control of the internal environment: homeostatic control ap biology ch. 44

Control of the Internal Control of the Internal Environment: Homeostatic Environment: Homeostatic

ControlControl

AP BiologyAP Biology

Ch. 44Ch. 44

ThermoregulationThermoregulation 4 physical processes 4 physical processes

account for heat gain/lossaccount for heat gain/loss ConductionConduction—direct transfer —direct transfer

of heat between of heat between environment and the body environment and the body (hot (hot ➞➞coldcold))

ConvectionConvection—transfer of —transfer of heat by movement of air or heat by movement of air or liquid past the body surfaceliquid past the body surface

RadiationRadiation—emission of —emission of electromagnetic waves electromagnetic waves produced by warmer produced by warmer objects (body and sun)objects (body and sun)

EvaporationEvaporation—loss of heat —loss of heat from the surface of a liquidfrom the surface of a liquid

Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

Ectotherms v. EndothermsEctotherms v. Endotherms

EctothermsEctotherms Derive body heat from environmentDerive body heat from environment Most invertebrates, fishes, amphibians, Most invertebrates, fishes, amphibians,

and reptilesand reptiles EndothermsEndotherms

Derive body heat from metabolismDerive body heat from metabolism Mammals, birds, some fishes, and Mammals, birds, some fishes, and

numerous insectsnumerous insects

Endothermic AdvantagesEndothermic Advantages

High and stable body temperatures, along High and stable body temperatures, along with other biochemical and physiological with other biochemical and physiological adaptations, give these animals very high adaptations, give these animals very high levels of aerobic metabolism. levels of aerobic metabolism. This allows endotherms to perform vigorous This allows endotherms to perform vigorous

activity for much longer than is possible for activity for much longer than is possible for ectotherms.ectotherms.

Solves problem of living on landSolves problem of living on land Can maintain stable internal temperature when Can maintain stable internal temperature when

faced with fluctuating environmental faced with fluctuating environmental temperaturestemperatures

Thermoregulation involves Physiological and Thermoregulation involves Physiological and Behavioral AdaptationsBehavioral Adaptations

Adjusting the rate of heat exchange between Adjusting the rate of heat exchange between the animal and its surroundingsthe animal and its surroundings Insulation, such as hair, feathers, and fat located Insulation, such as hair, feathers, and fat located

just beneath the skin, reduces the flow of heat just beneath the skin, reduces the flow of heat between an animal and its environment.between an animal and its environment.

Other mechanisms usually involve adaptations of Other mechanisms usually involve adaptations of the circulatory system.the circulatory system.

VasodilationVasodilation, expansion of the diameter of , expansion of the diameter of superficial blood vessels, elevates blood flow in superficial blood vessels, elevates blood flow in the skin and typically increases heat transfer to a the skin and typically increases heat transfer to a cool environment.cool environment.

VasoconstrictionVasoconstriction reduces blood flow and heat reduces blood flow and heat transfer by decreasing the diameter of superficial transfer by decreasing the diameter of superficial vessels.vessels.


Another circulatory adaptation is a special Another circulatory adaptation is a special arrangement of blood vessels called a arrangement of blood vessels called a countercurrent heat exchangercountercurrent heat exchanger that helps trap that helps trap heat in the body core and reduces heat loss.heat in the body core and reduces heat loss. For example, marine mammals and many birds For example, marine mammals and many birds

living in cold environments face the problem of living in cold environments face the problem of losing large amounts of heat from their losing large amounts of heat from their extremities as warm arterial blood flows to the extremities as warm arterial blood flows to the skin.skin.

However, arteries carrying warm However, arteries carrying warm blood are in close contact with blood are in close contact with veins conveying cool blood back veins conveying cool blood back toward the trunk. toward the trunk.



Cooling by evaporative heat loss.Cooling by evaporative heat loss. Terrestrial animals lose water by evaporation Terrestrial animals lose water by evaporation

across the skin and when they breathe. across the skin and when they breathe. Water absorbs considerable heat when it Water absorbs considerable heat when it

evaporates.evaporates. Some organisms can augment this cooling Some organisms can augment this cooling

effect.effect. For example, most mammals and birds can For example, most mammals and birds can

increase evaporation from the lungs by increase evaporation from the lungs by panting.panting.

