Survey
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
CHAPTER 44 CONTROLLING THE INTERNAL ENVIRONMENT I. REGULATION OF BODY TEMPERATURE • THERMOREGULATION: THE MAINTENANCE OF BODY TEMPERATURE WITHIN A RANGE THAT ENABLES CELLS TO FUNCTION EFFICIENTLY. • INVOLVES HEAT TRANSFER BETWEEN THE ORGANISM AND THE EXTERNAL ENVIRONMENT. A. FOUR PHYSICAL PROCESSES ACCOUNT FOR HEAT GAIN OR LOSS • THEY ARE: – CONDUCTION: DIRECT TRANSFER OF THERMAL MOTION (HEAT) FROM HIGH TO LOW CONCENTRATION – CONVECTION: TRANSFER OF HEAT BY THE MOVEMENT OF AIR OR LIQUID – RADIATION: EMISSION OF ELECTROMAGNETIC WAVES (ALL ORGANISMS) – EVAPORATION: LOSS OF HEAT FROM THE SURFACE OF A LIQUID B. ECTOTHERMS DERIVE BODY HEAT MAINLY FROM THEIR SURROUNDINGS; ENDOTHERMS DERIVE IT MAINLY FROM METABOLISM • MOST INVERTEBRATES, FISHES, AMPHÍBIANS, AND REPTILES ARE ECTOTHERMS. • ENDOTHERMY ENABLES ANIMAIS TO MAINTAIN A RELATIVELY UNIFORM BODY TEMPERATURE AND A HIGH LEVEL OF AEROBIC METABOLISM. C. THERMOREGULATION INVOLVES PHYSIOLOGICAL AND BEHAVIORAL ADJUSTMENTS • ECTOTHERMS AND ENDOTHERMS ADJUST THE RATE OF HEAT EXCHANGE WITH THEIR SURROUNDINGS BY EVAPORATIVE COOLING AND BY BEHAVIORAL RESPONSES. • BIRDS AND MAMMALS CAN ALSO CHANGE THE RATE OF METABOLIC HEAT PRODUCTION. • INSULATION, VASODILATION, VASOCONSTRICTION, AND COUNTERCURRENT HEAT EXCHANGERS ALTER THE RATE OF HEAT EXCHANGE. • PANTING, SWEATING, AND BATHING INCREASE EVAPORATION. D. MOST ANIMALS ARE ECTOTHERMIC, BUT ENDOTHERMY IS WIDESPREAD • SOME LARGE ACTIVE INSECTS AND FISHES GENERATE METABOLIC HEAT BY MUSCLE CONTRACTIONS, AND MANY RETAIN IT BY COUNTERCURRENT HEAT EXCHANGERS. • SOME INVERTEBRATES, AMPHIBIANS, AND REPTILES MAINTAIN TOLERABLE INTERNAL TEMPERATURES BY BEHAVIORAL MEANS. • THERMOREGULATORY MECHANISMS IN MAMMALS AND BIRDS INCLUDE: – – – – 1. 2. 3. 4. SHIVERING AND NONSHIVERING THERMOGENESIS INSULATION BY FAT, HAIR, OR FEATHERS PANTING COUNTERCURRENT HEAT EXCHANGE. • PHYSIOLOGICAL ADJUSTMENT TO SEASONAL TEMPERATURE CHANGES MAY INVOLVE CHANGES IN AN ANIMAL'S THERMOSTATIC CONTROL MECHANISMS AND VARIOUS RESPONSES AT THE CELLULAR LEVEL. III. EXCRETORY SYSTEMS • 1. 2. 3. FUNCTIONING IN BOTH WASTE DISPOSAL AND WATER BALANCE, EXCRETORY S ARE CENTRAL TO HOMEOSTASIS. A MOST EXCRETORY SYSTEMS PRODUCE URINE BY REFINING A FILTRATE DERIVED FROM BODY FLUIDS KEY FUNCTIONS OF MOST EXCRETORY SYSTEMS ARE: FILTRATION (PRESSURE-FILTER OF BODY FLUIDS, PRODUCING A FILTRATE) REABSORPTION: THE PRODUCTION OF URINE FROM THE FILTRATE (RECLAIMING VALUABLE SOLUTES FROM THE FILTRATE) SECRETION (ADDITION OF TOXINS AND OTHER SOLUTES FROM THE BODY FLUIDS TO THE FILTRATE). B. DIVERSE EXCRETORY SYSTEMS ARE VARIATIONS ON A TUBULAR THEME • EXTRACELLULAR