Chapter 40 Maintaining the Internal Environment

Albia Dugger • Miami Dade College

Chapter 40Maintaining the

Internal Environment

40.1 Truth in a Test Tube

• Kidneys rid the body of excess water, excess or harmful solutes, and drugs

• Physicians routinely check urine to monitor their patient’s health

• Athletic associations use urine tests to check for performance-enhancing substances as well as “street drugs”

17th Century Physician Examining a Urine Specimen

40.2 Regulating Fluid Volume and Composition

• All animals constantly acquire and lose water and solutes, and produce metabolic wastes

• Excretory organs keep the volume and the composition of their internal environment – the extracellular fluid – stable

• Metabolic wastes, particularly carbon dioxide and ammonia, affect the composition of the extracellular fluid

Products of Protein Breakdown

C uric acid

D urea

A amino group B ammonia

How Invertebrates Maintain Fluid Balance

• Marine invertebrates usually have body fluids with the same solute concentration as seawater – osmosis produces no net movement of water into or out of the body

• In planarian flatworms and other freshwater animals, body fluids have a higher solute concentration than the surrounding water, so water enters by osmosis

Flatworms and Earthworms

• Flatworms and earthworms have tubular excretory organs that deliver fluid with dissolved ammonia to a pore at the body surface

• Flatworms have protonephridia with ciliated flame cells

• Earthworms have nephridia that collect coelomic fluid

Planarian Protonephridia

nucleus offlame cell

pore at bodysurface

spacesthroughwhich waterenters tube

cilia offlame cell

Earthworm Nephridia

pore through which waste exits

funnel that collectscoelomic fluid

storage bladder

loops where exchangeswith blood in adjacentvessels occur

Arthropods

• Insects convert ammonia to uric acid crystals, which Malpighian tubules deliver to the gut

• Excreting uric acid rather than ammonia reduces water loss

Malpighian Tubules

part of gut

Malpighiantubule

Fluid Regulation in Vertebrates

• Vertebrates have a urinary system that filters water, metabolic wastes and toxins out of the blood, and reclaims water and certain solutes

• All vertebrates have paired kidneys – excretory organs that

filter blood and adjust the level of solutes

Fluid Balance in Fishes

• Bony fishes have body fluid that is saltier than freshwater, but less salty than seawater

• Marine fish drink water, pump excess salt out through gills, and produce small amounts of urine

• Freshwater fish do not drink, and produce large amounts of dilute urine

Marine Bony Fishes

water loss by osmosis

A Marine bony fish with body fluids less salty than the surroundingwater; the fish is hypotonic relative to its environment.

cells in gillspump solutes out

gulpswater

water loss in very small volumeof concentrated urine

Freshwater Bony Fishes

water loss in large volumeof dilute urine

B Freshwater bony fish with body fluids saltier than the surroundingwater; the fish is hypertonic relative to its environment.

does notdrink water

cells in gillspump solutes in

water gain by osmosis

Land Vertebrates

• Waterproof skin and highly efficient kidneys help adapt amniotes to land

• Reptiles and birds conserve water by converting ammonia to uric acid

• Mammals excrete urea, which requires 20 times more water to excrete than uric acid

• Mammals with limited access to fresh water tend to have large kidneys for their size and lose little water in their urine

Comparing Fluid Balance

Take-Home Message: Volume and composition of body fluid

• All animals must rid the body of waste carbon dioxide and ammonia; many convert ammonia to urea or uric acid before excreting it.

• Most animals have excretory organs that interact with a circulatory system to remove wastes from the blood and excrete them.

Take-Home Message: (cont.)

• Invertebrate excretory organs include the ammonia-excreting nephridia of earthworms and the uric acid–excreting Malpighian tubules of insects.

• All vertebrates have two kidneys. The volume of urine and the type of nitrogen-containing wastes excreted (ammonia, urea, or uric acid) vary among groups

40.3 The Human Urinary System

• Kidneys filter blood and form urine:• Fibrous outer layer (renal capsule)• Two inner zones: renal cortex and renal medulla

• The body reclaims most of the filtrate; urine flows through ureters into a bladder that stores it

• Urine flows out of the body through the urethra

Figure 40-8a p718

UrethraUrine flow channelbetween urinarybladder andbody surface

Kidney (one of a pair)Blood-filtering organ;filters water, all solutesexcept proteins fromblood; reclaims onlyamounts body requires,excretes rest as urine

