1 12 1 Terrestrial Osmoregulation BIO 361T Fall 2014 Needing Water 1 Why do animals need water Briefly explain two reasons that apply generally to the body see sub questions for clarification Maintain cell volume for chemical reaction speed hydrolysis of macromolecules dilute toxic effects of nitrogenous waste products a Why does the circulatory system need water Maintain fluid volume blood pressure to deliver gas and solutes to and from cells b Why does the respiratory system need water Maintain moistness of respiratory surface to facilitate gas dissolving 2 Why do animals need to control their ion concentrations Regulates chemical reactions structure and function of enzymes cell volume pressure on tissues a Why do neurons need to control their ion concentrations To maintain membrane potential and excitability b Why do myocytes need to control their ion concentrations To maintain excitability and contractility Obtaining Water 1 What is the primary source of water in terrestrial animals Diet in humans it is 60 drinking 30 eating 2 How does this water get into the blood ECF Paracellular and transcellular transport between through the epithelial cells of the gut Then diffuses short distance across interstitial space between endothelial cells into nearby blood vessels 3 What will happen if a terrestrial animal drinks distilled water Because it is hypoosmotic to the ECF when it reaches the gut epithelia which is thin enough for diffusion it will draw solutes out of the ECF lowering concentration of solutes and other ions in the ECF which will translate to osmotic stress on the cells If this occurs beyond the extent that the body can compensate for it can cause neural damage and even death as neurons lose their membrane potentials 4 About 10 of daily water requirements in humans come from metabolic water Which type of macromolecule would you expect to yield the most metabolic water carbohydrates proteins or lipids Explain your answer Carbohydrates 15 mL H2O 100 kcal metabolizable energy because they are the most efficient starting material for cellular respiration lipids 11 1 mL proteins 10 5 mL 2 Retaining Water 1 Do terrestrial animals need adaptations to primarily retain or excrete water Support your answer Retain due to evaporative water loss to dry environment and dilution of nitrogenous waste 2 Most terrestrial animals have adaptations to prevent dehydration but some are adapted to tolerate dehydration as an alternative survival strategy When it rains in Austin snails appear all over the ground Have you ever thought about where they all come from Propose two adaptations in a terrestrial snail that would allow it to tolerate long periods without water Estivation long periods underground with little to no metabolic activity Seal off shell to retain moisture Still may lose 50 of its body mass Concomitant decreases in body mass thus less need for water 3 Describe two ways a turtle can prevent water loss Modified integument shell Solute reabsorption which will cause water reabsorption Excreting Solutes 1 Why do aquatic animals excrete their nitrogenous waste as ammonia given its high toxicity Toxicity is not an issue due to immediate dilution It is energetically free no additional processing steps after it is produced as a by product of protein metabolism 2 Explain the trade off involved in excreting nitrogenous waste as uric acid or urea instead of ammonia Advantage less toxic requires less water to dilute Disadvantage more energetically costly processing steps some of which require ATP 3 Uric acid is only slightly toxic urea even less so Given this hypothesize as to why all animals do not primarily excrete urea More energetically costly than uric acid 2 5 ATP per nitrogen vs 1 75 4 Some species can convert uric acid directly into urea Ureoteles have a separate pathway for producing urea that does not use uric acid as an intermediate which occurs in cells of the liver The urea is then released into the blood Use what you know about vascularization of alveoli and ECF filtration in metanephridia to hypothesize as to how the urea ends up in the urine Urea is in the blood which transports it to capillaries that vascularize part of the renal gland vertebrate kidney The capillaries there have podocytes like in metanephridia which push urea out via blood pressure and into the tubules of the kidney where urine is formed 5 Some animals can change their primary mode of nitrogen excretion Predict how this will change in lungfish when water availability is low and they burrow into the mud and switch to airbreathing Lungfish usually excrete ammonia When they burrow they switch to urea Lungfish secrete a mucous cocoon that helps them retain water in dry conditions but also results in concentration of their nitrogenous waste around their bodies 6 Although aquatic animals typically excrete their nitrogenous waste as ammonia some still produce uric acid or urea e g sharks Why do sharks produce high amounts of urea To maintain osmolarity in seawater which they counteract with methylamine oxides 3 7 Terrestrial arthropods like insects excrete primarily uric acid using Malpighian tubules a Which cells in the tubules are responsible for water secretion Stellate cells type II have aquaporins b Which cells in the tubules are responsible for cation secretion Principal cells type I have a variety of proteins that actively transport solutes c What do you notice about the generic solute transports in the principal cell that distinguish them from the other channels They are bi directional d How does this allow the principal cells to control water secretion By moving solutes in or out of the tubule lumen this will effect water movement through the aquaporins of the stellate cells e The main portion of each Malpighian tubule is responsible for fluid and cation secretion What cells would you expect to find in this portion Explain your answer Both types Stellate cells will secrete fluids while principal cells will secrete cations Cation secretion will affect fluid water secretion f The lower portion of each tubule is responsible for reabsorption not secretion What cells would you expect to find in this portion Explain your answer Only principal cells because solutes can be transported into the cells out of the lumen Stellate cells do not have the correct membrane proteins to do this g What molecular mechanism is responsible for generating an electrical gradient that controls cation secretion The apical H ATPase
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