Urinary System
Dr. Raeesa Mohammed
Associate professor of Histology
Urinary System
Includes:
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2 Kidneys.
2 Ureters.
Single Urinary
bladder.
Single Urethera.
Kidney
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Bean-shaped organ
Covered by dense
irregular collagenous
connective tissue
capsule
Has a lateral convex
border & a medial
concave border with
hilum, where the:
 Arteries enter
 Ureter & veins leave
the kidney
Kidney cont’d
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Each kidney is divided into:
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Outer Cortex
Inner Medulla: which is
composed of 10-12 renal
pyramids
The base of pyramid is
toward the cortex, and the
apex (renal papilla) toward
the hilum
Renal pyramids are
separated by cortical tissue
called renal columns of Bertin
P
Kidney cont’d
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The apex of each pyramid
is perforated by 15-20
large collecting ducts
(papillary ducts of Bellini)
that open into the minor
calyx
The minor calyx,
surrounds the apex of
each pyramid
3 or 4 minor calyces join
to form a major calyx
The major calyces, 3-4 in
number open into the
renal pelvis.
Nephron
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It is composed of :
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Renal corpuscle
Proximal tubule
Loop of Henle
Distal tubule
Renal Corpuscle
Composed of:
Glomerulus:
Tuft of fenestrated capillaries.
Afferent & efferent arterioles supply
& drain the glomerulus at the
vascular pole
 Bowman’s capsule:
Encloses the glomerulus. It has two
layers:
• Parietal layer formed by simple
squamous epithelium.
• Visceral layer formed by
podocytes
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Renal Corpuscle cont’d
Bowman’s (urinary or
glomerular) space:
Space between the parietal
and visceral layers, drains
at the urinary pole into the
proximal convoluted
tubule
 Interstitial tissue is
composed of mesengium
(mesangial cells & the
extracellular matrix
manufactured by them)
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Podocytes
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Are modified cells with
multiple processes and
pedicles
Form the visceral layer of
Bowman’s capsule
Their processes and
pedicles surround the
glomerular capillaries.
The spaces between
adjacent pedicles, called the
filtration slits are covered by
slit diaphragms.
Form a thick basal lamina
that is interposed between
the podocytes and the
endothelial cells
Glomerular Filtration Barrier
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The barrier is formed
by:
• the podocyte layer
of Bowman's
capsule
• the fenestrated
endothelium of the
glomerulus
• a thick basement
membrane shared
between the two
cellular components
GFB
Collecting Tubule
Is composed of:
 Proximal convoluted tubule:
 Loop of Henle:
It has 3 regions:
• Descending thin limb.
• Henle’s loop
• Ascending thin limb
 Distal convoluted tubule:
Proximal tubule:
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It is composed of
simple cuboidal
epithelium with:
• Extensive striated
or brush border
Thin limb of Henle’s Loop:
It is composed of simple
squamous epithelium
Distal Tubule
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It is composed of simple
cuboidal epithelium.
Juxtaglomerular Apparatus
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It has 3 components:
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The macula densa of distal tubule.
Juxtaglomerular cells of glomerular
arterioles (modified smooth muscle of
tunica media); they secrete renin,
angiotensin-converting enzyme and
angiotensin.
The extraglomerular mesangial cells
called lacis cells.
Collecting Duct
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Several distal convoluted
tubules join each collecting
duct
Are composed of simple
cuboidal epithelium.
Renal medulla contains:
 Collecting tubules (ducts)
Henle’s loop
Peritubular blood vessels (vasa recta)
 Renal interstitium
Ureter
Is composed of:
 Mucosa: formed of
transitional epithelium &
lamina propria.
 Muscularis (muscular
coat): is formed of 2
layers of smooth muscle:
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Inner longitudinal
Outer circular
Adventitia: fibrous
connective tissue
covering
Urinary bladder
It has the same structure
as the ureter, except:
a. The muscularis has 3
layers of smooth
muscle, inner
longitudinal, middle
circular and outer
longitudinal.
 Serosa/adventitia is
outer covering
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Practical Slides
Kidney Cortex
Kidney Medulla
Urinary Bladder
Urinary Bladder