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C H A P T E R

The Urinary System

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The Urinary System

• Kidneys • Maintain the chemical consistency of the blood• Filter many liters of fluid from blood• Send toxins, metabolic wastes, and excess

water out of the body• Main waste products

• Urea, uric acid, and creatinine

Organs of the Urinary System

• Kidneys• Ureters• Urinary bladder• Urethra

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Organs of the Urinary System

Renal arteryRenal hilumRenal vein

Kid

Esophagus (cut)Inferior venacava Adrenal gland

Hepatic veins(cut)

Aorta

Figure 24.1

Kidney

Ureter

Urinarybladder

Urethra

Iliac crest

Rectum (cut)Uterus

Location and External Anatomy of Kidneys

• Located retroperitoneally• Lateral to T12–L3 vertebrae • Average kidney – 12 cm tall, 6 cm wide, 3 cm

thick• Hilus – on concave surface

• Vessels and nerves enter and exit• Renal capsule (Fibrous capsule) surrounds the

kidney

Relationship of the Kidneys to Vertebra and Ribs

Figure 24.2b

12th rib

(b)

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Position of the Kidneys with in the Posterior Abdominal Wall

Inferiorvena cava

Aorta

Peritoneum Peritoneal cavity(organs removed)

Anterior

Figure 24.2a

Body wall

Perirenalfat capsule

Renalartery

Renalvein

Fibrouscapsule

Renal fasciaanteriorposterior

Supportivetissue layers

Body ofvertebra L2

Posterior(a)

Internal Gross Anatomy of the Kidneys

• Frontal section through the kidney• Renal cortex, renal pyramids, and renal pelvis

• Gross vasculature • Nerve supply – renal plexus

• A network of autonomic fibers• An offshoot of the celiac plexus

Internal Gross Anatomy of the Kidneys

Renal cortex

Renalmedulla

Major calyx

Renalhilum

Figure 24.3

Major calyx

Papilla ofpyramidRenal pelvis

UreterMinor calyx

Renal column

Renal pyramidin renal medulla

Fibrous capsule

(a) Photograph of right kidney, frontal section (b) Diagrammatic view

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Summary of Blood Vessels Supplying the Kidney

Cortical radiate vein Cortical radiate artery

Arcuate veinArcuate arteryInterlobar veinInterlobar arterySegmental arteriesRenal vein

Figure 24.4a

Renal arteryRenal pelvis

Ureter

Renal medulla

Renal cortex

(a) Frontal section, posterior view, illustratingmajor blood vessels

Summary of Blood Vessels Supplying the Kidney

Aorta

Renal artery

Segmental artery

Interlobar artery

Inferior vena cava

Renal vein

Interlobar vein

Arcuate vein

Figure 24.4b

Arcuate artery

Cortical radiate artery

Afferent arteriole

Glomerulus (capillaries)

Nephron-associated blood vessels(see Figure 24.9)

Cortical radiate vein

Peritubular capillariesand vasa recta

Efferent arteriole

(b) Path of blood flow through renalblood vessels

Microscopic Anatomy of the Kidneys

• Uriniferous tubules • Composed of:

• Nephron – Basic unit of the kidney• renal corpuscle• renal tubules

• Collecting duct – involved in concentrating urine

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Uriniferous Tubule

Fenestrated endothelium of the glomerulus

Microvilli

Podocyte

Basementmembrane

Mitochondria

Proximal l t d

Distalconvolutedtubule

Glomerular capsuleRenal corpuscle

Glomerulus

Glomerular capsule: parietal layer

Glomerular capsule: visceral layer

Renal cortex

Renal medulla

Renal pelvis

UreterKidney

Figure 24.7

Cortex

Medulla

Highly infolded plasmamembrane

convolutedtubule

Descending limbNephron loop

Ascending limb

Thick segment

Collectingduct

Intercalatedcell

Principal cell

Thin segment

Proximal convoluted tubule cells

Distal convoluted tubule cells

Nephron loop (thin-segment) cells

Collecting duct cells

Mechanisms of Urine Production

• Filtration• Filtrate of blood leaves kidney capillaries

• Reabsorption• Most nutrients, water, and essential ions

reclaimed• Secretion

• Active process of removing undesirable molecules

Basic Kidney Functions

Corticalradiateartery

Afferent arterioleGlomerularcapillaries

Efferent arteriole

Glomerular capsule

Rest of renal tubule

Figure 24.5

Rest of renal tubulecontaining filtrate

Peritubularcapillary

To cortical radiate vein

Urine

Glomerular filtrationTubular resorptionTubular secretion

Three majorrenal processes

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Nephron Structure

• Nephron is composed of• Renal corpuscle• Renal tubule

Uriniferous Tubule

Fenestrated endothelium of the glomerulus

Microvilli

Podocyte

Basementmembrane

Mitochondria

Proximal l t d

Distalconvolutedtubule

Glomerular capsuleRenal corpuscle

Glomerulus

Glomerular capsule: parietal layer

Glomerular capsule: visceral layer

Renal cortex

Renal medulla

Renal pelvis

UreterKidney

Figure 24.7

Cortex

Medulla

Highly infolded plasmamembrane

convolutedtubule

Descending limbNephron loop

Ascending limb

Thick segment

Collectingduct

Intercalatedcell

Principal cell

Thin segment

Proximal convoluted tubule cells

Distal convoluted tubule cells

Nephron loop (thin-segment) cells

Collecting duct cells

Renal Corpuscle

• Renal corpuscle—first part of nephron• Glomerulus and glomerular capsule

• Glomerulus—tuft of capillaries• Capillaries of glomerulus are fenestrated

• Glomerular (Bowman’s) capsuleGlomerular (Bowman s) capsule• Parietal layer—simple squamous

