© 2014 Pearson Education, Inc. The Urinary System.

© 2014 Pearson Education, Inc.

The Urinary System


The Urinary System

• Important functions of the kidneys

• Maintain the chemical consistency of blood

• Filters 1 liter of blood every minute, but only 125 ml will enter the tubular system which will eventually form 1cc/minute of urine

• Send toxins, metabolic wastes, and excess water out of the body

• Main waste products are three nitrogenous compounds

• Urea

• Uric acid

• Creatinine


Organs of the Urinary System

• Kidneys – filter blood

• Ureters – transport urine from each kidney to

• Urinary bladder – stores urine

• Urethra – expels urine from bladder outside of the body


Figure 24.1 Organs of the urinary system.

Hepatic veins (cut)

Esophagus (cut)

Inferior vena cava

Adrenal gland

Aorta

Iliac crest

Renal artery

Renal hilum

Renal vein

Kidney

Ureter

Urinarybladder

Rectum (cut)

Uterus

Urethra


Location and External Anatomy of Kidneys

• Kidneys are red-brown in color

• Located retroperitoneally

• Behind the peritoneum

• Lateral to T12–L3 vertebrae

• Average kidney is 12 cm tall, 6 cm wide, 3 cm thick

• Hilum

• Is the concave surface

• Vessels and nerves enter and exit


Location and External Anatomy of Kidneys

• Fibrous capsule

• Capsule of dense connective tissue surrounds the kidney

• Inhibits spread of infections

• Perirenal fat capsule

• External to renal capsule

• Renal fascia

• External to perirenal fat capsule

• Contains fat


Figure 24.2b Position of the kidneys abutting the posterior abdominal wall.

12th rib


Figure 24.2a Position of the kidneys abutting the posterior abdominal wall.

Peritoneum

Anterior

Peritoneal cavity(organs removed)

Renalvein

Renalartery

Posterior

Aorta

Inferiorvena cava

Renal fascia

posterior

Perirenalfat capsule

Supportivetissue layers

Fibrouscapsule

Body wall

anterior


Figure 24.2c Position of the kidneys abutting the posterior abdominal wall.

Left renal vein

Left kidney

Erector spinaemuscle in posteriorabdominal wall

Jejunum

Duodenum

Liver

Inferiorvena cava

Aorta

Rightkidney

Vertebra L1


Internal Gross Anatomy of the Kidneys

• Frontal section through the kidney• Renal cortex

• Superficial region, granular appearance

• Renal medulla consists of

• Cone-shaped renal pyramids

• Renal pelvis

• Major calices

• Minor calices



• Gross vasculature

• Renal arteries branch into segmental arteries

• Segmental arteries branch into interlobar arteries

• Arcuate arteries branch from interlobar arteries


Figure 24.3 Internal anatomy of the kidney.

Renal hilum

Renal cortex

Renal medulla

Renal pelvis

Major calyx

Papilla ofpyramid

Minor calyx

Ureter

Renal pyramid inrenal medulla

Renal column

Fibrous capsule

Diagrammatic viewPhotograph of right kidney,frontal section


Figure 24.4a Blood vessels of the kidney.Cortical radiatevein

Cortical radiateartery

Arcuate vein

Arcuate artery

Interlobar vein

Interlobar artery

Segmental arteries

Renal vein

Renal artery

Renal pelvis

Ureter

Renal medulla

Renal cortex

Frontal section, posterior view,illustrating major blood vessels


Figure 24.4b Blood vessels of the kidney.

Path of blood flow through renal blood vessels

Glomerulus (capillaries)

Nephron-associated blood vessels

Afferent glomerulararteriole

Efferent glomerulararteriole

Cortical radiate arteryPeritubular capillaries

and vasa recta

Arcuate artery

Interlobar artery

Segmental artery

Renal artery

Aorta Inferior vena cava

Renal vein

Interlobar vein

Arcuate vein

Cortical radiate vein



• Nerve supply—renal plexus

• A network of autonomic fibers

• An offshoot of the celiac plexus

• Supplied by sympathetic fibers from

• Lowest thoracic splanchnic nerve

• First lumbar splanchnic nerve


Microscopic Anatomy of the Kidneys

• Nephron is the functional unit of the kidney

• Over 1 million nephrons in each kidney


Mechanisms of Urine Production

• Filtration

• Filtrate of blood leaves kidney capillaries

• Resorption

• Most nutrients, water, and essential ions reclaimed

• Secretion

• Active process of removing undesirable molecules


Figure 24.5 Basic mechanisms of urine formation.

