1. Examples of Negative Feedback Systems
HOMEOSTASIS
Examples of
Negative Feedback Systems

2. Homeostasis
def.- a stable internal environment; a set of conditions that need to be maintained in a relatively narrow range
Controlled by negative feedback systems
the response is opposite the stimulus
works similar to a thermostat in a house
Examples include: body temperature, blood sugar levels, blood pH (and many others)

3. Example 1: Regulation of Body Temperature

4. REGULATION OF BODY TEMPERATURE * CONTROLLED BY HYPOTHALAMUS IN BRAIN
Body Temp too High:
Vasodilation of superficial blood vessels – blood vessels near skin open up, face turns red
Increase sweating – evaporation cools body by removing heat energy

5. REGULATION OF BODY TEMPERATURE * CONTROLLED BY HYPOTHALAMUS IN BRAIN
Body Temp too Low:
Shivering – involuntary contractions of skeletal muscles (produce heat)
Superficial vasoconstriction – vessels near skin close off; directs warm blood to core of body for heat conservation; skin has blue tint
Goosebumps – arrector pili muscles in skin contract; pull hairs upwards creating a layer of warm air just above skin surface

6. EXAMPLE 2: REGULATION OF BLOOD SUGAR

7. Glucose levels need to be maintained
Cells need a constant supply of glucose for energy
transfer energy from glucose to ATP by using cellular respiration
food is the only source of glucose; all is taken in right after a meal
Pancreas releases two hormones to control the amount of sugar in the blood.

8. REGULATION – GLUCOSE LEVELS TOO HIGH
Occurs after a meal
Pancreas secretes insulin
insulin converts glucose into glycogen
glycogen – long chains of glucose; more stable and unable to be used by cells directly
stored primarily in liver and muscle tissue

9. REGULATION – GLUCOSE LEVELS TOO LOW
In between meals, glucose levels drop because cells are using the glucose to make ATP (energy)
Stimulates pancreas to release glucagon
Glucagon is a hormone that causes liver cells to break down glycogen into glucose
Interaction of insulin and glucagon keep blood sugar levels at normal levels
Normal level: below 100 mg/ deciliter of blood after 8 hrs of not eating

10. Diabetes
Diabetes is a disorder where a person is not able to maintain a homeostatic blood sugar level.
Type I: (juvenile or insulin dependent)
body doesn’t make insulin – blood sugar levels get too high
Type II: (late onset or non-insulin dependent)
body cannot use the insulin that it makes

11. pH of blood
The pH of the blood should be between 7.4 and 7.7 (slightly basic)
Carbon Dioxide (byproduct of cellular respiration) causes the pH to drop by producing carbonic acid
Alkalosis – pH is too high
Acidosis – pH is too low

12. Basic Equation Bicarbonate ion acts as a buffer
A buffer is a chemical that regulates pH of a solution
Carbon dioxide (CO2) combines with water to form carbonic acid (H2CO3), which dissociates into bicarbonate ions (HCO3-) and hydrogen ions (H+)
CO2 + H2O  H2CO3  HCO3- + H+

13. REGULATION: CO2 + H2O  H2CO3  HCO3- + H+
If pH is too high (basic)
Reaction proceeds to the right
Carbonic acid dissociates into bicarbonate and hydrogen ions
Increase hydrogen ions  lower pH
If pH is too low (acidic)
Reaction proceeds to the left
Bicarbonate and hydrogen ions bond to form carbonic acid
Removes hydrogen ions from blood  raises pH