Download Anatomy of the Urinary System

Exercise 28
natomy of the Urinary System Laboratory Objectives
n ompletion of the activities in this exercise, you will be able to:
Describe the gross and microscopic anatomy of the urinary
svstem,
Trace the path of materials through the urinary system, from
when they enter the kidneys to when they leave the body.
Describe the functions of the various components of the
urinary system,
Explain the positions of the two types of nephrons,
Detail the blood supply of the kidneys,
Materials
Compound light microscope Prepared microscope slides • Human kidney
• Kidney, injected to demonstrate renal blood supply
• Ureter
• Urinary bladder
• Urethra Torso model Dissectable kidney model, coronal section Model of a nephron Model of the female pelvis Model of the male pelvis • Injected sheep or pig kidney for dissection
Dissection tools (scalpel , probe, forceps , dissecting pan)
he kidneys (Figure 28,1), which are the principal organs
of the urinary system, perform several essential regulatory
functions, As they produce urine , the kidneys remove
metabolic wastes and toxins from the blood and conserve glu­
cose, water, and many essential electrolytes, These activities are
critical for maintaining osmotic and pH balance in the blood
plasma, The kidneys also have an endocrine function, They se­
crete erythropoietin, which promotes red blood cell production
in the bone marrow, and renin, which plays a role in maintain­
ing normal blood pressure,
The ureters, urinary bladder , and urethra are accessory or­
gans of the urinary system ( Figure 28,1), Collectively, these
structures transport, store, and excrete urine,
T
Anatomy of the Urinary System
The two retroperitoneal kidneys are located on each side of the
venebral column on the posterior abdominal "vaIL They extend,
approximately, from the T12 vertebra to the L3 vertebra, The
~
right kidney rests 1.5 to 2 cm (0,5 to 0,7 in) lower than the left
kidney due to the large area taken by the liver (Figure 28, 1a),
Each kidney is approximately 12 cm (5 in) long, 6 cm (2,5 in)
wide, and 3 cm 0,25 in ) thick, Its lateral surface is convex and
its medial surface is concave, A central region along the medial
surface, called the hilus, serves as a point of entry and exit for
the renal artery and vein , ureter, nerves, and lymphatic vessels
(Figures 28,1 and 28,2),
Each kidney is surrounded by three connective tissue cover­
ings (Figure 28, 1b), The renal fascia is the outer fibrous con­
nective tissue covering that anchors the kidney to the
peritoneum and abdominal walL The middle adipose capsule is
a fatty layer that provides shock-absorbing protection for the
kidney. The inner renal capsule is a strong fibrous layer that
tightly adheres to the kidney surface, It provides a protective bar­
rier that prevents infections from spreading to renal tissue,
In a coronal section of the kidney, three regions can be iden­
tified (F igure 28,2), The outer renal cortex and the middle
renal medulla contain the various urine-producing tubules that
comprise the nephrons. The inner region of the kidney is a cav­
ity known as the renal sinus. It serves to collect urine that is
produced in the nephrons , and to transport this fluid to the
ureter.
The ureters are retroperitoneal, tubular organs that are ap­
proXimately 25 cm (10 in) long, They begi:n at the renal pelviS
(Figure 28.2) and travel inferiorly along the posterior abdominaI
wall, They enter the pelViC cavity and terminate at the posterior
aspect of the urinary bladder (Figure 28.1a). The primary func­
tion of the ureters is to transport urine from the kidneys to the
urinary bladder.
The urinary bladder is located within the pelvic cavity, pos­
terior to the pubic symphysis and anterior to the rectum
(Figures 28.3a and b), It serves as a temporary storage sac for
urine, and its shape is determined by the volume of urine it con­
tains, An empty bladder has a pyramidal shape, with the base
forming its posterior surface and the apex oriented anteroinferi­
orly. When the bladder is full , it becomes ovoid and the superior
surface bulges into the abdominal cavity.
The urethra is a muscular tube that conveys urine from the
bladder to the outside of the body (F igure 28,3). At the junc­
tion with the bladder, a thick band of smooth muscle surrounds
the urethra to form the internal urethral sphincter (F igure
28,3c). This sphincter is involuntary and keeps the urethra
closed to prevent urine from leaking between periods of mic­
turition (urination). A second sphincter, the external urethral
sphincter, consists of skeletal muscle, In females, this volun­
tary sphincter is located near the external urethral orifice
(F igure 28,3b); in males, it is found just below the prostate
gland (Figures 28,3a and c).
