Homeostasis

Homeostasis

Definition: “Compensatory processes by which the body functioned to limit variations in the internal environment”- Walter Cannon; preventing change

Claude Bernard

• French physiologist, mid- 1800s

• Noted outside environment differs from animal’s internal environments

• Organs and functions constantly work to maintain internal environment

Walter Cannon

• American physiologist, around 1927; aware of Bernard’s work
• Coined the term homeostasis
• Published The Wisdom of The Body in 1932

Homeostatically Regulated Parameters: body temperature, blood pressure, blood glucose concentrations, blood gas concentrations, fluid volume, sodium concentration, pH (less than 7.35: acidosis,gGreater than 7.45: alkalosis), oxygen tension/partial pressure, carbon dioxide tension

• Homeostasis is a dynamic process (Cannon)

• Regulated parameters fluctuate (ever-changing system)

Negative Feedback Regulation/Loop

• Sensor: body part that senses/detects the regulated variable (ex. thermometer)
• Integrator: body part that interprets the sensor’s information and sends messages to the effector (ex. Brain/central nervous system, computer chip in thermostat)
• Effector: body part that affects/changes the regulated variable (ex. furnace/AC unit)
• Set Point: desired range for regulated value (ex. Temperature selected on thermostat)
• Threshold: deviation between the desired and actual value of the variable (decided by integrator) (ex. Desired temp. Vs. actual temp.)
• Error Signal: deviation between the actual value of the variable and the set point value (negative feedback part of the loop) (ex. The degree difference between the actual temp. and the set temp.)

Dr. Donald Jackson

• Value ranges change with the animal's circumstances (ex. ambient conditions, physical demands, hibernation)

Steady-State: parameter constant over a period of time; may or may not be homeostatically regulated

9/6 Lecture

• Breathing helps control the ph of blood (which is homeostatically regulated)