Homeostasis

• homeostasis

  maintenance of a constant internal environment via physiological control systems within set limits around an optimum
• what does homeostasis control

  blood glucose

  body temperature

  blood ph

  blood water potential
• role of negative feedback

  stimulus -> sensor -> control -> effector

  brings internal conditions back towards equilibrium
• why do multicellular organisms need a communication system

  to respond when internal and external environment changes

  to coordinate organ function
• receptors

  detect a change in the internal and external environment by responding to a stimulus
• effectors

  muscles and glands that enable a physical response to a stimulus
• ectotherm

  relies on external sources to regulate its body temperature

  only be controlled through behavioural adaptations
• thermoregulation

  insufficient kinetic energy for enzyme-controlled reactions

  enzymes could denature
• role of the skin in thermoregulation

  vasodilation -> where the arterioles by the skins surface dilate to increase blood flow to the capillaries increasing heat loss

  piloerection -> hair erector muscles contract and hair follicles trap air for insulation
• why do fish not need to regulate their body temperature much

  water has a high specific heat capacity

  temperatures remain relatively constant
• endotherm

  organisms that can maintain a core body temperature within strict limits around an optimum that is largely independent of that organisms environment

  through physiological and behavioural responses
• ectotherm temperature control

  basking in the sunlight

  changing orientation of body exposed to sunlight

  burrowing underground
• endotherm temperature control (behavioural)

  move into shade

  burrow underground

  remain inactive

  basking in the sunlight

  curl up to reduce surface area
• endotherm temperature control (physiological)

  internal detected by the hypothalamus

  external detected by peripheral temperature receptors in the skin
• hypothalamus if temperature increases

  vasodilation of superficial arterioles

  onset of sweating

  hairs lower as hair erector muscles relax

  decreased metabolic rate
• hypothalamus if temperature decreases

  vasoconstriction of superficial arterioles

  secrete less sweat

  less heat is lost from the blood to the surroundings
• sweat as a temperature control

  evaporates and cools the body by transferring heat energy to the surroundings
• cell signaling

  1. covers the whole body
  2. enable cell to cell communication
  3. specific and rapid speed
  4. provide long and short term responses