491
EXERCISE TWENTY-EIGHT
Esophagus (cut)
Inferior
vena cava
Aorta
Left adrenal
gland
Inferior
vena cava
Psoas
major
muscle
I
Quadratus
lumborum
muscle
Adipose
capsule
Left kidney
Right
adrenal
gland
Left renal artery
Left renal vein
Renal
fascia
sup~
Right kirl,nAv-~~r
mesenteric
artery
Renal
capsule
Kidney
Ureter
Spleen
Left common
iliac artery
Ureter
artery
and vein
Parietal
peritoneum
Urinary
bladder
Rectum
(cut)
Renal
artery
(a)
Renal
vein
Hilus
External
oblique muscle
(b)
Figure 28.1 Overview of the urinary system. a) Anterior view in the male illustrating anatomical relationships
of the kidneys and ureters with posterior abdominal muscles, and major abdominal blood vessels; b) transverse sec­
tion of the left posterior abdominal wall, showing the position of the kidney in relation to other abdominal organs.
Cortex !iiIO;:;;;;;:-- - - - ­
Medulla
Renal
pyramids
Renal
pyramid
Renal sinus - ­
-4,,........;= --.:
Renal pelvis
Hilum
Renal papilla
~~I;t!JIL----:!!I--­ Renal sinus
Connection to
minor calyx
Minor calyx
Major calyx
Adipose tissue - - - - ­
in renal sinus
Renal capsule
Renal pelvis
------,~-­
Major calyx
--~=--------i
--r"'":--~=-""~­ Minor calyx
Renal lobe
-~---,>i~¥,-..,...,,~~. J
Renal papilla
Renal columns
Ureter
...r-- - - ­ Renal lobe
Renal capsule
(a)
(b)
Figure. 28.2 Internal structure of the kidney. a) Diagram of a coronal sedion of the left kidney; b) corre­
spondi ng cadaver dissedion.
ACTIVITY 28.1
Examining Gross Anatomy
of the Urinary System
1. On the torso model , identify the two kidneys along the
posterior abdominal wall (Figure 28.1). Note their posi-
tions relative to the vertebrae. Also observe that the posi­
tion of the liver causes the right kidney to be more inferior
than the left kidney.
2. Observe the lateral convex surface and medial concave
surface, and identify the hilus along the center of the con-
ANATOMY O F TH
Rectum
:>en oneum URI NARY SYSTEM
Figure 28.1 Position of the urinary bladder. Midsagittal sections of
a) the male pelvic cavity, and b) the fema le pelvic cavity, illustrating the posi­
tion of the urinary bladder in relation to other pelvic structures. c) Internal
view of the male urinary bladder, illustrating the rugae and the trigone.
Urinary
bladder
Pubic - -77--,-;:i-r-:::­
symphysis External----:-..;-.;c..:;c:..,...:;-......,.,y;.;.~
urethral sphincter Penile
urethra
Prostate gland
Urogenital
diaphragm
External
urethral
meatus
(a) Male
Peritoneum
Urinary
bladder
Uterus
6. Locate the middle portion , the renal medulla, and identify
~
the cone-shaped renal pyramids. They are separated by
inward extensions of cortical tissue known as renal
columns. Note that the base of each renal pyramid forms
a border with the cortex, while the apex, known as a renal
papilla, projects inwardly.
7. Identify the inner region of the kidney, which is called the
renal sinus. It consists of the calyces (singular = calyx)
and the renal pelvis (Figure 28.2).
8. Locate a minor calyx. Urine formed \>vithin a renal pyra­
mid drains through the renal papilla to enter the minor
calyx.
9. Follow the minor calyx inward until it joins at least one
more minor calyx. The larger area marked by this junction
is a major calyx.
10. Locate the renal pelvis , a funnel-shaped cavity continuous
with the ureters. The renal pelvis collects urine from three
to six major calyces and transmits it to the ureter.
11. On the torso model, identify the two ureters where they
exit the kidneys. Observe that these tubes travel inferiorly
along the posterior abdominal wall and enter the pelvic
cavity (Figure 28.1a).
12. In the pelvic cavity, locate the termination of the ureters at
the posterior aspect of the urinary bladder (Figures 28.3a
and c).
Urethra _ _ _~_~_ _ _~
Vagina -----7-----.....,.*~
Vestibule
(b) Female
Middle umbilical
ligament
1
Lateral­ umbilical ligament Rugae - --'::':--7':':'"*- -- ---""'- -­
Ureteral ---':-'~~-~------:--­
openings --:--:-=~'"-+- Center of
trigone
~________~~~~~~-------Neck
External urethral
sphincter (in
urogenital diaphragm)
(e) Urinary bladder .in male
-t--+-- - - Prostate
gland
I------:;~----
3. Identify the adrenal glands that rest on the superior sur­
face of each kidney.
