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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

Figure 24.1

Renal arteryRenal hilumRenal vein

Kidney

Ureter

Urinarybladder

Urethra

Esophagus (cut)Inferior venacava Adrenal gland

Hepatic veins(cut)

Iliac crest

Aorta

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

Figure 24.2a

Body wall

Perirenalfat capsule

Renalartery

Renalvein

Inferiorvena cava

Aorta

Fibrouscapsule

Renal fasciaanteriorposterior

Supportivetissue layers

Body ofvertebra L2

Peritoneum Peritoneal cavity(organs removed)

Anterior

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

Figure 24.3

Renal cortex

Renalmedulla

Major calyx

Papilla ofpyramidRenal pelvis

UreterMinor calyx

Renal column

Renal pyramidin renal medulla

Fibrous capsule

Renalhilum

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

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Summary of Blood Vessels Supplying the Kidney

Figure 24.4a

Cortical radiate vein Cortical radiate artery

Arcuate veinArcuate arteryInterlobar veinInterlobar arterySegmental arteries

Renal artery

Renal vein

Renal pelvis

Ureter

Renal medulla

Renal cortex

(a) Frontal section, posterior view, illustratingmajor blood 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

Uriniferous Tubule

Figure 24.7

Fenestrated endothelium of the glomerulus

Microvilli

Cortex

Medulla

Podocyte

Basementmembrane

Mitochondria

Highly infolded plasmamembrane

Proximal convolutedtubule

Distalconvolutedtubule

Descending limbNephron loop

Ascending limb

Glomerular capsuleRenal corpuscle

Glomerulus

Thick segment

Collectingduct

Intercalatedcell

Principal cell

Thin segment

Proximal convoluted tubule cells

Glomerular capsule: parietal layer

Glomerular capsule: visceral layer

Distal convoluted tubule cells

Nephron loop (thin-segment) cells

Collecting duct cells

Renal cortex

Renal medulla

Renal pelvis

UreterKidney

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Summary of Blood Vessels Supplying the Kidney

Figure 24.4b

Aorta

Renal artery

Segmental artery

Interlobar artery

Arcuate artery

Cortical radiate artery

Afferent arteriole

Glomerulus (capillaries)

Nephron-associated blood vessels(see Figure 24.9)

Inferior vena cava

Renal vein

Interlobar vein

Arcuate vein

Cortical radiate vein

Peritubular capillariesand vasa recta

Efferent arteriole

(b) Path of blood flow through renalblood vessels

The Nephron

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

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Basic Kidney Functions

Figure 24.5

Corticalradiateartery

Afferent arterioleGlomerularcapillaries

Efferent arteriole

Glomerular capsule

Rest of renal tubulecontaining filtrate

Peritubularcapillary

To cortical radiate vein

Urine

Glomerular filtrationTubular resorptionTubular secretion

Three majorrenal processes

Nephron Structure

• Nephron is composed of• Renal corpuscle• Renal tubule

Uriniferous Tubule

Figure 24.7


Microvilli

Cortex

Medulla

Podocyte

Basementmembrane

Mitochondria





Ascending limb


Glomerulus

Thick segment

Collectingduct

Intercalatedcell

Principal cell

Thin segment







Renal cortex

Renal medulla

Renal pelvis

UreterKidney

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Renal Corpuscle

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

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

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

epithelium• Visceral layer—consists of podocytes

Filtration Membrane

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

• Water• Ions• Glucose• Amino acids• Urea

(b) Glomerular capillary surrounded by podocytes

Glomerularcapillary endothelium (podocyte covering and basement membrane removed)

Fenestrations(pores)

Podocytecell body

Foot processesof podocyte

Filtration slits

Cytoplasmic extensionsof podocytes

Renal Corpuscle and the Filtration Membrane

Figure 24.6a, b

Glomerular capillarycovered by podocyte-containing visceral layerof glomerular capsule

