1. Creating models of physical systems
BIOE 4200

2. Creating models Describe how system works in words
Draw schematic or block diagram
Identify variables/quantities in system
Recast block diagram based on variables of interest
Derive mathematical equations for components within block diagrams
Lecture limited to first three steps
Remaining steps will be discussed later

3. Cruise control example
Set desired speed
System depresses accelerator if measured speed is below desired speed
System releases accelerator if measured speed exceeds desired speed
Engine revs or idles in response to accelerator
Drive shaft & transmission translate engine rpm into wheel rpm
Speedometer measures actual speed
System compares measured & desired speed

4. Cruise control schematic
Set desired speed
Depress or release accelerator
Engine revs or idles
Speedo-meter
Drive shaft and transmission

5. Cruise control variables
Desired speed
Accelerator depth
Set desired speed
Depress or release accelerator
Engine revs or idles
Measured speed
Engine rpm
Actual speed
Speedo-meter
Drive shaft and transmission

6. Blood glucose regulation
Body sets desired blood glucose levels
Pancreatic a cells release glucagon if measured blood glucose falls below desired blood glucose
Pancreatic b cells release insulin if measured blood glucose exceeds desired blood glucose
Various organs release glucose in response to glucagon or uptake glucose in response to insulin
Release or uptake of glucose changes glucose levels
a and b cells measure blood glucose levels
a and b cells compare measured & desired blood glucose levels

7. Blood glucose schematic
Set desired blood glucose
a & b cells release hormones
Release or uptake glucose
a & b cells measure glucose
Glucose diffusion in bloodstream

8. Blood glucose variables
Desired glucose
Glucagon
Set desired blood glucose
a & b cells release hormones
Release or uptake glucose
Insulin
Measured glucose
Glucose release
Actual glucose
a & b cells measure glucose
Glucose diffusion in bloodstream

9. What to include & ignore
No model exactly reproduces the physical system!
Therefore different models could be used
Factors to consider:
Level of detail needed
Time scale under consideration
External factors not under control of the system
Example: add glucose intake (eating) and metabolism (exercise, etc.) to blood glucose regulation model

10. Adding external factors
Desired glucose
Glucagon
Set desired blood glucose
a & b cells release hormones
Release or uptake glucose
Insulin
Measured glucose
Glucose release
Actual glucose
a & b cells measure glucose
Glucose diffusion in bloodstream
Eating
Exercise

11. One small step ... Created simplistic diagrams of two systems
Next we need to identify what physical quantities we need to look at
Blood glucose change after eating a candy bar
Activity of a specific insulin receptor after eating a candy bar
Then we will discuss the process of replacing the various blocks in these schematics with mathematical equations