Sweating or bathing to make the skin wet Sweating or bathing to make the skin wet also enhances evaporative cooling.also enhances evaporative cooling.


Behavioral responses.Behavioral responses. Both endotherms and ectotherms use Both endotherms and ectotherms use

behavioral responses, such as changes in behavioral responses, such as changes in posture or moving about in their environment, posture or moving about in their environment, to control body temperature.to control body temperature.

Many terrestrial animals will bask in the sun or Many terrestrial animals will bask in the sun or on warm rocks when cold and find cool, shaded, on warm rocks when cold and find cool, shaded, or damp areas when hot.or damp areas when hot.

Many ectotherms can maintain a very constant Many ectotherms can maintain a very constant body temperature by these simple behaviors.body temperature by these simple behaviors.

More extreme behavioral adaptations in some More extreme behavioral adaptations in some animals include hibernation or migration to a animals include hibernation or migration to a more suitable climate.more suitable climate.


Changing the rate of metabolic heat Changing the rate of metabolic heat production.production. Many species of birds and mammals can Many species of birds and mammals can

greatly increase their metabolic heat greatly increase their metabolic heat production when exposed to cold.production when exposed to cold.

Feedback Mechanisms in Feedback Mechanisms in ThermoregulationThermoregulation


OsmoregulationOsmoregulation

Largely based on controlling Largely based on controlling movements of solutes between movements of solutes between internal fluids and the external internal fluids and the external environment.environment. This also regulates water movement, This also regulates water movement,

which follows solutes by osmosis.which follows solutes by osmosis. Animals must also remove metabolic Animals must also remove metabolic

waste products before they accumulate waste products before they accumulate to harmful levels.to harmful levels.

Nitrogenous WastesNitrogenous Wastes Nitrogenous breakdown products of proteins and Nitrogenous breakdown products of proteins and

nucleic acids are among the most important nucleic acids are among the most important wastes in terms of their effect on osmoregulation. wastes in terms of their effect on osmoregulation.

During their breakdown, enzymes remove During their breakdown, enzymes remove nitrogen in the form of nitrogen in the form of ammoniaammonia, a small and , a small and very toxic molecule.very toxic molecule.

In general, the In general, the kindskinds of nitrogenous wastes of nitrogenous wastes excreted depend on an animal’s evolutionary excreted depend on an animal’s evolutionary history and habitat --especially water availability.history and habitat --especially water availability. The The amountamount of nitrogenous waste produced is of nitrogenous waste produced is

coupled to the energy budget and depends on coupled to the energy budget and depends on how much and what kind of food an animal how much and what kind of food an animal eats.eats.

Nitrogenous WastesNitrogenous Wastes


Animals that excrete nitrogenous wastes as Animals that excrete nitrogenous wastes as ammonia need access to lots of water.ammonia need access to lots of water.

This is because ammonia is very soluble but This is because ammonia is very soluble but can only be tolerated at very low can only be tolerated at very low concentrations.concentrations.

Therefore, ammonia excretion is most Therefore, ammonia excretion is most common in aquatic species.common in aquatic species.

Many invertebrates release ammonia across Many invertebrates release ammonia across the whole body surface.the whole body surface.

In fishes, most of the ammonia is lost as In fishes, most of the ammonia is lost as ammonium ions (NHammonium ions (NH44

++) at the gill epithelium.) at the gill epithelium. Freshwater fishes are able to exchange NHFreshwater fishes are able to exchange NH44

++ for for NaNa++ from the environment, which helps maintain from the environment, which helps maintain NaNa++ concentrations in body fluids. concentrations in body fluids.

