Ch49%20Answers056 - CHAPTER 49 MAINTAINING THE‘INTERNAL...

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Unformatted text preview: CHAPTER 49 MAINTAINING THE‘INTERNAL ENVIRONMENT TIPS FOR MASTERING KEY CONCEPTS To remain alive and functioning properly, organisms and cells need to maintain homeostasis. Unless they are isotonic with their surrounding environment, all organisms tend to gain water and lose salts, or lose water and gain salts, depending on the relative osmolality of the organism and the environment. Such gains and losses can be lethal if they are too extreme. Organisms also need to dispose of nitrogenous wastes. In vertebrates, osmoregulation and nitrogenous waste excretion are carried out by the kidney, regulated by‘the central nervous system and hormones. 49.1 The regulatory systems of the body maintain homeostasis. 0 Organisms cannot survive extreme fluctuations in internal conditions such as temperature, pH, or water and salt balance. G Various organ systems interact to help maintain relatively constant internal conditions. a Negative feedback loops prevent conditions from straying too far from the set point. ' o By having antagonistic effectors influencing the same parameter, the body can achieve finer scale control and minimize fluctuations even more. 49.2 The extracellular fluid concentration is constant in most vertebrates. 0 Most marine invertebrates are isotonic with the surrounding water and so do not have to deal with gaining or losing water and salts. - Terrestrial and freshwater invertebrates, as well as vertebrates, are not isotonic with their environments and have evolved a variety of structures and processes to deal with osmoregulation (regulating the levels of water and ions in their blood and extracellular fluids). I The kidneys carry out osmoregulation in the vertebrates. - While all vertebrate kidneys are structurally similar, the kidneys of freshwater fish excrete very dilute urine, the kidneys of marine bony fish excrete isotonic urine, and the kidneys of birds and mammals excrete hypertonic urine. In addition to its osmoregulation functions, the vertebrate kidney also gets rid of nitrogenous waste products that come from the metabolism of proteins and nucleic acids. Different vertebrates produce different nitrogenous wastes (cg, ammonia, urea, uric acid), each with different properties and advantages and disadvantages. 49.3 The functions of the vertebrate kidney are performed by nephrons. Microscopic nephron tubules in the kidneys receivefiltrate from the blood. Water and certain materials such as glucose and amino acids are reabsorbed from the filtrate back into the blood, While other substances are actively secreted into the filtrate. By thetime the filtrate leaves the nephron, its composition has changed significantly, and it is called urine. Urine is excreted from the body after leaving the kidneys and being stored temporarily in the bladder. . The nephrons of birds and mammals have loops of Henle that allow the urine to be hypertonic relative to the blood; the longer the loop of Henle, the more concentrated the urine can be. The loop of Henle works by setting up a strong osmotic gradient that pulls water back out of the filtrate. ADH increases the reabsorption of water from the filtrate by making the collecting ducts more permeable to water. Aldosterone and atrial natriuretic hormone are antagonistic, with aldosterone promoting reabsorption of NaCl and water and ANH decreasing NaCl and Water reabsorption. Aldosterone also promotes secretion of K+ into the filtrate. "‘ ‘m‘a'mmammm;Hulk...» ' . MAP OF UNDERSTANDING The following map shows the relationships of the chapter concepts to each other. KEY TERMS 49.1 homeostasis sensors integrating center effectors 49.2 osmolality hypertonic osmotic pressure MAINTAINING HOMEOSTASIS: THE MAMMALIAN KIDNEY AND OSMOREGULATION Blood enters capillaries in the kidney Water and small molecules are forced out of capillaries into kidney tubules by pressure Kidney returns needed amounts of water and small molecules to blood; the rest is excreted as urine; reabsorption of needed substances done by osmosis, diffusion, and active transport End result: Osmotic concentration of blood maintained at fairly constant levels hypotonic isotonic osmoconformers flame cells nephrons nitrogenous wastes ammonia urea uric acid allantoin 49.3 ureter urinary bladder renal cortex renal medulla ‘ glomerulus glomerular filtrate proximal convoluted, , tubule loop of Henle distal convoluted tubule collecting duct antidiuretic hormone- (ADH) vasopressin LEARNING BY EXPERIENCE 1. Complete the following chart by answering each question for both-freshwater fishes and marine bony fishes (not sharks or other elasmobranchs). Questions Freshwater Fishes Marine Bony Fishes a. Are they hyperosmotic or hypoosmotic relative to their environment? 1). Do they drink a lot or very little? c. Do they produce a lot of ' dilute urine or less urine that is isotonic? d. Do their gills pump ions into or out of the blood? 