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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
•
•
•
•
•
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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)