Osmoregulation and Excretion Chapter 44 Osmoregulation and Excretion

Figure 44.1 Salvin’s albatrosses (Diomeda cauta salvini), birds that can drink seawater with no ill effects

Figure 44.2 Largemouth tilapia (Tilapia mossambica), an extreme euryhaline osmoregulator

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 by gills large amounts of water in dilute (a) Osmoregulation in a saltwater fish (b) Osmoregulation in a freshwater fish

(a) Hydrated tardigrade Figure 44.4 Anhydrobiosis (a) Hydrated tardigrade (b) Dehydrated tardigrade 100 µm

Figure 44.5 Water balance in two terrestrial mammals a human (2,500 mL/day = 100%) balance in a kangaroo rat (2 mL/day Ingested in food (0.2) in food (750) in liquid (1,500) Derived from metabolism (250) metabolism (1.8) gain Feces (0.9) Urine (0.45) Evaporation (1.46) Feces (100) Evaporation (900) loss

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) 4 3 2 1 (L/100 kg body mass) Water lost per day EXPERIMENT Removing the fur of a camel increased the rate of water loss through sweating by up to 50%.

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 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)

Figure 44.8 Nitrogenous wastes Proteins Nucleic acids Amino acids Nitrogenous bases –NH2 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 NH3 NH2 O C N H HN

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 1 2 3 4

Figure 44.10 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)

Figure 44.11 Metanephridia of an earthworm Nephrostome Metanephridia Nephridio- pore Collecting tubule Bladder Capillary network Coelom

Figure 44.12 Malpighian tubules of insects Digestive tract Midgut (stomach) Malpighian tubules Rectum Intestine Hindgut Salt, water, and nitrogenous wastes Feces and urine Anus tubule Reabsorption of H2O, ions, and valuable organic molecules HEMOLYMPH

Figure 44.13 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 Collecting duct To renal pelvis Renal cortex medulla 20 µm (b) Kidney structure Kidney Section of kidney from a rat 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 Loop of Henle Vasa recta Distal tubule (d) Filtrate and blood flow (c) Nephron

Figure 44.14 The nephron and collecting duct: regional functions of the transport epithelium Proximal tubule Filtrate H2O Salts (NaCl and others) HCO3– H+ Urea Glucose; amino acids Some drugs Key Active transport Passive transport CORTEX OUTER MEDULLA INNER Descending limb of loop of Henle Thick segment of ascending limb Thin segment limbs Collecting duct NaCl Distal tubule Nutrients HCO3 K+ NH3 1 4 3 2 5

Paired Activity Explain how nephrons function to filter the blood. Be sure to discuss the structure of nephrons in your explanation. Generate a standards list if this was an essay on the AP exam Create multiple sections and list exactly what would be needed to earn each point

Osmolarity of interstitial fluid (mosm/L) Figure 44.15 How the human kidney concentrates urine: the two-solute model (layer 1) H2O 300 100 400 600 900 1200 700 200 Active transport Passive transport OUTER MEDULLA INNER MEDULLA CORTEX Osmolarity of interstitial fluid (mosm/L)

Osmolarity of interstitial fluid (mosm/L) Figure 44.15 How the human kidney concentrates urine: the two-solute model (layer 2) H2O Nacl 300 100 400 600 900 1200 700 200 Active transport Passive transport OUTER MEDULLA INNER MEDULLA CORTEX Osmolarity of interstitial fluid (mosm/L)

Osmolarity of interstitial fluid (mosm/L) Figure 44.15 How the human kidney concentrates urine: the two-solute model (layer 3) H2O Nacl 300 100 400 600 900 1200 700 200 Active transport Passive transport OUTER MEDULLA INNER MEDULLA CORTEX Urea Osmolarity of interstitial fluid (mosm/L)

Figure 44.16 Hormonal control of the kidney by negative feedback circuits Osmoreceptors in hypothalamus Drinking reduces blood osmolarity to set point Increased Na+ and H2O reab- sorption in distal tubules Homeostasis: Blood pressure, volume STIMULUS: The juxtaglomerular apparatus (JGA) responds to low blood volume or blood pressure (such as due to dehydration or loss of blood) H2O reab- sorption helps prevent further osmolarity increase The release of ADH is triggered when osmo- receptor cells in the hypothalamus detect an increase in the osmolarity of the blood Blood osmolarity Hypothalamus ADH Pituitary gland Increased permeability Thirst Aldosterone Adrenal gland Angiotensin II Angiotensinogen Renin production Collecting duct Distal tubule Arteriole constriction JGA Antidiuretic hormone (ADH) enhances fluid retention by making the kidneys reclaim more water. The renin-angiotensin-aldosterone system (RAAS) leads to an increase in blood volume and pressure. (a) (b)

Figure 44.17 A vampire bat (Desmodus rotundas), a mammal with a unique excretory situation

Figure 44.18 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)