Chapter 44

1. Chapter 44 Regulating the Internal EnvironmentThermoregulation, Osmoregulation & Excretion

2. Thermoregulation: A Balancing Act • Thermoregulation contributes to homeostasis and involves anatomy, physiology, and behavior • Thermoregulation is the process by which animals maintain an internal temperature within a tolerable range • Ectotherms include most invertebrates, fishes, amphibians, and non-bird reptiles • Endotherms include birds and mammals

3. Radiation is the emission of electromagnetic waves by all objects warmer than absolute zero. Radiation can transfer heat between objects that are not in direct contact, as when a lizard absorbs heat radiating from the sun. Evaporation is the removal of heat from the surface of a liquid that is losing some of its molecules as gas. Evaporation of water from a lizard’s moist surfaces that are exposed to the environment has a strong cooling effect. Conduction is the direct transfer of thermal motion (heat) between molecules of objects in direct contact with each other, as when a lizard sits on a hot rock. Convection is the transfer of heat by the movement of air or liquid past a surface, as when a breeze contributes to heat loss from a lizard’s dry skin, or blood moves heat from the body core to the extremities. Modes of Heat Exchange

4. 40 River otter (endotherm) 30 Body temperature (°C) 20 Largemouth bass (ectotherm) 10 0 10 20 30 40 Ambient (environmental) temperature (°C) Ectotherms • In general, ectotherms tolerate greater variation in internal temperature than endotherms Figure 40.12

5. Endotherms • Endothermy is more energetically expensive than ectothermy • But buffers animals’ internal temperatures against external fluctuations • And enables the animals to maintain a high level of aerobic metabolism

6. Insulation • In mammals, the integumentary system acts as insulating material Hair Epidermis Sweat pore Muscle Dermis Nerve Sweat gland Hypodermis Adipose tissue Blood vessels Oil gland Figure 40.14 Hair follicle

7. Circulatory Adaptations • Many endotherms and some ectotherms • Can alter the amount of blood flowing between the body core and the skin • In vasodilation • Blood flow in the skin increases, facilitating heat loss • In vasoconstriction • Blood flow in the skin decreases, lowering heat loss

8. Pacific bottlenose dolphin Arteries carrying warm blood down the legs of a goose or the flippers of a dolphin are in close contact with veins conveying cool blood in the opposite direction, back toward the trunk of the body. This arrangement facilitates heat transfer from arteries to veins (black arrows) along the entire length of the blood vessels. 1 Canada goose Blood flow 1 Artery Vein Vein Near the end of the leg or flipper, where arterial blood has been cooled to far below the animal’s core temperature, the artery can still transfer heat to the even colder blood of an adjacent vein. The venous blood continues to absorb heat as it passes warmer and warmer arterial blood traveling in the opposite direction. 2 Artery 3 35°C 33° 3 30º 27º 20º 18º 2 10º 9º In the flippers of a dolphin, each artery is surrounded by several veins in a countercurrent arrangement, allowing efficient heat exchange between arterial and venous blood. As the venous blood approaches the center of the body, it is almost as warm as the body core, minimizing the heat lost as a result of supplying blood to body parts immersed in cold water. 2 3 Countercurrent Heat Exchangers • Many marine mammals and birds have arrangements of blood vessels called countercurrent heat exchangers that are important for reducing heat loss 3 1 Figure 40.15

9. 21º 23º 25º 27º 29º 31º Body cavity Skin Artery Vein Blood vessels in gills Capillary network within muscle Heart Artery and vein under the skin Dorsal aorta Countercurrent Heat Exchangers • Some specialized bony fishes and sharks also possess countercurrent heat exchangers (a) Bluefin tuna. Unlike most fishes, the bluefin tuna maintains temperatures in its main swimming muscles that are much higher than the surrounding water (colors indicate swimming muscles cut in transverse section). These temperatures were recorded for a tuna in 19°C water. (b) Great white shark. Like the bluefin tuna, the great white shark has a countercurrent heat exchanger in its swimming muscles that reduces the loss of metabolic heat. All bony fishes and sharks lose heat to the surrounding water when their blood passes through the gills. However, endothermic sharks have a small dorsal aorta, and as a result, relatively little cold blood from the gills goes directly to the core of the body. Instead, most of the blood leaving the gills is conveyed via large arteries just under the skin, keeping cool blood away from the body core. As shown in the enlargement, small arteries carrying cool blood inward from the large arteries under the skin are paralleled by small veins carrying warm blood outward from the inner body. This countercurrent flow retains heat in the muscles. Figure 40.16a, b