4. Examine a coronal sect,ion of a kidney and identify the three internal regions (Figure 28.2): renal cortex, renal medulla , and renal sinus. 5. Locate the outer renal cortex and note its appearance.
Rectum
Pubic
symphysis
Internal ­
urethral
sphincter
cave surface (Figures 28.Ia and 28.2). At the hilus identify
the ureter, renal artery, and renal vein entering or exiting
the kidney.
Prostatic
urethra
H"--'--'-- - - - - Membranous
urethra
13. On models of the female and male pelvic cavities, observe
the relative position of the urinary bladder to other ab­
dominopelvic organs. in both sexes, the urinary bladder is
posterior to the pubic symphysis and anterior to the rec­
tum (Figures 28.3a and b). In females, it is anterior to the
uterus and the vagina (Figure 28.3b). In males, it is s11pe­
rior to the prostate gland (Figure 28.3a).
14. Obtain a model with an open bladder. Along the internal
surface of the contracted bladder, identify the numerous
rugae (Figure 28.3c), which are folds of the mucous mem­
brane. They are present when the bladder is empty. When
the bladder fills with urine, the wall stretches and the ru­
gae disappear.
EXERCIs e TWEl\TY-EIGHT
15. Identify the trigone, which is a triangular region marked
by the connections of the two ureters and the urethra to
the bladder wall (Figure 28.3c). This region lacks rugae
and remains smooth at all times. It is noteworthy because
bladder infections seem to occur most often in this area.
The reason for this is not known.
16. Identify the urethra where it emerges from the inferior
aspect of the urinary bladder. Notice that in females , the
urethra is relatively short (approximately 3.5 cm or
1.5 in) and travels anterior to the vagina. The external
urethral orifice is located anterior to the vaginal orifice
and posterior to the clitoris (Figure 28.3b). Observe
tha·t the male urethra is relatively long (approximately
20 em or 8 in) and has the following three sections
(Figures 28.3a and c).
• The prostatic urethra passes through the prostate gland.
• The membranous urethra passes through a band of
muscle called the urogenital diaphragm.
• The penile urethra travels through the shaft of the penis.
CLINICAL CORRELATION
For two reasons, females are more susceptible to urinary tract in­
fections than males. First, the female urethra is much shorter and
inflammatory infections of this structure (urethritis) can easily
spread to the bladder (cystitis) and possibly to the kidneys
(pyelitis or pyelonephritis). Second, the external urethral ori­
fice is very dose to the anal opening. Fecal bacteria can be trans­
ferred to the urethra particularly if an individual wipes with toilet
paper in a posterior to anterior direction after defecation.
~!lfilWi'M~~ On a torso model, identify the two kidneys and
lriiIIi·iIIIli6lli·...1I describe their anatomical relations to other ab­
dominal organs.
Right kidne y:
Left kidney:
• Tubular reabsorption, during which useful substances
such as water, glucose , amino acids, and ions are returned to
the blood
• Tubular secretion, during which unwanted substances such
as excess potassium and hydrogen ions, drugs, creatinine,
and metabolic acids are transported from the capillaries into
the tubules
Each nephron begins with Bowman's capsule, a cup-shaped
structure that surrounds a tuft of capillaries called a glomerulus
(plural = glomeruli). Together, the two structures comprise a
renal corpuscle (Figure 28.4). In each corpuscle, fluid passes
across a filtration membrane from the glomerulus to Bowman's
capsule. The !1uid entering Bowman's capsule is called the filtrate.
WHArS IN A WORD The term glomerulus comes from the
Latin term meaning "bal\" or "globe. " Indeed, the glomemlus is
like a ball or tuft of capillaries. This arrangement, rather than a
Single straight capillary, dramatically increases the amount of
capillary surface area through which filtration can occur, allow­
ing the kidneys to filter the blood much more rapidly.
After Bowman's capsule, filtrate travels through three additional
components of a nephron in the follOWing sequence: the proximal
convoluted tubule, the loop of Henle, and the distal convoluted
tubule (Figure 28.4). Together, these structures form a long, twist­
ing passageway known as the renal tubule. The convoluted
tubules and the loop of Henle are capable of both reabsorption and
secretion. However, there are regional speCializations. For example,
most reabsorption occurs in the proximal convoluted tubules,
while the distal convoluted tubules have a more impoaanr role in
secretion. Other tubules, the collecting ducts, are straight tubular
passageways that receive urine from the nephrons and transport it
to the minor calyces (Figure 28.4a).
