1. Body Systems and Homeostasis
October 27th, 2008

2. Levels of Organization
The body has different levels of organization, from simple (1) to more complex (4).
Cells Tissue Organ Organ System

3. Homeostasis The organ systems must maintain homeostasis.
Homeostasis is when organisms keep the environment inside their body stable, despite changes in the external environment.
Homeostasis in the body is maintained by feedback loops.

4. A Nonliving Example
The thermostat in your house (negative feedback loop)
Temperature
set to 75o
Thermostat senses temperature
change and switches on heating
system
Room temperature decreases
Room temperature increases
Thermostat senses temperature
change and switches off heating
system

5. Feedback Loops
Negative Feedback Loop – reverse direction of change back to set point.
Sweating when hot
Shivering when cold
Positive Feedback Loop – change continues away from set point.
Fever

6. Positive Feedback or
Negative Feedback

7. Body Systems
There are 11 distinct organ systems in your body (see pages 892 & 893 in your text).

8. Cardiovascular System
Structures include:
Nose
Trachea
Lungs
Heart
Blood vessels
Blood
Function:
Provides oxygen needed for cellular respiration and removes excess carbon dioxide from the body.
Brings oxygen, nutrients, and hormones to cells; fights infection; removes cell waste; helps to regulate body temperature.

9. Nervous System Structures include: Brain Spinal cord Peripheral nerves
Function:
Recognizes and coordinates the body’s response to changes in its internal and external environment.

10. Endocrine System Structures include: Hypothalamus Pituitary Thyroid
Parathyroid
Adrenals
Pancreas
Ovaries (in females)
Testes (in males)
Function:
Controls growth, development, and metabolism, and maintains homeostasis.