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BIOA02H3 (153)
Chapter 51

Chapter 51 Study Guide

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University of Toronto Scarborough
Biological Sciences
Mary Olaveson

Chapter 51 Salt and Water Balance and Nitrogen Excretion Blood, sweat, and tears -blood, sweat, tears taste salty because they have similar ionic concentrations as interstitial fluids -excretory system is responsible for maintaining homeostasis of interstitial fluid -all animals derive water from metabolism of food -desert animals must conserve water -they excrete wastes that are extremely concentrated, urine that is so concentrated that it contains crystals of solute -insects excrete semisolid wastes -animals that live in fresh water must constantly bail themselves out by producing copious amounts of dilute urine while they conserve solute -vampire bats feed on blood of unsuspecting (usually sleeping) mammal -blood is a high-protein, liquid food -to maximize volume of blood it can ingest, it eliminates water from its food by producing a lot of very dilute urine -when feeding ends, high rate of water loss must stop -produce small amounts of concentrated urine What Roles do Excretory Organs Play in Maintaining Homeostasis? -excretory organs control volume, concentration, and composition of extracellular fluids -concentration of solutes in extracellular fluid determines water balance of its cells Water enters or leaves cells by osmosis -movement of water across cell plasma membranes depends on differences in solute concentration -water flow from high to low solvent concentration across a water permeable membrane -solute concentration of extracellular fluid affects both volume and solute concentration of cells -osmolarity of a solution is the number of moles of osmotically active solutes per L of solvent -glucose is a one osmolar solution -NaCl is a 2 osmolar solution because NaCl dissociates into 2 osmotically active ions Excretory organs control extracellular fluid osmolarity by filtration, secretion, and reabsorption -excretory organs control osmolarity and volume of extracellular fluids by excreting solutes that are in excess (NaCl) and conserve solutes that are in short supply (glucose and amino acid) -eliminate waste products of nitrogen metabolism -output of excretory organ is urine -filters extracellular fluid to produce a filtrate that contains no cells or large molecules, like protein -in closed circulatory system, blood plasma is filtered across walls of capillaries -filtration is driven by blood pressure -water and small molecular weight solutes can cross capillary wall www.notesolution.com-large molecules and cells remain in blood -flitrate (water and small molecules) flows through tubules -tubules change composition of filtrate by active secretion and reabsorption of specific solute molecules -3 mechanisms: filtration, secretion, reabsorption are used in excretory system -no active transport of water -water must be moved either by pressure difference or difference in osmolarity Animals can be osmoconformers or osmoregulators -osmolarity of ocean water is high -osmoconformers are marine invertebrates that equilibrate extracellular fluid osmolarity with ocean water -osmoregulators are marine animals that maintain extracellular fluid osmolarities much lower than seawater -all marine vertebrates, except for shark and ray are osmoregulator -no animal can survive if its extracellular fluid has osmolarity of fresh water too few solutes in extracellular fluid, nutrients and ions necessary for cell functions -high solute concentrations can cause proteins to denature -brine shrimp Artemia can survive in environment of any osmolarity -insolute concentrated environment, it maintains tissue fluid osmolarity below that of environment -its mechanism of osmoregulation is active transport of Cl- from extracellular fluid to surrounding environment, followed by Na+ ions -cannot survive in fresh water, but dilute seawater -maintains osmolarity of extracellular fluid above environment -reverse direction of Cl- transport across gill membranes Animals can be ionic conformers or ionic regulators -osmoconformers can be ionic conformers, ionic composition and osmolarity of extracellular fluid match that of environment -most osmoconformers are ionic regulators -employ active transport mechanism to excrete ions and maintain other ions in extracellular fluid at optimal concentrations -herbivores conserve Na+ because plants contain low concentration of Na+ -birds that feed on marine animals must excrete excessive sodium they ingest with their food -nasal salt glands excrete concentrated solution of NaCl through a duct that empties into nasal cavity -ex. penguin and seagull How Do Animals Excrete Toxic Wastes from Nitrogen Metabolism? -end products of metabolism of carbohydrates and fats are water and carbon dioxide -protein and nuclei acids contain nitrogen -their metabolism produces nitrogenous wastes, water, and carbon dioxide www.notesolution.com
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