Two types of nephrons exist in the kidney. The vast majority
(80% to 85%) are cortical nephrons (Figures 28.4a and b). The
second type , called juxtamedullary nephrons (figures 28.4a
and c), is less abundant but plays a critical role in conserving wa­
ter by producing a concentrated urine.
ACTIVITY 28.2
Examining the Nephron
1. Obtain a model or illustration of a nephron and distin­ guish between the following structures (Figure 28.4). • Renal corpuscle
• Renal tubule
The Nephron
The functional units of the kidney are the nephrons (Figure 28.4).
They consist of various types of tubules that closely interact with
capillaries during urine formation. To produce urine , the
nephrons perform three basic activities.
• Glomerular filtration, during which water, glucose , amino
acids, and nitrogen-containing wastes are passed from blood
to the nephrons along a pressure gradient
• Collecting duct
2. In their correct sequence, identify the specific segments of
the renal tubule (Figure 28.4a).
• Proximal convoluted tubule
• Descending limb of the loop of Henle
• Ascending limb of the loop of Henle
• Distal convoluted tubule
3. Closely examine the pattern of a typical nephron and no­
tice the follOWing general features (Figure 28.4).
A NATOMY OF THE URINARY SYSTEM
Glomerulus
Distal
convoluted
tubule
Proximal
convoluted
tubule
~,.,....=----or--
Peri tubular
capillaries
corpuscle
Peritubular --..,--:;;!./ I
capillaries
Collecting
duct
Loopof---~~~
Henle
Loop of Henle
Descending limb
(b) Cortical nephron
Proximal
convoluted
tubule
Ascending limb
Glomerulus----l~
1- 1 - - - Collecting
duct
i----+--,,..--_ Vasa
recta
I+---Collecting
duct
oj--+r---==_ Loop of
Henle
Minor calyx Papillary ducts
(a) (c) Juxtamedullary nephron
Figure 28.4
The kidney nephrons. a) Positions of cortical and Juxtamedullary nephrons in relation to the re­
nal cortex and medulla; b) blood supply to a cortical nephron; c) blood supply to a juxtamedullary nephron .
• All renal corpuscles are located in the cortex.
• The cortex also contains the proximal and distal convo­
luted tubules.
• The loops of Henle begin and end in the cortex but de­
scend and ascend in the medulla.
• The distal convoluted tubules drain urine directly into
collecting ducts.
4. Identify a collecling duct and notice that it receives urine
from several nephrons. Trace its path as it begins in the
cortex and descends through a renal pyramid in the
medulla. At the renal papilla, the collecting duct empties
into a minor calyx.
5. Observe that the kidney has two types of nephrons
(Figures 28.4b and c).
• In cortical nephrons, renal corpuscles originate in the
outer two thirds of the cortex and the loops of Henle do
not travel deeply into the medulla.
• In juxtamedullary nephrons, renal corpuscles originate
in the inner one third of the cortex and the loops of
Henle extend deep within the medulla.
EXERCISE TWENTY-EI G HT
fw!HMWNtJ
1. Inflammation of the renal cortex is likely to
affect the functIon of which segments of the
nephrons Explain why.
'
2. Kidney stones are deposits of calcium and magnesium salts
or uric acid crystals that can obstruct the urinary passageways.
Which condition is likely to be more serious: a kidney stone
blocking a collecLing duct , or one blocking a ureter? Explain
why.
7. Locate the peritubular capillaries and the vasa recta,
which arise from the efferent arteriole. The peritubular
capillaries are closely associated with renal tubules in
the cortex and the loops of Henle of cortical nephrons.
The vasa recta surround the loops of Henle of jux­
tameclullary nephrons (Figures 28.4b and c). Note that
these capillaries empty into the venous system that
drains blood from the kidney (Figure 28.5c)
8. Return to the model of the kidney and examine the ve­
nous drainage of the organ. The veins in the kidney par­
allel the arteries and are aSSigned identical names
(Figure 28.5).
9. On a torso model , identify the renal vein and notice that it
empties into the inferior vena cava (Figure 28.1 a).
Blood Supply of the Kidney
Under normal conditions, about 25% of total cardiac output trav­
els through the kidneys at a rate of about 1.2 liters per minute.
Each kidney receives its blood supply from a renal artery, which
is a direct branch of the abdominal aorta (Figure 28.1a). The re­
na'l artery ancl its branches deliver blood to the glomeruli
(Figure 28.5a), which are surrounded by Bowman's capsules in
the renal cortex and are the sites of blood filtration.
