11.3 The kidney Objectives Define excretion. Draw and label a diagram of the kidney. Annotate a diagram of a glomerulus and associated nephron to show.

11.3 The kidneyObjectives

• Define excretion.• Draw and label a diagram of the kidney.• Annotate a diagram of a glomerulus and associated nephron to

show the function of each part.• Explain the process of ultrafiltration, including blood pressure,

fenestrated blood capillaries and basement membrane.• Define osmoregulation.• Explain the reabsorption of glucose, water and salts in the

proximal convoluted tubule, including the roles of microvilli, osmosis and active transport.

Objectives of Topic 11.3

• Explain the roles of the loop of Henle, medulla, collecting duct and ADH (vasopressin) in maintaining the water balance of the blood

• Explain the differences in the concentration of proteins, glucose and urea between blood plasma, glomerular filtrate and urine.

• Explain the presence of glucose in the urine of untreated diabetic patients.

Why do we need excretory system?

• To remove toxic wastes.

• Metabolism produces toxic by-products.

• Nitrogenous wastes are toxic breakdown products of proteins and nucleic acids.

• Animals dispose of nitrogenous wastes in different ways.

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1- Ammonia (NH3) is

– poisonous,– too toxic to be stored in the body,– soluble in water, and– easily disposed of by aquatic animals.

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TOXIC WASTES

2- Urea is– produced in the vertebrate liver by combining

ammonia and carbon dioxide,– less toxic,– easier to store, and– highly soluble in water.

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TOXIC WASTES

3. Uric acid is– excreted by some land animals (insects, land

snails, and many reptiles),– relatively nontoxic,– largely insoluble in water,– excreted as a semisolid paste, conserving

water, but– more energy expensive to produce.

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TOXIC WASTES

Figure 25.5

Proteins

Ammonia

Nitrogenous bases

NH2

(amino groups)

Nucleic acids

Urea

Uric acid

Mammals, mostamphibians, sharks,some bony fishes

Birds and many otherreptiles, insects, landsnails

Most aquatic animals,including most bonyfishes

Amino acids

• The urinary system– forms and excretes urine and– regulates water and solutes in body fluids.

• In humans, the kidneys are the main processing centers of the urinary system.

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Figure 25.6_1

Aorta

Kidney

The urinary system

Inferiorvena cava

Renal artery (red)and vein (blue)

Ureter

Urethra

Urinary bladder

Figure 25.6_2

Renal cortex

Renal medulla

Ureter

Renal pelvis

The kidney

Figure 25.6_3

Bowman’s capsule

Tubule

Collectingduct

To renalpelvis

Branch ofrenal artery

Branch ofrenal vein

Renal cortex

Orientation of a nephron within the kidney

Renal medulla

Figure 25.6

Aorta

Kidney

The urinary system

Inferiorvena cava

Renal artery (red)and vein (blue)

Ureter

Urethra

Urinary bladder

Renal cortex

Renal medulla

Renal pelvis

Ureter

The kidney

Proximal tubule

Bowman’s capsule

Tubule

Collectingduct

To renalpelvis

Branch ofrenal artery

Branch ofrenal vein

Renal cortex

Renal medulla

CapillariesGlomerulus

Distaltubule

Fromanothernephron

Bowman’s capsuleArteriole

from renalartery

Arteriolefrom glomerulus

Branch ofrenal vein

Loop of Henlewith capillarynetwork

Detailed structure of a nephron

1

3

2

Orientation of a nephron within the kidney

Collectingduct

• Nephrons

– are the functional units of the kidneys,

– extract a fluid filtrate from the blood, and

– refine the filtrate to produce urine.

• Urine is

– drained from the kidneys by ureters,

– stored in the urinary bladder, and

– expelled through the urethra.

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Figure 25.6_4

Proximal tubuleGlomerulus

DistaltubuleCollectingDuct

Fromanothernephron

Bowman’s capsule

Arteriolefrom renalartery

Arteriolefrom glomerulus

Branch ofrenal vein

Loop of Henlewith capillarynetwork

Detailed structure of a nephron

Capillaries

1

3

2

Overview: The key processes of the urinary system are filtration, reabsorption, secretion, and excretion

• Filtration– Blood pressure forces water and many small

molecules through a capillary wall into the start of the kidney tubule.