Ureter (one of a pair)Channel for urine flowfrom one kidney tourinary bladder

Urinary BladderStretchable urinestorage container

inferiorvena cava

heart

diaphragm

adrenalgland

abdominalaorta

Figure 40-8bc p718

renalvein

renalmedulla

renalpelvis

renalartery

ureter

renal cortex

renalcapsule

abdominalcavity

(front of body)

(back of body)

rightkidney

leftkidney

backbone

peritoneum

ANIMATED FIGURE: Human urinary system

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Nephron Structure

• Nephron• A microscopic tube with a wall one cell thick• Begins in the cortex, where it folds to form a cup-shaped

Bowman’s capsule• Enters the medulla as a proximal tubule, turns at the

loop of Henle, reenters the cortex as a distal tubule which drains into a collecting duct

Blood Vessels Around Nephrons

• Renal arteries branch into afferent arterioles, which branch into a capillary bed (glomerulus) inside a Bowman’s capsule, which filters blood

• Efferent arterioles branch into peritubular capillaries around the nephron, which converge into venules and veins leaving the kidney

Figure 40-9a p719

A Nephrons extend from thecortex into the medulla.

Figure 40-9b p719

RenalMedulla

B Tubular portion of one nephron, cutawayview. The tubule starts at Bowman’s capsule.

Bowman’scapsule

(red)

proximaltubule

(orange)

distaltubule

(brown)

loop of Henle(yellow)

collectingtubule (tan)

RenalCortex

Figure 40-9c p719

renalvein

C Blood vessels associated with the nephron. The glomerulusis a ball of capillaries that have unusually leaky walls.

efferent arteriole

glomerulus

afferent arteriole

peritubularcapillaries

renalartery

ANIMATED FIGURE: Human kidney



Take-Home Message: Components of the human urinary system

• The human urinary system has two kidneys, two ureters, a urinary bladder, and a urethra. Kidneys filter the blood and form urine. Urine flows out of the kidney through ureters, and into a hollow, muscular bladder. When the bladder contracts, urine flows out of the body through the urethra.

• The functional unit of the kidneys is the nephron, a microscopic tubule that interacts with two systems of capillaries to filter blood and form urine.

ANIMATION: Tubular reabsorption



40.4 How Urine Forms

• Urine consists of water and solutes filtered from blood and not returned to it, plus unwanted solutes secreted from blood into the nephron’s tubular regions

• Urine forms by three physiological processes: glomerular filtration, tubular reabsorption, and tubular secretion

Glomerular Filtration

• Glomerular filtration is the first step in urine formation

• Occurs at glomerular capillaries in Bowman’s capsule

• The force of the heartbeat drives protein-free plasma out of glomerular capillaries and into the nephron’s tubular portion as filtrate

Figure 40-10a p720

glomerulus insideBowman’s capsule

Figure 40-10b p720

afferent arteriole(from renal artery)

glomerulus insideBowman’s capsule

filtrate (toproximaltubule)

outer wall ofBowman’s capsule

efferent arteriole(to peritubularcapillaries)

Tubular Reabsorption

• Tubular reabsorption returns most water and solutes to the blood

• Occurs all along a nephron’s tubular parts

• Nearly all water and solutes that leave the blood as filtrate later leave the tubule and return to the blood in peritubular capillaries

Tubular Secretion

• Tubular secretion is the movement of substances from the blood in peritubular capillaries into the filtrate

• Starts at the proximal tubule and continues all along a nephron’s tubular parts

• Urine forms from water and solutes that remain in the tubule, and solutes secreted into the tubule along its length

Concentrating the Urine

• Concentration of urine flowing down through the loop of Henle sets up a solute concentration gradient in surrounding interstitial fluid of the renal medulla

• This gradient allows urine to become concentrated as it flows through the collecting duct to the renal pelvis

• The body can adjust how much water is reabsorbed at distal tubules and collecting tubules

Urine Formation

Bowman’scapsule

renal cortex

renal medulla

collectingtubule

increasing soluteconcentration ininterstitial fluid

Glomerularfiltration

proximal tubule

ascending armof loop of Henle

Tubularreabsorption

Tubularsecretion

H+

distal tubule

peritubular capillary

H2O

H2O

H2O

Na+, Cl–, K+,nutrients, H2O Na+, Cl–,

H2O

descending armof loop of Henle

H+, K+

Na+

Na+ urea

protein-free plasma

urine to renal pelvis

1 23

4

ANIMATED FIGURE: Urine formation



Take-Home Message:How is urine formed and concentrated?

• During glomerular filtration, pressure generated by the beating heart drives water and solutes out of glomerular capillaries and into kidney tubules.

