to cool down
Many live in underground burrows - fewer temperature variations

8. How do endotherms regulate body temperature?
Endotherms, such as birds and mammals have high metabolic rates that generate heat, even when resting
Animals have developed a series of ways to regulate temperature
Birds have feathers, mammals fat and hair for insulation
Panting helps get rid of excess heat
Humans sweat
As sweat evaporated, heat is removed from skin and the blood in capillaries just below the surface
As warm blood flows through capillaries, heat is lost

9. Which is better, being an ectotherm or an endotherm?
Both has advantages and disadvantages
Endotherms move around easily during col weather because they generate their own body heat
But, a lot of fuel is required – food!
The amount of food for one cow is enough to feed 10 cow sized lizards
In environments with stable temperatures, ectothermy is more energy efficient
For large animals though, it can take a long time to warm up if there has been a sudden drop in temperature
Lost of ectotherms live in tropical or subtropical areas

10. What came first, ectotherms or endotherms?
The first land vertebrates were ectotherms
Not exactly clear when the first endotherms evolved
Possibility that some dinosaurs were endotherms
Current evidence suggests that endothermy has evolved twice in vertebrates
Once in the lineage of ancient reptiles that led to birds
Once in the lineage of ancient reptiles that led to mammals

11. Key point questions
How to the immune system and endocrine glands help maintain homeostasis?
Give an example of how multiple body systems function together to maintain homeostasis
Define Ectotherm and Endotherm
Why do Endotherm’s eat more than an ectotherm of the same size?
Why do birds and mammals have different ways of insulating their bodies?