Module 11: Renal
11 February 2010
Marivic V. Bustos, MD
Histology of the Renal System
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Know where a structure is located because if you
know what to look for in the cortex/medullar,
you’ll not be confused
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Medullary rays – do not look for it in the gross
specimen, only in histologic slides
Arcuate – found in the arch of the
corticomedullary junction
Interlobar – side of medullary pyramid
o Vein – bigger lumen
o Artery – smaller lumen
In the gross anatomy, it’s not wise to ask
interlobar and arcuate, difficult to differentiate.
It can be asked in Histology.
OUTLINE
Don’t be alarmed! It’s long because of the pictures 
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I. URINARY SYSTEM
A.
Nephron
1. Renal Corpuscle
Uriniferous Tubules – old term for the Renal Corpuscle;
refer to the NEPHRON and collecting tubules
Other Names:

nephrons - excretory collecting tubules

ureter - collecting system
Nephron – functional unit of the kidney; concerned with
urine formation
Includes corpuscle, Proximal Convoluted Tubule
(PCT), Henle’s Loop, Distal Convoluted Tubule (DCT)
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Nephrons
There are 2 kinds
o Juxtamedullar – makes up 1/7 of the
cortex
o Cortical – makes up 6/7; up the cortex
o Both participates in filtration of blood,
absorption and secretion
“Convoluted portion” also refer to PCT and DCT
“Straight portions” refer to Henle’s Loop
Kidney (monkey) Jones'
methenamine silver
AA arcuate artery
Ai interlobar artery
AV arcuate vein
C calyx
Cx cortex
G glomerulus
IA interlobular artery
MR medullary ray
P renal pelvis
RC renal corpuscles
RP renal papilla
T tubule
U ureter
V interlobular vein
Figure 1. Anatomic and Histologic Picture
Cortex
-
Straight layer of in the gross anatomy of the
kidney
Conains renal corpuscle
Medullary Pyramid
Collecting tubules
Henle’s Loop
Some Henle’s loop and collecting tubules in the
cortex, but I’m going to ask them in the medulla
so you’ll be sure about the structures
Group 01
Figure 2. Histologic Scan of the Kidney
2.
-
Renal Corpuscle
Try to differentiate the renal corpuscles (ONLY
found in the CORTEX), and the medullary
pyramid
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Absence of corpuscles means you are in looking
at the Renal Pyramid
Arcuate Artery - Vessel between the cortex and
medulla
Figure 3. Renal Corpuscle
in the
Renal
Cortex
Renal
Corpuscle
A afferent- arteriole
BC Bowman's
capsule
BS Bowman's
space
C glomerular
- capillary
E endothelial cell
GBM glomerular
basement membrane
I interstitium
M mesangium
N mesangial cell nucleus
P podocyte
PCT proximal convoluted
tubule
S squamous cell
-
-
BS
-
BC
Physiology: Afferent arteriole comes from the
interlobar artery  enters corpuscle  divides
into 4 branches  forms several capillaries
forming the GLOMEROLUS
Thus, glomerulus is made of cup of capillaries,
where blood enters to be filtered
Glomerular capsule divides into two:
o Parietal layer – external layer; will form the
outer limit of renal corpuscle
o Visceral layer – envelops the glomerulus; this
layer cannot be differentiated from glomerulus
in the light microscope
Figure 4. Renal Cortex showing parts of two renal corpuscles, macula
densa, and distal and proximal convoluted tubules.
Arrows - Collagen type IV of the basement membrane of the
glomerular capillaries
Arrowheads - collagen of the parietal layer of Bowman's capsule and
the basal membrane of a distal tubule are shown
Group 09
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Bowman’s Space – receives filtered fluid from the
glomerulus
Vascular pole
o Area where afferent and efferent can
be found
o But afferent and efferent are difficult
to see through the light microscope
o Once parietal and visceral meet = area
of vascular pole
Urinary pole
o If you have found the vascular pole, the
opposite of it is the urinary pole (forms
an indention at the upper part of the
corpuscle but not very clear in all
specimens)
o Break in the parietal layer  becomes
continuous as PCT, that’s your urinary
pole
o Thus, what is brought to the Bowman’s
space will be brought to PCT
Tips for the exam:
When the whole structure is bracketed – that’s
your renal corpuscle
But when pointed, or there’s an arrow – that’s
your glomerulus
Glomerulus + BowmanS capsule = renal corpuscle
Parietal layer – where you see the Bowman’s
capsule
It’s not right to write Bowman’s capsule – write
parietal layer of Bowman’s capsule since the
capsule and the parietal is not that differentiated
-
Bowman’s capsule
As the parietal layer approachesthe vascular
polem, the simple squamous epithelium
becomes simple cuboidal
Visceral Layer
o Cannot be well-delineated
o Envelopes glomerulus
o Cannot be separated from glomerulus
using the microscope
o No epithelium but visceral layer is
made of cells called Podocytes
o Structure: Cell body of podocyte 
foot podocytes/foot processes/primary
process  several finger like
extensions, secondary processes or
pedicles.
o Pedicles interdigitate with other
pedicles, forming spaces in between
called filtration pits (spaces found
between the pedicles)
o In between endothelium of capillaries
and filtration pits are your Glomerular
Basement membrane, serving as
filtration barrier composed of 2 layers
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



