Transcript HISTOLOGY OF THE RENAL SYSTEMx

Dr Rania Gabr

To describe the microscopic structure of
the kidney, ureter,urinary bladder and
urethra
Uriniferous tubules are
Composed of:
1- Nephron :
Renal corpuscle
plus renal tubules
2-Collecting duct
Involved in
concentrating
urine
(1) Cortical nephrons are the most common
type of nephrons.
(2) Juxtamedullary nephrons account for
approximately 20% of all nephrons; their
corpuscles are found adjacent to the
medulla. These nephrons are responsible
for producing the urine-concentrating
mechanism of the kidney.
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
Renal corpuscle
› 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

The podocytes possess processes called
pedicles that wrap around the capillaries
and interdigitate to form filtration slits
approximately 25nm wide.

In addition to capillary endothelial cells and
podocytes, renal corpuscles also contain
mesangial cells.

The mesangial cells serve a phagocytic
function and keep the basement
membrane clear of debris.
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
Consist of 3 layers
› 1- Fenestrated
Capillary
endothelium
› 2- Basement
membrane
› 3- Foot processes
of podocytes of
glomerular
capsule.
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Copyright © 2008 Pearson
Education, Inc., publishing as
Benjamin Cummings
Figure 23.6c
At the vascular pole, smooth
muscle cells in the tunica media
of the afferent glomerular
arteriole are replaced by highly
modified epithelioid cells
containing cytoplasmic granules.
These are the juxtaglomerular
cells,.

In the adjacent segments of distal
convoluted tubules the cells that border
the juxtaglomerular area, are narrow
and more columnar than elsewhere in
the tubule.

This darker and more compact area is
called macula densa. The
juxtaglomerular cells and macula densa
constitute the juxtaglomerular apparatus

Filtrate proceeds to renal tubules from
glomerulus
› Proximal convoluted tubule
› Loop of Henle
 Descending limb
 Thin segment
 Thick segment( Ascending limb)
› Distal convoluted tubule
 The
proximal convoluted tubule is
formed of simple cuboidal to low
columnar epithelium.
 They are large cells, each transverse
section of PCT contain only 3-5 nuclei
 The
apical surface is covered with
microvilli creating a light microscopic
brush border that increases the
surface area for ion absorption.


the walls formed by
cuboidal epithelial
cells
Their Luminal surfaces
have dense microvilli.
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
Descending limb
› Proximal part:
similar cells of the
PCT
› Thin segment:
simple sequamous
epithelium

Ascending limb
› Cuboidal
epithelium or low
columnar→ thick
segment
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P
P
D
D

Distal convoluted tubules are
located within the cortex.

They are approximately 1/3rd
as long as their proximal
counterparts.

They contact the renal
corpuscle forming the macula
densa which is part of the
juxtaglomerular apparatus



The wall: cuboidal
epithelium (like PCT)
Thinner
Lack micrivilli
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
Collecting tubules
› Receive urine from distal convoluted tubules
Figure 23.8
 The
collecting system starts in the cortex
as a continuation of the distal convoluted
tubules and descend through the medulla.
 As
the ducts coalesce and increase in
size, the cells of the tubes change from
somewhat squamous to cuboidal to
columnar and similarly become increasing
stratified.
 They terminate at the tip of the renal
pyramid as the papillary ducts .
Long section of Collect tubules (CT) and PCT (P)
CT
P
CT
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
Histology of ureter
› Mucosa – transitional epithelium
› Lamina propria: CT
› Muscularis – two layers
 Inner longitudinal layer
 Outer circular layer
› Adventitia – typical connective tissue
Copyright © 2008 Pearson
Education, Inc., publishing as
Benjamin Cummings
Figure 23.12
Ureter – folded mucus membrane
Transitional Epithelium
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
Wall of bladder
› Mucosa
 Transitional epithelium
› Muscular layer
 Detrusor muscle: 3 layers of smooth muscles
› Adventitia
Copyright © 2008 Pearson
Education, Inc., publishing as
Benjamin Cummings
Figure 23.15a, b
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
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)
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