chapter 20: urinary system

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Hole’s Human Anatomyand Physiology

Twelfth Edition

Shier Butler Lewis

Chapter 20

Urinary System

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

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20.1: Introduction• A major part of homeostasis is maintaining the composition, pH, and volume of body fluids within normal limits

• The urinary system removes metabolic wastes and substances in excess, including foreign substances like drugs and their metabolites that may be toxic

• It consists of a pair of kidneys, a pair of ureters, a urinary bladder and a urethra

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Kidney

Hilum

Ureters

Urethra

Renalvein

Renalartery

Inferiorvena cava

Abdominalaorta

Urinarybladder


© CNRI/SPL/Photo Researchers, Inc.

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20.2: Kidneys

• A kidney is a reddish brown, bean-shaped organ with a smooth surface• In the adult it is about 12 centimeters long, 6 centimeters wide, and 3 centimeters thick• It is enclosed in a tough, fibrous capsule

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Location of the KidneysCopyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Inferior vena cava

Pancreas

(a)

(b)

Adrenal gland

Kidney

Adipose tissue

Kidney

Spleen

Large intestineSmall intestineAorta

Stomach

Liver

Parietal peritoneum

Renal fasciaRenal fascia

Large intestineHip bone (cut)

Parietalperitoneum

Twelfth rib

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Kidney StructureCopyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Renal pelvis

Minor calyx

Major calyx

Renal papilla

Renal pyramid

Nephrons

Renal sinus

Renal medulla

Renal capsuleRenal cortex

Ureter

(a)

(b) (c)

Renal corpuscle

Papilla

Minor calyx

Renal column

Fat in renal sinus

Collectingduct

Renalmedulla

Renalcortex

Renaltubule

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Inferior vena cava

Renal cortex

Renal pyramid

Renal medulla

Minor calyx

Renal column

Renal papilla

Renal pelvis

Suprarenal artery

Abdominal aorta

Adrenal gland

Renal capsule

Hilum

Renal vein

Suprarenal vein

Ureter

Renal artery

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Function of the Kidneys

• The main function of the kidneys is to regulate the volume, composition, and pH of body fluids

• The kidneys remove metabolic wastes from the blood and excrete them to the outside of the body, including nitrogenous and sulfur-containing products of protein metabolism

• The kidneys also help control the rate of red blood cell production, regulate blood pressure, and regulate calcium ion absorption

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Renal Blood VesselsCopyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

b: © L.V. Bergman/The Bergman Collection

(a)

(b)

Cortex

Medulla

Renal pelvis

Ureter

Afferent arteriole

Cortical radiateartery and vein

Arcuate veinand artery

Interlobarvein and artery

RenalarteryRenalvein

Peritubularcapillary

Efferentarteriole

Proximalconvolutedtubule


Distal convolutedtubule


(a) : Tissues and Organs: A Text-Atlas of Scanning Electron Microscopy, by R.G. Kessel and R.H. Kardon. © 1979 W.H. Freeman and Company (b) : Courtesy of R.B. Wilson MD, Eppeley Institute for Research in Cancer, University of Nebraska Medical Center

Glomerulus(a)

Renal tubules

Glomerulus(b)


Efferentarteriole

Afferentarteriole

Glomerularcapsule

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NephronsCopyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Glomerulus

Visceral layer ofglomerular capsule


Parietal layerof glomerularcapsule

Glomerularcapsule

Bloodflow

Afferentarteriole

Efferentarteriole

Bloodflow


© David M. Phillips/Visuals Unlimited

Slit pore Pedicel

Slit pore

Pedicel

Primary processof podocyte

Primary processof podocyte

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Glomerulus

Collecting duct

Nephronloop Ascending

limb

Descendinglimb


Efferentarteriole


Renalmedulla

Renalcortex

Cortical radiateartery

Cortical radiatevein

Glomerularcapsule

Afferentarteriole

Distalconvolutedtubule

From renalartery

To renalvein


Collecting ducts

Epithelial cell

Blood vessel

Glomerulus(a)

(b)

Renaltubules

Glomerularcapsule

Renalcorpuscle

a: © Biophoto Associates/Photo Researchers, Inc., b: © Manfred Kage/Peter Arnold

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Juxtaglomerular ApparatusCopyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Glomerulus