Lamina densa- acts as physical barrier,
molecules of >10nm in diameter cannot pass
through
Lamina rara – negatively charged; anionic;
acts as negative barrier with regards to
substances that are negatively charged like
proteins except albumin which can pass
through
In the urinalysis, you can only find <5 WBC,
RBC and a trace of protein
Problem in this membrane: substances that
should not pass through this barrier like in
patients with glomerular nephritis or
neprhotic syndrome  heavy proteinuria
(heavy protein in the urine); protein normally
does not pass through
FILTRATION Barrier (Berns, Scribe na to)
Other structures in the nephron, near the corpuscle
Mesangial (means “between capillaries”)
o Found in glomerulus
o Angiotensin II is for Vasoconstriction 
decreased blood flow
o NF – produced in the cardiac atrial
cells; a vasodilator; opposite of
angiotensin II; favors blood filtration
o Thus, depends on the needs of the body
a hormone is released appropriately
o Macrophage for substances trapped
inside the glomerulus

Ex: Mesangial hypercellularity –
there’s inflammation inside the
glomerulus
o Dr. Bustos: Honestly, I don’t know
where we can find the mesangial cells
 it’s not even pointed in the book. But
renal pathologists can identify.
o 2-3 cells should be between renal
capillaries
Figure 5. Schematic representation of a
glomerular capillary with the visceral layer of
Bowman's capsule (formed by podocytes).
Figure 7. Mesangial Cells
1
2
1
P
2
Figure 6 Electron Micrograph
P – Podocytes; 1 – primary process; 2 – secondary
process/pedicels; arrows – filtration pits
Group 09
Uriniferous Tubules
Blood filtration
o Afferent arteriole  glomerulus
(filtered substances pass through) 
Bowman’s space  PCT
PCT
Found only in the CORTEX (!!!)
Seen near the renal corpuscles; surrounding….
Lined by simple cuboidal or low columnar WITH
BRUSH BORDER
Function: increased surface area for absorption;
numerous in PCT because it needs toABSORB!
o About 85% of fluid and Na is
reabsorbed in PCT
o Reabsorbed any AA and glucose that
will pass through
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o
Otherwise, it EXCRETES your creatinine
(substances not needed by the body) so
it will not accumulate in the body,
indicates renal failure
Laboratory: Need to Differentiate from DCT
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Figure 8. Renal Cortex
P- Proximal CT; D – Distal CT;
proximal (P) and distal (D) convoluted
tubules.
Henle’s Loop (refer back to Figure 1)
Straight portions of the nephron
Abundant in medulla / medullary pyramid
Two types of nephrons
o Significance: juxtamedullary – important in
maintenance of hypertonicity within the
medullary pyramid
o Compositions:

