Anatomy and Human Biology 2214
September 28, 2009
M. Hall
URINARY SYSTEM
Objectives: You should be able to identify the following in the class slide sets:
Kidney
capsule
cortex
labyrinth
medullary ray
medulla
renal papilla
calyx
lobe
lobule
arcuate artery
interlobular artery
afferent/efferent arteriole
peritubular capillary
vasa recta
nephron
renal corpuscle
Bowman's capsule
parietal layer
visceral layer
glomerulus
juxtaglomerular apparatus
macula densa
proximal convoluted tubule
proximal straight tubule
thin limb of loop of Henle
distal straight tubule
distal convoluted tubule
collecting duct
Ureter
transitional epithelium
muscle layers
Bladder
stretched
relaxed
transitional epithelium
umbrella cells
muscle layers
Urethra (female)
various epithelia
smooth muscle
Urethra male
mucosa
submucosa (erectile tissue)
Slide descriptions
D-43, Kidney (H&E). . This slide was prepared from well-preserved animal kidneys and
stained with H & E. It is the best slide for studying the various blood vessels and ducts of the
kidney. By eye locate the major gross divisions of the kidney: capsule, cortex, medulla, renal
pyramid, calyx and hilus. Using your low-power objective distinguish cortex from medulla and
medullary rays from areas of labyrinth in the cortex. Use the diagram on the last page as a
guide. Each nephron consists of a renal corpuscle, a proximal tubule with a convoluted and
straight portion, a thin limb of the loop of Henle and the convoluted and straight portion of a
distal tubule. List the structures you expect to find in the:
1. labyrinth area (high mag) _____________________________________________
2. medullary ray (high mag) _____________________________________________
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3. upper medulla
_____________________________________________
4. lower medulla
_____________________________________________
With the aid of the diagram, identify the various segments of the nephron and the collecting
ducts in each area.
Renal corpuscles show up well. Spend some time comparing their appearance with the
diagram. In some cases you should be able to see the simple squamous epithelium of
Bowman's capsule, lining the urinary space. It is not feasible to distinguish podocytes from
endothelial cells in the glomerulus. Nor can one satisfactorily identify the mesangeal cells in a
thick section, such as this.
When you find a properly oriented section, you will be able to recognize the macula densa. It
appears as a clustering of nuclei on one side of a distal tubule which lies against the vascular
pole of the renal corpuscle. You probably will not be able to recognize the juxtaglomerular
cells of the afferent arteriole. But you should be able to regurgitate the function of the JG
apparatus?
The blood supply in the kidney is highly important. It is unusual in having an arterial portal
system. If you search in the appropriate regions of your slide, you can see sections of most of
the named divisions of the arterial supply. Identify interlobar arteries located in the renal
pelvis region. Arcuate arteries and veins run between the cortex and medulla. You can see
them as tiny white holes if you hold the slide up to the light. Hold each of the other slides up
similarly and note them there as well. Slide D-44 shows them especially well as a line of holes
along the medullary-cortex border. Examine them under low power and distinguish the
adjacent artery and vein. Interlobular arteries branch off from the arcuate arteries and course
upwards towards the capsule. They form the boundaries between lobules, hence their name.
Your section will cut through an occasional one with the typical appearance of a small artery.
The efferent arterioles from those nephrons situated near the boundary between the cortex and
medulla take a different course. They break up into long, thin capillary vessels which descend
straight down into the medulla, and then loop back to the boundary. These capillaries are called
the vasa recta. They provide nourishment to, and resorb water from, the medulla. The best
place to observe the vasa recta is on slide D-45 stained with PASH, after which you will easily
find them on this slide.
Since this slide contains a complete section of a small kidney, the pelvis region is easily seen
and understood. The ureter enters and its expanded end pushes up against the medullary
papilla to form a calyx which is lined by transitional epithelium, recognizable by the darker
staining top layer of cells some of which have two nuclei. Transitional epithelium lines the
entire urinary passageway down to, and including part of, the urethra.
Take a look at the very large terminal portions of the collecting ducts. If you are lucky you will
see one or two ducts emptying through the epithelium lining the papilla into the calyx.
D-42 Kidney monkey (FeH). Slide D-42 in an exceptionally fine slide. It has a section of a
well preserved unilobular kidney cut thinly and stained with iron hematoxylin. Although the
stain is just "black and white" it emphasizes cytological detail. The lobular organization is
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especially visible as you scan around the cortex at low power. Check your identifications for
the various parts of the nephron and collecting ducts. Find a macula densa.
The pelvis, calyx with transitional epithelium, an interlobar artery and arcuate vessels show up
well. Also there is a section though the ureter just outside of the pelvis. Do not miss examining
it. It shows excellently preserved transitional epithelium in the stretched configuration right
next to relaxed areas.
D-45 Kidney human (PASH). The PASH stain emphasizes the basement membranes which are
particularly prominent in the kidney. The cells have a very washed out appearance but the
entire organization of the kidney is graphically outlined by basement membranes.