Maintaining Water BalanceMaintaining Water Balance

OsmoconformerOsmoconformer Available for marine fish to be isoosmotic Available for marine fish to be isoosmotic

with its saltwater environmentwith its saltwater environment OsmoregulatorOsmoregulator

Adjusts internal osmolarityAdjusts internal osmolarity Discharges excess water if it lives in a Discharges excess water if it lives in a

hypoosmotic environmenthypoosmotic environment Or, continuously takes in water to offset Or, continuously takes in water to offset

osmotic loss if it lives in a hyperosmotic osmotic loss if it lives in a hyperosmotic environmentenvironment

Osmoregulation in Marine and Osmoregulation in Marine and Freshwater FishesFreshwater Fishes


Excretory SystemsExcretory Systems

While excretory systems are diverse, While excretory systems are diverse, nearly all produce urine by a two-nearly all produce urine by a two-step process.step process. First, body fluid (blood, coelomic fluid, or First, body fluid (blood, coelomic fluid, or

hemolymph) is collected.hemolymph) is collected. Second, the composition of the collected Second, the composition of the collected

fluid is adjusted by fluid is adjusted by selective selective reabsorptionreabsorption or or secretionsecretion of solutes. of solutes.

Most excretory systems Most excretory systems produce a filtrate by produce a filtrate by pressure-filtering body pressure-filtering body fluids into tubules.fluids into tubules. This filtrate is then This filtrate is then

modified by the modified by the transport epithelium transport epithelium which reabsorbs which reabsorbs valuable substances, valuable substances, secretes other secretes other substances, like substances, like toxins and excess toxins and excess ion, and then ion, and then excretes the contents excretes the contents of the tubule. of the tubule.


Fig. 44.17

The initial fluid collection usually The initial fluid collection usually involves involves filtrationfiltration through the through the selectively permeable membranes of selectively permeable membranes of transport epithelia.transport epithelia. These membranes retain cells as well as These membranes retain cells as well as

proteins and other large molecules from proteins and other large molecules from the body fluids.the body fluids.

Hydrostatic pressure forces water and Hydrostatic pressure forces water and small solutes, such as salts, sugars, small solutes, such as salts, sugars, amino acids, and nitrogenous wastes, amino acids, and nitrogenous wastes, collectively called the collectively called the filtratefiltrate, into the , into the excretory system.excretory system.


Fluid collection is largely Fluid collection is largely nonselective.nonselective. Excretory systems use active transport to Excretory systems use active transport to

selectively reabsorb valuable solutes selectively reabsorb valuable solutes such as glucose, certain salts, and amino such as glucose, certain salts, and amino acids.acids.

Nonessential solutes and wastes are left Nonessential solutes and wastes are left in the filtrate or added to it by selective in the filtrate or added to it by selective secretion.secretion.

The pumping of various solutes also The pumping of various solutes also adjusts the osmotic movement of water adjusts the osmotic movement of water into or out of the filtrate.into or out of the filtrate.


MetanephridiumMetanephridium, another tubular , another tubular excretory system, consists of internal excretory system, consists of internal openings that collect body fluids from the openings that collect body fluids from the coelom through a ciliated funnel, the coelom through a ciliated funnel, the nephrostome, and release the fluid through nephrostome, and release the fluid through the nephridiopore.the nephridiopore. Found in most annelids, each segment of Found in most annelids, each segment of

a worm has a pair of metanephridia. a worm has a pair of metanephridia.


Fig. 44.19

An earthworm’s metanephridia have An earthworm’s metanephridia have both excretory and osmoregulatory both excretory and osmoregulatory functions.functions. As urine moves along the tubule, the As urine moves along the tubule, the

transport epithelium bordering the lumen transport epithelium bordering the lumen reabsorbs most solutes and returns them reabsorbs most solutes and returns them to the blood in the capillaries.to the blood in the capillaries.

Nitrogenous wastes remain in the tubule Nitrogenous wastes remain in the tubule and are dumped outside.and are dumped outside.

Because earthworms experience a net Because earthworms experience a net uptake of water from damp soil, their uptake of water from damp soil, their metanephridia balance water influx by metanephridia balance water influx by producing dilute urine. producing dilute urine.


Insects and other terrestrial arthropods Insects and other terrestrial arthropods have organs called have organs called Malpighian tubulesMalpighian tubules that remove nitrogenous wastes and also that remove nitrogenous wastes and also function in osmoregulation.function in osmoregulation. These open into the These open into the

digestive system digestive system and dead-end at and dead-end at tips that are tips that are immersed in immersed in the hemolymph. the hemolymph.