3. Match the following types of organisms with their type of osmoregulatory organ. a. insects i. protonephridia b. flatworms ‘ ii. kidneys c. annelids iii. Malpighian tubules ' d. mammals iv. nephridia EXERCISING YOUR KNOWLEDGE 5. What are the advantages and disadvantage Briefly answer each of the following questions in the the vertebrate kidney filtering almost everyt space provided. out of the blood plasma and then putting a i it back into the blood? ‘ 1. Maintaining homeostasis is a necessity of life for organisms. Does this mean there can be no fluctuation in internal conditions—that homeostasis means no change? 2. » Do positive feedback loops help maintain homeostasis? ‘ 7. If urine is formed by filtering blood, why isn’t urine normally red in color like blood? 3. What are the advantages and disadvantages of being an osmoregulator as opposed to an osmoconformer? 8. Why does penicillin have to be given inhigh doses and. several times a day to be effective in fighting infections? (Hint: It has to do with kidney function.) 4. Insects and vertebrates filter their blood to remove nitrogenous wastes and other substances. Explain what is meant by the statement that insects pull their blood through the filter while vertebrates push theirs through. 9- HOW W0111d b100d pressure disorders (e.g., How is this related to the type of circulatory pressure or low Pressure) affect the function system each has? of the kidneys? 10. If humans cannot produce aldosterone, they will. . die if they don’t receive treatment. Why is this? ~ Circle the letter of the one best answer in each of the following questions. 11. 12. l3. 14. 15. Which type of feedback system is more common in vertebrates, positive or negative? a. positive ' b. negative c. They are both very common. (1. They are both extremely rare. Which of the following is an example of a positive feedback loop? a. blood clotting b. temperature regulation in ectotherms ,c. temperature regulation in endotherms d. regulation of glucose levels in the blood e. all of these In a negative feedback loop, the system operates to minimize fluctuations away from the a. I effectors. b. integrating center. c. sensors. d. set point. e. stimulus. Which of the following animals have loops of Henle? a. insects b. fish c. birds d. all of these e. none of these Aquatic organisms that are hypoosmotic relative tothe surrounding water tend to a. gain water from the environment. b. gain salt from the environment. c. Both of these are correct. (1. None of these are correct. 16. Which of the following is an osmoconformer? 17. a. an earthworm b. a human c. a freshwater fish d. a bird e. a shark The osmoregulatory organs of insects are called a. flame cells. b. contractile vacuoles. c. nephrostomes. d. collecting ducts. e. Malpighian tubules. l8. 19. 20. 21. 22. 23. 24. Marine reptiles and marine birds eliminate excess salt through 3. Salt glands. in their heads. b. their kidneys. c. their general body surface. d. their flippers and feet. e. None of these; marine reptiles and marine birds don’t eliminate excess salt. The major cation in the extracellular fluids of vertebrates is a. Cl" b. K+ c. Na+ (1. Mg“ e. Ca++ The more concentrated the urine an animal can produce, the longer are its ‘ a. ureters. b. proximal convoluted tubules. c. distal convoluted tubules. d. loops of Henle. e. glomeruli. How many nephrons does a typical human have? a; 2 ' b. 20 c. aboirt 200 d. about 20,000 6. about 2 million The part of the nephron that is least permeable to water is the wall of the a. ascending limb. b. descending limb. c. collecting duct. (1. proximal convoluted tubule. e. distal convoluted tubule. Which of the following would be least likely to be found in the filtrate in the nephrons? a. plasma proteins b. glucose and amino acids c. water d. urea . e. All of these are likely to be found in the filtrate. The greatest amount of filtrate gets reabsorbed from what part of the nephron? a. the loop of Henle b. the distal convoluted tubule c. the proximal convoluted tubule d. the glomerulus 25. Freshwater fish excrete 29. ADH 1ncreases the permeability of the a. urea. a. loop of Henle to water. b. ammonia. b. loop of Henle to salt. c. uric acid. c. collecting duct to water. d. none of these. d collecting duct to salt. 26. - Urea is formed in the ' 30. Which of the following statements about the a. loop of Henle. . human kidney 1s true? b glomerulus. a. More than one hormone influences the c collecting duct. ‘ fimctioning of the kidney. d. liver. . b. When a lot of salt and water are reabsorbed e ' urinary bladder. from the filtrate, blood volume and pressure , tend to go up. 27. Filtrate moves into the proximal convoluted c. Some substances are actively secreted from ' tubule from the the blood into the capillaries. . a. collecting duct. d. The proximal and distal convoluted tubules b Bowman’s capsule. are located primarily in the renal cortex; c. distal convoluted tubule. c. All of these are true. d. glomerulus. ' e loop of Henle. 28. The osmolality of the kidney tissue is highest 3. at the top of the renal cortex. b at the bottom of the renal cortex. c. at the top of the renal medulla. d. at the bottom of the renal medulla. c It is the same throughout the kidney. ...
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