Chapter 44

1. Chapter 44 Osmoregulation and Excretion

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

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

4. Osmotic water gain through gills and other parts of body surface Gain of water and salt ions from food and by drinking seawater Osmotic water loss through gills and other parts of body surface Uptake of water and some ions in food Uptake of salt ions by gills Excretion of large amounts of water in dilute urine from kidneys Excretion of salt ions and small amounts of water in scanty urine from kidneys Excretion of salt ions from gills (a) Osmoregulation in a saltwater fish (b) Osmoregulation in a freshwater fish Figure 44.3 Osmoregulation in marine and freshwater bony fishes: a comparison

5. 100 µm 100 µm (a) Hydrated tardigrade (b) Dehydrated tardigrade Figure 44.4 Anhydrobiosis

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

7. 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. EXPERIMENT RESULTS Removing the fur of a camel increased the rate of water loss through sweating by up to 50%. 4 3 Water lost per day (L/100 kg body mass) 2 1 0 Control group (Unclipped fur) Experimental group (Clipped fur) The fur of camels plays a critical role in their conserving water in the hot desert environments where they live. CONCLUSION Figure 44.6 What role does fur play in water conservation by camels?

8. Nasal salt gland (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. Nostril with salt secretions Lumen of secretory tubule Vein (c) Capillary 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. Secretory tubule Artery NaCl Transport epithelium Direction of salt movement Secretory cell of transport epithelium Blood flow (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. Central duct Figure 44.7 Salt-excreting glands in birds

9. Nucleic acids Proteins Nitrogenous bases Amino acids –NH2 Amino groups Many reptiles (including birds), insects, land snails Most aquatic animals, including most bony fishes Mammals, most amphibians, sharks, some bony fishes O H C N C HN C O NH2 C C C O N N O NH3 NH2 H H Ammonia Urea Uric acid Figure 44.8 Nitrogenous wastes

10. Capillary 1 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. Excretory tubule Filtrate 2 Reabsorption. The transport epithelium reclaims valuable substances from the filtrate and returns them to the body fluids. 3 Secretion. Other substances, such as toxins and excess ions, are extracted from body fluids and added to the contents of the excretory tubule. 4 Urine Excretion. The filtrate leaves the system and the body. Figure 44.9 Key functions of excretory systems: an overview

11. Nucleus of cap cell Cilia Interstitial fluid filters through membrane where cap cell and tubule cell interdigitate (interlock) Tubule cell Flame bulb Protonephridia (tubules) Tubule Nephridiopore in body wall Figure 44.10 Protonephridia: the flame-bulb system of a planarian

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

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

14. Posterior vena cava Renal artery and vein Aorta Renal medulla Kidney Ureter Renal cortex Urinary bladder Urethra Renal pelvis (a) Excretory organs and major associated blood vessels Ureter Juxta- medullary nephron Section of kidney from a rat Cortical nephron (b) Kidney structure Afferent arteriole from renal artery Glomerulus Bowman’s capsule Renal cortex Proximal tubule Peritubular capillaries Collecting duct SEM 20 µm Efferent arteriole from glomerulus Distal tubule Renal medulla To renal pelvis Collecting duct Branch of renal vein Descending limb Loop of Henle (c) Nephron Ascending limb Vasa recta (d) Filtrate and blood flow Figure 44.13 The mammalian excretory system

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

16. 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

17. Osmolarity of interstitial fluid(mosm/L) 300 100 300 100 300 300 H2O CORTEX Activetransport 200 400 400 400 H2O Passivetransport H2O OUTERMEDULLA H2O 400 600 600 600 H2O 900 H2O 700 900 H2O INNERMEDULLA 1200 1200 1200 Figure 44.15 How the human kidney concentrates urine: the two-solute model (layer 1)

18. Osmolarity of interstitial fluid(mosm/L) 300 100 300 100 300 300 Nacl H2O CORTEX Activetransport 200 400 400 400 Nacl H2O Passivetransport H2O Nacl OUTERMEDULLA Nacl H2O 400 600 600 600 H2O Nacl Nacl 900 H2O 700 900 Nacl H2O INNERMEDULLA 1200 1200 1200 Figure 44.15 How the human kidney concentrates urine: the two-solute model (layer 2)

19. Osmolarity of interstitial fluid(mosm/L) 300 100 300 100 300 300 Nacl H2O H2O CORTEX Activetransport 200 400 400 400 Nacl H2O H2O Passivetransport H2O Nacl H2O OUTERMEDULLA Nacl H2O H2O 400 600 600 600 H2O Nacl H2O Urea Nacl 900 H2O H2O 700 900 Urea Nacl H2O H2O INNERMEDULLA 1200 Urea 1200 1200 Figure 44.15 How the human kidney concentrates urine: the two-solute model (layer 3)

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

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

22. BIRDS AND OTHER REPTILES MAMMALS Bannertail Kangaroo rat (Dipodomys spectabilis) Roadrunner (Geococcyx californianus) Desert iguana (Dipsosaurus dorsalis) Beaver (Castor canadensis) FRESHWATER FISHES AND AMPHIBIANS MARINE BONY FISHES Northern bluefin tuna (Thunnus thynnus) Rainbow trout (Oncorrhynchus mykiss) Frog (Rana temporaria) Figure 44.18 Environmental Adaptations of the Vertebrate Kidney