BIO 311D 1st Edition Lecture 21 Outline of Last Lecture I Clicker questions II Osmoregulation III Seawater fish IV Freshwater fish V Land Animals VI Transport Epithelia Outline of Current Lecture I Forms of Nitrogenous wastes II Ammonia III Urea IV Uric acid V Excretory Processes VI Kidneys VII Loop of Henle Current Lecture Uric acid is the nitrogenous waste excreted by birds insects and many reptiles An advantage of excreting uric acid is that it but a disadvantage is that it A Saves water costs energy B Saves energy is highly toxic C Is not very toxic wastes a lot of water D Is much more soluble in water than other wastes costs energy E Saves water is highly toxic Forms 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 them Ammonia Animals that excrete nitrogenous wastes as ammonia need access to lots of water They release ammonia across the whole body surface or through gills Urea 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 less water than ammonia Uric 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 urea The 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 budget Diverse excretory systems are variations on a tubular theme Excretory systems regulate solute movement between internal fluids and the external environment Excretory 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 body Survey of Excretory Systems Systems that perform basic excretory functions vary widely among animal groups They usually involve a complex network of tubules Protonephridia 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 osmoregulation Metanephridia 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 excretion Malpighian 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 air Which of the following describes the route of urine out of the body after it leaves the kidney A Renal vein bladder urethra ureter B Urethra bladder ureter C Renal vein ureter bladder urethra D Ureter bladder urethra E Ureter urethra bladder Kidneys Kidneys the excretory organs of vertebrates function in both excretion and osmoregulation The 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 molecules From Blood Filtrate to Urine A Closer Look Proximal 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 concentrated Descending 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 hyperosmotic to the filtrate The filtrate becomes increasingly concentrated Ascending 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 dilute Ascending 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 dilute Distal Tubule The distal tubule regulates the K and NaCl concentrations of body fluids The controlled movement of ions contributes to pH regulation Collecting 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 fluids Collecting 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 fluids
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