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Ch. 44: REGULATING THE INTERNAL ENVIRONMENT I. Introduction A.Homeostasis: 1.Thermoregulation = Regulation of Body Temperature 2.Osmoregulation = Regulation of solute and water balance 3.Excretion = Control of Nitrogen containing waste B.Regulators v. Conformers: 1.Regulators: Maintain constant internal environment 2.Conformers: Allow for internal environment to change over a range of external conditions. II.Thermoregulation: Regulation of Body Temp. A. Q10 Effect: The rate at which an enzymemediated chemical reactions increases for every 10° C temperature increase. Ex. Rate of glycogen hydrolysis in a frog is 2.5 time greater at 30° C than 20° C. It’s Q10 for that reaction is 2.5. B.Temperature has a great effect on an animal’s ability to do work. C.Four physical processes account for heat gain or loss: 1.Conduction: direct transfer of thermal motion (heat) between molecules of objects in direct contact with each other, as when an animal sits on a pool of cold water or on a hot rock. 2.Convection: is the transfer of heat by the movement of air or liquid past a surface. 3.Radiation: is the emission of electromagnetic waves by all objects warmer than absolute zero, including an animal’s body, the environment, and the sun. Ex. Transfer of heat from animal’s body. 4.Evaporation: Loss of heat from liquid to gas. D.Sources of Body Heat: 1.Ectotherms: determined by the surrounding environment. 2.Endotherms: determined by metabolic rates. E.Advantages of endothermy: 1.High level of cellular respiration; allows for endotherms to perform vigorous activities much longer than ectotherms. 2.Stable body temperature allows for an endotherm to live in fluctuating temps, that are characteristics of terrestrial landscape. However, endothermy requires much more energy intake than ectothermy. Example: 20°C, a human at rest has a metabolic rate of 1,300 to 1,800 kcal/day and an American alligator, has a metabolic rate of only about 60 kcal per day at 20°C. F.Thermoregulation involves physiological and behavioral adjustments that balance heat gain and loss. Four categories of adpations that help animals thermoregulate: 1.Adjusting the rate of heat exchange between the animal and its surroundings: a.Insulation (hair, fur, feathers, fat) reduces the flow of heat between an animal and its environment. b.Adaptations of the circulatory system: Vasodilation: an increase in the diameter superficial blood vessels, increasing the transfer of body heat to a cool environment by radiation, conduction, and convection. Vasoconstriction: Reduces blood flow and heat transfer by decreasing the diameter of superficial vessels. Countercurrent heat exchanger: special arrangement of blood vessels that help trap heat in the body core; helps reduce heat loss in many endotherms. Heat from the body core in the arteries are transferred to the veins. 2.Cooling by evaporative heat loss: evaporation at skin and by breathing; as water evaporates, it also removes the heat. -Panting -Sweating -Bathing 3.Behavioral responses: Sun basking, lying in shade, hibernation, and migration, etc. 4.Changing the rate of metabolic heat production: greatly increase heat production when exposed to cold (will be discussed further in the next section) -Applies only to endotherms G.Endothermy: Mammals and Birds 1.Body temp range: mammals = 36-38° C birds = 39-42° C 2.Must counteract the constant heat loss to the environment by: a.High metabolic rate b.Shivering to produce heat c.Certain hormones can cause mitochondria to increase their metabolic activity and produce heat instead of ATP. This is called NST (Nonshivering Thermogenesis). It takes place throughout the body, and also in a specialized region called “brown fat.” d.Insulation: Hair, feathers, fat e.Vasodilation/Vasoconstriction f. Panting g.Sweating/Spreading saliva on body surfaces H.Ectothermy: Amphibians and Reptile 1.Body temp range: 7° to 25° C. 2.Behavioral adaptations: Moving to shade or sunny spots. 3.Galapagos Island Iguana: vasoconstrict their superficial blood vessels to conserve body heat. 4.Large Endothermic Reptiles: Female pythons, incubating eggs, increase their metabolic rates by shivering, generating heat (Dinosaurs endothermic??). I. Ectothermy: Fishes 1.Conformers: within 1-2° C of their surroundings. 