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Chapter 25

Chapter 25. 0. Control of the Internal Environment. Let Sleeping Bears Lie Bears do not actually hibernate but are dormant during the winter Animals have internal homeostatic mechanisms to compensate for fluctuations in the external environment

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Chapter 25

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  1. Chapter 25 0 Control of the Internal Environment

  2. Let Sleeping Bears Lie • Bears do not actually hibernate but are dormant during the winter • Animals have internal homeostatic mechanisms to compensate for fluctuations in the external environment • Thermoregulation: maintenance of internal temperature • Endothermy: body heat derived largely from metabolism • Ectothermy: heat absorbed from surroundings

  3. Excretion: Disposal of nitrogen-containing wastes • Osmoregulation: Control of gain and loss of water and solutes

  4. THERMOREGULATION • 25.1 Heat is gained or lost in four ways • An animal exchanges heat with the environment by four physical processes • Conduction: transfer of heat between molecules of objects in direct contact • Convection: transfer of heat by movement of air or water past a surface • Radiation: emission of electromagnetic waves • Evaporation: loss of heat from the surface of a liquid transforming to a gas

  5. LE 25-01 Radiation Convection Evaporation Conduction

  6. 25.2 Thermoregulation involves adaptations that balance heat gain and loss • Each species has an optimal internal temperature range • Endotherms and many ectotherms maintain a fairly constant internal temperature through five types of adaptation • Metabolic heat production • Hormonal changes, movement, clustering

  7. Insulation • Hair, feathers, fat • Circulatory adaptations • Dilation or constriction of blood vessels • Countercurrent heat exchange: warm and cold blood flow in opposite directions in adjacent vessels

  8. LE 25-02b Blood returning to body core in vein Blood from body core in artery Blood from body core in artery 35 33C Blood returning to body core in vein 30 27 20 18 10 9

  9. Evaporative cooling • Panting, sweating, spreading saliva • Behavioral responses • Migration, basking, burrowing, bathing

  10. 25.3 Reducing metabolic rate and body temperature saves energy • Some ectotherms can spend the winter “frozen” • Endotherms have various adaptations to adjust to temperature extremes • Torpor: state of reduced activity in which metabolic rate and body temperature decrease • Hibernation: long-term torpor in cold weather • Estivation: summer torpor

  11. OSMOREGULATION AND EXCRETION • 25.4 Osmoregulation: Animals balance the gain and loss of water and solutes • Animal cells cannot survive net water gain or loss • Osmoregulation is based largely on regulating solutes • Water follows the movement of solutes by osmosis

  12. Osmoconformers have the same internal solute concentration as seawater • Only marine animals • Expend some energy to maintain ion concentrations • Osmoregulators have different solute concentration in body fluid than environment • Use energy to regulate water gain or loss • Freshwater and saltwater fishes have different adaptations • Fishes that change habitat use freshwater or saltwater strategies as necessary

  13. LE 25-04a Osmotic water gain through gills and other parts of body surface Uptake of some ions in food Excretion of large amounts of water in dilute urine from kidneys Uptake of salt by gills

  14. LE 25-04b Gain of water and salt from food and by drinking seawater Osmotic water loss through gills and other parts of body surface Excretion of excess ions and small amounts of water in scanty urine from kidneys Excretion of salt from gills

  15. Land animals are osmoregulators • Cannot exchange water directly with environment • Like marine fishes, their primary problem is losing water and becoming dehydrated • Arthropods and vertebrates have adaptations that have made them the most successful land colonizers

  16. CONNECTION • 25.5 Do we need to drink eight glasses of water each day? • The Institute of Medicine has found that most people get sufficient water in their daily food and beverages • Men need an average of 3.8 liters daily • Women need about 2.6 liters • Caffeinated beverages do not remove water from the body • Athletes or people living in hot climates may need more water

  17. 25.6 Animals must dispose of nitrogenous wastes • Metabolism produces nitrogenous wastes from the breakdown of proteins and nucleic acids • Most aquatic animals dispose of their nitrogenous wastes as ammonia • Highly soluble in water • Diffuses rapidly across cell membranes

  18. Land animals convert ammonia to less toxic compounds • Can be safely stored and transported in the body • Released periodically by the excretory system • Requires energy for conversion • Different adaptations and type of reproduction determine excretion as urea or uric acid

