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Home , Osmoregulation, Salt gland, Stenohaline

Osmoregulation &

Anhydrobiosis: Life without ? 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 ! structure & function of macromolecules.

Osmoregulation & 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 to maintain a constant internal – pumping water in or out environment (). – pumping ions in or out • Balance between water gain & water loss Which is related to • Balance between () 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 , marine mamms,

balance freshwater, & terrestrial  include most marine

Heyer 1 Osmoregulation & Excretion

Osmoconformers & Aquatic — most water Osmoregulators & salt exchange occurs in • cannot tolerate Δ osmolarity • Large, thin exposed surface area to • can tolerate Δ • , tidepools exchange gases – some are facultative osmoregulators • Permeable to water

Salinity

Time

Osmoregulation: A Marine Fish Osmoregulation: A Marine Fish • • 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 — saltfaster diffuses than water in; water diffuses diffuses away out • Secrete salts faster than water diffuses away

Secretion: 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 – , 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: & 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, & and rectal gland – Use trimethylamine oxide (TMAO) to block toxic effect of high urea on structure actively secrete • Actually overcompensate: slightly hypertonic to seawater – Passively gain water. Do not need to drink.

Osmoregulation: Speaking of noses, … • Transport epithelia & Water reclamation in counter-current salt exchange

Turbinals: ↑sa in nasal passages 1. Inspired air warmed & humidified 2. Evaporative cooling of nasal surface – May also cool cerebral flow • Similar 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 regulation of water & salt exchange occurs in • ↑Osm → drink water & concentrate • ↓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 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 (ctenidium) • Heart  Lose 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

• 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 Renal Excretory System : 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 !

. ↑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 tubule

Distal Renal capsule convoluted tubule

Loop of Collecting Henle duct

 All blood passes through kidney 200-300 times/day.  Highest blood flow & metabolic rate per gram of any tissue.

Filtration, Reabsorption & Secretion The nephron: vascular structure in Tubule Renal Corpuscle Ultrafiltrate from glomerulus to Bowman’s capsule Efferent Glomerulus Proximal Tubule arteriole Reabsorb nutrients (Glucose, aa’s) + most water & salt

Afferent Descending arteriole Get back more Water Peritubular Ascending Loop of Henle capillary Pump back more Salt bed Distal Tubule Vasa recta Secrete Drugs Into Urine Reabsorb more Salts

Collecting Duct Get Back Additional Water

Heyer 6 Osmoregulation & Excretion

Glomerular Ultrafiltrate Glomerular Filtration • Fluid in glomerular capsule is called ultrafiltrate. >99% – Glomerular filtration: • Mechanism of producing ultrafiltrate under hydrostatic pressure of the blood. – Process similar to the formation of tissue fluid by other capillary beds. • Glomerular filtration rate (GFR): – Volume of filtrate 100% produced by both • 20% of plasma that enters glomerulus is filtered kidneys each minute. into nephron • Averages ~120ml/min (115 ml/min. in women; • Kidneys filter 180 liters of fluid per day, but 125 ml/min. in men.) produce only ~1.5 liter of urine • Minimum of 400 ml/day urine necessary to excrete metabolic wastes (obligatory water loss).

Salt and Water Reabsorption in Reabsorption of Circulating Energy 65% of Na+, Proximal Tubule Substrates in Proximal Tubule – Cl , & H2O reabsorbed

Insert fig. 17.14 Insert fig. 17.13

Normally, 100% of glucose, amino acids, & other nutrients reabsorbed

Loop of Henle — countercurrent multiplier Loop of Henle & the Vasa Recta — Proximal tubule

Decending Ascending Ascending Decending Limb Limb Vessel Vessel • ↑Osm of • ↓Osm of • Collects • Collects filtrate in filtrate in H2O from Distal NaCl from tubule tubule tubule Decending Ascending Collecting Limb duct • ↓volume of • ↑Osm of Limb • ↓ Osm & Descending filtrate in medulla Loop limb • ↑Osm of ↑ volume of tubule Henle Ascending plasma of plasma limb Vasa recta

impermeable to salt After PCT & LoH, 90% of NaCl & 85% of H2O reabsorbed

Heyer 7 Osmoregulation & Excretion

Osmolality of Different Regions of Distal Convoluted Tubule the Kidney & cortical region of Collecting Duct • Filtrate hypotonic from LoH Bowman’s capsule • Continue active Insert fig. 17.19 Proximal Na+ transport & convoluted Cl– cotransport tubule • 98–100% of filtered NaCl now reabsorbed Distal – Actual amount convoluted tubule regulated by Loop of Henle Collecting duct