2.Specialized endothermic fishes: powerful swimmers like bluefin tuna, swordfish, and great white sharks, have circulatory adaptations that retain metabolic heat in the body. -Endothermy in great white sharks: countercurrent heat exchanger in its swimming muscles. J. Ectothermy: Invertebrates 1.Aquatic Invertebrates: conformers 2.Terrestrial Invertebrates are actually endothermic as they can elevate body temp by moving their powerful flight muscles. -Bees and moths (Ex. Hawk moth) -Countercurrent heat exchanger at the thorax -Honeybee social behavior: huddle and shiver together in cold weather K.Feedback Mechanisms in Thermoregulation: 1.Nerve cells that regulate thermoregulation is concentrated in the hypothalamus. 2.The hypothalamus is like a thermostat, responding to changes in body temperature above and below a set point by activating mechanisms that promote heat loss or gain. L.Adjusting to Changing Temperature: 1.Many animals adjust to a new range of environmental temperatures over a period of days or weeks. This is called acclimatization. a.Acclimatization in birds and mammals: Adjust the amount of insulation (thicker coat of fur in the winter, etc), adjust the metabolic heat production. b.Acclimatization in ectotherms: process of compensating for changes in body temperature through adjustments in physiology and temperature tolerance. Ex. Winter-acclimated catfish can only survive temps as high as 28°C, but summer-acclimated fish can survive temps to 36°C. -Acclimation in ectotherms often include adjustments at the cellular level: Variant enzymes are produced that have the same function, but has a different optimal temperature. Membranes can also change the proportions of saturated and unsat. lipids they contain, which helps keep membranes fluid at different temps. Antifreeze chemical: prevents ice from forming in cells. Ex. Cryoprotectants Stress-Induced proteins (i.e., heatshock proteins): help maintain the integrity of other proteins that would otherwise be destroyed by heat. M.Torpor conserves energy during environmental extremes. 1.Torpor: a physiological state in which activity is low and metabolism decreases. 2.Hibernation: long-term torpor a.Body temp declines b.Low metabolic rate Allows for survival on limited supplies of energy Belding squirrel: hibernates for 8 months; body temp during hibernation is near freezing; arouses for a few hours every week or two. Body temp and metabolism during Hibernation of Belding’s ground squirrel: 3.Estivation: Summer torpor; slow metabolism and inactivity during high temps and when water is scarce. 4.Daily torpor: Small endotherms; occurs at night or during the day (during hours when they cannot feed). III.Water Balance and Waste Disposal A.Osmoregulation: management of water content and solute composition. B.Water balance and waste depends on transport epithelia. 1.Transport epithelium: layers of epithelial cells that move specific solutes in controlled amounts in particular directions. C.An animal’s nitrogenous wastes are correlated with is phylogeny and habitat. -Nitrogenous waste is produced when macromolecules are broken down for energy. -Nitrogen is removed in the form of ammonia. 1.Ammonia: small and very toxic molecule created when macromolecules are broken down. a.Can only be tolerated at low concentrations requires access to lots of water. b.Ammonia release is common in aquatic species. c.Released easily by diffusion to the surrounding water. -Marine invertebrates: Diffuses across the entire body surface. -Fish: lost as ammonium ions (NH4+) across the epithelium of gills, while the kidneys extract minor amounts of nitrogenous wastes. 2.Urea: Made in the liver by combining ammonia with carbon dioxide and excreted by the kidneys. a.Low toxicity allows for animals to store and transport urea safetly at high concentrations. b.Disadvantage: Requires energy to convert ammonia into urea. 3.Uric Acid: Land snails, insects, birds, and reptiles excrete uric acid. a.Insoluble in water and can be excreted as a semisolid paste with very little water loss (advantage). b.Disadvantage: Requires a considerable amount of ATP to synthesize it from ammonia. D.Osmoregulation: 1.Osmoconformers: internal osmolarity is the same as that of its environment. Osmoconformers often live in water that has a very stable composition. 