Proximal – 85%

Thin descending – 5%

thin ascending (juxta) – impermeable
to water

Thick ascending – transports chloride
from tubule to medullary interstitium
 increased hypertonicity of medullary
interstitium
Thin loops – NOT found in the cortex
o Look for it in the medulary pyramid
In the laboratory:Thick ascending and
descending – cannot differentiate between the
two because they are in cross-section;
Looks similar to DCT and PCT; can differentiate
from them because Henle’s Loop has no renal
corpuscle
Thin Loop of Henle – Simple Squamous
o In some instances, you can see
structures with simple squamous but
with RBCs, that’s your vasa recta (a
capillary)
o Thus, without RBC – that’s your thin
loops,
o Iif with blood - that’s your vasa recta
As thick descending penetrates the cortex, it
becomes the DCT
Only in the CORTEX! Near renal corpuscle
Just like PCT and thick loop of Henle – simple
cuboidal epithelium WITHOUT brush border
In the presence of vasopressin, they reabsorb
some amounts of water
Functions are important in Physiology 
Exam Tips
DCT vs PCT is always asked beside the RENAL
CORPUSCLE, so you’ll not mistake it as the Thick
Loop of Henle
DCT and PCT – simple cuboidal epithelium
(Berns, eto ata ay nasa table din so you can opt
to erase this and highlight na lang yung contents
ng table)
o PCT – more acidophilic
o Brush border function – PCT for
majority of reabsorption
o DCT – no brush border  thus, larger
lumen

Numerous nuclei, nicely spaced
even in the lateral border
o PCT – not well delineated
Figure 9. Distal convoluted tubules (DCT)
Note: absence of brush border.
THL: thin portion of Henle's loop
Arrowhead: blood capillary
Macula Densa
As the DCT approaches the vascular pole
A portion of DCT actually becomes columnar,
closely-packed, appear dark in color
Juxtaglomerular cells (JG cells)
Near vascular poles, where your a. arteriole, can
be modified, named JG Cells
Very important because it secretes RENIN
(important in conversion of Angiotensinogen to
Angiotensin I)
Angiotensin II – important in cases of
hemorrhage where the body has the converse
fluid
Aldosterone – secreted from the adrenal cortex
DCT
Group 09
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o
o
helps reabsorb the sodium and in the
process, also reabsorb water  fluid
retention  maintains blood pressure;
BUT fluid retention can occur only at a
certain time i.e. immediate response of the
body to cope with fluid loss
Figure 10.
Collecting Ducts
Figure 10. Note Juxtaglomerular Cells
Erythropoietin – produced in the cortical interstitial cells
(cells found in between the PCT and DCT)
COLLECTING DUCTS
More
columnar, like the
tubules
Exam Tips:
For the
exam, its hard to
distinguish
Collecting ducts
from tubules, you
can write either 
But differentiate from Thick descending loop
RENAL INTERSTITIUM
Spaces found between the tubules
Increased in medulla
Erythpoeitin is secreted here
Laboratory: No need to identify this!
Mahirap hanapin ang afferent and efferent arteriole
COLLECTING TUBULES
Filtrate from renal corpuscle  PCT  loop of
Henle  DCT  Collecting tubules
Found in the cortex and in the medulla
Found in the medullary rays, but more abundant
in the medullary pyramid
Forms collecting ducts
Collecting Ducts
As collecting ducts approaches apex of medullary
pyramid  enlarges
Initially lined by simple cuboidal but as it
approaches the deep part of medullary pyramid,
becomes simple columnar (since they grow
bigger)
Collecting tubules:
Laboratory: Principal and intercalated cells – no
need to find in histologic slides
ADH –produced in hypothalamus and stored in
posterior pituitary
Collecting tubules – very sensitive to ADH
o I.e. when you’re trapped in the desert,
you won’t urinate
CALYCES, RENAL PELVIS, URETER, and URINARY BLADDR
Grouped together because they are lined with
transitional epithelium
Also lined by smooth muscle layer
Urinary bladder – covered by peritoneum,
making up the serosa
URETER
Figure 11. Ureter
Exam
Group 09
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Tip: Should be able to identify this even if natutulog kayo!
It has the distinct stellate-shpaed lumen
Middle to lower part of the ureter: muscle layer
is complete…
-
Internal smooth muscle forms internal urethral
sphincter
It’s above the urogenital diaphragm
URINARY BLADDER
Serosa: transitional epithelium
What is unique about the bladder’s epithelium:
varies if full or empty
o Empty: 6-8 layers of thickness
o Full: 3-4 layer of thickness
o Note: Only true for epithelium of
urinary bladder, not for ureter and
calyces
Smooth muscle is called the detrusor muscle
Figure 12. Bladder
IL – Inner Longitudinal
OC – Outer Circular Muscle
OL – Outer Longitudinal Muscle
A - Adventitia
URETHRA
Male
Lining is still transitional because it is continuous
with the bladder
As it approaches your external urethral meatus,
becomes stratifed squamous non keratinized
(Laboratory: no slide for this but you may find it
in the penis)
Female
Close to vagina
Lined by stratified (or for some satisfied
squamous  ) squamous non keratinizing
Group 09
Figure 13. Male Urethra
EMBRYOLOGY
(so you’ll be able to appreciate some abnormalities huhu)
Three embryonic stages of kidney
o Pronephros
o Mesonephros

