Osmoregulation & Excretion Anhydrobiosis: Life without water? How to acquire body water? • Drink water & dilute fluids • Moisture in food • Metabolic water (85% water) Organic food molecules + O2 → CO2 + H2O + energy (2% water) Fat yields 2.5x as much energy and 2.5x as much water Water is needed to maintain the per gram than do carbs or proteins! structure & function of macromolecules. Osmoregulation Osmoconformers & Osmoregulators The exchange of water and ions between • Osmoconformers don’t adjust osmolarity the environment and the body fluids of an • Osmoregulators adjust osmolarity by organism to maintain a constant internal – pumping water in or out environment (homeostasis). – pumping ions in or out • Balance between water gain & water loss Which is related to • Balance between electrolyte (salt) gain & loss brine shrimp spend 30% of metabolism on osmoregulation Osmoregulation Osmoregulation Osmoconformers: Osmoregulators: body fluids are isotonic to their body fluids are not isotonic to their environment environment Different solutes, but same total Osm have to actively maintain water Must maintain membrane potential of balance cells with certain ion gradients do not have to actively maintain water Include bony fish, marine mamms, balance freshwater, & terrestrial organisms include most marine invertebrates Heyer 1 Osmoregulation & Excretion Osmoconformers & Aquatic animals — most water Osmoregulators & salt exchange occurs in gills • Stenohaline cannot tolerate Δ osmolarity • Large, thin exposed surface area to • Euryhaline can tolerate Δ • Estuaries, tidepools exchange gases – some are facultative osmoregulators • Permeable to water Salinity Time Osmoregulation: A Marine Fish Osmoregulation: A Marine Fish • •Seawater Replace = 3.5%lost waterNaCl (1 by Osm); drinking Body large fluids volumes= 1% (0.3 Osm) • Replace lost water by drinking large volumes • •Across Secrete gills salts — saltfaster diffuses than water in; water diffuses diffuses away out • Secrete salts faster than water diffuses away Secretion: active transport out against conc gradient Chloride cells in gills: Active transport of Cl– Na+ ions follow Osmoregulation: A Freshwater Fish Osmoregulation: A Freshwater Fish • NoBody drinking. fluids = 1% Consume NaCl; Freshwater salts & some<0.01% water in food • No drinking. Consume salts & some water in food • DumpAcross water. gills — Uptake water diffusessalts faster in; saltthan diffuses water out • Dump water. Uptake salts faster than water Chloride cells in gills: pump Cl– in opposite direction than marine fish Heyer 2 Osmoregulation & Excretion Osmoregulation: Euryhaline fish Osmoregulation: Euryhaline fish • Anadromous: juveniles in freshwater; adults at sea • Anadromous: juveniles in freshwater; adults at sea – Salmon, striped bass – Salmon, striped bass • Catadromous: juveniles in saltwater; adults in fresh • Catadromous: juveniles in saltwater; adults in fresh – Anguillid eels – Anguillid eels • Must transition gills & • Must transition gills & kidneys before migrating kidneys before migrating – Chloride cells must – Chloride cells must reverse direction reverse direction – Smoltification – Smoltification Life Cycle of Atlantic Salmon http://www.nefsc.noaa.gov/sos/ Life Cycle of Japanese eel (unagi) http://www.fao.org/fishery/ spsyn/af/salmon/images/fig41_2.gif culturedspecies/Anguilla_japonica/en Osmoregulation: Sharks & Rays Osmoregulation: Sharks & Rays almost osmoconformers almost osmoconformers • Tissue salt concentration same as bony fish • Kidneys retain urea • Make up the difference from seawater with urea • Don’t need to worry about water, but must dump salt – Need carnivorous diet for sufficient organic nitrogen • Chloride cells in gills, intestines, kidney & and rectal gland – Use trimethylamine oxide (TMAO) to block toxic effect of high urea on protein structure actively secrete • Actually overcompensate: slightly hypertonic to seawater – Passively gain water. Do not need to drink. Osmoregulation: Seabirds Speaking of noses, … • Transport epithelia & Water reclamation in mammals counter-current salt exchange Turbinals: ↑sa in nasal passages 1. Inspired air warmed & humidified 2. Evaporative cooling of nasal surface – May also cool cerebral blood flow • Similar salt gland tissue in nasal passages of marine 3. Expired air cooled → iguanas & tear glands of water reclaimed sea turtles Heyer 3 Osmoregulation & Excretion Dense hair reduces evaporative Terrestrial animals — most water loss from skin regulation of water & salt exchange occurs in excretory system • ↑Osm → drink water & concentrate urine • ↓Osm → dilute urine Sacrifice cooling efficiency for water retention Nitrogenous wastes • Waste by-products of metabolism Excretory Systems • Degradation of organic nitrogen