1. Structural Levels, continued…
Organism – any living thing considered as a whole
Unicellular, multicellular
Human organism is a complex of organ systems that are mutually dependent on one another

2. Characteristics of Life
Six Essential Characteristics of Life
Organization – an organism’s parts are interrelated
All living things are composed of cells
Metabolism (Energy) – ability to use energy to perform vital functions such as growth, movement, and reproduction
Energy from sun (plants) or food (animals)

3. Six Essential Characteristics of Life, continued…
Homeostasis – ability of an organism to sense changes in the environment and make the adjustment that help maintain its life
Growth – ability of an organism to increase in size (partially or totally)
Either by increasing cell number or cell size

4. Six Essential Characteristics of Life, continued…
Cells – all organisms are made of one more cells
Reproduction – the formation of new cells or organisms
a. Sexual or asexual reproduction

5. Environmental Requirements of Organisms
Organisms require certain factors in their environment
or surroundings:
Water
Foods
Oxygen
Heat – energy from metabolic reactions
Pressure
Atmospheric  breathing
Hydrostatic  blood pressure

6. Homeostasis – Maintenance of Life
The existence and maintenance of a relatively constant environment within the body
Narrow range of conditions (variables)
Temperature, volume, chemical content
Set point = ideal normal value
Normal range = range of values in which an organism can operate normally

7. Examples: Cold = shiver
Hot = sweat

8. Negative Feedback
Maintains homeostasis by resisting deviation from the set point
Three components:
Receptor – monitors the value of a variable
Control center – establishes the set point around which the variable is maintained
Effector – can change the variable

9. Negative Feedback, continued…
Hole’s Essentials of Human Anatomy and Physiology, 8th ed., Shier, et al, 2003, McGraw-Hill Higher Education
Negative Feedback, continued…
Example:
Stimulus/Response: exercise increases HR and blood pressure increases
Receptor: blood vessels near heart
Control center: brain receives message and sends message to decrease HR
Effector: heart decreases HR
Response: blood pressure decreases

10. Negative Feedback, continued…

11. Positive Feedback
Mechanism by which any deviation from an ideal normal value or set point is made greater
Does not maintain homeostasis

12. Positive Feedback, continued…
Example