Nephron loop

Glomerulus

Afferent arteriole

Glomerular capsule

Efferent arteriole

Podocyte

Macula densa

(a)

(b)

Glomerularcapsule

Afferentarteriole

Juxtaglomerularapparatus


Efferentarteriole


Juxtaglomerularapparatus

Juxtaglomerularcells

Ascending limbof nephron loop

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Cortical and Juxtamedullary Nephrons


Cortical nephron

Juxtamedullarynephron

Collectingduct

Renalmedulla

Renalcortex

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Blood Supply of a Nephron


Glomerulus

Nephron loop

Collecting duct

Afferent arteriole

Vasa recta

Peritubularcapillaries

Efferentarteriole


Glomerularcapsule




Renal artery

Cortical radiate artery

Afferent arteriole

Efferent arteriole

Cortical radiate vein

Renal vein

Arcuate artery

Interlobar artery

Glomerular capillaries

Peritubular capillaries

Arcuate vein

Interlobar vein

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20.3: Urine Formation• The main function of the nephrons and collecting ducts is to control the composition of body fluids and remove wastes from the blood, the product being urine

• Urine contains wastes, excess water, and electrolytes

• Urine is the final product of the processes of:

• Glomerular filtration

• Tubular reabsorption

• Tubular secretion

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Urine FormationCopyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Arteriole Venule

Venule

Renal tubule

Tubular fluid Urine

Net reabsorption

Net filtrationInterstitial fluid

Bloodflow

(a) In most systemic capillaries, filtration predominates at the arteriolar end and osmotic reabsorption predominates at the venular end.

Peritubularcapillaries

Afferentarteriole

Glomerularcapillaries

Efferentarteriole

Bloodflow

Tubularreabsorption

Tubularsecretion

Glomerularfiltration

(b) In the kidneys, the glomerular capillaries are specialized for filtration. The renal tubule isspecialized to control movements of substances back into the blood of the peritubularcapillaries (tubular reabsorption) or from the blood into the renal tubule (tubular secretion).

Filteredfluid

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Glomerular Filtration• Glomerular filtration

• Substances move from the blood to the glomerular capsuleCopyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Fenestrae

(a) (b)

Podocyte

Podocyte

Glomerulus

Glomerularcapsule


Capillaryendothelium

Glomerularfiltrate

Efferentarteriole

Bloodflow

Afferentarteriole

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Plasma, Glomerular Filtrate, and Urine Components

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Filtrate Pressure

• The main force that moves substances by filtration through the glomerular capillary wall is hydrostatic pressure of the blood inside


Hydrostaticpressure ofblood

Glomerular hydrostaticpressure

Capsularhydrostaticpressure

Plasma colloidosmotic pressure

Net Outward PressureOutward force, glomerular hydrostatic pressure = +60 mmInward force of plasma colloid osmotic pressure = –32 mmInward force of capsular hydrostatic pressure = –18 mmNet filtration pressure = +10 mm

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Filtrate Rate

Net filtration pressure = force favoring filtration – forces opposing filtration (glomerular capillary (capsular hydrostatic pressure hydrostatic pressure) and glomerular capillary osmotic pressure)

• Glomerular filtration rate (GFR) is directly proportional to the net filtration pressure

• Normally the glomerular net filtration pressure is positive causing filtration• The forces responsible include hydrostatic pressure and osmotic pressure of plasma and the hydrostatic pressure of the fluid in the glomerular capsule


0

10

20

30

40

50

60

70

80

90

100

110

120

130

Lit

ers

140

150

160

170

180180 Liters

Glomerular filtrate

(a) (b)

Urine

0.6 – 2.5 Liters

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Control of Filtrate Rate• GFR remains relatively constant through a process called autoregulation• Certain conditions override autoregulation, including when GFR increases• Primarily three mechanisms are responsible for keeping the GFR constant:

• Autoregulation• Increased sympathetic impulses that decrease GFR by causing afferent arterioles to constrict• The hormone-like renin-angiotensin system• There also is the hormone atrial natriuretic peptide (ANP) affects sodium causing an increase in GFR

