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

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings A balancing act The physiological systems of animals – Operate in a fluid environment The relative concentrations of water and solutes in this environment – Must be maintained within narrow limits  Homeostasis

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Freshwater animals  Adaptations for reducing water uptake and conserve solutes Desert & marine animals  desiccating environment, conserve water Figure 44.1

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Osmoregulation Balances uptake and loss of water and solutes – based on controlled movement of solutes between internal fluids and the external environment

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Osmosis Osmotic gain and loss of water at the level of the cell Balanced by osmoregulation

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Osmotic Challenges Osmoconformers – Isoosmotic with their surroundings and do not regulate their osmolarity, e.g. marine inverts. Osmoregulators expend energy to control water uptake and loss, e.g. marine verts.

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Marine bony fishes are hypoosmotic to sea water – lose water by osmosis and gain salt by both diffusion and from food they eat – Sm. Volume, highly conc. urine Figure 44.3a 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 (a) Osmoregulation in a saltwater fish

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Freshwater Animals Take in water from their hypoosmotic environment Lose salts by diffusion

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Freshwater animals excrete large amounts of dilute urine Salts lost by diffusion – Are replaced by foods and uptake across the gills Figure 44.3b 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 (b) Osmoregulation in a freshwater fish

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Land Animals Manage their water budget by drinking and by using metabolic water Figure 44.5 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 Transport Epithelia Specialized cells that regulate solute movement

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings e.g. salt glands of marine birds – remove excess NaCl from the blood Figure 44.7a, b Nasal salt gland Nostril with salt secretions Lumen of secretory tubule NaCl Blood flow Secretory cell of transport epithelium Central duct Direction of salt movement Transport epithelium Secretory tubule Capillary Vein Artery (a) 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. (b) 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. (c) 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.

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings ProteinsNucleic 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 Nitrogenous Waste Nitrogenous breakdown products of proteins and nucleic acids Figure 44.8

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Ammonia Animals that excrete ammonia need access to lots of water

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Urea Liver of mammals convert ammonia to less toxic urea  kidneys  excreted (w/ minimal loss of water)

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Uric Acid Insects, land snails, reptiles, birds Little water loss

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Excretory Processes Urine produced by refining a filtrate derived from body fluids Figure 44.9 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 – Filtration, pressure-filtering of body fluids – Reabsorption, reclaiming valuable solutes – Secretion, addition of toxins and other solutes to the filtrate – Excretion, the filtrate leaves the system

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 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) Protonephridia: Flame-Bulb Systems, flatworm Figure 44.10

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

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 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 Malpighian Tubules, insects Figure 44.12

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Vertebrate Kidneys Function in both excretion and osmoregulation

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Nephrons  functional unit

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Figure 44.13a Posterior vena cava Renal artery and vein Aorta Ureter Urinary bladder Urethra (a) Excretory organs and major associated blood vessels Kidney

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings (b) Kidney structure Ureter Section of kidney from a rat Renal medulla Renal cortex Renal pelvis Figure 44.13b 2 distinct regions – An outer renal cortex and an inner renal medulla

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Nephron Figure 44.13c, d Juxta- medullary nephron Cortical nephron Collecting duct To renal pelvis Renal cortex Renal medulla 20 µm 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 Distal tubule Collecting duct (c) Nephron Vasa recta (d) Filtrate and blood flow

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Filtration occurs in the glomerulus

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Glomerulus of Bowman’s capsule  proximal tubule  the loop of Henle  distal tubule  collecting duct

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 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 limb 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 Filtrate becomes urine Figure 44.14

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings The mammalian kidney’s ability to conserve water is a key terrestrial adaptation

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings NaCl and urea, contribute to the osmolarity of the interstitial fluid Figure H2OH2O H2OH2O H2OH2O H2OH2O H2OH2O H2OH2O H2OH2O NaCl Active transport Passive transport OUTER MEDULLA INNER MEDULLA CORTEX H2OH2O Urea H2OH2O H2OH2O H2OH2O H2OH2O H2OH2O H2OH2O Osmolarity of interstitial fluid (mosm/L) 300

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Regulation of Kidney Function Osmolarity of the urine regulated by nervous and hormonal control

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Antidiuretic hormone (ADH) – Increases water reabsorption in the distal tubules and collecting ducts Figure 44.16a Osmoreceptors in hypothalamus Drinking reduces blood osmolarity to set point H 2 O reab- sorption helps prevent further osmolarity increase STIMULUS: The release of ADH is triggered when osmo- receptor cells in the hypothalamus detect an increase in the osmolarity of the blood Homeostasis: Blood osmolarity Hypothalamus ADH Pituitary gland Increased permeability Thirst Collecting duct Distal tubule (a ) Antidiuretic hormone (ADH) enhances fluid retention by making the kidneys reclaim more water.

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings The South American vampire bat, which feeds on blood – Has a unique excretory system in which its kidneys offload much of the water absorbed from a meal by excreting large amounts of dilute urine Figure 44.17

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Environmental adaptations of the vertebrate kidney Figure 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)

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings