homeostasis

• Homeostasis


  Regulation and internal maintenance of the body
• The body works best when internal conditions are within an acceptable range; homeostasis helps with this
• Feedback loops


  Homeostasis controls internal conditions with feedback loops
• Negative feedback


  • Product inhibits (slowdowns) process that creates them
  • Common homeostasis mechanism
  • Example: control of body temp by sweating or shivering
• Positive feedback


  • Product amplifies (quickens) process that creates them
  • Example: global warming, labor
• Examples of homeostasis happening in the body


  • Thermoregulation (temp)
  • Osmoregulation (water)
  • Gas exchange
  • Blood glucose
  • Guard cells
  • pH, blood pressure, hormone levels, metabolism
• Homeostasis


  State of balance in the body that has to be maintained so cells can function properly
• Each cell is surrounded by a small amount of fluid, its amount, temp and chemical component must remain at a certain range for cells to do their job properly
• Variables that must remain at a set point


  • Volume
  • Temperature
  • Chemicals
• Feedback loop


  1. Stimulus

  2. Receptor/Sensor

  3. Control center

  4. Effector

  5. Physiological response that returns variable to normal range

  6. Control center allows effector to return to normal
• Feedback loop for blood pressure


  1. Stimulus: BP increases above normal

  2. Receptors: In blood vessels detect change in BP, relay info to control center

  3. Control center: Receives info, determines BP above normal, sends signals to effector cells

  4. Effector cells: In heart and blood vessels decrease heart rate and increase diameter of blood vessels
• Feedback loop for body temperature


  1. Stimulus: Body temp decreases below normal

  2. Receptors: Detect temp change, relay info to control center

  3. Control center: Receives info, determines body temp below normal, sends signals to effector cells

  4. Effector cells: Nerve cells activate skeletal muscles to shiver and produce heat
• Positive feedback


  • Reinforce initial change in variable
  • Increase output
  • Result in more of a product
  • Occurs when something needs to happen quickly
  • Brings body farther away from normal variable
  • Stopped by negative feedbacks once the process is complete
• Positive feedback in childbirth


  1. Stimulus: Baby's head stretches cervix

  2. Receptor: Stretch sensitive nerve cells in cervix signal control center

  3. Control center: Causes pituitary gland to release oxytocin

  4. Effectors: Oxytocin causes stronger contractions of smooth muscles in uterus, moving baby's head farther down birth canal

  5. Response: Forceful contractions and oxytocin release continue to increase until baby is born

  6. End point: Stretching of cervix stops which stops oxytocin release