• In tubular reabsorption, water, some ions, glucose, and other solutes move out of the filtrate and return to the blood in peritubular capillaries.

• In tubular secretion, active transport proteins move solutes such as H+ and K+ from peritubular capillaries into the nephron for excretion.

Take-Home Message:How is urine formed and concentrated?

• Differential permeability of the two arms of the loop of Henle sets up a concentration gradient in the interstitial fluid that draws water out of the collecting tubule.

• Urine concentration depends on how much water flows out of the distal tubule and the collecting tubule. Hormones affect the concentration of solutes in urine by their effects on the permeability of these tubules.

40.5 Regulating Thirst and Urine Concentration

• When you don’t drink enough water, a region of the hypothalamus (thirst center) notifies your cerebral cortex that you need to search for water

• Hormonal controls act to conserve water already in the body

Effects of Antidiuretic Hormone

• Antidiuretic hormone (ADH)• Released by the pituitary when sodium levels rise• Increases water reabsorption by stimulating insertion of

aquaporins into plasma membranes of distal tubules and collecting ducts

• Concentrates urine

Feedback Control of ADH Secretion

Response

pituitary gland

ADH alert! Stimulus

hypothalamus

1

2

3

4

5

Effects of Aldosterone

• Aldosterone • Released by the adrenal cortex• Increases salt reabsorption in collection ducts; water

follows by osmosis; urine is concentrated

• Decrease in volume of extracellular fluid stimulates arterioles in nephrons to release renin• Renin converts angiotensinogen to angiotensin I,

converted to angiotensin II, which acts on the adrenal cortex to secrete aldosterone

Figure 40-13a p723

acts onkidneys toincrease Na+

reabsorption

Angiotensinogen

is converted to

Angiotensin I

is converted to

Angiotensin II

encouragessecretion of

Aldosterone

Effects of Atrial Natriuretic Peptide

• Atrial natriuretic peptide (ANP)• Released by muscle cells in the heart’s atria when high

blood volume causes walls to stretch• Directly inhibits secretion of aldosterone by acting on

adrenal cortex• Indirectly inhibits secretion of aldosterone by inhibiting

renin release• Increases glomerular filtration rate, makes urine more

dilute

Take-Home Message: How do hormones affect urine concentration?

• Antidiuretic hormone released by the pituitary causes an increase in water reabsorption. It concentrates the urine.

• Aldosterone released by the adrenal cortex increases salt reabsorption, and water follows. It concentrates the urine.

• Atrial natriuretic peptide released by the heart makes urine more dilute by discouraging secretion of aldosterone and increasing the rate of glomerular filtration.

40.6 Acid–Base Balance

• Normal pH of extracellular fluid is 7.35 to 7.45

• Kidneys, buffering systems, and respiratory system work together to maintain the acid-base balance (H+ concentration) within a tight range

• Kidneys are the only organs that can selectively rid the body of H+ ions

Acid-Base Balance

• A bicarbonate-carbonic acid buffer system minimizes pH changes by binding excess H+

H+ + HCO3- ↔ H2CO3 ↔ CO2 + H20

• Kidneys adjust blood pH by bicarbonate reabsorption and H+ secretion

• Respiration adjusts blood pH by removing CO2

Take-Home Message: What mechanisms maintain the pH of the extracellular fluid?

• Metabolic reactions produce H+ that enters extracellular fluid, acidifying it.

• Bicarbonate in the blood serves as a buffer, bonding with H+ to form CO2 and water. Thus bicarbonate helps maintain the pH of the extracellular fluid.

• The kidney helps to maintain the pH of the extracellular fluid by adjusting its reabsorption of bicarbonate and secretion of H+. The H+ secreted into the filtrate combines with other ions and is excreted in urine.

40.7 When Kidneys Fail

• Most kidney problems occur as complications of diabetes mellitus or high blood pressure

• Infections, toxins, drugs, and high-protein diets can also damage kidneys

• Kidney failure can be treated with dialysis, but only a kidney transplant can fully restore function

Treating Kidney Failure

• Kidney dialysis temporarily restores proper solute balance in a person with kidney failure

• Hemodialysis pumps blood through a machine that cleans blood and adjusts solutes

• In peritoneal dialysis, a dialysis solution is pumped into the peritoneal cavity at night and removed in the morning

A Hemodialysis Tubes carry blood from a patient’s body through a filter with dialysis solution that contains the proper concentrations of salts. Wastes diffuse from the blood into the solution and cleansed, solute-balanced blood returns to the body.