10. Sweat glands secrete sweat that evaporates, cooling the body. Thermostat in hypothalamus activates cooling mechanisms. Blood vessels in skin dilate: capillaries fill with warm blood; heat radiates from skin surface. Increased body temperature (such as when exercising or in hot surroundings) Body temperature decreases; thermostat shuts off cooling mechanisms. Homeostasis: Internal body temperature of approximately 36–38C Body temperature increases; thermostat shuts off warming mechanisms. Decreased body temperature (such as when in cold surroundings) Blood vessels in skin constrict, diverting blood from skin to deeper tissues and reducing heat loss from skin surface. Thermostat in hypothalamus activates warming mechanisms. Skeletal muscles rapidly contract, causing shivering, which generates heat. Feedback Mechanisms in Thermoregulation • Mammals regulate their body temperature by a complex negative feedback system that involves several organ systems • In humans, a specific part of the brain, the hypothalamus contains a group of nerve cells that function as a thermostat Figure 40.21

11. Torpor, Hibernation, and Energy Conservation • Torpor is an adaptation that enables animals to save energy while avoiding difficult and dangerous conditions • Is a physiological state in which activity is low and metabolism decreases • Hibernation is long-term torpor that is an adaptation to winter cold and food scarcity during which the animal’s body temperature declines

12. Estivation & Daily Torpor • Estivation, or summer torpor • Enables animals to survive long periods of high temperatures and scarce water supplies • Daily torpor • Is exhibited by many small mammals and birds and seems to be adapted to their feeding patterns

13. Osmoregulation - 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 fairly narrow limits • Freshwater animals show adaptations that reduce water uptake and conserve solutes • Desert and marine animals face desiccating environments with the potential to quickly deplete the body water

14. Osmoregulation and Excretion • Osmoregulation regulates solute concentrations and balances the gain and loss of water • Osmoregulation is based largely on controlled movement of solutes between internal fluids and the external environment • Excretion gets rid of metabolic wastes

15. Osmosis: Osmoconformers & Osmoregulators • Cells require a balance between osmotic gain and loss of water • Water uptake and loss are balanced by various mechanisms of osmoregulation in different environments • Osmoconformers, which are only marine animals • Are isoosmotic with their surroundings and do not regulate their osmolarity • Osmoregulators expend energy to control water uptake and loss • In a hyperosmotic or hypoosmotic environment

16. Figure 44.2 Stenohaline Animals v. Euryhaline Animals • Most animals are said to be stenohaline • And cannot tolerate substantial changes in external osmolarity • Euryhaline animals can survive large fluctuations in external osmolarity

17. 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 and small amounts of water in scanty urine from kidneys Excretion of salt ions from gills Marine Animals • Most marine invertebrates are osmoconformers • Most marine vertebrates and some invertebrates are osmoregulators • Marine bony fishes are hypoosmotic to sea water and 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 (a) Osmoregulation in a saltwater fish

18. Osmotic water gain 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 Freshwater Animals • Freshwater animals constantly take in water from their hypoosmotic environment and lose salts by diffusion • 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 (b) Osmoregulation in a freshwater fish

19. 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) Land Animals • Land animals manage their water budgets by drinking and eating moist foods and by using metabolic water Figure 44.5

20. EXPERIMENT 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. Removing the fur of a camel increased the rateof water loss through sweating by up to 50%. 4 RESULTS 3 CONCLUSION The fur of camels plays a critical role intheir conserving water in the hot desertenvironments where they live. Water lost per day (L/100 kg body mass) 2 1 0 Control group (Unclipped fur) Experimental group (Clipped fur) Desert Animals • Desert animals get major water savings from simple anatomical features Figure 44.6

21. Transport Epithelia • Transport epithelia • Are specialized cells that regulate solute movement • Are essential components of osmotic regulation and metabolic waste disposal • Are arranged into complex tubular networks

22. Nasal salt gland (a) An albatross’s salt glands empty via a duct into thenostrils, 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 Capillary (c) The secretory cells actively transport salt from theblood into the tubules. Blood flows counter to the flow of salt secretion. By maintaining a concentrationgradient of salt in the tubule (aqua), this countercurrentsystem enhances salt transfer from the blood to the lumen of the tubule. Secretory tubule Artery NaCl Transport epithelium (b) One of several thousand secretory tubules in a salt-excreting gland. Each tubule is lined by a transportepithelium surrounded by capillaries, and drains intoa central duct. Direction of salt movement Blood flow Secretory cell of transport epithelium Central duct Transport Epithelia • An example of transport epithelia is found in the salt glands of marine birds which remove excess sodium chloride from the blood Figure 44.7a, b

23. 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 Nitrogenous Waste in Animals • 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 • Among the most important wastes are the nitrogenous breakdown products of proteins and nucleic acids Figure 44.8

24. Forms of Nitrogenous Wastes • Different animals excrete nitrogenous wastes in different forms • Animals that excrete nitrogenous wastes as ammonia need access to lots of water • Ammonia is released across the whole body surface or through the gills • The liver of mammals and most adult amphibians converts ammonia to less toxic urea which is carried to the kidneys in a concentrated form • Urea is excreted with a minimal loss of water • Insects, land snails, and many reptiles, including birds excrete uric acid as their major nitrogenous waste • Uric acid is largely insoluble in water and can be secreted as a paste with little water loss

