2. The Urinary System
• The urinary system functions primarily in
osmoregulation and excretion of toxic
metabolic waste products. In this
laboratory, we will examine the components
of the urinary system: the
kidneys, ureters, bladder, and urethra.
3. Kidney:
Overview & Anatomy
• The two kidneys lie behind the peritoneum on either side
of the upper lumbar vertebrae, embedded in fat in the
paravertebral gutters of the posterior abdominal wall
(dissection). The left kidney usually lies at a higher level
than the right.
• Covered by a thin capsule, the kidney comprises an outer
cortex and an inner medulla (schematic; dissection). The
medulla contains numerous pyramids; the apex of each
pyramid, called a renal papilla, projects into the renal sinus.
Urine discharged from the papillae is collected by about ten
trumpet-shaped chambers, the minor calyces, which unite
to form two or three major calyces. These then fuse into
the single, funnel-shaped renal pelvis, which is continuous
with the ureter.
4. Kidney:
Cortex
• Identify the cortex below the kidney capsule (4X).
• At higher magnification, identify the regions of the cortex. Note that the renal corpuscles (4X) are readily
visible.
• Identify medullary rays (4X, 4X, schematic) alternating with regions containing renal corpuscles and their
convoluted tubules (pars convoluta). Note that medullary rays are actually in the cortex. On the trichrome-
stained slide (O-031), the middle section is a cross-section of the kidney cortex that illustrates this
relationship very well.
5. Kidney:
Medulla
• Identify medullary pyramids, best seen in O-062B (1X).
• Identify the outer medulla and the inner medulla, best seen in slide SCPM070 (1X). The "outer stripe" and
"inner stripe" together comprise the outer medulla. What structural features make the inner and outer
stripes look different from each other (hint)?
• Identify papillae (1X, 4X).
6. Kidney:
Renal Sinus
• Identify minor calyces, best seen in O-062A and SCPM -070 (2X, 10X). Make sure you understand the
relationship of minor calyces to the major calyces and renal pelvis.
• Identify the renal pelvis.
7. Kidney:
Uriniferous Tubules
• Each uriniferous tubule is comprised of a nephron and
a collecting tubule (schematic). Although of different
embryological origins, these two tubular structures
unite during development to form an anatomical and
functional unit. The blind start of the uriniferous
tubule, Bowman's capsule, is intimately associated
with a vascular structure, the glomerulus.
Together, these structures form the renal corpuscle. At
this site, an ultrafiltrate of blood enters the lumen of
the nephron, and the process of urine formation
begins. The nephron has several regions, each with its
own distinct function in the production of urine (table).
8.
9. Renal Corpuscle
• Identify a glomerulus and the
surrounding Bowman's capsule
(20X, 40X).
• Look for a vascular pole (40X, 40X) and a
urinary pole (40X, 50X).
• Identify an afferent arteriole (10X, 50X);
you can be sure of its identity if it
branches from an intralobular artery.
You can try to find an efferent
arteriole, but this is only possible if you
find a lucky section that contains both
types of vessel.
• The visceral and parietal layers of
Bowman's capsule form during
development, when a knot of capillaries
invaginates into the tip of a primitive
renal tubule, much like a finger pushing
into an inflated balloon (schematic).
11. Kidney:
Proximal Convoluted Tubules
• Proximal convoluted tubules are
located around the renal corpuscles in
the pars convoluta, but are not
present in the medullary rays.
• Look for a proximal convoluted tubule
emerging from the urinary pole (40X)
of Bowman's capsule.
• Note that proximal convoluted tubules
(20X, 50X) have simple, low columnar
epithelium with a prominent apical
brush border, best seen in O-030
(50X, 100X, 100X). Typically, the brush
border is poorly preserved in most LM
slide preparations; only remnants of it
are observed in the lumen. You can
identify proximal tubules by their
brush border; distal tubules and
collecting tubules don't have a brush
border.
12. Kidney:
Proximal Convoluted Tubules
• PCT cells have basal striations, too
small to see at 40x; these represent
infoldings of the basal surface
membrane, into which are packed
large numbers of mitochondria
(arrows, EM). These infoldings increase
the basal surface area of the tubule
cells, much like the microvilli do on
their apical surfaces. Why do these
cells need such a large basal surface
area?
– Na/K ATPase present on the basal surface
to pump Na out into the blood (drives
reabsorption of both Na and water)
– Water enters/exits the PCT at both the
apical and basolateral surfaces
• The majority of tubules in regions
surrounding the renal corpuscles are
proximal convoluted tubules
(20X, 20X). Why is this the case?
– PCTs are the longest segments of the
nephron in the cortex, so there are more
PCT profiles in the cortical regions
containing renal corpuscles
14. Kidney:
Loop of Henle
• Thick descending limbs
of the loop of Henle.
These are located in
medullary rays
(20X, 50X), and continue
into the medulla. They
are histologically similar Contains both thick descending
to proximal convoluted and thick ascending limbs
tubules (although they
are straight, not
convoluted). They are
also called proximal
straight tubules.
15. Kidney:
Loop of Henle
• Thin limbs of the loop of Henle. These
loops connect the descending thick
and ascending thick limbs, and are only
found in the medulla. In
juxtamedullary nephrons, the thin
segment forms the loop of
Henle, while in cortical nephrons it
forms only part of the descending limb
of the loop.
• Examine several regions of medulla for
thin limbs, which are tubes made of
simple squamous epithelium. In cross-
section, the thin limbs (50X, 100X) look
like empty capillaries.
• In longitudinal views, you can
appreciate why the capillaries of the
medulla are called "straight vessels"
(vasa recta) (100X, 100X). These
capillaries often contain
erythrocytes, so you can distinguish
them easily from the thin limbs, which
are always empty.
