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Biology Lecture #6 - Excretion and Ion Transport.docx

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Queen's University
BIOL 103
Virginia K Walker

Biology Lecture #6 – Excretion and Ion Transport  Lecture covers nitrogenous wastes, salt and water balance as well as kidney function Obligatory Exchanges  Many vital processes have potential to disturb the balance between salt and water concentrations  Obligatory exchanges are necessary as part of respiration or elimination of wastes  Water and salt will be loss through body respiration, ingestion of food will be eliminated as waste (unnecessary parts) as well as through metabolism Nitrogenous Waste  Product of the breakdown of amino acids and nucleic acid degradation  The waste produced is species and environment dependent, such as ammonia, urea and uric acid  Most aquatic animals excrete ammonia or ammonium ions  Little energy required for production, high amount of water needed to excrete and has high toxicity  Most mammals, amphibians, marine fishes and terrestrial invertebrates excrete urea  Requires moderate energy and moderate amount of water for excretion, has a low toxicity  Birds, insects and most reptiles excrete uric acid  Requires a lot of energy but little water to excrete, and has a low toxicity  Example of a freshwater fish  Body is hyperosmotic and danger of being water logged due to constant osmotic pressure of water which is why water travels in from gills via osmosis  Produce large amount of dilute urine to remove water  Risk of losing salts, so taken in by active up taking of na+ and cl- into their capillaries  Example of a Saltwater fish  Body is hyperosmotic and in danger of dehydrating with water lost across their gills  Need to drink much seawater  Excreted ammonia is diluted with as little water as possible, meaning urine is concentrated  Excess salt is transported out of body by specialized cells in the gills Anatomy of Bird Egg  Uric acid is stored in allantois and left behind at hatching  Metabolic processes still occur inside an egg Excretory Organs  Filtration – remove water and small concentrations of solutes from body fluids or blood while leaving behind important things such as blood cells, proteins and other large solutes  Reabsorption – useful material in the filtrate, recaptured and sent to blood stream  Secretion – put additional solutes into the filtrate and can help aid in elimination of toxins Kidney Function  Vertebrates have a kidney containing specialized tubules with cells that actively transport ions for salt and water homeostasis and nitrogenous waste elimination  Renal cortex – outer structure  Renal medulla – inner structure  Nephrons cross between the two above sections  Main functional unit of the kidney, several million of these exist in the kidney  Composed of … 
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