FLUID IS FILTERED INTO PROTONEPHRIDIA OF THE FLAME-BULB SYSTEM IN FLATWORMS; • THESE TUBULES EXCRETE A DILUTE FLUID AND ALSO FUNCTION IN OSMOREGULATION. • EACH SEGMENT OF AN EARTHWORM HAS A PAIR OF OPENENDED METAHRIDIA, TUBULES THAT COLLECT COELOMIC FLUID AND PRODUCE DILUTE URINE FOR EXCRETION. • IN INSECTS, MALPIGHIAN TUBULES FUNCTION IN OSMOREGULATION AND REMOVAL OF NITROGENOUS WASTES FROM THE HEMOLYMPH. • INSECTS PRODUCE A RELATIVELY DRY WASTE MATTER, AN IMPORTANT ADAPTATION TO TERRESTRIAL LIFE. • KIDNEYS, THE EXCRETORY ORGANS OF VERTEBRATES, FUNCTION IN BOTH EXCRETION AND SMOREGULATION. C. NEPHRONS AND ASSOCIATED BLOOD VESSELS ARE THE FUNCTIONAL UNITS OF THE MAMMALIAN KIDNEY • • • • • • EXCRETORY TUBULES (CONSISTING OF NEPHRONS AND COLLECTING DUCTS) AND ASSOCIATED BLOOD VESSELS PACK THE KIDNEY. EACH NEPHRON CONSISTS OF A BOWMAN’S CAPSULE, WHICH SURROUNDS A BALL OF CAPILLARIES CALLED THE GLOMERULUS; A PROXIMAL TUBULE; A LOOP OF HENLE; AND A DISTAL TUBULE. FLUID FROM SEVERAL NEPHRONS FLOWS INTO A COLLECTING DUCT AND PASSES URINE INTO THE KIDNEY’S CENTRAL RECEPTACLE, THE RENAL PELVIS. A URETER CONVEYS URÍNE FROM THE RENAL PELVIS TO THE URÍNARY BLADDER. BLOOD SUPPLY TO THE NEPHRON IS THROUGH AN AFFERENT ARTERIOLE, WHICH SUPPLIES INTO THE CAPILLARIES OF THE GLOMERULUS. AN EFFERENT ARTERIOLE CARRIES BLOOD AWAY FROM BOWMAN’S CAPSULE AND SUBDIVIDES INTO THE PERITUBULAR CAPILLARIES EMBRACING THE PROXIMAL AND DISTAL TUBULES. D. FROM BLOOD FILTRATE TO URINE: A CLOSER LOOK • • • • • • SUBSTANCES REABSORBED FROM THE FILTRATE IN THE PROXIMAL TUBULE INCLUDE MOST OF THE SALT AND WATER FILTERED FORM THE BLOOD, AND GLUCOSE AND AMINO ACIDS (BY ACTIVE TRANSPORT) DRUGS, AMMONIA, AND HYDROGEN IONS (FOR THE CONTROL OF BODY PH) ARE SELECTIVELY SECRETED INTO THE FILTRATE. THE DESCENDING LIMB OF THE LOOP OF HENLE IS PERMEABLE TO WATER BUT NOT TO SALT; WATER MOVES BY OSMOSIS INTO HYPEROSMOTIC INTERSTITIAL FLUID. SALT DIFFUSES OUT OF THE CONCENTRATED FILTRATE AS IT MOVES THROUGH THE SALT-PERMEABLE ASCENDING LIMB OF THE LOOP OF HENLE. SECRETION AND REABSORPTION BY THE DISTAL TUBULE PLAY KEY ROLES IN REGULATING POTASSIUM CONCENTRATION AND BLOOD PH. F. NERVOUS AND HORMONAL FEEDBACK CIRCUITS REGULATE KIDNEY FUNCTIONS • TWO HORMONES INFLUENCE OSMOREGULATION : 1. ANTIDIURETIC HORMONE: INCREASES REABSORPTION OF WATER BY THE BODY 2. ALDOSTERONE: INCREASES BOTH THE REABSORPTION OF WATER AND NA+ H. INTERACTING REGULATORY SYSTEMS MAINTAIN HOMEOSTASIS NITROGEN FORMS A MAJOR WASTE PRODUCT IN ANIMALS AQUATIC ANIMALS: EXCRETE NH3+ (AMMONIA) INTO THE WATER MAMMALS: CONVERT NH3+ TO UREA (SECRETED IN URINE) BIRDS, INSECTS, AND REPTILES: CONVERT UREA TO URIC ACID (FORMS A SOLID WASTE PRODUCT)