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Chapter 15

The Urinary System

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Outline• Functions of the Urinary System• Overview of the Urinary System• Kidney Structure• Urine Formation

– Glomerular Filtration– Tubular Reabsorption– Tubular Secretion

• Maintaining Water-Salt Balance• Maintaining Blood pH• Homeostasis

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Functions of the Urinary System• Carry out excretion of metabolic wastes.

– Excretion is the removal of metabolic waste products- Elimination is the removal of un-used or un-usable material from the body

– Urea is the primary nitrogenous end product, but ammonium, creatinine, and uric acid are also excreted.

• Maintains salt-water balance of blood and thus regulates blood volume and blood pressure.– Ions regulated include sodium (Na+),

potassium (K+), and calcium (Ca2+).

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Functions of the Urinary System (Con’t)

• Maintains acid-base balance of the blood.– Regulates bicarbonate ions (HCO3

-) and hydrogen ions (H+).

• Performs these functions by producing urine and conducting it outside the body.

• Has a hormonal function.– Produces erythropoietin.– Produces renin for the renin-angiotensin-

aldosterone system.• Activates inactive form of Vitamin D

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Overview of the Urinary System

• Kidneys are primary organs of the urinary system.– The concave side of a kidney has

depression called the hilum where the renal artery enters and the renal vein and ureters exit the kidney.

• Urinary bladder gradually expands as urine enters.

• Urethra extends from the urinary bladder to an exterior opening.

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Figure 15.1a Organs of the urinary system.

Hepatic veins (cut)

Inferior vena cava

Adrenal gland

Aorta

Iliac crest

Rectum (cut)

Uterus (partof femalereproductivesystem)

(a)

Renal arteryRenal hilumRenal vein

Kidney

Ureter

Urinarybladder

Urethra

Overview of the Urinary System

© 2015 Pearson Education, Inc.

Figure 15.1b Organs of the urinary system.

12th rib

(b)

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Kidney Structure• The kidney contains three major regions:

– Renal cortex.– Renal medulla.– Renal pelvis.

• Additional structures of importance– Renal columns– Renal papilla– Renal pyramids– Minor & major calyces

• Microscopically, the kidney is composed of over one-million nephrons that produce urine.

(a) Anterior view of dissection of right kidney

Renal cortex

Renal medulla

Renal column

Renal pyramidin renal medulla

Renal papilla

Renal capsule

Renal artery

Renal vein

Nephron

Collecting duct

PATH OF URINE DRAINAGE:

Minor calyx

Major calyx

Renal pelvis

Ureter

Urinary bladderRenal lobe

Renalhilum

Frontal plane

(a) Frontal section of right kidney

Renal capsule

Renal cortex

Renal pyramidin renal medulla

Blood supply of nephron

Interlobular artery

Arcuate artery

Interlobar artery

Segmental artery

Renal artery

Renal vein

Interlobar vein

Arcuate vein

Interlobular vein

Afferentarteriole

Efferentarteriole

Peritubularcapillary

Interlobularvein

Glomerulus

Vasa recta

Blood Supply to the Kidney

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Kidney Structure: The Nephron• Nephron is functional unit of the kidney.

– Two types of nephrons Coritcal: 80-85%, normal renal function Juxtamedullary: 15-20%, involved with generation of

very dilute or very concentrated urine

• Each nephron has its own blood supply.– From the renal artery, afferent arteriole leads to the

glomerulus, then to the efferent arteriole and then to the peritubular capillary network (or vasa recta of juxtamedullary nephrons) which surrounds the nephron.

– From there blood goes into a venule that joins the renal vein.

© 2015 Pearson Education, Inc.

Figure 15.3a Structure of the nephron.

Renal cortex

Renal medulla

Renal pelvis

Renal cortex

Ureter

Renal medulla

Cortical nephron Fibrous capsule

Juxtamedullarynephron

Collectingduct

Proximalconvoluted tubule

Glomerulus

Distalconvoluted tubule

Nephron loop

(a)

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Kidney Structure: The Nephron (Con’t)

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Kidney Structure: The Nephron (Con’t)• Each nephron is composed of several parts.

– Glomerular capsule (Bowman’s capsule). Filtration

– Proximal convoluted tubule. Tubular reabsorption

– Loop of the nephron (loop of Henle). Tubular reabsorption and secretion

– Distal convoluted tubule. Tubular reabsorption and secretion

– Collecting duct. Tubular reabsorption

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© 2012 Pearson Education, Inc. Figure 15.7

a) The outer surface of several glomerular capillaries.

