1. Osmoregulation and Excretion A.P. Biology Ch. 44 Rick L. Knowles Liberty Senior High School

2. Osmoregulation Maintaining a balance of both water and ions across a membrane/organism. Solute and water homeostasis. Osmolarity – moles of total solute per liter of water; usually in milliosmoles/L. Mechanism of homeostasis varies with the environment in which they’ve adapted (freshwater, saltwater, terrestrial).

3. Some Comparison 0 Milliosmoles/L (mosm/L) Distilled,deionized Water Freshwater 0.5 -15 300 Human Plasma 1,000 Seawater 5,000 Dead Sea

4. Most animals are said to be stenohaline: –And cannot tolerate substantial changes in external osmolarity; both osmoconformers and osmoregulators. Euryhaline animals: –Can survive large fluctuations in external osmolarity. Figure 44.2 Tilapia, freshwater up to 2,000 mosm/L

5. Osmoregulation and Nitrogenous Wastes Other waste solutes must be removed from cells and organisms. A waste product of metabolizing amino acids and nucleic acids (deamination)- ammonia.

6. Concept 44.2: An animal’s nitrogenous wastes reflect its phylogeny and habitat. The type and quantity of an animal’s waste products: –May have a large impact on its water balance.

7. Ammonia Direct by-product of protein and nucleic acids (deamination). Very toxic to cells. Highly soluble in water. Molecule of choice for freshwater organisms; eliminated easily through kidneys, gill epithelia, etc. Downside: requires a lot of water.

8. Urea Saltwater and terrestrial mammals convert ammonia into urea. Less toxic; accumulate more in tissue. Less soluble in water than ammonia. Allows conservation of water.

9. Uric Acid Birds and reptiles accumulate waste in an egg. Convert ammonia into uric acid. Insoluble in water; crystallizes. Semisolid paste-guano. Requires less water to eliminate.

10. 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 Among the most important wastes –Are the nitrogenous breakdown products of proteins and nucleic acids Figure 44.8

11. Osmoconformers Most marine protists and invertebrates. Are isoosmotic with marine environment. Open channels and carriers for most ion transport (Not all ions are in equilibrium). Ex. Invertebrates like sea anemones, jellyfish, and only vertebrate, Class Agnatha- hagfish.

12. Class Agnatha- Hagfish

13. Show me a real hagfish! Video: Discovery- Blue Planet: Ocean World

14. Osmoregulators Maintain constant osmotic concentration in body fluids and cytoplasm despite external variations. Continuous regulation since environment and intake (diet) changes. Evolved special mechanisms for different environments. Ex. Most Vertebrates

15. The Problems Freshwater Vertebrates- are hyperosmotic, water enters body, tend to lose ions. Marine Vertebrates- are hypoosmotic, water leaves body, tend to gain ions. Terrestrial Vertebrates- are hypoosmotic, water leaves body through respiration, perspiration, skin.

16. Freshwater Protists Problem: hyperosmotic; impossible to become isoosmotic with dilute fresh water; tend to gain water; lose ions; no excretory organ. Solution: Contractile Vacuoles – active transport of water out of cell; less permeable to ions Downside: Active transport requires energy.

17. Freshwater Invertebrates Water and wastes are passed into a collecting vessel or primitive excretory organ. Membrane retains proteins and sugars and allows water and dissolved wastes to leave-selectively permeable. Ex. Freshwater jellyfish, etc,

18. Concept 44.3: Diverse excretory systems are variations on a tubular theme. Excretory systems: –Regulate solute movement between internal fluids and the external environment.

19. Excretory Processes Most excretory systems –Produce urine 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 1 2 3 4

20. 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 A protonephridium: –Is a network of dead-end tubules lacking internal openings. Figure 44.10

21. The tubules branch throughout the body: –And the smallest branches are capped by a cellular unit called a flame bulb. These tubules excrete a dilute fluid: –And function in osmoregulation

22. Metanephridia Each segment of an earthworm –Has a pair of open-ended metanephridia Figure 44.11 Nephrostome Metanephridia Nephridio- pore Collecting tubule Bladder Capillary network Coelom

23. Metanephridia consist of tubules: –That collect coelomic fluid and produce dilute urine for excretion.

24. Terrestrial Insects Problem: Must minimize water loss. Solution: Use chitin as an exoskeleton.

26. 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 In insects and other terrestrial arthropods, malpighian tubules –Remove nitrogenous wastes from hemolymph and function in osmoregulation Figure 44.12

27. Malpighian Tubules K+K+ K+K+ K+K+ Hemolymph Water and waste Hindgut Water and K + Na + /K + -ATPase Conc. Waste

28. Malpighian Tubules Use Malpighian tubules- blind end tubules that extend into hemocoel (body cavity). Cells  waste and salts into hemolymph  lumen of tubule by diffusion and active transport. K + are actively transported into lumen; set up a gradient. Water and other ions leave the hemolymph and follow into the lumen by passive diffusion. Empty into hindgut; water reabsorbed; urine is concentrated. Na + /K + -ATPase moves ions from lumen of hindgut into hemolymph.

