1ExcretionChapter 9Functions of Excretory Organs • Maintain solute concentrations• Maintain body fluid volume• Remove metabolic end products• Remove foreign substances Nitrogen Excretion• Nitrogen-based waste compounds derived from proteins and nucleic acids• Excretion classified by major waste produced– Ammonotelic – ammonia is the principle waste– Ureotelic – urea is the principle waste– Uricotelic – uric acids and urate salts are the principle wastesExcretory Processes• Ultrafiltration– Movement of fluid (e.g. blood) through a semipermeable membrane– Membrane allows small particles to pass with the water, large particles (proteins etc.) remain• Active Transport– Movement of solutes against their electrochemical gradients (requires energy)– Secretion – movement of solute into the lumen of the excretory organ– Reabsorption – movement of solute out of lumenGeneralized Excretory Organs• Sponges, Coelentrates and Echinoderms –none• Playhelminths, Nematodes, Annelids –nephridial organs• Crustaceans – antenna glands• Insects – Malpighian tubules• Mollusks and Vertebrates – kidneys Nephridial Organs• Common in invertebrates• System of tubes – connected to the outside through nephridial pore• Protonephridia– Found in acoelous and pseudocoelous animals (platyhelminths, nematodes, etc.)– Blind-ended tubes with flame cells or solenocytes at closed end• Create current• Draw fluid in from surrounding tissues (filtration)• Water then reabsorbed2Nephridial Organs• Metanephridia– Coelous Animals (e.g., annelids)– Inner cells open into coelomic cavity– Four components:• Nephrostome – funnel-shaped filter• Coiled tubule – secretion and absorption• Bladder –storage• Nephridial poreAntennal Gland• Crustaceans• Paired glands located in the head• Consist of initial sac, long coiled excretory tubule and terminal bladder– Excretory pore at base of antennaMalpighian Tubules• Arachnids and insects• Specialized region of digestive tract– Located btw midgut and hindgut• Blind-ended tubules– Blind ends locates in hemocoel– Some end near rectumMalpighian Tubules and Rectum• NO ultrafiltration– Active secretion of K+into lumen–H2O follows passively along osmotic gradient– Content altered by secretion and absorption• Fluid secreted into hindgut• Water and solutes reabsorbed in rectum• Uric acid precipitatesMolluscan Kidneys• Associated with pericardial cavities– Ultrafiltration from heart– Secretion/reabsorption by renopericardial canal– Stored in bladder (renal sac)– Released into mantle and expelledVertebrate Kidneys• Ultrafiltration followed by reabsorption– Blood plasma is filtered, then important solutes and water reabsorbed into the blood– 99% of filtered material is reabsorbed– Allows animals to filter out new substances without developing new specialized secretorymechanisms3Vertebrate Kidneys• Consists of numerous tubular units called nephronsKidney• Blood delivered into the glomerulus– Tuft of fenestrated capillaries– Site of filtration (blood pressure forces filtered plasma out)– Filtrate collected by Bowman’s capsuleKidney• Enters tubular structures• Proximal tubule– Reabsorption of solutes and water• Distal tubule– Further reabsorption and secretion• Collecting duct– Join several distal tubulesKidney• Loop of Henle(mammals and birds)• Thin, single loop between proximal and distal tubules• Allows formation of hyperosmotic urineGlomerular Filtration• Occurs through fenestrated capillaries– Plasma with small particles filters out– Blood cells and plasma proteins remain• Blood pressure must exceed colloid osmotic pressureTubular Secretion• Removal of excess ions (K+, Ca2+, Mg2+, H+)• Removal of foreign substances• Active Transport4Tubular Reabsorption• Active transport of inorganic ions Na+• Coupled transport of glucose, amino acids, etc.• Osmotic uptake of waterHyperosmotic Urine• Mammal kidneys can excrete a hyperosmotic urine – concentrating mechanism occurs in the Loop of Henle• Countercurrent Multiplication – generates osmotic gradient that draws H2O out of the tubules to be reabsorbed– due to active reabsorption of Na+and Cl-Loop of Henle• Mechanism– descending limb• permeable to water– ascending limb • impermeable to water • lined w/ ion pumps (Na+or Cl-)Loop of Henle:Ascending Limb• Na and Cl actively transported out of lumen• urea flows out of lumen in thin segment of ascending limb• Creates osmotic gradientLoop of Henle:Descending limb• osmotic gradient generated btw interstitial fluid and lumen•H2O moves out of the lumen• Filtrate concentrated to hyperosmotic levels• Water leaving lumen diffuses into the vasarecta (re-enters blood)Loop of Henle:Ascending limb• osmotic concentration ↓’sas solutes are moved out of the filtrate by active Na+transport5Collecting Duct• Water flows out as tubule descends into medulla• Water leaving lumen diffuses into the vasarecta (re-enters blood)• Final urine produced is hyperosmoticLoop Length and Aridity• Relative length of the loops is longer in animals adapted to dry habitats than in those from wetter