Podocyte

Filtrate

Proximal tubule Capillary wall

Glomerularcapsule

Glomerularspace

Glomerulus Blood flowMovement of glomerular filtrate

Afferent arteriole

Efferent arteriole

b) A highly magnified view of the inner surface of a single glomerular capillary, revealing its porous sievelike structure.

Peritubular capillaries

Afferentarteriole

Renal corpuscle Renal tubule and collecting duct

Glomerular filtration (filtrationof blood plasma by glomerulus)

Efferentarteriole

Tubular reabsorption from glomerular filtrate into blood

Tubular secretion from blood into glomerular filtrate

Urine(containsexcretedsubstances)

GlomerulusGlomerular

capsule

Blood(containsreabsorbedsubstances)

1

2 3

Glomerular filtratein renal tubule

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Urine Formation• Urine formation is divided into three steps.

1. Glomerular filtration. Filterable blood components

water nitrogenous wastes nutrients salts (ions)

Nonfilterable blood components white and red blood cell, platelets plasma proteins

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Urine Formation (Con’t)2. Tubular reabsorption.

Reabsorbed filtrate components most water nutrients required salts (ions)

Nonreabsorbed filtrate components some water much nitrogenous waste excess salts (ions)

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Urine Formation (Con’t)

3. Tubular secretion. Active removal from the blood of

some compounds, such as drugs, with secretion into the distal convoluted tubule

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Filtration and Reabsorption

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Maintaining Salt-Water Balance• Reabsorption of Water- Water Balance

– Very dilute or very concentrated urine Dependent upon reabsorption of water from the

descending limb of loops of Henle and collecting ducts

Mostly juxtamedullary nephrons– Osmotic gradient exists within the tissues of the renal

medulla.– Antidiuretic hormone (ADH) released by the posterior

lobe of the pituitary (due to osmolarity of plasma) causes more water to be reabsorbed in collecting ducts and less urine to form

Diuretics increase urine flow Alcohol- inhibits ADH release from posterior

pituitary Caffeine- inhibits reabsorption of Na+

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Maintaining Salt-Water Balance• Reabsorption of Water- Water Balance

– Osmotic gradient exists within the tissues of the renal medulla

Creation of osmotic gradient Countercurrent multiplication- nephron

tubules Maintenance of osmotic gradient

Countercurrent exchange- vasa recta blood vessels

Vasarecta

300

Loop ofHenle

Juxtamedullary nephron and its blood supply together

380

580

780

980

1200

800

600

400

200

100

H2O

H2OH2O

200

300

300

320

400

600

800

1000

1200

1200

Glomerular (Bowman’s) capsule

Glomerulus

Distal convoluted tubule

Efferentarteriole

Afferent arteriole

Proximal convoluted tubule

Interstitial fluidin renal medulla

Osmoticgradient

Symporters in thick ascending limb cause buildup of Na+ and Cl– in renal medulla

Countercurrent flow through loop of Henle establishes osmotic gradient

300

400

600

800

1000

1200

300 320

400

600

800

1000

1200

1100

900

700

500

Principal cells in collecting duct reabsorb more water when ADH is present

Urea recycling causes buildup of urea in renal medulla

Papillary duct

Concentrated urine

Collecting duct

Loop of Henle

Urea

Na+Cl–

H2O

Na+Cl–

H2O

Na+Cl–H2O

Na+Cl–

H2O

Na+Cl–

Interstitialfluid inrenal cortex

H2ONa+Cl–

Blood flowPresence of Na+–K+–2Cl– symporters

Flow of tubular fluid

1

2

3

4

H2O

H2O

H2O

H2O

H2O

H2O

H2O

(a) Reabsorption of Na+, Cl–, and water in long-loop juxtamedullary nephron

(b) Recycling of salts and urea in vasa recta

Creation of Osmotic Gradient

Maintenance of Osmotic Gradient

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Maintaining Salt-Water Balance• Reabsorption of Water- Water Balance

– Very dilute or very concentrated urine Dependent upon reabsorption of water from the

descending limb of loops of Henle and collecting ducts

Mostly juxtamedullary nephrons– Antidiuretic hormone (ADH) released by the posterior

lobe of the pituitary (due to osmolarity of plasma) causes more water to be reabsorbed in collecting ducts and less urine to form