29. Insects versus other Vertebrates Insects use a gradient to pull water through a membrane; open circulatory system = low blood pressure. Vertebrates- push water through a membrane; closed circulatory system = higher blood pressure.

30. More Complex Organisms Need Another Solution Introducing the Vertebrate Kidney!

31. Nephron (Tubule)

40. Gill Epithelia is Permeable

41. Hypertonic Cells Hypotonic Env. Water

42. Freshwater Bony Fishes Problems: Water enters cells from environment, solutes leave cells. Solutions: Drink very little water; excrete large amounts of dilute (hypoosmotic) urine with large kidneys; reabsorb ions in kidney tubules (active transport) back into blood; use chloride cells in gill epithelium (active transport).

43. Freshwater animals maintain water balance: –By excreting 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

44. Hypotonic Cells Hypertonic Env. Water

45. Saltwater Bony Fishes Problem: Tend to lose water, gain ions, mostly at gills. Solutions: Drink large amount of water; kidney retains water and excretes ions (isoosmotic urine); use chloride cells in gills to actively transport some ions across gill epithelium.

46. Marine bony fishes are hypoosmotic to sea water: –Lose water by osmosis and gain salt by both diffusion and from food they eat. These fishes balance water loss: –By drinking seawater. 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

47. Cartilaginous Fishes Problem: Same as marine bony fishes. Solution: Reabsorb urea from nephron tubule back into the blood; 100X blood [urea] than mammals (special protective solute,TMAO to protect proteins)  blood is slightly hyperosmotic  kidneys and gills do not have to remove ions; do not have to drink large volume of water.

48. Cartilaginous Fishes Problem: Still must remove excess Na + and Cl - that diffuse across gills, diet, etc. Solution: Rectal Gland- uses Na + /K + -ATPase pumps to actively transport Na + and Cl - out of blood by setting up a gradient.

51. How the Rectal Gland Works Na + /K + -ATPase Extracellular Fluid Lumen of Rectal Gland Na + K+K+ Cl - Cotransporter Na + Cl - Chloride Channel Cl - Na+ To Rectum

52. How could a marine shark enter freshwater? By controlling the amount of solutes! Video: National Geographic Presents: Attacks of the Mystery Shark

53. Rectal Gland Very common mechanism for removing salt in marine animals. Problem: Marine birds and reptiles have freshwater kidneys designed to reabsorb salt from urine into blood. Use similar salt glands in nostrils to excrete salt.

54. An example of transport epithelia is found in the salt glands of marine birds. R emove excess sodium chloride from the blood. Figure 44.7a, b Nasal salt gland Nostril with salt secretions Lumen of secretory tubule NaCl Bloo d 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.

55. Show me some marine reptiles! Salt glands in action! Video: Corwin Experience- Galapagos

56. Animals That Live in Temporary Waters Some aquatic invertebrates living in temporary ponds –Can lose almost all their body water and survive in a dormant state This adaptation is called anhydrobiosis. Figure 44.4a, b (a) Hydrated tardigrade (b) Dehydrated tardigrade 100 µm

67. The nephron, the functional unit of the vertebrate kidney –Consists of a single long tubule and a ball of capillaries called the glomerulus 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

71. Vertebrate Kidneys Four Functions: 1. Filtration 2. Reabsorption 3. Secretion 4. Excretion

77. 1. Filtration Glomerulus- tightly-woven ball of capillaries embedded in a cup-shaped tubule- Bowman’s capsule. Slits/pores in capillaries and capsule allow liquid/solutes through but prevent cells and large proteins from entering the nephron. Produces isoosmotic filtrate with blood

78. Filtration of the Blood Filtration occurs as blood pressure: –Forces fluid from the blood in the glomerulus into the lumen of Bowman’s capsule.

