BIO 311D 1st Edition Lecture 21 Outline of Last LectureI. Clicker questionsII. OsmoregulationIII. Seawater fishIV. Freshwater fishV. Land AnimalsVI. Transport EpitheliaOutline of Current Lecture I. Forms of Nitrogenous wastesII. AmmoniaIII. UreaIV. Uric acidV. Excretory ProcessesVI. KidneysVII. Loop of HenleCurrent LectureUric acid is the nitrogenous waste excreted by birds, insects, and many reptiles. An advantage ofexcreting uric acid is that it ______, but a disadvantage is that it ________.A. Saves water, costs energyB. Saves energy, is highly toxicC. Is not very toxic, wastes a lot of waterD. Is much more soluble in water than other wastes, costs energyE. Saves water, is highly toxicForms of Nitrogenous Wastes• Animals excrete nitrogenous wastes in different forms: ammonia, urea, or uric acid• These differ in toxicity and the energy costs of producing themAmmonia• Animals that excrete nitrogenous wastes as ammonia need access to lots of water• They release ammonia across the whole body surface or through gillsUrea• The liver of mammals and most adult amphibians converts ammonia to the less toxic urea• The circulatory system carries urea to the kidneys, where it is excreted• Conversion of ammonia to urea is energetically expensive; excretion of urea requires lesswater than ammoniaUric Acid• Conserves water but costs more energy compared to making urea• Has the most nitrogen, so it is a good fertilizer• Insects, land snails, and many reptiles, including birds, mainly excrete uric acid • Uric acid is relatively nontoxic and does not dissolve readily in water• It can be secreted as a paste with little water loss• Uric acid is more energetically expensive to produce than ureaThe Influence of Evolution and Environment on Nitrogenous Wastes• The kinds of nitrogenous wastes excreted depend on an animal’s evolutionary history and habitat, especially water availability• Another factor is the immediate environment of the animal egg• The amount of nitrogenous waste is coupled to the animal’s energy budgetDiverse excretory systems are variations on a tubular theme• Excretory systems regulate solute movement between internal fluids and the external environmentExcretory Processes• Most excretory systems produce urine by refining a filtrate derived from body fluids• Key functions of most excretory systems– Filtration: Filtering of body fluids– Reabsorption: Reclaiming valuable solutes– Secretion: Adding nonessential solutes and wastes from the body fluids to the filtrate– Excretion: Processed filtrate containing nitrogenous wastes, released from the bodySurvey of Excretory Systems• Systems that perform basic excretory functions vary widely among animal groups• They usually involve a complex network of tubulesProtonephridia (Flat worm)• A protonephridium is a network of dead-end tubules connected to external openings• The smallest branches of the network are capped by a cellular unit called a flame bulb• These tubules excrete a dilute fluid and function in osmoregulationMetanephridia (Earth Worm)• This is the next complex class• Segmented unlike the flat worm• Each segment of an earthworm has a pair of open-ended metanephridia• Metanephridia consist of tubules that collect coelomic fluid and produce dilute urine for excretionMalpighian Tubules (Insects)• In insects and other terrestrial arthropods, Malpighian tubules remove nitrogenous wastes from hemolymph and function in osmoregulation• Insects produce a relatively dry waste matter, mainly uric acid, an important adaptation to terrestrial life• Some terrestrial insects can also take up water from the airWhich of the following describes the route of urine out of the body after it leaves the kidney?A. Renal vein-bladder-urethra-ureterB. Urethra-bladder-ureterC. Renal vein-ureter-bladder-urethraD. Ureter-bladder-urethraE. Ureter-urethra-bladderKidneys• Kidneys, the excretory organs of vertebrates, function in both excretion and osmoregulationThe nephron is organized for stepwise processing of blood filtrate• The filtrate produced in Bowman’s capsule contains salts, glucose, amino acids, vitamins,nitrogenous wastes, and other small moleculesFrom Blood Filtrate to Urine: A Closer LookProximal Tubule• Reabsorption of ions, water, and nutrients takes place in the proximal tubule• Molecules are transported actively and passively from the filtrate into the interstitial fluid and then capillaries• Some toxic materials are actively secreted into the filtrate• As the filtrate passes through the proximal tubule, materials to be excreted become concentratedDescending Limb of the Loop of Henle• Reabsorption of water continues through channels formed by aquaporin proteins• Movement is driven by the high osmolarity of the interstitial fluid, which is hyperosmoticto the filtrate• The filtrate becomes increasingly concentratedAscending Limb of the Loop of Henle• In the ascending limb of the loop of Henle, salt but not water is able to diffuse from the tubule into the interstitial fluid• The filtrate becomes increasingly diluteAscending Limb of the Loop of Henle• In the ascending limb of the loop of Henle, salt but not water is able to diffuse from the tubule into the interstitial fluid• The filtrate becomes increasingly diluteDistal Tubule• The distal tubule regulates the K+ and NaCl concentrations of body fluids• The controlled movement of ions contributes to pH regulationCollecting Duct• The collecting duct carries filtrate through the medulla to the renal pelvis• One of the most important tasks is reabsorption of solutes and water• Urine is hyperosmotic to body fluidsCollecting Duct• The collecting duct carries filtrate through the medulla to the renal pelvis• One of the most important tasks is reabsorption of solutes and water• Urine is hyperosmotic to body
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