25. Capillary 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. 1 Excretory tubule Filtrate 2 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. 3 4 Excretion. The filtrate leaves the system and the body. Urine Excretory Processes • Most excretory systems produce urine by refining a filtrate derived from body fluids Figure 44.9

26. Survey of Excretory Systems • The systems that perform basic excretory functions • Vary widely among animal groups • Are generally built on a complex network of tubules

27. 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 Protonephridia: Flame-Bulb Systems • A protonephridium is a network of dead-end tubules lacking internal openings • 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 Figure 44.10

28. Coelom Capillary network Bladder Collecting tubule Nephridio- pore Metanephridia Nephrostome Metanephridia • Each segment of an earthworm • Has a pair of open-ended metanephridia • Metanephridia consist of tubules • That collect coelomic fluid and produce dilute urine for excretion Figure 44.11

29. 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 Malpighian Tubules • In insects and other terrestrial arthropods, malpighian tubules remove nitrogenous wastes from hemolymph and function in osmoregulation • Insects produce a relatively dry waste matter - an important adaptation to terrestrial life Figure 44.12

30. Vertebrate Kidneys • Kidneys, the excretory organs of vertebrates • Function in both excretion and osmoregulation • Nephrons and associated blood vessels are the functional unit of the mammalian kidney • The mammalian excretory system centers on paired kidneys • Which are also the principal site of water balance and salt regulation

31. Posterior vena cava Renal artery and vein Kidney Aorta Ureter Urinary bladder Urethra (a) Excretory organs and major associated blood vessels Kidneys • Each kidney is supplied with blood by a renal artery and drained by a renal vein • Urine exits each kidney through a duct called the ureter • Both ureters drain into a common urinary bladder Figure 44.13a

32. Renal medulla Renal cortex Renal pelvis Ureter Section of kidney from a rat Figure 44.13b (b) Kidney structure Structure and Function of the Nephron and Associated Structures • The mammalian kidney has two distinct regions • An outer renal cortex and an inner renal medulla

33. Juxta- medullary nephron Cortical nephron Afferent arteriole from renal artery Glomerulus Bowman’s capsule Renal cortex Proximal tubule Peritubularcapillaries 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 Ascending limb Vasarecta (d) Filtrate and blood flow (c) Nephron Nephron • 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

34. Distal tubule Proximal tubule 4 1 NaCl Nutrients H2O HCO3 H2O K+ NaCl HCO3 H+ K+ H+ NH3 CORTEX Thick segment of ascending limb Descending limb of loop of Henle 2 3 Filtrate H2O Salts (NaCl and others) HCO3– H+ Urea Glucose; amino acids Some drugs NaCl H2O OUTER MEDULLA NaCl Thin segment of ascending limb Collecting duct 3 5 Key Urea NaCl H2O Active transport Passive transport INNER MEDULLA From Blood Filtrate to Urine: A Closer Look • Filtrate becomes urine as it flows through the mammalian nephron and collecting duct Figure 44.14

35. The Mammalian Kidney is an Adaptation • 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 • 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

36. 300 100 300 NaCl H2O Activetransport Osmolarity of interstitial fluid(mosm/L) 400 NaCl H2O Passivetransport 300 NaCl 100 H2O 300 300 CORTEX H2O OUTERMEDULLA NaCl H2O 200 400 400 600 H2O NaCl H2O H2O NaCl H2O H2O 400 600 600 900 H2O NaCl Urea H2O 900 H2O 700 Urea H2O INNERMEDULLA 1200 1200 Urea 1200 Osmolarity of Interstitial Fluid • Two solutes, NaCl and urea, contribute to the osmolarity of the interstitial fluid, which causes the reabsorption of water in the kidney and concentrates the urine Figure 44.15

37. Osmoreceptors in hypothalamus Thirst Hypothalamus Drinking reduces blood osmolarity to set point ADH Increased permeability Pituitary gland Distal tubule 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 Collecting duct Homeostasis: Blood osmolarity Hormones of the Kidney – Blood Osmolarity • Antidiuretic hormone (ADH) increases water reabsorption in the distal tubules and collecting ducts of the kidney (negative feedback system) Figure 44.16a (a) Antidiuretic hormone (ADH) enhances fluid retention by makingthe kidneys reclaim more water.

38. Homeostasis: Blood pressure, volume Increased Na+ and H2O reab- sorption in distal tubules STIMULUS: The juxtaglomerular apparatus (JGA) responds to low blood volume or blood pressure (such as due to dehydration or loss of blood) Aldosterone Arteriole constriction Adrenal gland Angiotensin II Distal tubule Angiotensinogen JGA Renin production Renin Hormones of the Kidney – Blood Pressure Volume • The renin-angiotensin-aldosterone system (RAAS) is part of a complex feedback circuit that functions in homeostasis • Another hormone, atrial natriuretic factor (ANF) opposes the RAAS Figure 44.16b (b) The renin-angiotensin-aldosterone system (RAAS) leads to an increasein blood volume and pressure.

39. 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) Environmental Adaptations of the Vertebrate Kidney Figure 44.18