epithelium• Visceral layer—consists of podocytes

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Filtration Membrane

• Basement membrane and slit diaphragm• Hold back most proteins• Allow through

• Water• Ions• Glucose• Amino acids• Urea

Filtration slits

Cytoplasmic extensionsof podocytes

Renal Corpuscle and the Filtration Membrane

Proximal

Afferentarteriole

Glomerularcapsular spaceEfferent

arteriole

(b) Glomerular capillary surrounded by podocytes

Glomerularcapillary endothelium (podocyte covering and basement membrane removed)

Fenestrations(pores)

Podocytecell body

Foot processesof podocyte

Filtration slits

Figure 24.6a, b

Glomerular capillarycovered by podocyte-containing visceral layerof glomerular capsule

convolutedtubuleParietal layer

of glomerular capsule

(a) Renal corpuscle

Renal Corpuscle and the Filtration Membrane

Basement membraneCapillary endotheliumCapillary

Filtration membrane

Foot processes of podocyteof glomerular capsule

Figure 24.6d(d) Three parts of the filtration membrane

Fenestration(pore)

Filtrate in capsularspace

Foot processesof podocyte

Filtrationslit

SlitdiaphragmPlasma

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Renal Tubule

• Filtrate proceeds to renal tubules from glomerulus • Proximal convoluted tubule• Nephron loop

• Descending limb• Thin segment• Thick segment

• Distal convoluted tubule

Collecting ducts• Receive urine from several nephrons• Play an important role in conserving body

fluids

Renal Tubule

Fenestrated endothelium of the glomerulus

Microvilli

Podocyte

Basementmembrane

Mitochondria

Proximal l t d

Distalconvolutedtubule

Glomerular capsuleRenal corpuscle

Glomerulus

Glomerular capsule: parietal layer

Glomerular capsule: visceral layer

Renal cortex

Renal medulla

Renal pelvis

UreterKidney

Figure 24.7

Cortex

Medulla

Highly infolded plasmamembrane

convolutedtubule

Descending limbNephron loop

Ascending limb

Thick segment

Collectingduct

Intercalatedcell

Principal cell

Thin segment

Proximal convoluted tubule cells

Distal convoluted tubule cells

Nephron loop (thin-segment) cells

Collecting duct cells

Renal TubuleRenal corpuscle

Glomerulus

Glomerular capsular spaceSquamous epithelium of parietal layer of glomerular capsule

Figure 24.8a

(a) Photomicrograph of renal cortical tissue (165X)

Distal convolutedtubules (clear lumens)

Proximal convolutedtubules (fuzzy lumensdue to long microvilli)

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Micrograph through the Renal Medulla

Thin segmentsof nephron loop

Vasa recta withblood cells

Figure 24.8b

(b) Photomicrograph through therenal medulla (215X)

Collectingducts

within

Classes of Nephron

• Cortical nephrons• 85% of nephrons

• Juxtamedullary nephrons• 15% of nephrons• Contribute to kidney’s ability to concentrate

urine

Classes of Nephron

Ureter

Renalpelvis

CortexMedulla

Cortical radiate veinCortical radiate arteryAfferent arteriole

Afferent arteriole

Collecting ductDistal convoluted tubule

Efferentarteriole

Peritubularcapillaries

Glomerular capillaries(glomerulus)

Glomerular (Bowman’s)capsule

Renalcorpuscle

Ascending orthick limb of thenephron loop

Efferentarteriole

Proximalconvolutedtubule

• Has short nephron loop and glomerulusfurther from the corticomedullary junction

• Efferent arteriole supplies peritubular capillaries

Cortical nephron• Has long nephron loop and glomeruluscloser to the corticomedullary junction

• Efferent arteriole supplies vasa recta

Juxtamedullary nephron

Figure 24.9

Corticomedullaryjunction

Peritubularcapillary bed

Efferentarteriole

Afferentarteriole

Glomerulus

(b)

Kidney

(a)

Vasa recta

Nephron loop

Arcuate artery

Arcuate vein

Descendingor thin limb of nephron loop

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Blood Vessels Associated with Nephrons

• Glomeruli• Produce filtrate that becomes urine• Fed and drained by arterioles

• Afferent and efferent arteriole• Efferent arteriole has a smaller diameter

than afferent arteriole• Generate 1 liter of fluid every 8 minutes

• 99% of filtrate is resorbed by tubules

Blood Vessels Associated with Nephrons

• Peritubular capillaries• Arise from the efferent arterioles• Are adapted for absorption