Afferent glomerulararteriole

Glomerularcapillaries

Efferent glomerulararteriole

Glomerular capsule

Renal tubule andcollecting ductcontaining filtrate

Peritubularcapillary

To cortical radiate vein

Corticalradiateartery

Urine

Glomerular filtration

Tubular resorption

Tubular secretion

Three majorrenal processes:

2

3

2

3

1

2

3

1

1

2

3


Nephron Structure

• Nephron is composed of

• Renal tubule

• Renal corpuscle


Nephron Structure

• 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

• The filtration membrane

• Filter that lies between blood in the glomerulus and capsular space

• Consists of three layers

1. Fenestrated endothelium of the capillary

2. Filtration slits between foot processes of podocytes

3. Basement membrane


Filtration Membrane

• Basement membrane and slit diaphragm

• Hold back most proteins

• Allow passage of

• Water

• Ions

• Glucose

• Amino acids

• Urea


Figure 24.6a Renal corpuscle and the filtration membrane.

Efferentglomerulararteriole

Afferentglomerulararteriole

Glomerularcapsular space

Proximalconvolutedtubule

Parietal layerof glomerularcapsule

Glomerular capillarycovered by podocyte-containing visceral layerof glomerular capsule

Renal corpuscle


Figure 24.6b Renal corpuscle and the filtration membrane.

Podocytecell body

Fenestrations(pores)

Glomerularcapillary endothelium(podocyte coveringand basementmembrane removed)

Cytoplasmic extensionsof podocytes

Filtration slits

Foot processesof podocyte

Glomerular capillary surrounded by podocytes


Figure 24.6d Renal corpuscle and the filtration membrane.

CapillaryCapillary endothelium

Basement membrane

Foot processes of podocyteof glomerular capsule

Filtration slit

Slit diaphragm

Filtration membrane

PlasmaFiltratein capsularspace

Foot processesof podocyteFenestration

(pore)Three parts of the filtration membrane


Renal Tubule

• Filtrate proceeds to renal tubules from glomerulus

• Proximal convoluted tubule

• Nephron loop

• Descending limb

• Descending thin limb (DTL)

• Ascending thin limb (ATL)

• Thick ascending limb (TAL)

• Distal convoluted tubule


Renal Tubule

• Collecting ducts

• Receive urine from several nephrons

• Play an important role in conserving body fluids

• Posterior pituitary secretes ADH

• Increases permeability of collecting ducts and distal convoluted tubules to water


Figure 24.7 Location and structure of nephrons.

Renal cortex

Renal medulla

Renal pelvis

Ureter

Kidney

Renal corpuscleGlomerular capsuleGlomerulus

Distalconvolutedtubule


Cortex

Medulla

Thick limbThin limb

Glomerular capsule: visceral layer

Proximal convoluted tubule cells

Fenestrated endotheliumof the glomerulus

Microvilli Mitochondria

Highly infolded plasma membrane

Podocyte

Basementmembrane

Distal convoluted tubule cells

Nephron loop (thin-limb) cells

Principal cell Intercalated cell

Collecting duct cells

Glomerular capsule: parietal layer

Nephron loopDescending limbAscending limb

Collectingduct


Classes of Nephron

• Cortical nephrons

• 85% of nephrons

• Juxtamedullary nephrons

• 15% of nephrons

• Contribute to kidney’s ability to concentrate urine


Figure 24.9 Cortical and juxtamedullary nephrons and their blood vessels.

Kidney

Nephron loop

Arcuate artery

Arcuate vein

Descendinglimb ofnephron loop

Ascendinglimb ofnephron loop

Peritubularcapillaries

Vasa recta

Cortex-medullajunction

Efferentarteriole

Afferent arteriole

Afferent arteriole

Efferentarteriole

Distal convoluted tubule

Collecting duct

Cortical radiate vein

Cortical radiate artery

Juxtamedullary nephron• Long nephron loop• Glomerulus closer to the cortex-medulla junction• Efferent arteriole supplies vasa recta

Cortical nephron• Short nephron loop• Glomerulus further from the cortex-medulla junction• Efferent arteriole supplies peritubular capillaries

Glomerulus(capillaries)

Renalcorpuscle

Glomerularcapsule


Peritubularcapillary bed

Glomerulus

Afferentarteriole

Efferentarteriole


Blood Vessels Associated with Nephrons

• Nephrons associate closely with two capillary beds

• Glomeruli

• Peritubular capillaries in cortical nephrons or vasa recta in juxtamedullary nephrons



• Glomeruli

• Produce filtrate that becomes urine

• Fed and drained by arterioles

• Afferent glomerular arteriole

• Efferent glomerular arteriole



• Glomeruli

• Efferent arteriole has a smaller diameter than afferent arteriole

• Generates approximately 1 liter of filtrate every 8 minutes

• 99% of filtrate is resorbed by tubules



• Peritubular capillaries

• Arise from the efferent arterioles draining cortical glomeruli

• Are adapted for absorption

• Low-pressure, porous 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


Juxtaglomerular Complex

• Juxtaglomerular complex

• Functions in regulating blood pressure

• An area of specialized contact between the terminal end of the ascending loop and afferent arteriole

• Granular cells—modified smooth muscle cells with secretory granules (similar to endocrine)

• Contain the hormone renin

• Renin—secreted in response to falling blood pressure in afferent arteriole



• Macula densa—end of nephron loop

• Adjacent to granular cells

• Tall, closely packed epithelial cells

• Monitor solute concentration in the filtrate

• Signal granular cells to secrete renin

• Initiates renin-angiotensin mechanism



• Mesangial cells

• Located around capillaries of the glomerulus and constrict to control blood flow

• They also detect glucose levels by sending processes (membrane extensions) into the lumen of the capillary

• Extraglomerular mesangial cells

• Interact with macula densa and granular cells

• Help regulate blood pressure


Figure 24.10 Juxtaglomerular complex.