Fig. 44.20

Mammals have a pair of bean-shaped Mammals have a pair of bean-shaped kidneys.kidneys. These are supplied with blood by a These are supplied with blood by a renal renal

arteryartery and a and a renal veinrenal vein.. In humans, the kidneys account for less In humans, the kidneys account for less

than 1% of body weight, but they receive than 1% of body weight, but they receive about 20% of resting cardiac output. about 20% of resting cardiac output.

Nephrons and associated blood Nephrons and associated blood vessels are the functional units of vessels are the functional units of

the mammalian kidneythe mammalian kidney


Urine exits each kidney through a Urine exits each kidney through a duct called the duct called the ureterureter, and both , and both ureters drain through a common ureters drain through a common urinary bladderurinary bladder.. During urination, urine is expelled from During urination, urine is expelled from

the urinary bladder through a tube called the urinary bladder through a tube called the the urethraurethra, which empties to the , which empties to the outside near the vagina in females or outside near the vagina in females or through the penis in males.through the penis in males.

Sphincter muscles near the junction of Sphincter muscles near the junction of the urethra and the bladder control the urethra and the bladder control urination. urination.


The mammalian kidney has two distinct The mammalian kidney has two distinct regions, an outer regions, an outer renal cortexrenal cortex and an and an inner inner renal medullarenal medulla.. Both regions are packed with microscopic Both regions are packed with microscopic

excretory tubules, excretory tubules, nephronsnephrons, and their , and their associated blood vessels.associated blood vessels.

Each nephron consists of a single long Each nephron consists of a single long tubule and a ball of capillaries, called the tubule and a ball of capillaries, called the glomerulusglomerulus..

The blind end of the tubule forms a cup-The blind end of the tubule forms a cup-shaped swelling, called shaped swelling, called Bowman’s Bowman’s capsulecapsule, that surrounds the glomerulus., that surrounds the glomerulus.

Each human kidney packs about a million Each human kidney packs about a million nephrons. nephrons.



Fig. 44.21

Filtration occurs as blood pressure Filtration occurs as blood pressure forces fluid from the blood in the forces fluid from the blood in the glomerulus into the lumen of glomerulus into the lumen of Bowman’s capsule.Bowman’s capsule. The porous capillaries, along with The porous capillaries, along with

specialized capsule cells called specialized capsule cells called podocytes, are permeable to water and podocytes, are permeable to water and small solutes but not to blood cells or small solutes but not to blood cells or large molecules such as plasma proteins.large molecules such as plasma proteins.

The filtrate in Bowman’s capsule contains The filtrate in Bowman’s capsule contains salt, glucose, vitamins, nitrogenous salt, glucose, vitamins, nitrogenous wastes, and other small molecules. wastes, and other small molecules.


From Bowman’s capsule, the filtrate From Bowman’s capsule, the filtrate passes through three regions of the passes through three regions of the nephron: the nephron: the proximal tubuleproximal tubule; the ; the loop of Henleloop of Henle, a hairpin turn with a , a hairpin turn with a descending limb and an ascending descending limb and an ascending limb; and the limb; and the distal tubuledistal tubule.. The distal tubule empties into a The distal tubule empties into a

collecting ductcollecting duct, which receives , which receives processed filtrate from many nephrons.processed filtrate from many nephrons.

The many collecting ducts empty into the The many collecting ducts empty into the renal pelvis, which is drained by the renal pelvis, which is drained by the ureter. ureter.


In the human kidney, about 80% of In the human kidney, about 80% of the nephrons, the the nephrons, the cortical cortical nephronsnephrons, have reduced loops of , have reduced loops of Henle and are almost entirely Henle and are almost entirely confined to the renal cortex.confined to the renal cortex. The other 20%, the The other 20%, the juxtamedullary juxtamedullary

nephronsnephrons, have well-developed loops , have well-developed loops that extend deeply into the renal that extend deeply into the renal medulla.medulla.

It is the juxtamedullary nephrons that It is the juxtamedullary nephrons that enable mammals to produce urine that is enable mammals to produce urine that is hyperosmotic to body fluids, conserving hyperosmotic to body fluids, conserving water. water.