  19. Urea • Excreted by mammals, most amphibians, sharks, and some bony fishes • Can be stored in concentrated solution but requires water for disposal • Uric acid • Excreted by birds, reptiles, insects, some amphibians • Excreted as solid paste • Uses more energy for excretion

  20. LE 25-06 Proteins Nucleic acids Amino acids Nitrogenous bases NH2 Amino groups Most aquatic animals, including most fishes Mammals, amphibians, sharks, some bony fishes Birds and many other reptiles, insects, land snails Ammonia Uric acid Urea

  21. 25.7 The liver performs many functions, including the production of urea • The liver performs more functions than any other organ in the body • Breaks down amino acids for energy or recycling • Produces urea • Breaks down toxins • Produces bile, plasma proteins, and lipoproteins

  22. Plays a key role in regulating body metabolism • Converts glucose to glycogen • Balances stored glycogen and released glucose • The hepatic portal vein transports nutrients absorbed by the intestines directly to the liver • Substances detoxified before going to the heart for distribution

  23. LE 25-07 Kidneys Liver Hepatic portal vein Intestines

  24. 25.8 Alcohol consumption can damage the liver • Some breakdown products of alcohol detoxification can cause liver cell damage • Heavy, frequent exposure to alcohol can produce cirrhosis, abnormal liver scarring • Impairs liver functioning • Cannot be reversed, but treatment can stop or delay progression • Also caused by hepatitis

  25. 25.9 The excretory system plays several major roles in homeostasis • The excretory system expels wastes and regulates water and ion balance • Kidneys are the main processing centers of the excretory system • Filled with tubules and intricate network of blood capillaries • Filter blood, which circulates through repeatedly

  26. Nephrons are the functional units of the kidneys • Extract filtrate, consisting of water, urea, and solutes, from the blood • Refine filtrate into small quantity of urine • Return most water and solutes to blood • Urine leaves the kidneys via ureters • Is stored in the urinary bladder and expelled through the urethra • About 1.5 L of urine are excreted each day

  27. LE 25-09a Aorta Inferior vena cava Renal artery and vein Kidney Ureter Urinary bladder Urethra The excretory system

  28. Animation: Nephron Introduction

  29. 25.10 Overview: The key processes of the excretory system are filtration, reabsorption, secretion, and excretion • Filtration • Blood pressure forces water and many small solutes into the nephron through the glomerulus • Reabsorption • Valuable solutes are returned to the blood from the filtrate

  30. Secretion • Substances such as excess H+ and toxins are transported into the filtrate • Excretion • Urine, the product of the earlier processes, passes from the kidneys to the outside

  31. LE 25-10 Filtration Reabsorption Secretion Excretion Nephron tubule H2O, other small molecules Urine Interstitial fluid Capillary

  32. 25.11 From blood to filtrate to urine: A closer look • The nephron returns much of the water that filters into it from the blood • Nutrients, salt, and water are reabsorbed into capillaries from the proximal and distal tubules • Secretion of excess H+, toxins, and K+ and reabsorption of HCO3– also occur in the tubules • High NaCl concentration in the medulla promotes reabsorption of water through the loop of Henle

  33. Final refining of the filtrate occurs in the collecting duct, where NaCl is reabsorbed • As filtrate moves through the medulla, more water is reabsorbed before the urine passes into the renal pelvis • Antidiuretic hormone (ADH) regulates the amount of water the kidneys excrete

  34. LE 25-11 Proximal tubule Distal tubule Bowman’s capsule H2O H2O Nutrients NaCI HCO3 – HCO3 – NaCI Blood K+ Some drugs and poisons H+ H+ Filtrate composition H2O Cortex NaCI Collecting duct Medulla HCO3 – H+ Loop of Henle Urea NaCI Glucose Amino acids NaCI Some drugs H2O Reabsorption Urea Secretion NaCI H2O Urine (to renal pelvis)

  35. Animation: Bowman's Capsule and Proximal Tubule Animation: Loop of Henle and Distal Tubule Animation: Collecting Duct Animation: Effect of ADH

  36. CONNECTION • 25.12 Kidney dialysis can be a lifesaver • Failure of both kidneys will lead to death if untreated • A dialysis machine is a type of artificial kidney • Blood is pumped from an artery through tubes made of selectively permeable membrane • As blood circulates, urea and excess ions diffuse out • Needed substances diffuse from the dialyzing solution into the blood

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