need for homeostasis - constancy of internal environment 

• controlled through negative feedback loop
• sensors - measure conditions of internal environment
• integrating center - contains set point (proper conditions)
• change occurs >> effectors told to increase/decrease activity
  • effectors - muscles/glands
• body temperature - set around 37 C
  • hypothalamus detects temperature changes
  • high temperature >> sweating, dilation of blood vessels
  • low temperature >> shivering, constriction of blood vessels
  • ectothermic (cold-blooded) animals use behavior, environment to control internal conditions
• glucose levels - controlled by islets of Langerhans
  • insulin secreted >> stimulates reuptake of blood glucose in tissues
• antagonistic effectors - push-pull relationship
  • sets of effectors used to better control homeostasis
• positive feedback loops - drives condition further from set point
  • don’t help maintain homeostasis
  • used in blood clotting, uterus contractions

osmolality - total moles of solute per kilogram of water 

• osmotic pressure - measures tendency of a solution to take in water (force placed on semi-permeable membrane)
• isotonic >> no net mov’t of water
• osmoconformers - animals w/ same osmolality in body fluids as surrounding seawater
• osmoregulators - animals w/ different osmolality from environment
  • must maintain constant blood osmolality
  • freshwater vertebrates = hypertonic to surrounds, tend to gain water
  • terrestrial vertebrates have more water than environment, tend to lose water
• urinary systems evolved to help retain water

osmoregulatory organs - water sometimes removed along w/ metabolic waste 

• protonephridia - tubules in flatworms, leads to pores on outside
  • doesn’t lead to outside/inside
• nephridia - tubules leading to outside/inside of earthworm
• Malphigian tubules - excretory organs in insects
• reabsorption - transport out of tubule, into surrounding body fluids
• vertebrate kidneys filter through pressure
• urea - form in which nitrogenous waste is removed in mammals
  • water soluble
  • uric acid (not as water soluble) >> can precipitate out, forms gout in humans, guano in