After passing through the glomeruli, blood enters the peri­
tubular capillaries and vasa recta (Figures 28.4b and c). Tubu­
lar reabsorption and secretion occurs between the renal tubules
and these capillary networks. The pentubular capillaries and
vasa recta drain into small venules that mark the beginning of ve­
nous drainage of the kidney.
f'JlWNtl
Explain why it is important for the kidneys to re­
__. __ ... _._ ceive a large daily volume of blood.
Microscopic Anatomy of the Urinary System
2. Identify the renal artery entering the kidney at the hilus.
Notice that the first branches of the renal artery are the
segmental arteries.
The histology of the kidney is centered on the structure of the
nephrons. As described earlier, each renal corpuscle consists of
a Bowman's capsule and a glomerulus. These structures have a
distinctive appearance and are easy to identify throughout the re­
nal cortex. The renal tubules and collecLing ducts, which are
found in both the cortex and medulla , are lined mostly by a sim­
ple cuboidal epithelium , although squamous and columnar ep­
ithelia are found in some regions. You will also observe arteries
and arterioles that supply blood to the kidney and capillary net­
works that surround the renal tubules. The capillaries are crit,i­
cal for normal renal function because of their active role in
reabsorption and secretion during the producLion of urine.
The accessory urinary organs are uni.que because they pos­
sess a mucous membrane with a transitional epithelium. This
epithelium is noteworthy for its ability to undergo dramatic
structural transformations to adjust for the changing physical
conditions of the organs where it is located.
3. The segmental arteries give rise LO a number of interlobar
arteries that travel toward the cortex through the renal
columns.
ACTIVITY 28.4
ACTIVITY 28.3 Examining
the Blood Supply
of the Kidney
1. Obtain a model of the kidney cut in a coronal plane to ex­
amine its arterial supply (Figure 28.5) .
4. At the junction between the cortex and medulla, observe
how interlobar arteries branch to form the arcuate arter­
ies. The arcuate arteries provide a good landmark for iden­
tifying the corticomedullary boundary.
5. The arcuate arteries give off several interlobular arteries,
which can be seen ascending into the cortex.
6. Obtain a model or illustration of a nephron. Identify the
afferent arteriole leading to a glomerulus , and Lhe efferent
arteriole which exits the glomerulus (Figure 28.4).
Examining the Microscopic
Anatomy of the Urinary System
The Kidney
1. Obtain a slide of the kidney.
2. Scan the slide under low magnification until your field of
view is .vithin the renal cortex. The cortex can be easily
identified because it contains numerous renal corpuscles,
each consisting of a glomerulus surrounded by Bowman's
capsule (Figure 28.6a). Each glomerulus will appear as a
ANATOMY OF THE URINARY SYSTEM
Interlobular
vein
Interlobular
artery
Arcuate artery
Interlobular
arteries
Arcuate vein
Interlobular
veins
-t~~S:~~~~::",.
Interlobar
arteries
.rf Af----lnterlobar vein
:~#----
Interlobar artery
Segmental
artery
Suprarenal
artery
(b)
Renal
artery
Renal vein
Renal
vein
Renal artery
1
Segmental arteries
!
Interlobar veins
Interlobar arteries
f
Interlobar """"I--++!---=-~l-----:..r."',
veins
Arcuate arteries
Arcuate veins
t
(a)
Interlobular veins
Interlobular arteries
t
Afferent arterioles
Venules
NEPHRONS
Peritubular
Glomerulus
capillaries
L.
Efferent
arteriole
(e)
Figure 28.5 Blood supply to the kidney. a) Coronal section of the kidney, ill ustratin g the major arteries and
veins; b) a closer view of the blood supply to a renal pyramid and the adjacent cortex; c) summary chart of the
blood flow through the kidney.
EXERCIS
TWENTY-EIGHT
spherical mass of pink- to red-staining tissue surrounded
by a clear space. This space, the capsular space, is the
cavil)' within Bowman's capsule that receives the filtrate
(Figure 28.6b).
3. Much of the field of v,iew consists of cross-sectional and lon­
gitudinal profiles of renal tubules typically lined by a simple
cuboidal epithelium (Figure 28.6). Locate these tubules.
Most of these are either proximal convoluted tubules or dis­
tal convoluted tubules, but collecting ducts are also present.
corpuscles
4. Switch to high power and examine a glomerulus and Bow­
man's capsule more carefully (Figure 28.6b). Like all blood
vessels, the walls of the glomerular capillaries are lined by
simple squamous epithelium (the endothelium). You can­
not clearly see the arrangement of this epithelium with
this preparation; however, many of the nuclei in the
glomerulus belong to the endothelial cells.
