Transcript No. 11

No. 11
1. Introduction of the Urinary System
2. Kidneys
3. Ureters
4. Urinary Bladder
5. Urethra
Introduction of the Urinary System

If the cells of the body are to survive
and carry out their functions
effectively, they must be surrounded
by a stable environment. The
relatively constant state of the
body’s internal environment is called
homeostasis.

To maintain homeostasis the
concentrations of such substances as
water, sodium, potassium, calcium,
and hydrogen ions must remain
relatively constant, as must the
concentrations of a wide variety of
cellular nutrients and products.

Maintaining homeostasis involves most of
the body systems. The digestive system,
for example, supplies nutrients and also
serves as a means of excreting some
waste products. The lungs supply oxygen
to the body and eliminate carbon dioxide
and some water. The skin also plays a
minor role in excretion-sweat, for example,
contains small amounts of urea and
ammonia.

The kidneys, however, as the main
excretory organs, are critically important
in maintaining the balance of substances
required for internal constancy. The
kidneys eliminate from the body a variety
of metabolic products, such as urea, uric
acid, and creatinine. Further the kidneys
conserve or excrete water and electrolytes
as required so that the internal balance of
these substances will be maintained. In
fact, kidney malfunction can cause severe
and even fatal problems as a result of
upsets in fluid and electrolyte balance.

To prevent death, it is necessary to
replace the nonfunctioning kidneys
with healthy ones by means of a
kidney transplant or to remove
potentially harmful substances
regularly from the blood with an
artificial kidney machine.
1. Components of the urinary
system:

Two kidneys, two ureters, one
urinary bladder and a single urethra
make up the urinary system.
2. Functions of the urinary system:
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Removing certain metabolic wastes and
excess water from blood in the form of
urine, maintaining the homeostasis of the
body’s internal environments are the main
functions of the urinary system.
Urine drains out of each kidney, is
conveyed through the ureter and is stored
in the urinary bladder until it is expelled
from the body through the urethra.
Also the kidney has the endocrine function,
producing erythropoietin, renin, and 1,
25-hydroxycholecalciferol.
Section 1 The Kidneys
Ⅰ. The Features of Kidneys
 The kidneys are a pair of beanshaped, reddish-brown organs.
 Each kidney has two extremities, two
surfaces, and two borders.
1. Superior extremity and inferior
extremity

The superior extremity (upper pole)
is broader and thinner than the
inferior extremity (lower pole).
2. Anterior and posterior surfaces

The anterior surface is slightly
convex and the posterior surface
contacting the posterior abdominal
wall is plane.
3. Lateral border and medial border
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The lateral border is convex.
On medial border of the kidney there is a
vertical slit, the renal hilum, which
transmits the renal vessels, nerves and a
part of pelvis. The renal hilum leads into a
central recess named the renal sinus,
which is filled with the branches of the
renal artery and vein, nerves, lymphatic
vessels, minor renal calices, major
renal calices, renal pelvis and adipose
tissue.

The structures which pass through
the renal hilum are enclosed
together by the connective tissue, to
form the renal pedicle. From the
front backward, the order of these
structures in the renal pedicle is
renal vein, renal artery, renal pelvis,
and from superior to inferior is the
renal artery, renal vein and renal
pelvis.
Ⅱ. The Location and Relations of
Kidneys
1. The position
 The kidneys lie on the posterior
abdominal wall one on each side of
the vertebral column with its long
axis almost parallel to the long axis
of the body. The right kidney is lower
than the left one.
Left kidney:
 The superior extremity of the left
kidney is at the level of the inferior
border of the body of the eleventh
thoracic vertebra, the inferior
extremity of the left kidney is at the
level with the intervertebral disc
between the second and third lumbar
vertebrae.
Right kidney:
 The superior extremity of the right
kidney is at the level with the
superior border of the body of the
twelfth thoracic vertebra, and the
inferior extremity with the superior
border of the body of the third
lumbar vertebra.
Renal hilum:
 The renal hilum is at the level of the
first lumbar vertebra, 5 cm lateral to
the midline of the body.
Twelfth rib:
 The left twelfth rib is behind the
middle part of the posterior surface
of the left kidney and the right
twelfth rib is behind the superior part
of the posterior surface of the right
kidney.
Renal region:
 The area between the twelfth rib and
the lateral border of the erector
spinae is called the renal region in
clinic.
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2. The relations
The upper poles of the kidneys are
covered by the suprarenal glands.
The renal pelvis is continuous with the
ureter.
The anterior surface of the upper part of
left kidney is in contact with the stomach
and spleen, the middle part with the tail of
pancreas and splenic vessels, and the
lower part with the coils of the jejunum
and the left colic flexure.
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The anterior surface of the upper part of
the right kidney is in contact with the right
lobe of the liver, the medial border of the
middle part with the descending part of
duodenum, and the inferior part with the
right colic flexure.
Posteriorly, each kidney lies on muscles, i.
e., the diaphragm above, the psoas major,
the quadratus lumborum and the
transversus abdominis below.
Ⅲ. The Structure of Kidney