Diuretics increase urine flow Alcohol- inhibits ADH release from posterior

pituitary Caffeine- inhibits reabsorption of Na+

Glomerular (Bowman's) capsule

Glomerulus

Distal convoluted tubule

Interstitial fluid in renal cortex

Collectingduct

Interstitialfluid inrenalmedulla

Papillaryduct

Diluteurine

Loop of Henle

Proximalconvolutedtubule

Afferentarteriole

300

300350

550

750

900

750 750550

550 350 550

300350 150 350

100

90

80

70

65

65

Efferentarteriole

ADH & Making Dilute Urine

Vasarecta

300

Loop ofHenle

Juxtamedullary nephron and its blood supply together

380

580

780

980

1200

800

600

400

200

100

H2O

H2OH2O

200

300

300

320

400

600

800

1000

1200

1200

Glomerular (Bowman’s) capsule

Glomerulus

Distal convoluted tubule

Efferentarteriole

Afferent arteriole

Proximal convoluted tubule

Interstitial fluidin renal medulla

Osmoticgradient

Symporters in thick ascending limb cause buildup of Na+ and Cl– in renal medulla

Countercurrent flow through loop of Henle establishes osmotic gradient

300

400

600

800

1000

1200

300 320

400

600

800

1000

1200

1100

900

700

500

Principal cells in collecting duct reabsorb more water when ADH is present

Urea recycling causes buildup of urea in renal medulla

Papillary duct

Concentrated urine

Collecting duct

Loop of Henle

Urea

Na+Cl–

H2O

Na+Cl–

H2O

Na+Cl–H2O

Na+Cl–

H2O

Na+Cl–

Interstitialfluid inrenal cortex

H2ONa+Cl–

Blood flowPresence of Na+–K+–2Cl– symporters

Flow of tubular fluid

1

2

3

4

H2O

H2O

H2O

H2O

H2O

H2O

H2O

(a) Reabsorption of Na+, Cl–, and water in long-loop juxtamedullary nephron

(b) Recycling of salts and urea in vasa recta

ADH & Making Concentrated Urine

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Maintaining Salt-Water Balance• Fluid Compartments & Fluid Balance

– Intracellular fluid (ICF)- inside cells– Extracellular fluid (ECF)- outside cells

Interstitial fluid- microscopic space outside every cell of the body

Plasma – Renal processes of filtration, reabsorption,

diffusion, and osmosis promote continuous exchange between the fluid compartments

Thus fluid balance is directly related to electrolyte (ions) balance

“Wherever salt goes water follows”

Total body mass (female)

(a) Distribution of body solids and fluids in average lean, adult female and male (b) Exchange of water among body fluid compartments

Total body mass (male)

45%Solids

40% Solids

55% Fluids

60% Fluids

2/3Intracellularfluid (ICF)

80%Interstitial

fluid

1/3Extracellularfluid (ECF)

20% Plasma Blood capillary

Tissuecells

Total body fluid

Extracellularfluid

Renal effects on salt distribution will affect fluid distribution

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Maintaining Salt-Water Balance• Reabsorption of Salt.

– Kidneys regulate blood’s salt balance by controlling excretion and reabsorption of various ions, most important one being Na+

Usually more than 99% of sodium filtered at the glomerulus is returned to the blood

– Hormonal control of salt reabsorption Starts at juxtaglomerular apparatus (JGA) Decrease in blood volume/pressure-renin from the

JGA is released into blood-enzymatically cleaves angiotensinogen to angiotensin-I, angiotensin-I converted to angiotensin-II in lungs, angiotensin-II stimulates release of aldosterone from adrenal cortex, aldosterone stimulates Na+ reabsorption

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Juxtaglomerular Apparatus

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Figure 15.3b Structure of the nephron.

Peritubularcapillaries

Glomerularcapillaries

Glomerular(Bowman’s)capsule

Efferent arteriole

Afferent arteriole

Cells of thejuxtaglomerularapparatusCortical radiatearteryArcuate artery

Cortical radiatevein

Arcuatevein

Distalconvolutedtubule(DCT)

Proximal convolutedtubule (PCT)

(b)

Collecting duct

Nephron loop

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Maintaining Salt-Water Balance• Reabsorption of Salt.

– Hormonal control of salt reabsorption (Cont.) Wherever salt goes water follows, thus increase

reabsorption of water Causes of decrease blood volume- blood loss

(hemorrhage), profuse sweating (includes loss of blood water/salt), profuse vomiting, profuse diarrhea

Reabsorption of water increases blood volume Decreased blood volume means decreased blood

pressure- hence increase in blood volume- increase in blood pressure

Thus direct link between salt regulation and blood pressure regulation

ADH increases to increase water reabsorption

© 2012 Pearson Education, Inc.

ADH

Save water

KidneysSavesalt

Blood volume

Increase

Set point

Decrease

Adrenal cortex

Angiotensin-converting

enzyme

Kidneys

Vasoconstriction, blood pressure

Liver

Angiotensinogen

Lungs

Ren

in

Figure 15.15

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Maintaining Salt-Water Balance• Reabsorption of Salt.