The nephron and the collecting duct The nephron and the collecting duct are lined by a transport epithelium are lined by a transport epithelium that processes the filtrate to form the that processes the filtrate to form the urine.urine. Their most important task is to reabsorb Their most important task is to reabsorb

solutes and water.solutes and water. The nephrons and collecting ducts The nephrons and collecting ducts

reabsorb nearly all of the sugar, reabsorb nearly all of the sugar, vitamins, and other organic nutrients vitamins, and other organic nutrients from the initial filtrate and about 99% of from the initial filtrate and about 99% of the water.the water.

This reduces 180 L of initial filtrate to This reduces 180 L of initial filtrate to about 1.5 L of urine to be voided. about 1.5 L of urine to be voided.


Filtrate from Bowman’s capsule flows Filtrate from Bowman’s capsule flows through the nephron and collecting through the nephron and collecting ducts as it becomes urine. ducts as it becomes urine.


Fig. 44.22

Structure Function

Proximal tubule Reabsorbs 75% NaCl and water of filtrate. Glucose and amino acids are reabsorbed unless their

conc. Is higher than the absorptive capacity. Glucose in urine is a sign of diabetes.

Decending loop of Henle

Freely permeable to water but not NaCl. Assists in control of water and salt conc.

Ascending loop of Henle

Freely permeable to NaCl but not water Assists in control of salt conc.

Distal tubule Regulates conc. Of K+ and NaCl Helps control pH by reabsorbing HCO3

- and secreting

H+

Collecting duct Determines how much salt is actually lost in urine Osmotic gradient created in the earlier regions of the

nephron allows the kidney control in the final conc. of the urine

The ability of the The ability of the mammalianmammaliankidney to convertkidney to convertinterstitial fluidinterstitial fluidat 300 mosm/Lat 300 mosm/Lto 1,200 mosm/Lto 1,200 mosm/Las urine dependsas urine dependson a counter-on a counter-current multiplier current multiplier betweenbetweenthe ascending the ascending and descending and descending limbslimbsof the loopof the loopof Henle. of Henle.


Fig. 44.23

As the filtrate flows from the cortex to the As the filtrate flows from the cortex to the medulla in the descending limb of the loop of medulla in the descending limb of the loop of Henle, water leaves the tubule by osmosis.Henle, water leaves the tubule by osmosis. The osmolarity of the filtrate The osmolarity of the filtrate

increases as solutes, including increases as solutes, including NaCl, become more concentrated. NaCl, become more concentrated.

The highest osmolarity occurs at the The highest osmolarity occurs at the elbow of the loop of Henle. elbow of the loop of Henle.

This maximizes the diffusion of salt This maximizes the diffusion of salt out of the tubule as the filtrate out of the tubule as the filtrate rounds the curve and enters rounds the curve and enters the ascending limb, which is permeable to salt the ascending limb, which is permeable to salt but not to water.but not to water.

The descending limb produces progressively The descending limb produces progressively saltier filtrate, and the ascending limb exploits saltier filtrate, and the ascending limb exploits this concentration of NaCl to help maintain a this concentration of NaCl to help maintain a high osmolarity in the interstitial fluid of the high osmolarity in the interstitial fluid of the renal medulla.renal medulla.


The loop of Henle has several The loop of Henle has several qualities of a countercurrent system.qualities of a countercurrent system. Although the two limbs of the loop are Although the two limbs of the loop are

not in direct contact, they are close not in direct contact, they are close enough to exchange substances through enough to exchange substances through the interstitial fluid.the interstitial fluid.

The nephron can concentrate salt in the The nephron can concentrate salt in the inner medulla largely because exchange inner medulla largely because exchange between opposing flows in the between opposing flows in the descending and ascending limbs descending and ascending limbs overcomes the tendency for diffusion to overcomes the tendency for diffusion to even out salt concentrations throughout even out salt concentrations throughout the kidney’s interstitial fluid.the kidney’s interstitial fluid.



Fig. 44.24a


Fig. 44.24b

control of the internal environment: homeostatic control ap biology ch. 44

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