Replaced pronephros
o Metanephros

Replaced mesonephros

Forms the definitive permanent
kidney, ONLY IN THIS STAGE

Just located in the pelvic region,
will ascend by the 8th week of fetal
life to lumbar region

Becomes functional beyond the 6th
week, around 7th to 8th so that
urine production starts by 9th week
Metanephros
o Development:

Metanephric mesoderm 
excretory system

Ureteric bud  collecting system

Urinary bladder is from cloaca 
urorectal septum divides into
urogenital sinus and anorectal
canal

Urogential sinus urinary
bladder and urethra
Formation of nephrons – until birth only; after
birth, no production
o 1-2M per kidney
o Begins functioning by the 9th week of
fetal life
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Fetal urine  goes to amniotic fluid so
that the fetus can also swallow the
urine
Trivia: The boxer Marquez drinks his
own urine (yuuuucccck)
Kidneys – may actually be lobated
o Disappears because nephrons starts to
grow
o But lobes do not increase in number
Urinary bladder – abdominal organ until 6., 6-12greater pelvis, puberty-lesser pelvis
o
-
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Abnormalities
Ectopic kidney
o Kidney is trapped in the pelvic area,
near pelvic vessels
Horsehoe
Polycystic kidney
o Accumulation of fluid/urine in the cyst
o What happens here: failure of union
between DCT with collecting tubules 
thus, urine is formed in the collecting
tubule  forming a cyst
Double collecting system
o 2 ureters and 2 renal pelvis
Vesico-ureteral reflux
o Ureter should be appropriately placed
to act as a physiologic valve and
prevent reflux
o Pathologic: intramural portion of
ureter is not inserted well in the
mucosa

Placement is not that oblique or
embedded in the detrussor muscle

Or obstruction from the urinary
bladder to urethra

Or poorly functioning bladder
where bladder contraction is not
synchronized with opening and
closing of urethral sphincter of
bladder
o Primary cause of UTI in children
o Bottomline: There should be a one way
flow traffic between urine (di pwedeng
may bumabalik)
o DIAGNOSTIC TEST: Radiocontrast (used
VCUG ) insert cathether and fill up
bladder with dye)

May see a Grade 1 or grade 2
reflux- that is, reflux up to mid
ureter
Bladder Extrophy
o Failure of fusion of abdominal wall
o Defect in ventral bladder wall
Followed by rupture of thin layer of
ectoderm  Protrusion of the bladder,
exposure of mucosa
o Can occur with here is not fused
Group 09
o
-
Sometimes, associated with
undescended testis
o Very hard to repair. It’s a multistage
repair and there are only a few
pediatric surgeons in the country
o Occurs in 1 in 25,000.
Hypospadias
o When External Urethral Meatus is in
the ventral portion of the penis
o In some instances, its dorsal – this is
called epispedias
Horseshoe-shaped Kidney
Ectopic Kidney
Horseshoe Shaped Kidney
Polycystic Kidney
Bladder Extrophy
Hypospadia
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Module 11: Renal
Histology of the Renal System
11 February 2010
Marivic V. Bustos, MD
APPENDIX
Summary of activities of different parts of the tubule and Comparison of epithelial structure in different parts of the renal tubule
Group 01
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