• Low-pressure, porous capillaries• All molecules secreted by nephrons into

urine are from peritubular capillaries

Blood Vessels Associated with Nephrons

• Vasa recta• Continue from efferent arterioles of

juxtamedullary nephrons• Are thin-walled looping vessels

• Descend into the medulla• Are part of the kidney’s urine concentrating

mechanism

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Microscopic Anatomy of the Kidney

• Juxtaglomerular apparatus• Functions in the regulation of blood pressure

• Granular cells – secrete renin • Macula densa – portion of distal convoluted tubule

• Tall, closely packed epithelial cellsTall, closely packed epithelial cells• Act as chemoreceptors

Juxtaglomerular ApparatusGlomerulusGlomerular capsule

Afferentarteriole

Efferentarteriole

Red blood cell

Podocyte cell body(visceral layer)

Foot processesof podocytes

Parietal layerof glomerularcapsule

Proximaltubule cell

Efferentarteriole

Capsularspace

Figure 24.10

Lumens of glomerularcapillaries

Endothelial cellof glomerularcapillary

Macula densa cells of the ascending limbof nephron loop

Granular cells

Extraglomerularmesangial cells

Afferent arteriole

Renal corpuscleJuxtaglomerularapparatus

Mesangial cellsbetween capillaries

Juxtaglomerularapparatus

Ureters

• Carry urine from the kidneys to the urinary bladder

• Oblique entry into bladder prevents backflow of urine

• Histology of ureter• Mucosa – transitional epithelium• Muscularis – two layers

• Inner longitudinal layer• Outer circular layer

• Adventitia – typical connective tissue

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Urinary Bladder

• A collapsible muscular sac• Stores and expels urine

• Full bladder—spherical• Expands into the abdominal cavity

• Empty bladder—lies entirely within the pelvisp y y p

Urinary Bladder

• Urachus—closed remnant of the allantois • Prostate gland

• In males• Lies directly inferior to the bladder• Surrounds the urethra

Urinary Bladder

Ureter notillustrated in (b)Uterus

Urinary bladderDuctus deferensP bi h i

Urachus

Figure 24.13

Pubic symphysisProstateVagina

Urethra

(a) Sagittal section through male pelvis,urinary bladder shown in lateral view

(b) Sagittal section throughfemale pelvis

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Structure of the Urinary Bladder and UrethraUreter

Trigone of bladder

ProstateMembranous urethraProstatic urethra

Peritoneum

RugaeDetrusor muscle

Bladder neckInternal urethral sphincter

Ureteric orificesAdventitia

Figure 24.15a

External urethral sphincterUrogenital diaphragm

Spongy urethra

Erectile tissue of penis

(a) Male. The long male urethra has three regions: prostatic, membranous, and spongy. External urethral orifice

Structure of the Urinary Bladder and Urethra

Ureter

Peritoneum

Rugae

Detrusor muscle

Ureteric orifices

Figure 24.15b

Trigone

Bladder neckInternal urethralsphincter

External urethralsphincter

Urogenital diaphragm

UrethraExternal urethralorifice(b) Female

Urethra

• Epithelium• Transitional epithelium – near the bladder• Stratified and pseudostratified columnar – mid

urethra• Stratified squamous epithelium – near the distal

end• Internal urethral sphincter – involuntary smooth

muscle• External urethral sphincter – voluntarily inhibits

urination

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Urethra

• In females – length of 3–4 cm• In males – 20 cm in length – three named regions

• Prostatic urethra – passes through the prostate gland

• Membranous urethra – through the urogenital diaphragm

• Spongy (penile) urethra – passes through the length of the penis

MicturitionPonsPontinemicturitioncenter

Lower thoracicor upper lumbarspinal cord

I f i

Visceral afferent impulses from stretch receptors in the bladder wall are carried to the spinal cord and then, via ascending tracts, to the pontine micturition center.

Integration in pontine micturition center initiates the micturition response. Descending pathways carry impulses to motor neurons in the spinal cord.

Parasympathetic efferents stimulate contraction of the d t l d th

(–)

(+)1

2

3

2

4

Figure 24.16

HypogastricnerveBladder

Pelvicnerves

Pelvicsplanchnicnerves

Sacral spinalcord

Internal urethralsphincter External urethral sphincter

Inferiorhypogastricganglion

detrusor muscle and open the internal urethral sphincter.

Somatic motor efferents to the external urethral sphincter are inhibited; the sphincter relaxes. Urine passes through the urethra; the bladder is emptied.

Sympathetic efferents to the bladder are inhibited.

(–)(+)

Visceral afferentSympatheticSomatic efferentParasympatheticInterneuron

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3

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Disorders of the Urinary System

• Urinary tract infections – more common in females• Burning sensation during micturition

• Renal calculi – kidney stones• Bladder cancer – 3% of cancers – more common in men• Kidney cancer – arises from epithelial cells of y p

uriniferous tubules

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The Urinary System Throughout Life

• Kidney and bladder function declines with advancing age• Nephrons decrease in size and number• Tubules less efficient at secretion and

reabsorption• Filtration declines • Desire to urinate is delayed• Loss of muscle tone in the bladder