5. Examine a Bowman's capsule, The epithelium lining it is
also a simple squamous type , Look carefully across the
capsular space from the glomerulus and identify the single
layer of squamous cells that line the outer wall of the cap­
sule (Figure 28,6b),
6. The afferent and efferent arterioles may be identified on some glomeruli; however, you will be unable to distin­ guish one vessel from the other (Figure 28.6b), 7. Switch back to low power amI move the slide to a region Renal tubules where glomeruli are absent. This is the renal medulla (Figure 28.7). The field of view is filled with cross­
sectional and longitudinal profiles of the loops of Henle and collecting ducts. 8. The collecting ducts are relatively easy to identify because
the cuboiual epithelium that lines these tubules stains
lighter than the other cells on the slide (Figure 2ft?).
(a)
Kidney tubules
with simple cuboidal
epithelium
Glomerulus
Glomerular
capsular space
9. Obtain a slide labeled, "kidney, injected." This slide has
been specially prepared so that renal blood vessels can be
easily identified.
10. Scan the slide under low power. Renal blood vessels ap­
pear as bright red channels traveling throughout the field
of view. Kidney tubules are barely visible, because they
stain very faintly (Figure 28.8). Do not be concerned
about identifying the tubules on this slide. Focus your at­
tention on the blood vessels.
Loops of Henle
Position of afferent/efferent
arterioles
Simple squamous
epithelium of
Bowman's capsule
Beginning
of a proximal
convoluted tubule
(b)
Figure 28.6 The renal cortex. a) low-power light micrograph of the renal
cortex. Renal corpuscles are distributed throughout the field of view
(lM x 100). b) High-power light micrograph of a renal corpuscle, which in­
cludes a glomerulus enclosed by a Bowman's capsule, Kidney tubules sur­
round the corpuscle (lM x 300),
Collecting ducts
Figure 28.7 The renal medulla. light micrograph of renal tu bules in the
medulla of the kidney, Notice the lack of renal corpuscles in this region of
the kidney (lM x 300).
ANATOMY OF THE URINARY SYSTEM
11. Locate the cortex by looking for glomeruli, which will no\\
appear as bright red spherical structures (Figure 28.8).
12. Identify the afferent and efferent arterioles. Depending on
the plane of section , you may see both vessels, only one
vessel, or no vessels at all. In most cases, it is not possible
to distinguish these vessels from each other, but if you
scan the slide carefully, you may see the afferent arteriole
branching off an interlobular artery and traveling to a
glomerulus (Figure 28.8a).
C"tIIUS
!:-
13. Other blood vessels in the cortex are the interlobular ar­
teries and peri tubular capillaries. These blood vessels can
be seen throughout a typical field of view of the cortex.
The interlobular arteries have a larger diameter and are
easily distinguishable from the narrower and more abun­
dant peri tubular capillaries (Figure 28.8a).
14. Move [he slide to a region where the glomeruli abruptly stop
occurring. This is the border between the cortex and
medulla. Scan the slide and attempt to find blood vessels
traveling along this border. These are the arcuate arteries
(Figure 28.8b). These vessels mayor may not be visible, de­
pending on the plane of section of the tissue you are viewing.
15. Move the slide deeper into the medulla. The blood vessels
that yo u see here are the vasa recta , which are intimately
associated with the loops of Henle (Figure 28.8b).
bular artery Peritubular +=~l:=====
:apillaries The Ureters
Afferent arteriole
(a)
Cortex Arcuate artery
Glomeruli
1. Obtain a slide of the ureter and examine it under low
power. Identify the three tissue layers in the wall of the
ureter (Figure 28.9a): the mucosa (mucous membrane),
the muscularis (smooth muscle layer), and the
adventitia (connective tissue layer).
2. Switch to high power and confirm the follOWing (Figure 28.9a) . • The inner mucous membrane contains a transitional ep­
ithelium and an underlying lamina propria.
• The middle muscle layer has an inner longitudinal and
an outer circular layer of smooth muscle.
• The outer adventitia is composed of fibrous connective
tissue.
The Urinary Bladder
Corticomedullary
boundary
Figure 28.8
Vasa recta
Medulla
(b)
Renal blood vessels. a) light micrograph of the blood ves­
sels in the renal cortex (lM x 60); b) light micrograph of blood vessels at
the border between the renal cortex and renal medulla (lM x 10).
1. Obtain a slide of the bladder. This slide has two sections of
tissue. Both are longitudinal sections of the urinary bladder
wall. View both sections under low power and notice that
one is much thicker than the other. The thicker section illus­
trates the contracted wall of an empty bladder (Figure 28.9b);
the thinner section is the distended wall of a full bladder.
