Examples of Negative Feedback Systems HOMEOSTASIS Examples of Negative Feedback Systems

CHARACTERISTICS OF LIFE: MOVEMENT INTERNAL AND EXTERNAL RESPONSIVENESS HOMEOSTASIS NEGATIVE FEEDBACK POSITIVE FEEDBACK GROWTH MITOSIS REPRODUCTION MEIOSIS FERTILIZATION DIGESTION BREAK DOWN ABSORPTION NUTRIENTS CIRCULATION BULK TRANSPORT ASSIMILATION BUILD UP EXCRETION WASTE REMOVAL

REQUIREMENTS: WATER FOOD OXYGEN HEAT PRESSURE UNIVERSAL SOLVENT TRANSPORT WET CHEMISTRY - ELECTROLYTES BODY TEMPERATURE FOOD ENERGY RAW MATERIALS OXYGEN RELEASE ENERGY FROM FOOD HEAT BYPRODUCT OF RXNS NEEDED FOR RXN TO HAPPEN QUICK ENOUGH PRESSURE AIR PRESSURE – BREATHING FLUID PRESSURE – BLOOD, KIDNEY FILTRATION

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:

Example 1: Regulation of Body Temperature

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

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

EXAMPLE 2: REGULATION OF BLOOD SUGAR

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.

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

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

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

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

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+

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