The Urinary System

1
The Urinary System
2
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

3
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

4
Figure 24.1 Organs of the urinary system.
Hepatic veins (cut)
Esophagus (cut)
Inferior vena cava
Renal artery
Adrenal gland
Renal hilum
Aorta
Renal vein
Kidney
Iliac crest
Ureter
Rectum (cut)
Uterus
Urinarybladder
Urethra
5
Location and External Anatomy of Kidneys

• Kidneys are red-brown in color
• Located retroperitoneally
• Behind the peritoneum
• Lateral to T12L3 vertebrae
• Average kidney is 12 cm tall, 6 cm wide, 3 cm
  thick
• Hilum
• Is the concave surface
• Vessels and nerves enter and exit

6
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

7
Figure 24.2b Position of the kidneys abutting
the posterior abdominal wall.
12th rib
8
Figure 24.2a Position of the kidneys abutting
the posterior abdominal wall.
Anterior
Inferiorvena cava
Aorta
Peritoneal cavity(organs removed)
Peritoneum
Supportivetissue layers
Renalvein
Renal fascia
anterior
Renalartery
posterior
Perirenalfat capsule
Fibrouscapsule
Body wall
Posterior
9
Figure 24.2c Position of the kidneys abutting
the posterior abdominal wall.
Jejunum
Duodenum
Liver
Inferiorvena cava
Left renal vein
Aorta
Left kidney
Rightkidney
Erector spinaemuscle in posteriorabdominal wall
Vertebra L1
10
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

11
Internal Gross Anatomy of the Kidneys

• Gross vasculature
• Renal arteries branch into segmental arteries
• Segmental arteries branch into interlobar
  arteries
• Arcuate arteries branch from interlobar arteries

12
Figure 24.3 Internal anatomy of the kidney.
Renal hilum
Renal cortex
Renal medulla
Major calyx
Papilla ofpyramid
Renal pelvis
Minor calyx
Ureter
Renal pyramid inrenal medulla
Renal column
Fibrous capsule
Diagrammatic view
Photograph of right kidney,frontal section
13
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
14
Figure 24.4b Blood vessels of the kidney.
Aorta
Inferior vena cava
Renal vein
Renal artery
Segmental artery
Interlobar vein
Arcuate vein
Interlobar artery
Cortical radiate vein
Arcuate artery
Peritubular capillariesand vasa recta
Cortical radiate artery
Afferent glomerulararteriole
Efferent glomerulararteriole
Glomerulus (capillaries)
Nephron-associated blood vessels
Path of blood flow through renal blood vessels
15
Internal Gross Anatomy of the Kidneys

• Nerve supplyrenal 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

16
Microscopic Anatomy of the Kidneys

• Nephron is the functional unit of the kidney
• Over 1 million nephrons in each kidney

17
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

18
Figure 24.5 Basic mechanisms of urine formation.
Afferent glomerulararteriole
Glomerularcapillaries
Efferent glomerulararteriole
Corticalradiateartery
Glomerular capsule
1
Renal tubule andcollecting ductcontaining
filtrate
Peritubularcapillary
2
2
3
3
To cortical radiate vein
Three majorrenal processes
Urine
Glomerular filtration
1
1
Tubular resorption
2
2
Tubular secretion
3
3
19
Nephron Structure

• Nephron is composed of
• Renal tubule
• Renal corpuscle

20
Nephron Structure

• Renal corpusclefirst part of nephron
• Glomerulus and glomerular capsule
• Glomerulustuft of capillaries
• Capillaries of glomerulus are fenestrated
• Glomerular (Bowmans) capsule
• Parietal layersimple squamous epithelium
• Visceral layerconsists of podocytes

21
Filtration Membrane

• The filtration membrane
• Filter that lies between blood in the glomerulus
  and capsular space
• Consists of three layers
• Fenestrated endothelium of the capillary
• Filtration slits between foot processes of
  podocytes
• Basement membrane

22
Filtration Membrane

• Basement membrane and slit diaphragm
• Hold back most proteins
• Allow passage of
• Water
• Ions
• Glucose
• Amino acids
• Urea