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Bloodstream

Angiotensin I

LiverKidney

Lung capillaries

Angiotensin II

• Increased thirst

Angiotensinogen

Renin

Stimulation

Angiotensin-convertingenzyme

Release intobloodstream

• Vasoconstriction• Increased aldosterone secretion• Increased ADH secretion

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Tubular Reabsorption

• Tubular reabsorption• Substances move from the renal tubules into the interstitial fluid where they then diffuse into the peritubular capillaries• The proximal convoluted tubule reabsorbs (70%):

• Glucose, water, urea, proteins, and creatine• Amino, lactic, citric, and uric acids• Phosphate, sulfate, calcium, potassium, and sodium ions

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Glomerulus

(a) (b)Blood flowBlood flow

Glomerulus

Bloodflow

Afferentarteriole

Glomerularcapsule

Glomerularfiltrate

Efferentarteriole


Tubularreabsorption

Renaltubule

Renaltubule

Tubularsecretion


Efferentarteriole

Afferentarteriole

Bloodflow

Glomerularcapsule

Glomerularfiltrate

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Peritubular capillary

Glomerulus

+

+

–

––

–

++–+–

+–

+–+–

–+

+++––+––++––

1

2

3

4

Bloodflow

Glomerularcapsule

BloodflowGlomerular

filtrate

Proximalconvolutedtubule Sodium ions

are reabsorbed byactive transport

Negatively charged ionsare attracted to positivelycharged ions

As concentration of ions(solute) increases in plasma,osmotic pressure increases

Water moves from proximaltubule to capillary byosmosis

Bloodflow

Isotonictubular fluid

Na+

Na+

PO4–3

N+

Cl–

HCO3–

Cl–

Na+

H2O

H2O

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Tubular Secretion• Tubular secretion

• Substances move from the plasma of the peritubular capillaries into the fluid of the renal tubules• Active transport mechanisms function here• Secretion of substances such as drugs and ions

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Blood flowPeritubular capillary

Distal convoluted tubule

Na+

Na+

Na+

Na+

Na+

K+ K+

K+

K+

H+

H+

Collecting duct

K+ or H+

Na+

Na+

Tubular reabsorption Tubular secretion

Tubular fluid

Ascending limbof nephron loop

Na+

Na+

Na+

Na+

Na+

Na+

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Regulation of Urine Concentration and Volume

• Hormones such as aldosterone and ANP affect the solute concentration of urine, particularly sodium• The ability of the kidneys to maintain the internal environment rests in a large part on their ability to concentrate urine by reabsorbing large volumes of water• The distal convoluted tubule and the collecting duct are impermeable to water, so water may be excreted as dilute urine• If ADH is present, these segments become permeable, and water is reabsorbed by osmosis into the extremely hypertonic medullary interstitial fluid• A countercurrent mechanism in the nephron loops (the descending and the ascending limbs) ensures that the medullary interstitial fluid becomes hypertonic• This mechanism is known as the countercurrent multiplier• The vasa recta also contributes as a countercurrent mechanism

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Collecting duct

Dilute urine Concentrated urine

Collecting duct

H2O

H2O

(a) (b)

Medullaryinterstitial fluid

Distal convolutedtubule

Hypertonicinterstitialfluid

Hypertonicinterstitialfluid

high ADH levelslow ADH levels

H2O

H2O H2O

H2OH2O

H2O

Medullaryinterstitial fluid

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Isotonic fluid

Hypotonic fluidNa+

Cl–

(a) (b)

Na+

Cl–

Salty

H2O1

2

3

Descendinglimb(permeableto water)

IncreasingNaClconcentration

Thick ascendinglimb (impermeableto water)

Hypertonicfluid

Medullaryinterstitialfluid

Moresalty

Evenmoresalty

Na+

Cl–H2O

Na+

Cl–H2O

H2O

H2O

H2O

Na+

Cl–

Na+

Cl–

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NaCl

NaCl

NaClNaCl NaCl

NaCl

NaCl

NaCl

Bloodflow

IncreasingNaClconcentration

Bloodflow

Medullaryinterstitialfluid

Vasarecta

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Urea and Uric Acid Excretion• Urea:

• A by-product of amino acid catabolism• The plasma concentration reflects the amount or protein in diet• It enters the renal tubules through glomerular filtration• It contributes to the reabsorption of water from the collecting duct• About 80% is recycled