2.Osmoregulator: animals that must control their internal osmolarity. 3.Most animals are stenohalines (animals that cannot tolerate substantial changes in external osmolarity. 4.Euryhalines are animals that can survive large fluctuations of external osmolarity. Example: Salmon migrate back and forth between fresh and salt water. E.Maintaining water balance in the sea: 1.Most marine invertebrates are osmoconformers. 2.Marine fishes (Class Osteichthyes) constantly lose water through their skin and gills. -gain water through food, and drinking large volumes of water (with salt disposed by active transport out of the gills) -very little urine is produced 3.Cartilagenous fish, like sharks (Class Chondrichthyes) do not have large water loss due to high concentrations of urea in their body fluids, along with trimethylamine oxide (TMAO), which protects proteins from the urea; body is hyperosmotic to seawater. F.Maintaining osmotic balance in freshwater: 1.Since freshwater fish are hypotonic to their surroundings, they are constantly gaining water by osmosis. 2.Freshwater fish excrete large amounts of very dilute urine and regain lost salts in food. 3.Paramecium have a contractile vacuole to pump water out: 4.Salmon must adjust to different environments as they migrate from freshwater to saltwater. Ocean: Salmon drink seawater and excrete salt from their gills. Freshwater: Salmon cease drinking, begin to produce lots of dilute urine and their gills take in salt from water. Freshwater fish are hypertonic to their environment. Saltwater fish are hypotonic to their environment. G.Special Problems of Living in Temporary Waters: Anhydrobiosis (“life without water”) 1.Example: Tardigrades, or water bears -Tiny invertebrates -Active, hydrated state (85%) -Inactive, dehydrate state (2%); can survive in this state for decades Active State Inactive State H.Maintaining Water Balance On Land: 1.Loss of water = Largest problem for terrestrial organisms 2.Adaptations: -Waxy cuticle -Skin -Drinking water and eating moist food IV.Excretory Systems A. An Overview: 1.Urine is produced in two steps: a. Body fluid is collected – Filtration b. Reabsorbtion 2.Filtrate: water and small solutes, such as salts, sugars, amino acids, and nitrogenous wastes After filtration, the filtrate is modified in the excretory tubule as valuable substances from the filtrate are reabsorbed. B.Diverse excretory systems: 1. Protonephridia: Flame-Bulb System a.Network of dead-end tubules lacking internal openings. b.Tubes branch throughout body, capped by a flame bulb. c.Cilia draws water and solutes into flame bulb. d.Urine is moved outwards through the nephridiopores. e.Urine = dilute f. Most metabolic waste diffuses out across the body surface or into body cavity and out through mouth 2.Metanephridia: tubular excretory system -Internal openings that collect body fluid -Ciliated funnel, the nephrostome, which collects fluids from coelom -Each body segment contains a pair of metanephridia 3.Malpighian Tubules: In insects and terrestrial arthropods -Remove nitrogenous wastes and osmoregulate -Tubes open to digestive tract and the tips are immersed in the hemolymph -Epithelial lining the tubules secrete solutes and nitrogen wastes -Water follows the solutes into tubule -Most solutes are pumped back into the hemolymph -Water follows the solutes, and nitrogen waste (uric acid) is eliminated as dry matter (conserves water!) 4.Vertebrate Kidneys: -Functions: osmoregulation and excretion -Compact, hightly organized tubules -Associated with capillaries and ducts -Mammals have a pair of kidneys: Bean shape Supplied with blood by the renal artery and a renal vein Urine exits each kidney through a duct called the ureter Each ureter drains into the bladder Urine is expelled through a tube called the urethra Female and Male urinary tracts C.Structure and Function of the Nephron and their Associated Structures: 1.Two distinct regions of the kidney: a. Renal Cortex b. Renal Medulla 2.Nephron = the functional unit of the kidney 3.A nephron is a long tubule and a ball of capillaries called the glomerulus 4.Bowman’s capsule: the end of the tubule that surrounds the glomerulus. 