lesson 9

• Homeostasis


  Internal equilibrium maintained by adjusting physiological processes

  
• Feedback Mechanism


  Physiological processes commonly moderated via two distinct mechanisms - positive and negative feedback
• Homeostatic processes


  • Maintain body temperature (36-38°C)
  • Maintain carbon dioxide concentration (35-45 mmHg)
  • Maintain blood pH (7.35-7.45)
  • Maintain blood glucose levels (75-95 mg/dL)
  • Maintain water balance (varies by individual)
• Homeostatic mechanisms


  1. Detect internal change

  2. Generate response to correct change

  3. Most responses involve antagonistic effect to detected stimulus (negative feedback)

  4. When levels return to equilibrium, effector ceases response

  5. If conditions move outside tolerance, disease occurs
• Negative feedback


  Response is reverse of change detected, functions to reduce change and promote equilibrium
• Processes using negative feedback

  • Thermoregulation
  • Blood sugar regulation
  • Osmoregulation

  
• Positive feedback


  Response reinforces and amplifies the change detected
• Homeostatic Process


  The varied processes by which the body regulates its internal environment to maintain a constant internal environment
• The human organism consists of trillions of cells working together for the maintenance of the entire organism</b>
• Maintaining a constant internal environment with everything that the cells need to survive (oxygen, glucose, mineral ions, waste removal, etc.) is necessary for the well-being of individual cells and the well-being of the entire body
• Homeostasis


  Stability, balance, or equilibrium
• Homeostasis


  • The body's attempt to maintain a constant and balanced internal environment
  • Requires persistent monitoring and adjustments as conditions change
• Homeostatic regulation


  1. Receptor receives information

  2. Control center receives and processes information from receptor

  3. Effector responds to commands of control center by opposing or enhancing the stimulus
• This ongoing process continually works to restore and maintain homeostasis
• As the internal and external environment of the body is constantly changing, adjustments must be made continuously to stay at or near a specific value: the set point
• Homeostasis


  The maintenance of equilibrium around the set point
• There are normal fluctuations from the set point, but the body's systems will usually attempt to revert to it
• Homeostatic process


  1. Change in the internal or external environment (stimulus) detected by a receptor

  2. Response to adjust the deviation parameter toward the set point
• Negative feedback mechanism


  A homeostatic process that changes the direction of the stimulus, either increasing or decreasing it, but not allowing the stimulus to continue as it did before the receptor sensed it
• Negative feedback loops are the predominant mechanism used in homeostasis
• Response to higher insulin levels

  1. Glucose is transported into cells

  2. Glucose is converted to glycogen

  3. Glucose levels drop
• Negative feedback loop


  Blood sugar levels are controlled by a negative feedback loop
• Positive feedback loop


  Maintains the direction of the stimulus and possibly accelerates it
• Positive feedback loops in animal bodies


  • Cascade of chemical reactions that result in blood clotting, or coagulation
• Umbilical cord


  Causes nerve impulses to be sent to the brain
• Cervix


  The brain stimulates the pituitary to release Oxytocin
• Set Point


  The body maintains its internal set point through homeostasis
• When the set point must be adjusted

  The feedback loop works to maintain the new setting
• Medication can lower blood pressure and lower the set point in the system to a healthier level through a process of alteration of the set point in a feedback loop
• Acclimatization


  Changes can be made in a group of body organ systems in order to maintain a set point in another system
• Thermoregulation


  Maintaining body temperature
• As internal body temperature increases


  Body functions are affected at higher temperatures
• Body temperature decreases below some point


  Body functions are affected
• Thermoregulation mechanisms


  • Various
• Ectotherms


  Organisms that rely on external sources of heat to regulate their body temperature
• Endotherms


  Organisms that regulate their own body temperature through internal metabolic processes
• Ectotherms rely on environmental temperature to regulate their body temperature
• Ectotherms usually live in environments like the tropics or oceans
• Ectotherms have developed mechanisms like basking in the sun to increase body temperature
• Endotherms regulate their own body temperature through internal metabolic processes