23
Figure 24.6a Renal corpuscle and the filtration
membrane.
Glomerularcapsular space
Efferentglomerulararteriole
Afferentglomerulararteriole
Proximal convolutedtubule
Glomerular capillarycovered by
podocyte-containing visceral layerof glomerular
capsule
Parietal layer of glomerularcapsule
Renal corpuscle
24
Figure 24.6b Renal corpuscle and the filtration
membrane.
Cytoplasmic extensionsof podocytes
Filtration slits
Podocytecell body
Fenestrations(pores)
Glomerularcapillary endothelium(podocyte
coveringand basementmembrane removed)
Foot processesof podocyte
Glomerular capillary surrounded by podocytes
25
Figure 24.6d Renal corpuscle and the filtration
membrane.
Filtration membrane
Capillary endothelium
Capillary
Basement membrane
Foot processes of podocyteof glomerular capsule
Filtration slit
Slit diaphragm
Plasma
Filtratein capsularspace
Foot processesof podocyte
Fenestration(pore)
Three parts of the filtration membrane
26
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

27
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

28
Figure 24.7 Location and structure of nephrons.
Renal cortex
Renal medulla
Renal pelvis
Glomerular capsule parietal layer
Ureter
Basementmembrane
Kidney
Podocyte
Renal corpuscle
Fenestrated endotheliumof the glomerulus
Glomerular capsule
Glomerulus
Glomerular capsule visceral layer
Distalconvolutedtubule
Microvilli
Mitochondria
Proximalconvolutedtubule
Highly infolded plasma membrane
Proximal convoluted tubule cells
Cortex
Medulla
Thick limb
Distal convoluted tubule cells
Thin limb
Nephron loop
Descending limb
Ascending limb
Nephron loop (thin-limb) cells
Collectingduct
Principal cell
Intercalated cell
Collecting duct cells
29
Classes of Nephron

• Cortical nephrons
• 85 of nephrons
• Juxtamedullary nephrons
• 15 of nephrons
• Contribute to kidneys ability to concentrate
  urine

30
Figure 24.9 Cortical and juxtamedullary nephrons
and their blood vessels.
Juxtamedullary nephron
Cortical nephron
Long nephron loop
Short nephron loop
Glomerulus closer to the cortex-medulla junction
Glomerulus further from the cortex-medulla
junction
Efferent arteriole supplies vasa recta
Efferent arteriole supplies peritubular
capillaries
Glomerulus(capillaries)
Efferentarteriole
Renalcorpuscle
Cortical radiate vein
Cortical radiate artery
Glomerularcapsule
Afferent arteriole
Collecting duct
Proximalconvolutedtubule
Distal convoluted tubule
Afferent arteriole
Efferentarteriole
Peritubularcapillaries
Ascendinglimb ofnephron loop
Cortex-medullajunction
Arcuate vein
Kidney
Vasa recta
Arcuate artery
Descendinglimb ofnephron loop
Nephron loop
Peritubularcapillary bed
Glomerulus
Afferentarteriole
Efferentarteriole
31
Blood Vessels Associated with Nephrons

• Nephrons associate closely with two capillary
  beds
• Glomeruli
• Peritubular capillaries in cortical nephrons or
  vasa recta in juxtamedullary nephrons

32
Blood Vessels Associated with Nephrons

• Glomeruli
• Produce filtrate that becomes urine
• Fed and drained by arterioles
• Afferent glomerular arteriole
• Efferent glomerular arteriole

33
Blood Vessels Associated with Nephrons

• 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

34
Blood Vessels Associated with Nephrons

• Peritubular capillaries
• Arise from the efferent arterioles draining
  cortical glomeruli
• Are adapted for absorption
• Low-pressure, porous capillaries

35
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 kidneys urine concentrating
  mechanism

36
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 cellsmodified smooth muscle cells with
  secretory granules (similar to endocrine)
• Contain the hormone renin
• Reninsecreted in response to falling blood
  pressure in afferent arteriole

37
Juxtaglomerular Complex

• Macula densaend 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

38
Juxtaglomerular Complex

• 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

39
Figure 24.10 Juxtaglomerular complex.
Glomerular capsule
Glomerulus
Efferentglomerulararteriole
Parietal layerof glomerularcapsule
Afferentglomerulararteriole
Foot processesof podocytes
Podocyte cell body(visceral layer)
Capsular space
Red blood cell
Efferentglomerulararteriole
Proximaltubule cell
Juxtaglomerularcomplex
Macula densa cellsof the ascending limbof
nephron loop
Extraglomerularmesangial cells
Lumens ofglomerularcapillaries
Granular cells
Endothelial cellof glomerularcapillary
Afferentglomerulararteriole
Mesangial cellsbetween capillaries
Juxtaglomerularcomplex
Renal corpuscle
40
Ureters

