Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Chapter 44: Osmoregulation and Excretion

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Figure 44.1 Salvin’s albatrosses (Diomeda cauta salvini), birds that can drink seawater with no ill effects

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Figure 44.3 Osmoregulation in marine and freshwater bony fishes: a comparison Gain of water and salt ions from food and by drinking seawater Osmotic water loss through gills and other parts of body surface Excretion of salt ions from gills Excretion of salt ions and small amounts of water in scanty urine from kidneys Uptake of water and some ions in food Osmotic water gain through gills and other parts of body surface Uptake of salt ions by gills Excretion of large amounts of water in dilute urine from kidneys (a) Osmoregulation in a saltwater fish(b) Osmoregulation in a freshwater fish

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Figure 44.4 Anhydrobiosis (a) Hydrated tardigrade (b) Dehydrated tardigrade 100 µm

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Figure 44.5 Water balance in two terrestrial mammals Water balance in a human (2,500 mL/day = 100%) Water balance in a kangaroo rat (2 mL/day = 100%) Ingested in food (0.2) Ingested in food (750) Ingested in liquid (1,500) Derived from metabolism (250) Derived from metabolism (1.8) Water gain Feces (0.9) Urine (0.45) Evaporation (1.46) Feces (100) Urine (1,500) Evaporation (900) Water loss

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Figure 44.6 What role does fur play in water conservation by camels? The fur of camels plays a critical role in their conserving water in the hot desert environments where they live. Knut and Bodil Schmidt-Nielsen and their colleagues from Duke University observed that the fur of camels exposed to full sun in the Sahara Desert could reach temperatures of over 70°C, while the animals’ skin remained more than 30°C cooler. The Schmidt-Nielsens reasoned that insulation of the skin by fur may substantially reduce the need for evaporative cooling by sweating. To test this hypothesis, they compared the water loss rates of unclipped and clipped camels. RESULTS CONCLUSION Control group (Unclipped fur) Experimental group (Clipped fur) Water lost per day (L/100 kg body mass) EXPERIMENT Removing the fur of a camel increased the rate of water loss through sweating by up to 50%.

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Figure 44.7 Salt-excreting glands in birds An albatross’s salt glands empty via a duct into the nostrils, and the salty solution either drips off the tip of the beak or is exhaled in a fine mist. (a) The secretory cells actively transport salt from the blood into the tubules. Blood flows counter to the flow of salt secretion. By maintaining a concentration gradient of salt in the tubule (aqua), this countercurrent system enhances salt transfer from the blood to the lumen of the tubule. (c) Nasal salt gland Nostril with salt secretions Lumen of secretory tubule NaCl Blood flow Central duct Direction of salt movement Transport epithelium Secretory tubule Capillary Vein Artery Secretory cell of transport epithelium One of several thousand secretory tubules in a salt-excreting gland. Each tubule is lined by a transport epithelium surrounded by capillaries, and drains into a central duct. (b)

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Figure 44.8 Nitrogenous wastes Proteins Nucleic acids Amino acids Nitrogenous bases –NH 2 Amino groups Most aquatic animals, including most bony fishes Mammals, most amphibians, sharks, some bony fishes Many reptiles (including birds), insects, land snails Ammonia Urea Uric acid NH3NH3 NH2NH2 NH2NH2 O C C C N C O N H H C O N C HNHN O H

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Figure 44.9 Key functions of excretory systems: an overview Filtration. The excretory tubule collects a filtrate from the blood. Water and solutes are forced by blood pressure across the selectively permeable membranes of a cluster of capillaries and into the excretory tubule. Reabsorption. The transport epithelium reclaims valuable substances from the filtrate and returns them to the body fluids. Secretion. Other substances, such as toxins and excess ions, are extracted from body fluids and added to the contents of the excretory tubule. Excretion. The filtrate leaves the system and the body. Capillary Excretory tubule Filtrate Urine

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Figure Protonephridia: the flame-bulb system of a planarian Nucleus of cap cell Cilia Interstitial fluid filters through membrane where cap cell and tubule cell interdigitate (interlock) Tubule cell Flame bulb Nephridiopore in body wall Tubule Protonephridia (tubules)

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Figure Metanephridia of an earthworm Nephrostome Metanephridia Nephridio- pore Collecting tubule Bladder Capillary network Coelom

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Figure Malpighian tubules of insects Digestive tract Midgut (stomach) Malpighian tubules Rectum Intestine Hindgut Salt, water, and nitrogenous wastes Feces and urine Anus Malpighian tubule Rectum Reabsorption of H 2 O, ions, and valuable organic molecules HEMOLYMPH

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Figure The mammalian excretory system Posterior vena cava Renal artery and vein Aorta Ureter Urinary bladder Urethra (a) Excretory organs and major associated blood vessels Juxta- medullary nephron Cortical nephron Collecting duct To renal pelvis Renal cortex Renal medulla 20 µm (b) Kidney structure Ureter Kidney Section of kidney from a rat Renal medulla Renal cortex Renal pelvis Afferent arteriole from renal artery Glomerulus Bowman’s capsule Proximal tubule Peritubular capillaries SEM Efferent arteriole from glomerulus Branch of renal vein Descending limb Ascending limb Loop of Henle Vasa recta Distal tubule Collecting duct (d) Filtrate and blood flow (c) Nephron

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Figure The nephron and collecting duct: regional functions of the transport epithelium Proximal tubule Filtrate H 2 O Salts (NaCl and others) HCO 3 – H + Urea Glucose; amino acids Some drugs Key Active transport Passive transport CORTEX OUTER MEDULLA INNER MEDULLA Descending limb of loop of Henle Thick segment of ascending limb Thin segment of ascending limbs Collecting duct NaCl Distal tubule NaClNutrients Urea H2OH2O NaCl H2OH2O H2OH2O HCO 3  K+K+ H+H+ NH 3 HCO 3  K+K+ H+H+ H2OH2O

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Figure Environmental Adaptations of the Vertebrate Kidney MAMMALS Bannertail Kangaroo rat (Dipodomys spectabilis) Beaver (Castor canadensis) FRESHWATER FISHES AND AMPHIBIANS Rainbow trout (Oncorrhynchus mykiss) Frog (Rana temporaria) BIRDS AND OTHER REPTILES Roadrunner (Geococcyx californianus) Desert iguana (Dipsosaurus dorsalis) MARINE BONY FISHES Northern bluefin tuna (Thunnus thynnus)