ProximalconvolutedtubuleParietal layer

of glomerular capsule

Afferentarteriole

Glomerularcapsular spaceEfferent

arteriole

(a) Renal corpuscle

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Renal Corpuscle and the Filtration Membrane

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

Fenestration(pore)

Filtrate in capsularspace

Foot processesof podocyte

Filtrationslit

Slitdiaphragm

Basement membraneCapillary endotheliumCapillary

Filtration membrane

Foot processes of podocyteof glomerular capsule

Plasma

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

Figure 24.7


Microvilli

Cortex

Medulla

Podocyte

Basementmembrane

Mitochondria





Ascending limb


Glomerulus

Thick segment

Collectingduct

Intercalatedcell

Principal cell

Thin segment







Renal cortex

Renal medulla

Renal pelvis

UreterKidney

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Renal Tubule

Figure 24.8a

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

Renal corpuscle

Distal convolutedtubules (clear lumens)

Proximal convolutedtubules (fuzzy lumensdue to long microvilli)

Glomerulus

Glomerular capsular spaceSquamous epithelium of parietal layer of glomerular capsule

Classes of Nephron

• Cortical nephrons• 85% of nephrons

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

urine

Classes of Nephron

Figure 24.9

Corticomedullaryjunction

Peritubularcapillary bed

Efferentarteriole

Afferentarteriole

Glomerulus

(b)

Ureter

Renalpelvis

Kidney

CortexMedulla

(a)

Cortical radiate veinCortical radiate arteryAfferent arteriole

Afferent arteriole

Collecting ductDistal convoluted tubule

Efferentarteriole

Vasa recta

Nephron loop

Arcuate artery

Arcuate vein

Peritubularcapillaries

Glomerular capillaries(glomerulus)

Glomerular (Bowman’s)capsule

Renalcorpuscle

Ascending orthick limb of thenephron loop

Descendingor thin limb of nephron 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 glomerulus

closer to the corticomedullary junction• Efferent arteriole supplies vasa recta

Juxtamedullary nephron

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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


• 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


• 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 cells• Act as chemoreceptors

Juxtaglomerular Apparatus

Figure 24.10

GlomerulusGlomerular capsule

Afferentarteriole

Efferentarteriole

Red blood cell

Podocyte cell body(visceral layer)

Foot processesof podocytes

Parietal layerof glomerularcapsule

Proximaltubule cell

Lumens of glomerularcapillaries

Endothelial cellof glomerularcapillary

Efferentarteriole

Macula densa cells of the ascending limbof nephron loop

Granular cells

Extraglomerularmesangial cells

Afferent arteriole

Capsularspace

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 pelvis

Urinary Bladder

• Urachus—closed remnant of the allantois • Prostate gland

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

Urinary Bladder

Figure 24.13

Ureter notillustrated in (b)Uterus

Urinary bladderDuctus deferensPubic symphysisProstateVagina

Urethra

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

(b) Sagittal section throughfemale pelvis

Urachus

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Structure of the Urinary Bladder and Urethra

Figure 24.15a

Ureter

Trigone of bladder

ProstateMembranous urethraProstatic urethra

Peritoneum

RugaeDetrusor muscle

Bladder neckInternal urethral sphincter

External urethral sphincterUrogenital diaphragm

Spongy urethra

Erectile tissue of penis

Ureteric orificesAdventitia

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

Structure of the Urinary Bladder and Urethra

Figure 24.15b

Ureter

Trigone

Peritoneum

Rugae

Detrusor muscle

Bladder neckInternal urethralsphincter

External urethralsphincter

Urogenital diaphragm

UrethraExternal urethralorifice

Ureteric orifices

(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

Micturition

Figure 24.16

HypogastricnerveBladder

Pelvicnerves

Pelvicsplanchnicnerves

PonsPontinemicturitioncenter

Lower thoracicor upper lumbarspinal cord

Sacral spinalcord

Internal urethralsphincter External urethral sphincter

Inferiorhypogastricganglion

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 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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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

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

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