• Carry urine from the kidneys to the urinary
  bladder
• Oblique entry into bladder prevents backflow of
  urine
• Histology of ureter
• Mucosatransitional epithelium
• Muscularistwo layers
• Inner longitudinal layer
• Outer circular layer
• Adventitiatypical connective tissue

41
Figure 24.11 Microscopic structure of the
ureter, cross section (12?).
Lumen
Mucosa
Transitionalepithelium
Laminapropria
Muscularis
Longitudinallayer
Circularlayer
Adventitia
42
Urinary Bladder

• A collapsible muscular sac
• Stores and expels urine
• Full bladderspherical
• Expands into the abdominal cavity
• Empty bladderlies entirely within the pelvis

43
Urinary Bladder

• Urachusclosed 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

44
Figure 24.12 Position of the urinary bladder in
reference to the pelvic organs.
Ureter notillustrated in (b)
Uterus
Urachus
Urinary bladder
Ductus deferens
Pubic symphysis
Prostate
Vagina
Urethra
Sagittal section throughmale pelvis, urinary
bladdershown in lateral view
Sagittal section throughfemale pelvis
45
Urinary Bladder

• Urinary bladder is composed of three layers
• Mucosatransitional epithelium
• Thick muscular layerdetrusor
• Fibrous adventitia

46
Figure 24.13 Histology of the bladder.
Lumen of the bladder
Transitionalepithelium
Laminapropria
Muscular layer(detrusor)
Transitionalepithelium
Basementmembrane
Laminapropria
Micrograph of the bladderwall (25? )
Epithelium lining the lumenof the bladder (285? )
47
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
Intermediate part of urethra
External urethralsphincter
Urogenital diaphragm
Spongyurethra
Erectile tissueof penis
External urethral orifice
Male. The long male urethra has three
regionsprostatic, intermediate part, and spongy.
48
Figure 24.14b Structure of the urinary bladder
and urethra.
Peritoneum
Ureter
Rugae
Detrusor
Ureteric orifices
Bladder neck
Internal urethralsphincter
Trigone
External urethralsphincter
Urogenital diaphragm
Urethra
External urethralorifice
Female
49
Urethra

• Epithelium of urethra
• Transitional epithelium
• At the proximal end (near the bladder)
• Stratified and pseudostratified columnarmid
  urethra (in males)
• Stratified squamous epithelium
• At the distal end (near the urethral opening)

50
Urethra

• Internal urethral sphincter
• Involuntary smooth muscle
• External urethral sphincter
• Voluntarily inhibits urination
• Relaxes when one urinates

51
Urethra

• In females
• Length of 34 cm
• In males20 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

52
Figure 24.15 Micturition.
1
Visceral afferent impulses fromstretch
receptors in the bladder wallare carried to the
spinal cord andthen, via ascending tracts, to
thepontine micturition center.
Pons
(?)
Pontinemicturitioncenter
2
2
Integration in pontine micturitioncenter
initiates the micturitionresponse. Descending
pathwayscarry impulses to motor neurons inthe
spinal cord.
Lower thoracicor upper lumbarspinal cord
(?)
4
3
Parasympathetic efferentsstimulate contraction
of thedetrusor and open the internalurethral
sphincter.
Inferiorhypogastricganglion
4
Sympathetic efferents to thebladder are
inhibited.
Sacralspinalcord
Hypogastricnerve
Pelvicnerves
5
Somatic motor efferents to theexternal urethral
sphincter areinhibited the sphincter
relaxes.Urine passes through the urethra the
bladder is emptied.
1
Bladder
(?)
(?)
3
Pelvic splanchnicnerves
Visceral afferent
Sympathetic
Somatic efferent
Internalurethralsphincter
5
Parasympathetic
External urethralsphincter
Interneuron
53
Disorders of the Urinary System

• Urinary tract infections
• More common in females
• Burning sensation during micturition
• Renal calculi
• Kidney stones
• Bladder cancer
• 3 of cancersmore common in men
• Kidney cancer
• Arises from epithelial cells of uriniferous
  tubules

54
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