Ch 48

• Protonephridia


  Excretory system in invertebrates
• Hemolymph


  Invertebrate circulatory fluid
• Protonephridia are the excretory system in invertebrates
• Helps correct H2O conserved
• Juxtaglomerular apparatus in kidney
• Glomeruli


  Microscopic tubules formed from a transport epithelium that carry out osmoregulation and excretion
• Homeostatic Control Systems


  • Osmoregulation is the regulation of water and ion balance
  • Excretion helps maintain the body's water and ion balance while ridding the body of metabolic wastes
  • Thermoregulation is the control of body temperature
• Osmosis


  The movement of water molecules through a selectively permeable membrane from a region of lower solute concentration (hypoosmotic) to a region of higher solute concentration (hyperosmotic)
• Osmoconformers


  Animals where the osmolarity of cellular and extracellular solutions matches that of the environment
• Osmoregulators


  Animals that use control mechanisms to keep the osmolarity of cellular and extracellular fluids the same, but at levels that may differ from the osmolarity of the surroundings
• Excretory tubules


  • Protonephridia, the simplest form of excretory tubule, found in flatworms and larval mollusks
  • Metanephridia, found in annelids and most adult mollusks
  • Malpighian tubules, found in insects and other arthropods
• Protonephridia


  1. Hemolymph enters tubule through membranes

  2. Cilia beat to move fluid through the tubule

  3. Flame cell, named because the movement of its cilia resembles a flickering flame

  4.Urine is released through pores at the distal ends of tubules when they reach body surface.
• Nephron regions


  1. Reabsorption - Na+/K+ pumps, Cl- reabsorption, nutrient reabsorption, water reabsorption

  2. Movement into tubule - H+ ions, detoxified poisons

  3. Movement out of filtrate - nutrients and water move into capillaries

  4. Descending loop of Henle - water reabsorption, increasing osmolarity

  5. Ascending loop of Henle - salt ion reabsorption, decreasing osmolarity
• Concentration in collecting ducts

  • Loop of Henle
  • Differences in permeability along the nephron
  • Concentration gradient in interstitial fluid
• Renin-angiotensin-aldosterone system (RAAS)


  1. Renin released

  2. Angiotensinogen cleaved to angiotensin I

  3. Angiotensin I converted to angiotensin II

  4. Angiotensin II raises blood pressure, stimulates aldosterone, stimulates thirst

  5. Aldosterone increases Na+ reabsorption, increasing osmolarity and water reabsorption
• Elevated blood pressure


  Stimulates atrial natriuretic factor (ANF) release, which inhibits renin release, dilates afferent arterioles, and inhibits aldosterone release
• Marine teleosts continually lose water to their environment by osmosis and must replace it by continual drinking
• Sharks and rays maintain osmolarity of their body fluids close to that of seawater by retaining high levels of urea and trimethylamine oxide (TMAO) in body fluids
• Excess salts ingested with food are excreted in the kidney and by a rectal salt gland located near the anal opening in sharks and rays
• Nitrogenous wastes


  Released from the gills as ammonia - kidneys play little role in nitrogenous-waste removal
• Sharks and rays


  • Maintain osmolarity of their body fluids close to that of seawater by retaining high levels of urea and trimethylamine oxide (TMAO) in body fluids
• Isoosmolarity


  Keeps sharks and rays from losing water to the surrounding sea by osmosis, and they do not have to drink seawater continually to maintain their water balance
• Excretion of excess salts

  Excreted in the kidney and by a rectal salt gland located near the anal opening

  
• Salt ions lost with urine are replaced by salt in foods and by active transport of Na+ and K+ into the body by the gills (in fishes) or across the skin (in amphibians)
• They rarely drink, and they excrete large volumes of dilute urine to get rid of excess water
• Body fluids of freshwater fishes and aquatic amphibians

  • Hyperosmotic to the surrounding water - water moves osmotically into their tissues
• Adaptations that conserve water

  • Water-conserving activities of the kidneys, length of loop of Henle
  • Location of the lungs deep inside the body reduces water loss by evaporation during breathing
  • A body covering of keratinized skin almost eliminates water loss by evaporation

  
• Water-conserving adaptations reach their greatest efficiency in desert rodents such as the kangaroo rat - 90% of its daily water supply is generated from oxidative reactions in its cells
• Conduction


  Flow of heat between atoms or molecules in direct contact
• Convection


  Transfer of heat from a body to a fluid, such as air or water, that passes over its surface
• Radiation


  Transfer of heat energy as electromagnetic radiation
• Evaporation


  Heat transfer through the energy required to change a liquid to a gas
• Ectotherms


  "Cold-blooded" animals including most invertebrates, fishes, amphibians, and reptiles, obtain heat primarily from the external environment and regulate body temperature by controlling the rate of heat exchange with the environment through behavioral and physiological mechanisms
• Endotherms


  "Warm blooded" animals that keep their bodies at optimal temperature by regulating two processes: amount of heat generated by internal oxidative reactions and amount of heat exchanged with the environment
• Aquatic invertebrates


  • Limited thermoregulators - their body temperature closely follows their surroundings
• Invertebrates living in terrestrial habitats

  • Regulate body temperatures more closely, often using behavioral responses such as moving between shaded and sunny regions
• Winged arthropods


  • Use behavioral and heat-generating physiological mechanisms for thermoregulation
• Fishes


  • Body temperatures of most fishes remain within one or two degrees of their environment, many use behavioral mechanisms to keep body temperatures at optimal performance levels
• Amphibians


  • Body temperatures closely match the environment, some terrestrial amphibians bask in the sun to raise their body temperature, and seek shade to lower body temperature
• Reptiles


  • Some lizard species can maintain temperatures that are nearly as constant as those of endotherms, small lizards commonly shuttle between sunny (warmer) and shady (cooler) regions, in deserts, lizards and other reptiles retreat into burrows during the hottest part of summer days, desert iguanas lose excess heat by panting