• Reabsorption– refines the filtrate,– reclaims valuable solutes (such as glucose,

salt, and amino acids) from the filtrate, and– returns these to the blood.

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Figure 25.7

Reabsorption Secretion Excretion

Urine

To renal vein

Filtration

Nephron tubule

Capillary

Interstitial fluid

H2O, other small molecules

Bowman’s capsule

Fromrenalartery

Figure 25.7_1

Filtration

Nephron tubule

Capillary

Interstitial fluid

H2O, other small molecules

Bowman’s capsule

Fromrenalartery

Figure 25.7_2

Reabsorption Secretion Excretion

Urine

To renal veinCapillary

Nephron tubule

• Substances in the blood are transported into the filtrate by the process of secretion.

• By excretion the final product, urine, is excreted via the ureters, urinary bladder, and urethra.

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Figure 25.7

Reabsorption Secretion Excretion

Urine

To renal vein

Filtration

Nephron tubule

Capillary

Interstitial fluid

H2O, other small molecules

Bowman’s capsule

Fromrenalartery

• Reabsorption in the proximal and distal tubules removes– nutrients,– salt, and– water.

• pH is regulated by– reabsorption of HCO3

– and

– secretion of H+.

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• High NaCl concentration in the medulla promotes reabsorption of water.

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Animation: Bowman’s Capsule and Proximal Tubule

Animation: Collecting Duct

Animation: Effect of ADH

Animation: Loop of Henle and Distal Tubule

Figure 25.8 Bowman’scapsule

Blood

Nutrients H2ONaCl

Proximal tubule

Somedrugsand poisonsCortex

Medulla

Interstitialfluid Loop of

Henle

H2O

Filtrate composition

Reabsorption

Filtrate movement

Secretion

Distal tubule1

2 NaCl

NaCl

NaCl

UreaH2O

3K

H

Collectingduct

Urine (torenal pelvis)

H2ONaCl HCO3

H2O

Salts (NaCl and others) HCO3

H

Urea Glucose Amino acids Some drugs

HCO3

H

Figure 25.8_1

Blood

Filtrate composition

Reabsorption

Filtrate movement

Secretion

Bowman’scapsule

Nutrients H2ONaCl HCO3

Proximal tubule

Somedrugsand poisonsCortex

Medulla

H

H2O

Salts (NaCl and others) HCO3

H

Urea Glucose Amino acids Some drugs

Figure 25.8_2

Reabsorption

Filtrate movement

Secretion

NutrientsNaCl HCO3

Somedrugsand poisonsCortex

Medulla

Proximal tubule

Interstitialfluid Loop of

Henle

H2O

NaCl

NaCl

NaCl

UreaH2O

Collectingduct

Urine (torenal pelvis)

Distal tubuleH2O

NaCl HCO3

1

3

2

H2O

H HK

• Antidiuretic hormone (ADH) regulates the amount of water excreted by the kidneys by– signaling nephrons to reabsorb water from the

filtrate, returning it to the blood, and– decreasing the amount of water excreted.

• Diuretics– inhibit the release of ADH and– include alcohol and caffeine.

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• Kidney failure can result from– hypertension,– diabetes, and– prolonged use of common drugs, including

alcohol.

• A dialysis machine– removes wastes from the blood and– maintains its solute concentration.

CONNECTION: Kidney dialysis can be lifesaving

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Figure 25.9

Line from artery to apparatus

Pump Tubing made of a selectively permeable membrane

Dialyzingsolution

Fresh dialyzingsolution

Used dialyzing solution(with urea and excess ions)

Line fromapparatusto vein

Figure 25.9_1

Line from artery to apparatus

Pump Tubing made of a selectively permeable membrane

Dialyzingsolution

Fresh dialyzingsolution

Used dialyzing solution(with urea and excess ions)

Line fromapparatusto vein

Figure 25.9_2