Look for four things:
1. The basement membrane of the glomerulus. You are aware of the importance of the
basement membrane to the renal function. Note as well, that the entire nephron is surrounded
by a very well developed basement membrane.
2. The brush borders of proximal tubules. These structures are rich in glycocalyx which stains
with PAS.
3. Vasa recta. You can see nicely the disposition of the vascular supply to the medulla of the
kidney. At low power find an area of the medulla in which all of the tubules are cut in crosssection. Note that some small, scattered areas here have more basement membrane and appear
darker or more cluttered than the surrounding areas. These areas contain clusters of vasa recta.
Switch to higher power and confirm this by noting the red blood cells in the vessels.
4. (For the diligent only:) Arterioles entering/leaving renal corpuscles. Arterioles happen to be
well distended on this slide and relatively easy to see. You can see the elongated smooth
muscle cells in their walls in appropriately oriented sections. (Don’t worry if you don’t find
any).
Now that you know how vasa recta are disposed in the medulla, return to slide D-43 to view
them stained with H & E. Obviously, if you are interested in looking for sections through the
thin limb of the loop of Henle you should avoid these areas where the vessels of the vasa recta
might confuse you. Compare these large capillaries at high power with nearby thin limbs of
Henle. They are of about the same caliber, but the thin limbs have somewhat thicker walls and
no blood cells inside of them.
D-47 Ureter (H&E) At low power, observe the three layers of the ureter: mucosa, muscularis
and adventitia. This tripartite organization is maintained throughout the urinary passage
system. The mucosa is thrown into characteristic longitudinal folds. It is made of transitional
epithelium underlain by a layer of fairly cellular connective tissue. Quite a few lymphocytes
are found in this lamina propria. A lymph nodule may be seen in some slides. The muscularis
layer consists of two somewhat diffuse sheets of smooth muscle: the inner is longitudinal, and
the outer is circular. Towards the bladder end it picks up a third oblique layer. This muscle
produces peristaltic waves that push the urine to the bladder even when you are lying down.
D-49 Urinary bladder (H&E). Lower power: the layers of the bladder are basically the same as
in the ureter. However, the muscle layer is much thicker and includes a third sheet of smooth
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muscle with oblique orientation. Of course for a spherical organ like the bladder
"longitudinal", "circular", and "oblique" are somewhat formalistic terms. In any case the sheets
of smooth muscle are indistinct, so do not waste time trying to distinguish them. This is a good
slide to use to study transitional epithelium. Look particularly at the umbrella cells and their
acidophilic apical borders. By examining the epithelium, determine the state of distention of
the bladder.
D-48 Bladder, stretched (H&E). You have just looked at transitional epithelium of the bladder
in the contracted state. In preparing D-48 care was taken to stretch the tissue while it was being
fixed (by about as much as two Australian beers and a bag of chips would.) Look in particular
at the mucosa. In some places the epithelium is not as well preserved as one might wish but it
is obviously stretched. There the umbrella cells have acquired a squamous shape.
Most of the bladder is covered by an adventitia; however, part of the organ has a free surface
in the body cavity. Here a layer of mesothelial cells covers the connective tissue. This layer is
therefore called a serosa. Its mesothelium is part of the peritoneum that lines the entire body
cavity and the organs which protrude into it. Does adventitia or serosa cover the pieces of the
bladder on your two slides?
D-50 Female urethra (H&E). Under low power locate the urethra. It repeats the same three
layers as the ureters, but is thicker. The two muscle layers are somewhat indistinct. The
epithelium will vary according to the region from which the section is taken. Near the bladder
it is transitional, at the external opening it is stratified squamous, and between those two
places the epithelium is pseudostratified or stratified columnar. What is your call on your
slide? Notice the small outpocketings of mucus-secreting cells which form clusters in the
epithelium and extend into the lamina propria as simple glands. These are called the lacunae of
Morgagni. How would you distinguish the urethra from the ureter? (Now is the time to think
about this.)
D-71 Penis (H&E). We will study the penis in more detail in the laboratory on the male
reproductive system. Its reproductive function is more interesting than its urinary function
(despite what your mother may have told you). Only the urethra concerns us at the moment.
Locate this structure in the spongy portion of erectile tissue. It is lined with stratified or
pseudostratified columnar epithelium with patches of stratified squamous epithelium. As the
urethra broadens to its terminal enlargement and opens at the apex of the penis, the epithelium
becomes predominantly stratified squamous in form. Notice the epithelial outpocketings for
mucous glands, called the Glands of Littre. The names of these urethral glands are
unimportant. In fact, the glands probably are not very important, just providing a bit of
protection to the non-transitional epithelium that is exposed to urine.
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Gross Structure of the kidney
Structure of a nephron
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D-43, Kidney (H & E)
D-42 Kidney monkey (FeH)
D-45 Kidney human (PASH)
D-47 Ureter (H & E)
D-49 Bladder (H & E)
D-50 Female urethra (H & E)
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