16. Kidney:
Loop of Henle
• Thick ascending limbs of
the Loop of Henle. Also
called distal straight
tubules, these structures
(20X, 50X, 50X) can be
observed in medullary
rays and the medulla.
• Note that, in cross-
section, they look very
similar to distal
convoluted tubules
(although they are
straight, not convoluted).
17. Kidney:
Distal Convoluted Tubules
• Distal convoluted tubules.
These structures can be
observed in the vicinity of renal
corpuscles and proximal
convoluted tubules.
• DCTs are considerably shorter
than proximal convoluted
tubules, so they are less
frequent in a cross section of
the cortex (20X).
• Note that DCTs have a simple
cuboidal epithelium with no
brush border, and an empty
lumen (40X, 50X).
• Like PCT cells, DCT cells have
basal infoldings with many
mitochondria (arrows, EM).
18. Kidney:
Collecting Tubules and Ducts
• This portion of the uriniferous
tubule is primarily excretory in
function, although some
modification of urine tonicity
does occur here. To identify
collecting tubules, you may
find it easiest to begin near the
tip of the medullary papilla of
slide O-062A, then follow the
tubules up towards the cortex
(schematic, 1X, A → B → C →
D).
• Papillary ducts (20X, 40X).
These are the large collecting
ducts of the papillary
region, and drain into the
calyceal space (2X, 4X). At this
level, the ductal epithelium is
tall columnar.
19. Kidney:
Collecting Tubules and Ducts
• Moving up towards the cortex, you
should first encounter thin limbs as
well as capillaries (vasa recta)
(40X).
• Slightly higher, thick limbs appear
(ascending and descending), while
the collecting ducts are smaller and
their epithelium has become less
columnar (40X).
• Near the medulla/cortex border,
the collecting ducts are almost the
same size as the thick limbs, and
their epithelium is cuboidal; the
two types of tubule are therefore
difficult to distinguish (40X). From
this point on (i.e. in medullary
rays), you will not be expected to
distinguish collecting ducts and
tubules from thick limbs.
20. Kidney:
Juxtaglomerular Apparatus
• Macula densa.
• Look near glomerular arterioles (at the
vascular pole) to identify this structure
(50X, 50X, 100X), which is a specialization
of the distal convoluted tubule.
• What does the term "macula densa"
mean?
• Juxtaglomerular cells.
• These cells are located in the afferent and
efferent arteriole walls next to a macula
densa; they are modified smooth muscle
cells with an epithelioid appearance (100X)
• JG cells contain renin granules, although
these cannot be distinguished at 40X on a
virtual slide.
• Lacis cells. Also called extraglomerular
mesangial cells, these are mesangial cells
that lie outside the renal corpuscle, and
that form part of the JG apparatus
(schematic). They cannot be reliably
identified in routine H&E preparations.
27. Renal Pelvis
• The renal pelvis is an expanded region of ureter that forms a cap over the renal papilla.
Hilum. Identify, where possible:
• Renal papilla.
– Identify Ducts of Bellini (4X, 10X) opening into the pelvicalyceal space.
• Minor calyx (4X, 10X) . Note the transitional epithelium lining the calyx.
28. Renal Ureter
Ureter (4X).
• Mucosa.
– Identify the characteristic transitional epithelium (50X).
– Note the stellate (star-shaped) lumen (4X).
– Identify lymphoid structures. (10X, 100X) PLASMA CELLS
• Muscularis.
– Identify smooth muscle layers (4X, 10X): inner longitudinal, outer circular (and outermost oblique or
longitudinal in lower ureter).
• Adventitia.
– This loose C.T. layer blends with the C.T. of neighbouring organs (10X).
29. Urinary Bladder
• The urinary bladder is structurally similar to the ureter. Compare the relaxed and distended sections.
Mucosa. (4X, 10X)
• Identify the transitional epithelium that forms the lining (40X).
• Muscularis. The greatest difference between ureter and bladder is found here.
• Note the significantly increased thickness of the smooth muscle tunic (4X).
• Identify autonomic ganglia (40X) embedded within the muscular wall. What is their function?
• Adventitia/Serosa.
• Note that the exposed regions of the bladder are covered by a serosa, while those regions that are
embedded within other bodily tissues are surrounded by a loose C.T. adventitia (20X).
• What are the two components of a serosa?
30. Histopathology:
Amyloidosis
• Amyloid is the general name for proteinaceous material that accumulates as abnormal deposits within
tissue spaces. Several different types of amyloid exist, but all are aggregates of polypeptides (protein
fragments) that have a beta-pleated sheet structure. In brain, amyloid accumulation accompanies
Alzheimer's disease; however, almost any organ can be affected.
In this kidney specimen (1X), the medulla contains aggregates of amorphous material surrounding the
ducts and tubules in this region (5X, 20X). The cortex appears relatively normal. Eventually, the deposits of
amyloid become so large that they obliterate the normal tissue structure.
32. Histopathology:
Renal Infarct
• An infarct is an area of ischemic necrosis (tissue damage caused by lack of oxygen) caused by blockage of
the arterial supply or the venous drainage in a tissue. In this case, blockage of an interlobar artery
(schematic) cut off blood flow to several interlobular arteries, resulting in necrosis of several kidney
lobules. Ischemic areas (1X) show severe structural damage (10X), while nearby areas appear normal
(10X).
33. Histopathology:
Polycystic Kidney Disease
• Polycystic kidney disease (specimen) is a relatively common (1/800 births) congenital, autosomal
dominant disease. Fluid-filled cysts develop from the PCT, DCT, and CT; these cysts disrupt the organ's
structure and function, leading to organ failure.