– Hormonal control of salt reabsorption (Cont.) Starts at atria of heart Increase in Na+ concentration in plasma- huge salt

filled meal 99% of Na+ reabsorbed- wherever salt goes water

follow Water enters blood from fluid compartments-

intracellular space, then interstitial space, then into plasma

Increase in blood volume Increase stretch of atria of heart- release atrial

natriuretic peptide Causes increased salt excretion (decrease Na+

reabsorption)

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Maintaining Salt-Water Balance• Reabsorption of Salt.

– Hormonal control of salt reabsorption (Cont.) Wherever salt goes water follows Increase removal of water from blood- decrease in

blood volume- decrease in blood pressure Hypertension- may be a defect in atrial

natriuretic peptide system What is happening to ADH during this situation? Increased osmolarity of blood should stimulate ADH

release but that can’t happen because that would increase blood volume when you want to decrease it

Thus ADH is mostly involved when you have changes in water affecting osmolarity not salt affecting osmolarity

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Fate of Some Compounds, Normal Amount of Urine

• Nutrients- amino acids, glucose / all filtered from blood into urine in glomerulus / all reabsorbed in proximal / none in urine

• Water and salts / most filtered from blood into urine in glomerulus / most reabsorbed in proximal and collecting duct / concentration in urine dependent on need and hormones

• Metabolic wastes- urea, uric acid/ all filtered from blood into urine in glomerulus / none reabsorbed / concentration in urine higher than blood

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Fate of Some Compounds, Low Amount of Urine- After Sleeping

• Nutrients- amino acids, glucose / all filtered from blood into urine in glomerulus / all reabsorbed in proximal / none in urine

• Water / most filtered from blood into urine in glomerulus / even more reabsorbed in proximal and collecting duct due to prevention of loss during sleep / ADH increases reabsorption in collecting duct

• Metabolic wastes- urea, uric acid/ all filtered from blood into urine in glomerulus / none reabsorbed / concentration in urine much higher than under normal condition due to less water

© 2012 Pearson Education, Inc. Table 15.1

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Fate of Some Compounds, High Amount of Urine- After McDonalds Meal

• Nutrients- amino acids, glucose / all filtered from blood into urine in glomerulus / all reabsorbed in proximal / none in urine

• Salt and water / most filtered from blood into urine in glomerulus / most reabsorbed in proximal and collecting duct / high salt in food, goes into blood, water follows, increase volume, increase pressure, ANH released, salt reabsorption decreased, ADH turned off, water follows salt into urine

• Metabolic wastes- urea, uric acid/ all filtered from blood into urine in glomerulus / none reabsorbed / concentration in urine lower than normal due to large amount of water in urine

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Maintaining Blood pH

• Reabsorption of bicarbonate ions and secretion of hydrogen ions

• Exhalation of Carbon Dioxide

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Maintaining Blood pH

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Homeostasis• In conjunction with the lungs, maintenance

of acid-base balance.• Maintenance of water-salt balance of blood

and the overall osmolarity.• Helps regulate blood volume and pressure.

– Releases-erythropoietin; increases number of red blood cells

• Regulates the concentration of important ions such as calcium (Ca2+) and potassium (K+).

• In conjunction with the liver, excretion of metabolic wastes.

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Need to Know1. Functions of the urinary system

A. Metabolic waste excretionB. Salt-Water balanceC. Blood pressure regulationD. Acid-base balanceE. Red blood cell quantity regulationF. Activation of inactive Vitamin D

2. Kidney Structure: The NephronA. Afferent and efferent arteriolesB. GlomerulusC. Peritubular capillary network

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Need to Know (Cont.)2. Kidney Structure: The Nephron (Cont.)

D. Glomerular capsuleE. Proximal convoluted tubuleF. Loop of the nephronG. Distal convoluted tubuleH. Collecting duct

3. Urine formationA. Glomerular filtration conceptB. Tubular reabsorption conceptC. Tubular secretion conceptD. Must know what’s filtered and not filtered, what’s

reabsorbed and not reabsorbed and what’s secreted

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Need to Know (Cont.)

4. Reabsorption of salt

A. Juxtaglomerular apparatus

B. Renin-angiotensin-aldosterone system

C. Atria natriuretic hormone

D. Blood pressure regulation

5. Acid-Base balance

A. Reabsorption of bicarbonate ion

B. Excretion of hydrogen ion

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Need to Know (Cont.)

6. Kidney Structure: Gross anatomyA. Renal cortexB. Renal medullaC. Renal pelvis

7. Urinary system: GeneralA. KidneyB. UretersC. Urinary bladderD. Urethra