most toxic “Conditioning” the body fluids • Water & electrolyte balance • Maintain extracellular fluid volume (ECF) – Including blood plasma volume & PB • Remove waste products – esp., nitrogenous wastes ________________ ________________ • Retain nutrients • Water soluble • Water soluble ________________ • Toxic • Much less toxic • Water insoluble - solid • Energetically cheap • Expensive • Minimally toxic • Very expensive Excretory System Processes Excretory System Components • Filtration: cells & macromolecules retained in body fluids; water & small solutes non-specifically enter tubule. • Secretion: additional, specific non-filtered solutes added to tubule filtrate. • Reabsorption: filtered water & specific solutes removed from filtrate back into body fluids • Excretion: water & solutes not reabsorbed are eliminated from body. Concentrated filter Concentrated filter wastes wastes Nutrients and tubule Nutrients and tubule most water return circulatory system most water return circulatory system to circulation to circulation Heyer 4 Osmoregulation & Excretion Protonephridial Excretory System Metanephridial Excretory System • Ciliated nephrostome Platyhelmintes (Planaria) draws filtered coelomic Freshwater flatworm fluid into tubule • Flame bulb: cap cell • Tubule reabsorbs (flame cell) interdigitates nutrients, most salt & with tube cell water into capillary bed • Cap cell cilia beat • Concentrated wastes collect in bladder until draw interstitial body fluid through slits excreted Annelid worm filter excludes cells & proteins • Pair of metanephridia in each segment selected solutes • Nephrostome draws from reabsorbed from filtrate adjacent segment excess water excreted • Excretion via nephridiopore via nephridiopore – External or into gut • http://www.biology.ualberta.ca/courses.hp/zool250/animations/Excretion.swf Metanephridial Excretory System Metanephridial Excretory System Aquatic Mollusc (clam) • Pericardium • Hemolymph drawn by afferent vein to • Coelom gill (ctenidium) • Heart Lose ammonia to water flowing through the mantle cavity • Nephrostome • Kidney • Hemolymph continues from gill • Nephridiopore by efferent vein to atrium of heart • Gill Water and small solutes permeate into pericardial (coelom) fluid • Mantle cavity Cells, respiratory pigments, and proteins retained in hemolymph, pumped by ventricle to arteries • Coelomic fluid drawn into tubules via Mollusc ciliated nephrostomes • Ultrafiltration of hemolymph across thin wall of cardiac atrium into pericardial coelom Essential solutes reabsorbed by kidney • Paired nephrostomes draw coelomic fluid into metanephridia tubules • Excretion via nephridiopore consolidated into kidney into mantle cavity • Excretion via nephridiopore into mantle cavity Swept away via excurrent siphon Probably not homologous to annelid metanephridia • (annelid origin = mesoderm; mollusk origin = ectoderm) antennal gland nephridia Malpighian Tubule Excretory System [“saccate metanephridia”] Aquatic arthropods (Crustaceans) • Most water/salt balance and ammonia excretion in gills • Additional secretion & excretion from antennal gland • Most body cavity is the hemocoel. Coelom reduced to small end sac. • Ultrafiltration of hemolymph through end Terrestrial sac to form tubule filtrate. arthropods • Hydrostatic pressure pushes filtrate into (Insects) tubules for selective reabsorption. – Remember — No cilia! • Wastes secreted from hemolymph into tubules. Water follows flushes into gut • Wastes excreted via nephidiopore on base of antennae. • Nitrogenous waste precipitated as uric acid. Water & salts reabsorbed in hind gut • Esp. large in freshwater spp. — need to dump water. • Almost solid feces+wastes excreted Heyer 5 Osmoregulation & Excretion Vertebrate Renal Excretory System Mammal Renal Excretory System Nephron: functional unit of the Nephron: functional unit of the vertebrate kidney vertebrate kidney – Tubule + associated capillary beds – Tubule + associated capillary beds • Filtration: PB pushes plasma water & small (non-protein) solutes from first (glomerular) capillary bed into tubule • Reabsorption: vital components (nutrients, most salt & water) actively/ specifically transported back into second (peritubular) capillary bed • Secretion: specific wastes or salt actively/specifically transported from second capillary bed into tubule filtrate Each kidney has ~1 million nephrons! . ↑F and/or ↑S → ↑excretion . ↑R → ↓excretion Human Renal Excretory System The nephron: tubule structure • 20% of systemic blood circulation flows through kidney • Urine from >1 million nephrons converges at renal pelvis Bowmanʼs Proximal# • Urine flows via ureter from each kidney to bladder capsule convoluted# • Bladder voids urine via urethra tubule$ Distal# Renal capsule convoluted#