2/11/2015. Body mass and total Glomerular area. Body mass and medullary thickness. Insect Nephridial Structure. Salt Gland Structure

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1 Body mass and medullary thickness Thicker medulla in mammals from dry climate Negative allometry why? Body mass and total Glomerular area Glomerular area is a measure of total ultrafiltration rate Slope ~ Hyperososmotic (amphibians, freshwater teleost) higher constant than hyposmotic animals Insect Nephridial Structure Salt Gland Structure Found in many reptiles (turtles, snakes, gulls) in marine habitats. No ultrafiltration, only salt secretion Similar principles Salts actively pumped into tubule Counter current exchange, osmotic flow produces high osmolarity urine Independently derived, typically from glands in the nasal region Rectal gland in elasmobranchs 1

2 Ingestion of salty meal results in a net loss of water. Salt load eliminated through salt gland and kidney. Forms of waste Ammonia (NH 3 ) Ammonotelic animals Soluble, diffuses well, toxic Efficient elimination of N High water loss Urea Ureotelic animals Less efficient elimination of N Less toxic, less water use Uric Acid Uricotelic animals Least water use, secreted as solid or paste Most metabolically expensive to produce Least toxic Form of waste Some animals flexible in which form is produced some dry environment frogs uricotelic Sap and nectar feeders High water content diet a potential problem Malpighian tubule close to foregut, draws water which leaves higher osm solution for digestion in midgut. 2

3 Ultimately, all gas exchange requires oxygen diffusion in water. Aquatic organisms gills or skin is wet, direct exchange Terrestrial organisms wet skin or lungs with wet exchange surface Osmolarity of water, humidity of air and type of repiratory structure determine flux rate. Evolutionary trends Aquatic organisms respiratory organ is also generally the major site of osmoregulation Eg. chloride cells in fish gills Terrestrial organisms In moist environments, rely on cutaneous exchange Earthworms, amphibians In dry environments, structures internalized, waterproof skin Flux rates can be substantial (except isosmotic organisms) Lung surface area has to be high and the surface wet for gas exchange Rate of O 2, CO 2 and H 2 O exchange based on diffusion constants and strength of gradients Adaptations to alter strength of gradients (increase O 2, decrease H 2 O) can reduce water loss Inhale Cool, low humidity Air passages and lungs Air warmed, exposed to wet surface for exchange Exhale Warm, moist Cooling exhaled air can reclaim water 3

4 Nasal Counter current exchange Higher surface area in nasal passages reduces heat and/or water loss Desert adapted kangaroo rat exhales air cooler than air inhaled Tracheal systems Directional control of ventilation Similar to counter current nasal exchange Control of openings Save water by closing spiracles for less active tissue Metabolic water Carbohydrates moderate energy, moderate water, highest water per unit energy Lipids high energy, high water, moderate water per unit energy (oxidative demand) Protein low energy, low water, lowest water per unit energy Eg. insect in flight (bees) produce more water (rapid carbohydrate metabolism) than lost through gas exchange Energetics of Osmoregulation Generally difficult to quantify, little data available Estimated 5% of energy spent is typical Lower for: Isosmotic Large body size Physiologically isolated (high R skin, lungs vs. cutaneous exchange) Reduced exposure (eg. smaller gills for fish) Stable environment As high as 20-25% for small, intertidal invertebrates 4

5 2/11/2015 Invertebrates Euryhaline invertebrates Marine Isosmotic Rely mostly on diffusion Active transport in tubule systems (proto/metanephridia) near GI tract No centralized organ for osmoregulation Terrestrial Malpighian tubules High R value for exoskeleton Trachea system minimizes respiratory flux ureotelic Open circulatory systems generally more tolerant of water loss (up to 80% of body mass) Many avoiders (shells or exoskeletons) Marine invertebrates often isosmotic Mosquito larvae size of salt secreting rectal papilla is plastic Brine shrimp adapted to hyper saline environments (generally predator free) Thick exoskeleton Absorb water through gut, expel salts through gills Compensatory osmolytes Early vertebrates (hagfish, lamprey) Teleost Fish Hagfish ( vertebrate ) Isosmotic, stenohaline Single kidney, rudimentary nephron structure, secretion only Osmoconformer Lamprey (ancestral vertebrate) Freshwater, marine, anadramous Chloride cells in gills like most fishes Paired kidneys, high urine production, glomerulus Capable of secretion in addition to ultrafiltration Freshwater Hyperosmotic High glomerular area Chloride cells take in ions Ammonotelic, large volume dilute urine Marine Hyposmotic Some secondary loss of glomerulus Chloride cells export ions Drink seawater Ammonotelic, up to 25% urea production Both ~300 mosm Ultrafiltration Secretion 5

6 2/11/2015 Elasmobranch Amphibians Isosmotic Ureotelic Urea retained as compensatory osmolyte TMAO neutralizes urea toxicity Rectal glands export salts Freshwater forms Reduced osmolarity Kidneys produce large volume of urine to compensate for osmotic intake Reduced rectal gland, no evidence it exports ions High cutaneous exchange, primarily freshwater High tolerance of water loss up to 50% body mass Some species can reabsorb water from bladder ureotelic Dry climate forms Waxy coverings, other adaptations to reduce evaporative loss Dormancy Some uricotelic Amphibians Marine Reptiles Physiologically isolated from marine water lungs Scales, keratinized skin, shells (low permeability) Salt glands (nasal, lingual) High Osm urine Able to drink low volumes 6

7 2/11/2015 Marine Mammal Physiologically isolated from marine water Respiratory surface not in contact with water Skin impermeable (high R) No salt glands, all salt loss through kidneys Ureotelic Do not drink No water loss for thermoregulation Salt in foods (variable) Carnivorous whales (low) Baleen whales (high) Evidence they may spit out saltwater after feeding Marine birds Physiologically isolated from marine water lungs Skin impermeable (high R) Uricotelic Nasal salt glands Able to drink seawater Desert Reptiles Chuckwalla - Lowest water flux of any vertebrate Large body size, low metabolic rate High R in skin (high lipid content) Uric acid production Store extracellular water Burrow, inactivity Desert tortoise Uric acid Bladder may be 40% of body mass, can reclaim water Kangaroo Rat Never drinks, all water metabolic or in food Extensive nasal counter current exchanger Secondary loss of sweat glands Highly concentrated urine, high Osm in kidney, long nephron loops Dry feces Burrow, Nocturnal High relative humidity Seed rotation 7

8 Camel Large body Poikilothermic Loss of sweat glands, thick fur Long limbs highly vascularized Extensive nasal counter current exchanges Can drink large volumes Tolerant of 30% loss of water Lower blood pressure, glomerular filtration rate Increase ADH production 8