FEEDBACK MECHANISMS

• Thermoregulation


  The process of maintaining a stable internal body temperature
• Endothermic animals


  • Maintain a constant body temperature in the face of environmental changes
  • Generate internal heat that keeps their cellular processes operating optimally even when the environment is cold
  • Birds and mammals have high metabolic rates that generate heat, even when they are resting
• Ectothermic animals


  • Do not have internal control of their body temperature
  • Body temperature is generally like the temperature of the environment
  • Have relatively low metabolic rates when resting, so their bodies do not generate much heat
  • Most reptiles, invertebrates, fishes, and amphibians are ectotherms that regulate body temperature primarily by absorbing heat from, or losing heat to, their environment
• Thermoregulation


  1. Coordinated by the nervous system

  2. Processes of temperature control are centered in the hypothalamus

  3. Hypothalamus maintains the set point for body temperature through reflexes that cause vasodilation or vasoconstriction and shivering or sweating
• During an infection


  Compounds called pyrogen are produced and circulate to the hypothalamus resetting the thermostat to a higher value, allowing the body's temperature to increase to a new homeostatic equilibrium point in what is commonly called a fever
• The increase in body heat makes the body less optimal for bacterial growth and increases the activities of cells so they are better able to fight the infection
• Osmoregulation


  The process of maintaining salt and water balance in the body
• Negative feedback loop


  • Serves to reduce an excessive response and keep a variable within the normal range
• Positive feedback loop


  • Serves to intensify a response until an endpoint is reached
• Electrolytes are compounds that dissociate into ions when dissolved in water
• Homeostasis is the maintenance of stable internal conditions in an organism
• Feedback


  A physiological loop that brings the body either toward or away from the normal, steady state
• Feedback mechanism


  • Amplifies or inhibits a biological pathway
  • Most commonly returns the body to homeostasis
• Homeostasis


  The stable state of the inner environment of organisms
• Maintaining body temperature


  1. Blood vessels dilate to allow more blood flow to skin surface

  2. Sweat glands activated to increase sweat output

  3. Breathing becomes deeper and through mouth
• Maintaining body temperature (heating up)

  1. Blood vessels contract to prevent blood flow to skin surface

  2. Skeletal muscles contract causing shivering

  3. Thyroid gland secretes more thyroid hormone

  4. Adrenal glands secrete adrenaline
• Negative feedback loop


  Feedback serves to reduce an excessive response and keep a variable within the normal range
• Processes controlled by negative feedback

  • Body temperature regulation
  • Control of blood glucose
• Positive feedback loop


  Feedback serves to intensify a response until an endpoint is reached
• Processes controlled by positive feedback

  • Blood clotting
  • Childbirth
• Electrolyte


  A compound that dissociates into ions when dissolved in water
• Nonelectrolyte


  A compound that does not dissociate into ions when dissolved in water
• Osmoregulation


  The process of maintaining salt and water balance (osmotic balance) across membranes within the body
• Components of homeostasis


  • Stimulus
  • Sensor
  • Control center
  • Effector
• Stimulus


  The variable that is being regulated, indicates the value has moved away from the set point
• Sensor


  Monitors the values of the variable and sends data to the control center
• Control center


  Matches the data with normal values and sends a signal to the effector if outside the normal range
• Effector


  An organ, gland, muscle, or other structure that acts on the signal from the control center to move the variable back toward the set point