Figure 44.16

Collecting Duct Osmolarity DCTs of several nephrons converge on each collecting duct of interstitial 300 300 • Filtrate travels through fluid 300 100 (mOsm/L) Osmolarity of collecting duct back 100 300 300 interstitial 300 fluid through medulla H O NaCl H O (mosm/L) vs. transport of: CORTEX 2 2 300 300 100 100 • Becomes isotonic to • H2O 300 300 400 200 400 400 + medulla by losing water • Na H2O NaCl H2O CORTEX H2O NaCl H2O • Cl– NaCl Active 400 200 400 400 • Some urea diffuses out transport H O NaCl H2O H2O NaCl H2O • urea 2 Passive adds to medulla Osm NaCl transport → H O NaCl 2 H2O H O NaCl H O • Rate of water OUTER 2 2 MEDULLA 600 400 600 600 OUTER H2O NaCl H2O 600 400 600 600 reabsorption depends on MEDULLA H2O NaCl H2O H O NaCl H O 2 2 # of aquaporins in Urea Urea H O NaCl H O H O NaCl 2 2 900 2 900 700 H2O 900 tubule membrane 900 700 Urea Urea H O NaCl H O Key H O NaCl 2 2 • # of aquaporins & urea 2 H2O INNER Urea 1200 INNER Urea MEDULLA 1200 1,200 transporters regulated by Active MEDULLA 1,200 1200 transport antidiuretic hormone 1,200 Passive (ADH) transport

Water Reabsorption Osmolality of fluid along nephron >99% • Red = water restriction • Blue = high water intake

100% Kidneys filter 180 liters of fluid per day, … • No ADH → 99.2% of filtered H2O reabsorbed – … but produce only ~1.5 liter of urine • Maximum ADH → 99.8% of filtered H2O reabsorbed – Minimum of 400 ml/day urine necessary to excrete metabolic wastes (obligatory water loss).

Heyer 8 Osmoregulation & Excretion

Regulation of plasma osmolarity Adjusting the Urine ⇔ Adjusting the Blood

Dehydration Increased water intake and/or Decreased water intake Thirst center Posterior Osmo- pituitary receptors Plasma osmolality

Retain Kidney water Increased reabsorbtion urine output of water

Glucose handling by nephron ADH Insufficiency Filtration rate

Good Normal Reabsorption

water production of reabs. rate ADH Kidney normal urine

ADH Poor Excretion Hypothalamus Increased

Posterior PituitaryPosterior water production of (in urine) reabs. Kidney dilute urine Diabetes insipidus

Glucosuria: glucose in urine “Diabetes” = increased urine output

• Glucose completely reabsorbed under normal conditions • Diabetes mellitis: insulin deficiency causes blood glucose levels to exceed renal threshold (more than can be reabsorbed) • Excess glucose excreted in urine • Glucose in urine osmotically holds more water in urine

Heyer 9 Osmoregulation & Excretion

Two kinds of nephrons Living in extreme environments — no fresh water  ~85% of nephrons in human kidney are cortical nephrons. Marine Mammals . short Loops of Henle • Higher proportion of juxtamedullary extend only to outer nephrons with very long Loops of Henle medulla – ↑Osm of → ↑Osm of urine  Cortical nephrons use the • Can drink seawater and dump salt for net osmotic gradient created by water gain juxtamedullary nephrons. • Human would take 135 ml of urine to dump salt from 100 ml seawater → net water loss • Dolphin takes only 65 ml urine to dump salt from 100 ml seawater → net water gain

Living in extreme environments Water — no fresh water Budgets

Desert Mammals — Kangaroo Rat • Forage at night; hide in humid burrow in daytime • Extensive nasal turbinates • Large kidney with higher proportion of juxtamedullary nephrons with very long Loops of Henle – ↑Osm of renal medulla → ↑Osm of urine • Does not drink! — Metabolic water • Eats almost exclusively seeds with high oil content • ↑fat → ↑water & energy yield • ↓↓protein → ↓↓nitrogenous wastes • ∴ no need to produce much urine

Avian Renal Excretory System Reptilian Renal Excretory System

• Drink little — Cannot afford the • Ectothermic — hot habitats weight of excess water • Cortical nephrons only! • Juxtamedullary nephrons only – no Loops of Henle have short Loops – (only in mamms & ) • ∴ urine only slightly hypertonic to • ∴ urine only isotonic to tissues tissues • But since nitrogenous wastes • But since nitrogenous wastes excreted as solid paste of uric excreted as solid paste of uric acid, ∴ no need to produce much acid, ∴ no need to produce much urine urine • Water reabsorbed in • Water reabsorbed in cloaca – Transport epithelia

Heyer 10