CHAPTER 44 CONTROLLING THE INTERNAL ENVIRONMENT

I. Cells require a balance between water uptake & loss Animal cells cannot survive a net gain or loss of water Solutes in blood ensure proper water balance in cells

A. How it is balanced 1.osmoconformers: do not actively adjust their internal osmolarity (ex: salt water animals – body fluids are isotonic) 2. osmoregulators: animals that regulate internal osmolarity by discharging excess water or taking in water (expends energy)

Large changes = usually fatal (stenohaline) euryhaline can survive

B. Maintaining water balance in different environments Most marine invertebrates – osmoconformers Sharks = pump salt out Marine bony fish = hypotonic (excrete little urine) Freshwater protozoa – contractile vacuole fish = large amounts of dilute urine

Terrestrial animals: protective outer layers (shells, skin) drinking & eating moist food behavior (nocturnal) excretory organs

II. Tubular systems function in osmoregulation & excretion in many invertebrates A.Protonephridia in Flatworms: - network of closed tubules lacking internal openings that branch thru body B.Metanephridia in Earthworms - each segment – pair of meta. - excretory tubules that have internal openings to collect body fluids

C.Malpighian Tubules in Insects - remove nitrogenous wastes from hemolymph

III. The kidneys of most vertebrates are compact organs with many excretory tubules A. The Mammalian Excretory System * bean-shaped organs in back * renal artery – kidney – renal vein (blood flow) * urine out kidney – ureter – bladder – urethra (urine flow)

B. The Nephron & Associated Structures 2 distinct regions: outer renal cortex & inner renal medulla (each w/ nephrons * collecting ducts) Nephron = functional unit of kidney Water, salts, urea pulled from blood when passing thru glomerulus into Bowman’s capsule

Filtrate passes thru loop of Henle & distal tubule then collecting duct filtrate goes out ureter Most of nephron in cortex

IV.The kidney’s transport epithelia regulate the composition of lood A.Production of Urine from Blood Filtrate 1. Filtration of Blood * molecules filter out of blood & filtrate will have concentration similar to plasma 2. Secretion * filtrate is joined by substances from interstitial fluid * selective process

3. Reabsorption * selective transport of filtrate substances back to interstitial fluid * kidneys = central to homeostasis (clean wastes from blood & respond to fluid imbalances)

B. Transport Properties of the Nephron & Collecting Duct 1. proximal tubule: alters volume & composition of filtrate by reabsorption & secretion (salt) 2. descending loop of Henle: water 3. ascending loop of Henle: salt 4. distal tubule: K + & NaCl conc. & pH 5. collecting duct: carries filtrate out (permeable to water --- conserves)

****** water-conserving ability of mammalian kidney = key terrestrial adaptation ** controlled by nerves & hormones

V. Diverse adaptations of the vertebrate kidney have evolved in different habitats Desert mammals: long loop of Henle to conserve water (urine is concentrated) Mammals in aquatic environment: short loops of Henle (urine is dilute)

VI. An animal’s nitrogenous wastes are correlated with its phylogeny & habitat Metabolism of proteins & nucleic acids makes ammonia A.Ammonia – excreted directly by aquatic B.Urea – requires much water & must be eliminated quickly ; excreted by mammals & amphibians C.Uric Acid – excreted by land snails, birds, reptiles; pastelike form thru cloaca (mixed w/ feces)

VII. Thermoregulation maintains body temperature within range conducive to metabolism 1.Conduction – direct transfer of heat between environment & body surface (water more effective) 2.Convection - transfer of heat by movement of air or liquid past body surface 3.Radiation – emission of electromagnetic waves produced by object (warmed by sun)

4. Evaporation – loss of heat from liquids surface by turning to gas (not in moist environments)

VIII. Ectotherms vs. Endotherms Ectotherms – warms body by absorbing heat from surroundings Endotherms – derives body heat from metabolism

IX. Thermoregulation involves physiological & behavioral adjustments 1.Adjusting rate of heat exchange between animal & surrounding: dilation & constriction 2.Cooling by evaporative loss: panting, sweating 3.Behavioral: sun, burrow, migrate 4.Changing rate of metabolic heat production: skeletal muscle activity

X. Comparative physiology reveals diverse mechanisms of thermoregulation A.Invertebrates: behavior (huddle) B.Amphibians & Reptiles: mucus, burrow C.Fishes: swim D.Mammals & Birds: muscles, hormones, dilation & constrict., fur & feathers, fat, blubber, saliva & urine E.Humans: controlled by hypothalamus; cooling=dilation, sweat; warm= constriction & shivering