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Chapter 44


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Chapter 44

  1. 1. Chapter 44 ~ Regulating the Internal Environment • KEY POINT! Homeostasis is the maintenance of a constant internal environment I.Regulation of Body Temperature • A. Thermoregulation-Maintenance of body temperature. • Ectothermic: body heat obtained from the environment • Endothermic: high metabolic rate generates high body heat 4 physical processes account for heat gain or loss: • 1.Conduction~transfer of heat between molecules of body and environment • 2.Convection~transfer of heat as water/air move across body surface • 3.Radiation~transfer of heat produced by organisms • 4.Evaporation~loss of heat from liquid to gas D.Regulation during environmental extremes • 1. Torpor~ low activity; decrease in metabolic rate – a.Hibernation long term or winter torpor (winter cold and food scarcity); bears, squirrels – B. Estivation short term or summer torpor (high temperatures and water scarcity); fish, amphibians, reptiles • II. Osmoregulation and waste disposal • A. Osmoregulation is the management of the body’s water content and solute composition, which is critical to survival and homeostasis.
  2. 2. B. Nitrogenous waste management is critical… • 1.Nitrogenous wastes form from the metabolism of proteins and nucleic acids-very toxic – Ammonia: formed and removed by most aquatic animals,fish – Urea: mammals, most amphibians, sharks, some fish – Uric acid: allows for little water loss-very concentrated form of liquid waste found in birds, insects, many reptiles, land snails • C. Methods of osmoregulation • 1. Osmoconformer: no active adjustment of internal osmolarity (marine animals); isoosmotic to environment (same) • 2. Osmoregulator: adjust internal osmolarity (freshwater, marine, terrestrial) Freshwater fishes (hyperosmotic)- gains water, loses salt; excretes large amounts of dilute urine. 3.Water balance is critical on Land • 1.Dessication is deadly (12% drop for human=death) • 2.Adaptations to retain water: – Cuticle, shells, exoskeletons, nocturnal behaviors III. Excretory Systems • A.Most excretory systems produce urine in 2 steps:
  3. 3. • Filtration (nonselective) – Reabsorption (secretion of solutes) • B.The Kidney is our organ of excretion • 1.Renal artery/vein: kidney • 5.Renal cortex (outer region) blood flow • 6.Renal medulla (inner region) • 2.Ureter: urine excretory duct • 7.Nephron: functional unit of • 3.Urinary bladder: urine storage kidney • 4.Urethra: urine elimination tube Nephron Function, I Nephron Function, III •Proximal tubule: secretion and •Collecting duct: reabsorbs water, salt, reabsorption some urea Nephron Function, II •Loop of Henle: reabsorption of water and salt •Distal tubule:secretion and reabsorption Kidney regulation: hormones • Antidiuretic hormone (ADH) ~ most important hormone for osmoregulation!) brings H2O back to body; inhibited by alcohol and coffee