2. Examine the section of the contracted bladder wall. Iden­
tify the mucous membrane , which consists of transitional
epithelium and a layer of connective tissue called the lam­
ina propria. Observe that the epithelium is relatively thick ,
with several layers of cuboidal cells. Also no tice that the
mucous membrane is arranged into a number of tissue
folds known as rugae (Figure 28.9b).
EXERCISE TWENTY-EIGHT
\--=----'-"'-'---+Smooth muscle
Outer connective
tissue layer
Lumen of urinary
bladder
(a) Ureter
Rugae
--~
Erectile tissue of penis
Transitional
epithelium
,
Mucosa
Lamina
propria
~~~~~~~~~
"""~~f-
Smooth
muscle
~~~~~~~l~~~~~~~~j- Mucosa
:~~'"'-2'+-
~=::L-
Submucosa
Blood
vessels
..........""'-'f--
Visceral
peritoneum
(e) Urethra
(b) Urinary bladder
Figure 28.9
Histology of the accessory organs of the urinary system. a) The ureter; b) the urinary blad­
der in the contracted state; c) the urethra . 3. Just below the mucous membrane, identify a second layer •.
of connective tissue, called the submucosa, and a region of
smooth muscle, known as the muscularis. The muscularis
consists of three layers of intersecting smooth muscle
rtbers , collectively rderred to as the detrusor muscle
(Figure 28.9b).
4. Identify the serosa (visceral peritoneum) that covers the
outer wall of the bladder (Figure 28 .9b). This is a very
thin serous membrane , which may not be present on
your slide.
S. Examine the section or the distended bladder. Notice that
the bladder wall here lacks rugae .
6. Examine the epithelium on this section. It is strikingly dif­
ferent on this section, consisting of only two or three lay­
ers of squamous cells. The transitional epithelium that
you are viewing on this slide and in the previous slide of
the ureter is unique to the urinary tract.
7. Identify the other layers in the bladder wall described
previously.
WHAT'S IN It. WORD The term transitional implies some kind
of change. The cells in transitional epithelium alter their shapes
with changing physical conditions. When the bladder is empty
and its wall is relaxed , the epithelium is relatively thick with se\'­
erallayers of cuboidal cells. As the bladder fills ,"vith urine , these
same cells become squamous and the epithelium is reduced to
two to three layers to allow for bladder expansion.
The Urethra
1. Obtain a slide of the urethra and examine it under low
power. Identify the epithelium and lamina propria in the
mucous membrane and circular layers of smooth muscle
(Figure 28.9c).
2. Switch to high powe r and examine the mucous membrane
more closely. The epithelium lining the mucous mem­
brane will vary depending on the region of the urethra
that you are viewing.
• Near the junction with the urinary bladder, the epithe­
lium is transiti onal.
ANATOMY OF THE URINARY SY STEM
• There is a gradual change to pseudostratified columnar
toward the middle section of the urethra. This is the pri­
mary epithelial type.
Renal
artery
and vein
Segmental
artery
Interlobar
artery
and vein
Minor
calyx
Cortex
• Near the urethra orifice, the epithelium changes to strat­
ified squamous.
Based on the epithelial type, what region of the urethra
are you viewing7
1. When examining a microscopic structure of
the kidney, the presence or absence of renal cor­
puscles is a reliable criterion for determining whether you are
Yie'wing the renal cortex or the renal medulla. Explain why.
2. Based on your microscopic observations in the previous ac­
tivity, identify structural similariti.es and differences in the
structure of the ureters , urinary bladder, and urethra. Focus
your attention on the organization of the mucous membrane
and muscle layers.
Similarities:
Differences:
Ureter Renal
pelvis
Renal
papilla
Renal
pyramid
Renal
column
Figure 28.10
Dissection of the sheep kidney. The kidney has been cut
along a frontal plane to expose internal stru ctures. The arteries have been in­
jected with red latex and th e veins with blue latex.
Kidney Dissection
In the folloWing activity, you will dissect an intact sheep or pig
kidney. Pig kidneys are much larger and flatter than sheep kid­
neys. However, both types are quite similar, anatomically, to the
human kidney and are excellent models for studying renal struc­
ture. As you dissect, have models, illustrations, or photographs
of the human kidney readily available so that you can make
structural comparisons.
ACTIVITY 18.5
Dissecting a Kidney
1. Obtain a preserved kidney from the laboratory instructor.
The kidneys may be double-injected specimens, meaning
the blood vessels have been injected with colored latex for
easier identification (red = arteries; blue = veins).
2. Before making any incisions, observe the external struc­
tures of the kidney. Similar to the human kidney, the sheep
(or pig) kidney has a lateral convex surface and a medial
concave surface. The hilus is located along the medial sur-
face. Identify the ureter, renal artery, and renal vein at the
hilus (Figure 28.10). From superior to inferior, these
structures are positioned in the folloWing order.
