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Common Requirements of living things ANIMALS – Chapter 5 Part D Excretion Elimination of Metabolic wastes The physiological systems of animals operate within a fluid environment. The relative concentrations of water and solutes must be maintained within narrow limits, despite variations in the animal’s external environment. Metabolism also poses the problem of disposal of wastes. The breakdown of proteins and nucleic acids is problematic because ammonia, the primary metabolic waste from breakdown of these molecules, is very toxic. An organism maintains a physiological favourable environment by : • Osmoregulation= regulating solute balance and the gain and loss of water and • Excretion, the removal of nitrogen-containing waste products of metabolism. Osmoregulators: expend energy to control their internal chemical balance Osmoconformers: organisms whose internal environment varies with their external environment. Waste Removal and Water balance • The human body and in fact all organisms are not 100% efficient at converting all the raw materials ingested into useful substances. • Which means we have waste products. – – – – – CO2 is a waste product of cellular respiration Water Salts Sugars if in extreme concentrations Protein breakdown( metabolism) results in nitrogenenous waste • This then is excreted as either ammonia, urea or uric acid Nitrogenous Wastes Excretion of Nitrogenous wastes Transport Epithelia • Transport epithelia are specialized cells that regulate solute movement • They are essential components of osmotic regulation and metabolic waste disposal • They are arranged in complex tubular networks • An example is in salt glands of marine birds, which remove excess sodium chloride from the blood LE 44-7b Lumen of secretory tubule Vein Capillary Artery Secretory tubule NaCl Transport epithelium Direction of salt movement Blood flow Secretory cell of transport epithelium Central duct Ammonia • Animals that excrete nitrogenous wastes as ammonia need lots of water • They release ammonia across the whole body surface or through gills Uric Acid • Insects, land snails, and many reptiles, including birds, mainly excrete uric acid • Uric acid is largely insoluble in water and can be secreted as a paste with little water loss Urea • The liver of mammals and most adult amphibians converts ammonia to less toxic urea • The circulatory system carries urea to the kidneys, where it is excreted Organs of Excretion: The Lungs Organs of Excretion : the Skin + some nitrogenous compounds Organs of Excretion : The Kidneys The kidneys are the organs that removes nitrogenous waste from the body. Urine : composition Creatinine :a break-down product of creatine phosphate in muscle, and is usually produced at a fairly constant rate by the body Mammalian Excretory Systems: deal with • • • • • • • Osmolarity Total body water Volume of extracellular fluid Cell volume (osmotic pressure) Individual ions Acid-base balance Metabolic waste products • Urea • Uric acid • Creatinin (from muscle) • Foreign chemicals • Drugs, pesticides, food additives, etc. Regulates: Eliminates: Vertebrate Excretory System Overview of Human Excretion • Kidneys, the excretory organs of vertebrates, – function in both excretion and osmoregulation • The mammalian excretory system centers on paired kidneys, which are also the principal site of water balance and salt regulation • Each kidney is supplied with blood by a renal artery and drained by a renal vein • Urine exits each kidney through a duct called the ureter • Both ureters drain into a common urinary bladder The Nephron The Glomerulus Glomerular filtration: Bulk flow of protein free plasma from glomerular capillaries to space of Bowman’s capsule. Bowman’s capsule: 2 walls 1) Outer wall – simple squamous epithelium 2) Inner wall – podocytes coat capillaries Glomerular capillaries Tuft of capillaries surrounded by Bowman’s space Supplied by afferent arterioles Kidney flowchart of events Glomerulus Bowman’s capsule Proximal tubule Distal tubule Loop of henle (ascending) Loop of henle (descending) Collecting ducts Bladder Excreted Posterior vena cava Renal artery and vein Kidney Renal medulla Renal cortex Renal pelvis Aorta Ureter Urinary bladder Urethra Ureter Excretory organs and major associated blood vessels JuxtaCortical medullary nephron nephron Afferent arteriole Glomerulus from renal Bowman’s capsule artery Proximal tubule Peritubular capillaries Renal cortex Collecting duct 20 µm Renal medulla To renal pelvis Nephron Section of kidney from a rat Kidney structure SEM Efferent arteriole from glomerulus Distal tubule Collecting duct Branch of renal vein Descending Loop limb of Henle Ascending limb Vasa recta Filtrate and blood flow Proximal tubule NaCl Nutrients HCO3– K+ H2O H+ NH3 Distal tubule H2O NaCl K+ HCO3– H+ CORTEX Descending limb of loop of Henle Filtrate H2O Salts (NaCl and others) HCO3– H+ Urea Glucose; amino acids Some drugs Thick segment of ascending limb NaCl H2O OUTER MEDULLA NaCl Thin segment of ascending limb Key Collecting duct Urea NaCl Active transport Passive transport INNER MEDULLA H2O Osmolarity of interstitial fluid (mosm/L) 300 300 100 300 100 CORTEX Active transport H2O H2O NaCl 400 NaCl 300 300 400 400 H2O 200 H2O Passive transport OUTER MEDULLA H2O NaCl H2O NaCl H2O INNER MEDULLA H2O 400 600 H2O H2O NaCl 900 NaCl NaCl H2O 600 H2O Urea 700 H2O Urea 900 H2O Urea 1200 1200 600 1200 Adaptation of Vertebrate Kidneys: Length of loop of Henle related to need for water conservation – longer loops, greater ability to conserve water. Protonephridia: Flame-Bulb Systems • A protonephridium is a network of dead-end tubules lacking internal 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 • 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 Digestive tract Rectum Hindgut Intestine Midgut (stomach) Malpighian tubules Feces and urine Salt, water, and nitrogenous wastes Anus Malpighian tubule Rectum Reabsorption of H2O, ions, and valuable organic molecules HEMOLYMPH