patient’s blood inside tubing

filter where blood flows through semipermeable tubes and exchanges substances with dialysis solution

B Peritoneal dialysis Dialysis solution is pumped into a patient’s abdominal cavity. Wastes diffuse across the lining of the cavity into the solution, which is then drained out.

dialysis solution with unwanted wastes and solutes draining out

dialysis solution flowing into abdominal cavity

abdominal cavity, lined with peritoneum (green)

Stepped Art

Figure 40-14 p724

Kidney Transplants

• A single kidney is adequate to maintain heath

• Transplants of kidneys from living donors, usually a relative, are more successful than kidneys donated after death

• More than 40,000 people remain on waiting lists because of a shortage of donated kidneys

Take-Home Message: What causes kidney failure, and how does it affect health?

• Kidney failure most often occurs as a complication of diabetes or high blood pressure.

• Untreated kidney failure is fatal. Dialysis can keep a person with kidney failure alive, but it must be continued until a person dies or receives a kidney transplant.

ANIMATION: Kidney dialysis



40.8 Heat Gains and Losses

• Maintaining the body’s core temperature is another aspect of homeostasis

• Some animals expend more energy than others to keep their body warm

Maintaining Core Temperature

• Internal core temperature is stable only when metabolic heat produced and heat gained from the environment balance heat lost to the environment

Change in body heat = heat produced + heat gained – heat lost

How Core Temperature Can Change

• Thermal radiation• Heat is emitted into space surrounding an object

• Conduction• Heat is transferred by direct contact

• Convection• Heat is transferred by movement of air or water

• Evaporation• Heat is lost when liquid is converted to a gas

Ectotherms, Endotherms, and Heterotherms

• Ectotherms (fishes, amphibians, reptiles)• Body temperature changes with the environment• Regulated by altering position, not metabolism

• Endotherms (most birds and mammals)• Body temperature maintained by metabolic heat

• Heterotherms (some birds and mammals)• Can maintain or decrease core temperature

Endotherm and Ectotherm

Take-Home Message: How do animals regulate their body temperature?

• Animals can gain heat from the environment, or lose heat to it. They can also generate heat by metabolic reactions.

• Fishes, amphibians, and reptiles are ectotherms that warm themselves mostly by heat gained from the environment.

• Most birds and mammals are endotherms that maintain body temperature with their own metabolic heat.

40.9 Responses to Heat or Cold

• A variety of mechanisms adapt animals to survive in habitats where the temperature fluctuates

• The hypothalamus functions like a thermostat to maintain the body’s core temperature via a negative feedback loop

• When the temperature deviates from a set point, the hypothalamus calls for responses that return temperature to the set point

Responses to Heat Stress

• Mammals counter heat stress by increasing blood flow to skin, sweating and panting (evaporation), and by reducing their activity level

• Failure to control body heat results in rising core temperature (hyperthermia) which can be fatal

• Fever is an increase in body temperature regulated by the hypothalamus, usually in response to infection

Responses to Cold Stress

• Mammals respond to cold with reduced blood flow to skin, fluffing up fur or hair, increased muscle activity, and increased heat production

• Failure to protect against cold can result in falling core temperature (hypothermia) which alters brain function, and can be fatal

Increasing Metabolic Heat Production

• Shivering response• With prolonged cold exposure, the hypothalamus

commands skeletal muscles to increase heat production by contracting 10 to 20 times/second

• Nonshivering heat production• Long-term or severe cold increases thyroid activity and

raises metabolic rate; reactions in cells of brown adipose tissue release energy as heat

Nonshivering heat production

Metabolic activity aftertwo hours at 16°C (61°F)

Metabolic activityat 22°C (72°F)

Table 40-1 p726

Seasonal Dormancy

• Hibernation• A period of dormancy during the cold season, during which

the animal is largely inactive, and its respiratory rate, heart rate, and body temperature decline dramatically

• Estivation• Desert reptiles and amphibians may become dormant

during the hot, dry summer – they spend this season inactive, inside a burrow deep beneath the soil surface

Take-Home Message:

How do animals adapt to heat and cold?

• Temperature shifts are detected by thermoreceptors that send signals to the hypothalamus, which serves as the body’s thermostat.

• Increasing blood flow to the skin, sweating, and panting dissipate heat.

• Shivering and nonshivering heat production warm mammals; fluffing up fur or feathers slows heat loss.

• Some animals become dormant during a cold or hot season.

ANIMATION: Feedback control of temperature



ANIMATION: Control of human body temperature



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Chapter 40 Maintaining the Internal Environment