Glomerular capsule



Glomerulus


Capsular space

Parietal layerof glomerularcapsule

Foot processesof podocytes

Podocyte cell body(visceral layer)

Red blood cell

Proximaltubule cell

Lumens ofglomerularcapillaries

Endothelial cellof glomerularcapillary

Mesangial cellsbetween capillaries

Renal corpuscle

Juxtaglomerularcomplex

Macula densa cellsof the ascending limbof nephron loop

Extraglomerularmesangial cells

Granular cells


Juxtaglomerularcomplex


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


Figure 24.11 Microscopic structure of the ureter, cross section (12).

Lumen

Mucosa

Adventitia

Transitionalepithelium

Laminapropria

MuscularisLongitudinallayer

Circularlayer


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 of umbilical cord – it looks like a raised ridge outside of the bladder

• Prostate

• In males

• Lies directly inferior to the bladder

• Surrounds the urethra


Figure 24.12 Position of the urinary bladder in reference to the pelvic organs.

Ureter notillustrated in (b)

Uterus

Urinary bladder

Ductus deferens

Pubic symphysis

Urethra

Urachus

Sagittal section throughmale pelvis, urinary bladdershown in lateral view

Sagittal section throughfemale pelvis

Prostate

Vagina


Urinary Bladder

• Urinary bladder is composed of three layers

1. Mucosa—transitional epithelium

2. Thick muscular layer—detrusor

3. Fibrous adventitia


Figure 24.13 Histology of the bladder.

Lumen of the bladder


Laminapropria

Muscular layer(detrusor)

Micrograph of the bladderwall (25 )

Epithelium lining the lumenof the bladder (285 )


Laminapropria

Basementmembrane


Figure 24.14a Structure of the urinary bladder and urethra.

Peritoneum

Ureter

Rugae

Detrusor

Adventitia

Ureteric orifices

Trigone of bladder

Bladder neck

Internal urethralsphincter

Prostate

Prostatic urethra

Spongyurethra

Erectile tissueof penis

External urethral orifice

Male. The long male urethra has three regions:prostatic, intermediate part, and spongy.

Intermediate part of urethra

External urethralsphincter

Urogenital diaphragm


Figure 24.14b Structure of the urinary bladder and urethra.

Peritoneum

Ureter

Rugae

Detrusor

Ureteric orifices

Bladder neck

Internal urethralsphincter


Urogenital diaphragm Urethra

Female

Trigone

External urethralorifice


Urethra

• Epithelium of urethra

• Transitional epithelium

• At the proximal end (near the bladder)

• Stratified and pseudostratified columnar—mid urethra (in males)

• Stratified squamous epithelium

• At the distal end (near the urethral opening)


Urethra

• Internal urethral sphincter

• Involuntary smooth muscle

• External urethral sphincter

• Voluntarily inhibits urination

• Relaxes when one urinates


Urethra

• In females

• Length of 3–4 cm

• In males—20 cm in length; three named regions

• Prostatic urethra

• Passes through the prostate gland

• Intermediate part of urethra

• Through the urogenital diaphragm

• Spongy (penile) urethra

• Passes through the length of the penis


Figure 24.15 Micturition.

Pons

Pontinemicturitioncenter

Lower thoracicor upper lumbarspinal cord

()

()

Inferiorhypogastricganglion

Hypogastricnerve

Bladder

Pelvicnerves 1

4

2

3

5

Pelvic splanchnicnerves


Internalurethralsphincter

Visceral afferent

Sympathetic

Somatic efferent

Parasympathetic

Interneuron

()()

Visceral afferent impulses fromstretch receptors in the bladder wallare carried to the spinal cord andthen, via ascending tracts, to thepontine micturition center.

Integration in pontine micturitioncenter initiates the micturitionresponse. Descending pathwayscarry impulses to motor neurons inthe spinal cord.

Parasympathetic efferentsstimulate contraction of thedetrusor and open the internalurethral sphincter.

1

2

3

Sacralspinalcord

Sympathetic efferents to thebladder are inhibited.

Somatic motor efferents to theexternal urethral sphincter areinhibited; the sphincter relaxes.Urine passes through the urethra;the bladder is emptied.

4

5


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


The Urinary System Throughout Life

• Kidney and bladder function declines with advancing age

• Nephrons decrease in size and number

• Tubules are less efficient at secretion and resorption

• Filtration declines

• Recognition of desire to urinate is delayed

• Loss of muscle tone in the bladder

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© 2014 Pearson Education, Inc. The Urinary System.

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