• Uric acid:• Is a product of nucleic acid metabolism• It enters the renal tubules through glomerular filtration• Most reabsorption occurs by active transport• About 10% is secreted and excreted

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Urine Composition• Urine composition reflects the volumes of water and solutes that the kidneys must eliminate from the body or retain in the internal environment to maintain homeostasis• It varies from time to time due to dietary intake and physical activity, but is:

• About 95% water• Usually contains urea, uric acid, and creatinine• May contain trace amounts of amino acids and varying amounts of electrolytes• Volume varies with fluid intake and environmental factors

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Renal Clearance• This is the rate at which a chemical is removed from the plasma• It indicates kidney efficiency• Tests of renal clearance:

• Inulin clearance test• Creatinine clearance test• Para-aminohippuric acid (PAH) test

• These tests of renal clearance are used to calculate the GFR (glomerular filtration rate)

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20.4: Elimination of Urine• After forming along the nephrons, urine:

• Passes the collecting ducts to:• Openings of the renal papillae:

• Enters the minor and major calyces:• Passes through the renal pelvis:• Enters into the ureters:• Enters into the urinary bladder:•The urethra carries the urine out of the body

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Ureters• The ureters:

• Each is about 25 centimeters long• Extends downward posterior to the parietal peritoneum• Runs parallel to vertebral column• Join the urinary bladder in the pelvic cavity• The wall of ureter has three layers:

• The inner mucous coat• The middle muscular coat• The outer fibrous coat

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Mucous coat

LumenMuscular coat

Fibrous coat

Adipose tissue

© Per H. Kjeldsen

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Urinary Bladder• The urinary bladder is a hollow, distensible, muscular organ located within the pelvic cavity, posterior to the symphysis pubis and inferior to the parietal peritoneum

• It contacts the anterior walls of the uterus and vagina in the female, and lies posteriorly against the rectum in the male

• The openings for the ureters is the area of trigone

• It has four layers: inner mucous coat, a submucous coat, a muscular coat, and an outer serous coat

• Smooth muscle fibers comprise the detrusor muscle which is the muscle of the bladder wall

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Symphysis pubis

Prostate gland

Urinary bladder

Urethra

Ureter

Rectum

Parietal peritoneum

Abdominal wall

Rectum

(a) (b)



(a) (b)

Mucous coat

Trigone

Internal urethral sphincter

Neck

Prostate gland

Urethra

Serous coatUrinary bladder

Ureter

Ureter

Prostate gland

UrethraRegion of externalurethral sphincter

Seminalvesicle

Ductus (vas)deferens

Detrusormuscle

Submucouscoat

Openings ofthe ureters

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Muscular coat Mucous coat

Lumen

Submucouscoat

© John D. Cunningham/Visuals Unlimited

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Trigone

Ureter

Penis

(b)

Urethra

Ureter

(a)

Urinarybladder

Externalurethral orifice

Urinarybladder

Prostategland

Bulbourethralgland

Membranousurethra

Prostaticurethra

Penileurethra

Externalurethral orifice

Trigone


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Urethra• The urethra is a tube that conveys urine from the urinary bladder to the outside of the body• Its wall is lined with a mucous membrane and it has a thick layer of longitudinal smooth muscle fibers• In a female:

• It is about 4 centimeters long• It runs obliquely

• In a male:• It is about 17.5 centimeters long• It has a dual function for both urination and reproduction• It has three sections:

• Prostatic urethra• Membranous urethra• Penile urethra

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Urethral glands

Muscle layer

Lumen of urethra

Mucous membrane

© Ed Reschke

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Micturition

• Urine leaves the urinary bladder by micturition or urination reflex

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Micturition

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20.5: Lifespan Changes• The urinary system is sufficiently redundant, in both structure and function, to mask age-related changes• The kidneys become slower to remove nitrogenous wastes and toxins and to compensate for changes that maintain homeostasis• Changes include:

• The kidneys appear scarred and grainy • Kidney cells die• By age 80 the kidneys have lost a third of their mass• Kidney shrinkage is due to loss of glomeruli• Proteinuria may develop• The renal tubules thicken• It is harder for the kidneys to clear certain substances• The bladder, ureters, and urethra lose elasticity• The bladder holds less urine

Education

chapter 20: urinary system