• Renal artery
• Renal vein
• Ureter
3. Of the three connective tissue capsules that cover the kid­
ney, only the innermost renal capsule is intact. It appears
as a thin, shiny membrane that adheres tightly to the sur­
face of the kidney. To observe this capsule more closely, lift
a portion of the membrane from the surface with a for­
ceps. The other two coverings, the renal fascia and adipose
capsule, have been removed, but remnants may remain
near the hilus.
4. With a scalpel, make an incision that will divide the kid­
ney into anterior and posterior halves. Begin at the supe­
rior margin and cut along the lateral convex surface,
toward the medial concave surface. Try to cut as close to
the midline as pOSSible. You can cut completely throug!1
EXERCISE TWENTY-EIGHT
the organ or, if you prefer, keep the two halves connected
at the hilus. The resulting incision will give you a coronal
section of the kidney (Figure 28.10).
5. Identify the following internal structures (Figure 28.10).
• The outer layer is the renal cortex, which has a granular
texture and light color.
• The middle layer is the renal medulla. Observe the alter­
nating renal pyramids and renal columns. The pyramids
have a darker color than the cortex and have a striped
appearance due to the longitudinal arrangement of kid­
ney tubules. The apex of each pyramid (renal papilla)
projects inward and the base borders the cortex. The re­
nal columns, located between the pyramids , are exten­
sions of and have the same appearance as the cortex .
• The inner region is the renal sinus, into which urine
drains before !1owing into the ureter. The sinus con­
sists of minor calyces, major calyces, and the renal
pelvis. Identify several minor calyces, located adjacent
to the renal papillae. Locate the major calyces as they
are formed by the convergence of several minor ca­
lyces. The renal sinus is formed by the merging of the
major calyces. Locate this funnel-shaped structure as
it joins the ureter.
6. Attempt to identify some of the blood vessels that serve
the kidney (Figure 28.10). Carefully dissect within a renal
column and locate an interlobar artery and vein. Along the
corticomedullary border, identify examples of the arcuate
blood vessels. Finally, try to id entify the fragile interlobu­
lar arteries and veins as they travel through the cortex.
Compare the anatomy of the human kidney with
the sheep or pig kidney and identify structural
similarities and differences.
Similarities:
Differences:
Exercise 28 Review Sheet
Name _______________________________________
Lab Section __________________________________
Anatomy of the Urinary System
Date __________----~----------------------
Questions 1-9: Match the structure in column A with the appropriate description in column B.
A
1. Renal artery
2. Bowman's capsule
3. Renal pyramid
4. Afferent arteriole
5. Minor calyx
6. Renal column
7. Distal convoluted tubule
8. Arcuate artery
9. Renal cortex
B
a. This structure is a branch of an interlobular artery and
delivers blood to a glomerulus.
b. An interlobar artery travels in this region of the kidney.
c. This structure is the first portion of a nephron. It receives
the blood filtrate.
d. This blood vessel travels along the border between the renal
medulla and cortex.
e. This portion of the renal sinus receives urine directly from
collecting ducts at a renal papilla.
r. This blood vessel is a direct branch of the aorta, and delivers blood to the kidney. g. This cone-shaped structure, located in the renal medulla ,
contains loops of Henle and collecting ducts.
h. Renal corpuscles are found in this region of the kidney.
i. This portion of a nephron drains urine directly into a collecting ducL. 10. Briefly describe the three functions that occur in the nephron during the process of
urine production.
11. Compare the two types of nephrons that are found in the kidney: cortical nephrons and
juxtamedullar nephrons.
12. Describe the pathway of blood through the kidney.
13. Why is transitional epithelium unique to other epithelial types? Why is it important
that this type of epithelium be located in the wall of the urinary bladder?
l
EXERCISE TWENTY-EIGHT
14. Compare the anatomical relationships of the urinary bladder in the male and female.
15. Explain why females are more vulnerable to urinary tract infections than males.
Questions 16-23: identify the Labeled structures Ln the following diagram.
16.
17.
16
18.
17
19.
19
18
20.
20
2l.
21
22.
22
23.
23
Questions 24-33: In the following diagram, identify the structures by labeling with the coLor
that is indicated.
24. Descending limb of the loop of Henle = green
25. Distal convoluted tubule = blue
26. Glomerulus = red
27. Efferent arteriole
= orange
28. Proximal convoluted tubule = brown
29. Ascending limb of the loop of Henle = purple
30. Afferent arteriole = black
3L Bowman's capsule = pink
32. interlobular artery = tan
33. Collecting duct = yellow
[