5.Average human kidney has a million nephrons, with a total tubule length of 80 km. 6.Filtration of blood: -Blood pressure forces fluid from blood in the glomerulus into the lumen of Bowman’s capsule -Specialized cells called podocytes are permeable to solutes and water -Filtrate: salts, glucose, and vitamins; & nitrogenous wastes 7.Pathway of the Filtrate - Passes through 3 regions of the nephron: Proximal tubules Loop of Henle Distal Tube (empties into collecting duct) 8.Two types of nephrons: -Cortical (reduced or no loop of henle) -Juxtamedullary well-developed loop of henle; goes into renal medulla) 9.Blood vessels associated with Nephrons: Key: 1.Bowman's capsule 2.Glomerulus 3.Afferent arteriole 4.Efferent arteriole 5.Proximal convoluted tubule 6.Distal convoluted tubule 7.Collecting duct 8.Loop of Henle 9.Peritubular capillary D.From Blood Filtrate to Urine: 1.Inside the proximal tubule: -maintain pH by secretion of H+, & ammonia. -HCO3- absorbed -Drugs/poison pass from the peritubular capillaries -Absorption of nutrients from filtrate -Reabsorption of NaCl and water 2.Inside the descending limb of the loops of Henle: -Water is reabsorption as the filtrate moves down the loop. 3.Inside the Ascending limb of the loop of Henle: -NaCl diffuses out -Filtrate becomes more dilute 4.Inside the distal tube: -K+ is secreted into the filtrate -NaCl is reabsorbed -pH is regulated (H+ and HCO3-) 5.Inside the collecting duct: -NaCl, Urea, and H2O is reabsorbed; the filtrate is hyperosmotic. E.The mammalian kidney’s ability to conserve water is a key terrestrial adaptation: The Two Solute Model: Osmolarity Of Interstitial Fluid Increases The cooperative action and precise arrangement of the loops of Henle and the collecting ducts are largely responsible for the osmotic gradients that concentrates the urine. F.Regulation of blood osmolarity is maintained by hormonal control of the kidney by negative feedback: 1.ADH (Antidiuretic Hormone): produced by the hypothalamus and stored in and released by the pituitary gland. a.Osmoreceptors cells in the hypothalamus monitor osmolarity of blood. b.Osmolarity rises: more ADH is released c.Increases permeability of the epithelium to water Water is absorbed at the distal tubes so that water is retained d.ADH also causes thirst Alcohol disturbs water balance by inhibiting the release of ADH, causing excessive water loss and dehydration. 2.The Renin-Angiotensin-Aldosterone System (RAAS): a.A drop in blood pressure or low blood volume triggers a release of renin from the juxtaglomerular apparatus (JGA). b.Renin converts Angiotensinogen into Angiotensin II, which stimulates the Adrenal glands (on kidneys) to release Aldosterone. This hormone causes the distal tubes to reabsorb NaCl and water. c.Angiotensin II raises blood pressure and blood volume by constricting arterioles. It also stimulates the proximal tubes to reabsorb NaCl and water. 3.ADH is released when the body is dehydrated or when there is excessive water loss. 4.RAAS will be stimulated when there is excessive loss of salt and body fluids due to an injury. 5.Atrial Natriuretic Factor (ANF): a hormone that opposes the RAAS response. -Atria of heart releases ANF in response to an increase in blood volume and pressure -ANF inhibits the release of renin and also inhibits the reabsorption of NaCl -Reduces aldosterone release -Lowers blood volume and pressure G.Diverse adaptations of the kidney: 1.Most mammals have a very long loop of Henle so to conserve as much water as possible. 2.Beavers have very short loops because they do not face the problem of dehydration. 3.Birds have kidneys with specialized juxtamedullary nephrons; shorter loop of Henle, but their main way of water conservation is by producing uric acid. 4.Reptiles have only cortical nephrons and their urine is isoosmotic to body fluids. However, their cloaca reabsorbs some water from their feces and urine. Also, they produce uric acid. 5.Freshwater fish produce very dilute urine. They conserve salts by reabsorbing them in the nephrons. 6.Amphibians in freshwater accumulate salts by active transport; they excrete very dilute urine. On land, they conserve water by reabsorbing water across the epithelium of their bladder. 7.Marine fish excrete very concentrated urine.