communication & homeostasis

• homeostasis

  maintaining a constant internal environment around an optimum despite external change
• homeostasis is important to ensure maintenance of optimal conditions for enzyme action and cell function
• physiological factors controlled by homeostasis

  • core body temperature
  • metabolic waste e.g carbon dioxide and urea
  • blood pH
  • concentration of glucose in blood
  • water potential of blood
  • concentration of respiratory gases in blood e.g carbon dioxide and oxygen
  • concentration of sodium ions and urea in blood
• 2 communication systems

  • nervous system
  • endocrine system
• receptors

  sensory receptors detect changes in the internal and external environment of an organism
• effectors

  muscles or glands that react to a motor stimulus to bring about a change in response to a stimulus
• information from sensory neurones is transmitted to brain and impulses are sent along the motor neurones to the effectors
• a coordination system

  transfer information between different parts of the body
• outcome of negative feedback loop

  • stimulus is continuously monitored
  • if there is increase in the factor, body responds to decrease the factor
  • vice versa
• negative feedback loops help maintain normal range within an organism by reducing initial effect of stimulus
• negative feedback

  
  

  internal/external stimuli -> receptor detects stimulus -> information sent to central control -> effector -> stimulus continuously monitored
• positive feedback

  original stimulus produces a response that causes the factor to deviate even more than the normal range and it enhances the effect of the original stimulus
• positive feedback system

  internal stimulus -> sensory receptors -> effectors stimulated -> change is reinforced and increased
• positive feedback example

  • during childbirth when baby's head is pushed against cervix, hormone oxytocin is released
  • oxytocin stimulates uterus to contract to push baby's harder against cervix
  • triggering more release of oxytocin
  • continues until baby is born
• thermoregulation

  maintenance of a constant core body temerature ro mainatin optimum enzyme activity
• endotherms

  • animals possess physiological mechanisms for the maintenance of internal body temperature
  • rely on metabolic processes to maintain internal temperature despite temperature of environment
  • metabolic rate higher than ectotherms
  • e.g mammals and birds
• ectotherms

  • their core body temperature is dependant on the environment
  • animal rely on behavioural mechanisms e.g huddling together for warmth
  • aquatic ectotherms don't need to thermoregulate because high heat capacity of water means environmental temperature won't change much
  • e.g fish, amphibians, reptiles, invertebrates
• physical processes for thermoregulation

  • exothermic chemical reactions
  • latent heat of evaporation
  • radiation
  • convection - heating and cooling by currents of air or water
  • conduction - heating as a result of collision of molecules
• thermoregulation in endotherms

  • detect external temperatures via peripheral receptors
  • impulses sent to hypothalamus
  • hypothalamus contain receptors that monitor temperature of blood flowing through it
  • information from receptors is processed by hypothalamus
  • homeostatic responses initiated when temperature is too high or low
• high body temperature in endotherms

  • vasodilation - arteriole muscles relax snd dilate allowing more blood to flow into skin capillaries so heat is lost to environment by radiation
  • sweating - sweat secreted by sweat glands in skin and skin is cooled by evaporation - less effective as a cooling mechanism in humid environments due to reduced concentration gradient
  • flattening of hairs - hair erector muscles relax to allow air to circulate over skin, removinf heat lost by radiation
• low body temperature in endotherms

  • vasoconstriction - arteriole muscle contract so arterioles near skin constrict causing less blood to flow through skin capillaries
  • increased metabolic rate - most metabolic reactions are exothermic so increased warmth to body
  • shivering - muscles contract and relax repeatedly, releasing heat energy to warm the blood
  • erection of hairs - hair erector muscles contract cauding hairs to be erect - traps an insulating layer of air over the skin's surface, reducing heat loss by raidation
• high body temperature in ectotherms

  • seek shade
  • move bodies into water
• low body temperatures in ectotherms

  • seek out the sun or warmer surfaces to bask in these locations
  • huddle together to retain heat
• thermoregulation in ectotherms

  • behaviour of ectotherms is restricted by environmental temperatures - can't colonise habitats with extreme temperatures
  • save lots of energy by not regulating body temperature internally so can survive in food limited environments