80. Pathway of the Filtrate From Bowman’s capsule, the filtrate passes through three regions of the nephron: –The proximal tubule, the loop of Henle, and the distal tubule Fluid from several nephrons: –Flows into a collecting duct

81. Blood Vessels Associated with the Nephrons Each nephron is supplied with blood by an afferent arteriole: –A branch of the renal artery that subdivides into the capillaries The capillaries converge as they leave the glomerulus –Forming an efferent arteriole. The vessels subdivide again: –Forming the peritubular capillaries, which surround the proximal and distal tubules.

82. 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 1 4 3 2 3 5 From Blood Filtrate to Urine: A Closer Look Filtrate becomes urine: –As it flows through the mammalian nephron and collecting duct. Figure 44.14

83. Transport Epithelium

85. 2. Reabsorption Must return most of the water and solutes to the blood. (2000 l of blood  180 l water  1-2 l urine daily). Reabsorb glucose, amino acids, divalent cations in proximal tubule by active transport carriers. If not reabsorbed, lost in the urine. Ex. Diabetes mellitus

86. 3. Secretion Foreign molecules and wastes (ammonia, urea) are secreted into lower portions of tubule. Opposite direction as reabsorption (Capillary  Tubule). Ex. Antibiotics and other drugs, bacterial debris

87. Secretion and reabsorption in the proximal tubule: –Substantially alter the volume and composition of filtrate Reabsorption of water continues: –As the filtrate moves into the descending limb of the loop of Henle

88. 4. Excretion Urine is a solution of: Harmful drugs, hormones, nitrogenous wastes, and excess K +, H +, water. Homeostasis of: pH, electrolytes, blood volume and pressure.

89. As filtrate travels through the ascending limb of the loop of Henle: –Salt diffuses out of the permeable tubule into the interstitial fluid. The distal tubule: –Plays a key role in regulating the K + and NaCl concentration of body fluids. The collecting duct: –Carries the filtrate through the medulla to the renal pelvis and reabsorbs NaCl.

90. Concept 44.5: The mammalian kidney’s ability to conserve water is a key terrestrial adaptation. The mammalian kidney: –Can produce urine much more concentrated than body fluids, thus conserving water.

91. Solute Gradients and Water Conservation In a mammalian kidney, the cooperative action and precise arrangement of the loops of Henle and the collecting ducts: –Are largely responsible for the osmotic gradient that concentrates the urine.

93. Two solutes, NaCl and urea, contribute to the osmolarity of the interstitial fluid. - Causes the reabsorption of water in the kidney and concentrates the urine. Figure 44.15 H2OH2O H2OH2O H2OH2O H2OH2O H2OH2O H2OH2O H2OH2O NaCl 300 100 400 600 900 1200 700 400 200 100 Active transport Passive transport OUTER MEDULLA INNER MEDULLA CORTEX H2OH2O Urea H2OH2O H2OH2O H2OH2O H2OH2O H2OH2O H2OH2O 1200 900 600 400 300 600 400 300 Osmolarity of interstitial fluid (mosm/L) 300

94. The countercurrent multiplier system involving the loop of Henle –Maintains a high salt concentration in the interior of the kidney, which enables the kidney to form concentrated urine.

95. The collecting duct, permeable to water but not salt: –Conducts the filtrate through the kidney’s osmolarity gradient, and more water exits the filtrate by osmosis.

96. Urea diffuses out of the collecting duct: –As it traverses the inner medulla Urea and NaCl: –Form the osmotic gradient that enables the kidney to produce urine that is hyperosmotic to the blood.

100. Antidiuretic Hormone (ADH) –Increases water reabsorption in the distal tubules and collecting ducts of the kidney 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.

101. The Renin-Angiotensin-Aldosterone System (RAAS) –Is part of a complex feedback circuit that functions in homeostasis Figure 44.16b Increased Na + and H 2 O 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) Aldosterone Adrenal gland Angiotensin II Angiotensinogen Renin production Renin Arteriole constriction Distal tubule JGA (b) The renin-angiotensin-aldosterone system (RAAS) leads to an increase in blood volume and pressure.

103. 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

104. Concept 44.6: Diverse adaptations of the vertebrate kidney have evolved in different environments. The form and function of nephrons in various vertebrate classes: –Are related primarily to the requirements for osmoregulation in the animal’s habitat.

105. Terrestrial Animals Land animals manage their water budgets –By drinking and eating moist foods 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

106. Desert animals: –Get major water savings from simple anatomical features Figure 44.6 Control group (Unclipped fur) Experimental group (Clipped fur) 4 3 2 1 0 Water lost per day (L/100 kg body mass) 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%. The fur of camels plays a critical role in their conserving water in the hot desert environments where they live. CONCLUSION

107. Exploring environmental adaptations of the vertebrate kidney Figure 44.18 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)