1. Homeostasis: The Foundation of Physiology
Keri Muma
Biology 6

2. What is Physiology?
Physiology – the study of body functions; how the body carries out its life-sustaining activities
Focuses on events happening on the cellular and molecular levels

3. Why should we study physiology?
Learn about the most fascinating subject, yourself!
Understand & appreciate emerging discoveries in genetic engineering
New medications & treatments for disease
How to stay healthy
Provide you with a strong foundation needed for your future job!

4. Associated Areas of Physiology
Anatomy - structure determines function
Physiological mechanisms are only possible through structural design
A slight change in anatomy can have a significant effect on physiology
Normal RBC
Sickle Cell Anemia

5. Other Associated Areas
Chemistry
Acid / Bases
Osmolarity
Biochemistry
Physics
Electrical currents
Blood pressure
Flow rates
Gas Laws

6. Homeostasis (main theme)
State of balance in which the body’s internal environment remains relatively stable despite changes in the internal and external environments.
Large external fluctuations
Homeostatic mechanisms
Small internal fluctuations

7. Relationship between organism’s internal and external environment
Most cells are not very tolerant of change
What types of things change the cell’s environment?
ECF is a buffer zone between cells and the external environment. Have students define ECF (interstitial, intravascular) and ICF.

9. Negative Feedback Internal values may vary within narrow limits
Deviation from a stable condition will trigger a sequence of events (compensatory responses) that will counteract the change
Negative Feedback - output or response of the effector counteracts the original stimulus, returning the variable to normal limits
Tends to be stabilizing
Can be a short-term immediate response or a long term adaptation
Example: Heart’s response to exercise

10. Law of Maximum and Minimum
Effects of various conditions on the functional efficiency of body processes
Optimal range – functions most efficiently
Range of tolerance – can still function
Minimum or Maximum condition
Moving past max or min may result in death
Examples: pH, body temperature, electrolytes, O2 , CO2, waste, nutrients, blood volume and pressure

12. Homeostatic Control Mechanisms
Variable
Stimulus
Receptor (sensor)
Control Center
Effector
Response
Input
Output

13. Negative Feedback

14. Sources of Homeostatic Controls
Extrinsic – control from outside the organ/tissue
Accomplished by the nervous and endocrine systems (Reflex control)
Several systems working towards a common goal
Example: sympathetic regulation of blood pressure
Intrinsic – control from within the organ/tissue
Self-serving the organ it occurs in (Local control)
Example: Decreased oxygen levels in skeletal muscle causes vasodilation of blood vessels

16. Reflex Loops
Neural Reflex
Endocrine Reflex
Neuroendocrine Reflex

17. Example of Neural Reflex: Blood Pressure

18. Example of Endocrine Reflex: Thyroid Hormones

19. Positive Feedback
Output of effector is amplified or the original stimulus is intensified
Variable moves further from set value
Tends to be destabilizing if not self limiting

20. Positive Feedback: Parturition (child birth)

21. Feed forward mechanism
Feed forward control – reflex that starts the response loop in anticipation of the stimulus or change
Examples:
Thought or smell of food triggers salivation
Increased respiratory rate in anticipation of exercise

22. Approaches to explaining physiology
Teleological – explanation is based on purpose, meeting body needs
Does not consider how it occurs. Focus on why.
Why do we sweat when we are hot?
To cool down
Mechanistic – in terms of cause and effect, sequence of events

23. Mechanistic Approach – why do we sweat when we are hot?
Thermoreceptors in hypothalamus detect temperature change
Motor pathways activated to stimulate sweat glands
As sweat evaporates it takes heat with it

24. Approach to explaining physiology
Explain the following question using the teleological and mechanistic approach:
Why do red blood cell transport oxygen?

25. Physiology as an integrative science:
Physiology integrates function across many levels of organization and information from different body systems

26. Levels of Organization

27. Physiology as an integrative science:
Emergent properties – properties that cannot be predicted based only on the knowledge of individual systems
Example: how blood pressure influences kidney function
Important to look at the human body as a whole and how the different systems work together and affect each other
Also depends on internal and external factors….bottom line NUMEROUS factors!

28. Cardiovascular and Renal Response to Blood Pressure

29. Mapping and Flow Charts
Concept mapping

30. Example of Mapping