On the coronal section of a kidney,
the renal tissue is divided into two
portions: the cortex and medulla.
Ⅰ) The Renal Cortex
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The renal cortex lies immediately
beneath the fibrous capsule, arch over the
bases of the pyramids.
It is rich in blood vessels and reddishbrown in colour. The parts from renal
cortex dipping in between the pyramids
are named the renal columns.
The renal cortex is composed of renal
glomeruli and renal tubules.
Ⅱ) The Renal Medulla
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The renal medulla is deep to the cortex.
It consists of a number of pale striated,
conical masses, termed the renal
pyramids.
The bases of pyramids are directed toward
the periphery of the kidney, while their
apices converge towards the renal sinus,
where they form prominent papillae
projecting into the minor calices.
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Sometimes two or three apices of renal pyramids
converge in one renal papilla. There are 7～12
renal papillae in each kidney.
The foramina on their apices are called the
papillary foramina.
The urine formed in the kidney passes through
these foramina into the lesser calices.
There are 7～8 minor renal calices in the renal
sinus. Each minor renal calyx is indented in a
cup-shaped fashion, receiving from one to three
papillae.
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Two or three minor renal calices converge
into one major renal calyx.
There are two or three major renal calices
in each kidney.
Finally the major renal calices join the
renal pelvis, which is flat funnel-shaped.
The renal pelvis becomes narrow at the
renal hilum, then passes downward to
continue with the ureter at the level of the
inferior extremity of the kidney.
Ⅳ. The Coverings of Kidneys

Each kidney is surrounded by three
layers of tissues.
Ⅰ) The Fibrous Capsule

The innermost layer, which covers
the surface of the kidney, is the
fibrous renal capsule. It can be
stripped easily from a normal but
can’t from a diseased kidney.
Ⅱ) The Adipose Capsule

The adipose capsule is outside the
fibrous capsule and continues with
the adipose tissue within the renal
sinus. The amount of fat is very
variable. Generally there are more
adipose tissue along the borders of
the kidney.
Ⅲ) The Renal Fascia
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The adipose capsule is surrounded by the renal
fascia which is divided into anterior and posterior
layers to enclose the kidneys and suprarenal
glands.
The anterior layer of two sides is continued
acrossing the median plane infront of the aorta
and inferior vena cava. Whereas the posterior
layer merges with the fascia of the psoas major
and the quadratus lumborum. Both layers also
merge with the connective tissue around the
renal vessels.
The two layers are fused each other above the
suprarenal gland and continue with
infradiaphragmatic fascia and transverse fascia.
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Supporting structures of the kidneys:
The connective trabeculae from renal fascia cross
the adipose capsule to the fibrous capsule to fix
the kidney.
Besides, the adipose capsule, the neighbouring
organs, the renal vessels, peritoneum and
pressure in the abdominal cavity play the role
also in maintaining the normal location of the
kidney.
If these supporting structures are abnormal the
kidney may descend to an abnormally low level.
This downward displacement of the kidney is
called nephroptosis.
Ⅴ. Renal Vessels and segments
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The renal arteries, one on each side,
arise directly from the aorta at the
level of the 2nd lumbar vertebra.
Each artery lies behind the
corresponding renal vein, and at or
just outside the hilum of kidney, it
divides typically into anterior and
posterior divisions.
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The anterior division passes in front of the
pelvis and divides into four segmental
arteries, while the posterior division
passes behind the pelvis and becomes the
posterior segmental artery.
The second grade branches of renal artery
are segmental arteries.
The area which each segmental artery
distributed is called a renal segment.
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Each kidney has five renal segments:
①Superior segment
②Superior anterior segment
③Inferior anterior segment
④Inferior segment
⑤Posterior segment.
When one segmental artery is obstructed,
the corresponding renal segment will be
necrosis. This is because of no
anastomosis between the segmental
arteries.
Section 2 The Ureters
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From the renal pelvis, urine is
transported to the urinary bladder by
ureters, one from each kidney.
The ureters are two muscular tubes
which convey the urine from the
renal pelvis to the urinary bladder.
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The ureters descend between the parietal
peritoneum and the body wall to the pelvic cavity,
where they turn medially and enter the urinary
bladder on its posterior lateral surfaces. Before
opening into the baldder, the ureters travel
obliquely through the bladder wall. As a result,
contraction of the muscles of the bladder wall can
compress the ureters and help prevent urine from
flowing back into the ureters from the bladder.
This occurs during bladder emptying. In effect,
the muscles of the bladder wall act as sphincters
on the ureters. Valve-like folds of the mucous
membrane lining of the bladder cover the orifices
of the ureters and assist in preventing urine from
flowing back into the ureters during micturition.
According to the course each ureter may be
divided into three parts:
Ⅰ. The Abdominal Part of the
Ureter
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The ureter is continuous superiorly with the renal
pelvis.
A slight constriction may mark the site of
transition.
This part runs downwards and slightly medially in
front of the psoas major and behind the
peritoneum.
At the superior pelvic aperture, the left ureter
crosses through the terminal part of the left
common iliac artery anteriorly, and the right
ureter passes the beginning of the right external
iliac artery anteriorly, to continue with the pelvic
part.
Ⅱ. The Pelvic Part of the Ureter
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It passes downwards along the lateral wall of the
lesser pelvis, then turns medially at the level of
the ischial spine to the base of the urinary
bladder. At here the ductus deferens crosses it
anteriorly to its medial side in the male.
In the female the pelvic part of the ureter turns
downwards, forwards and medially. At the level of
ischial spine, 2 cm lateral to the cervix of uterus,
it is crossed anteriorly by the uterine vessels.
It then runs along the lateral side and the
anterior surface of the vagina to the base of the
urinary bladder.
Ⅲ. The Intramural Part of the
Ureter

It passes obliquely through the wall
of the urinary bladder for 1.5 cm
long, before opening into the
superolateral angle of the bladder.
When the bladder is filled up, the
intramural part serves as a valve to
prevent the badckflow of urine.
Constricted parts:
 The ureters are not uniform in
calibere. Three constricted parts are
the places where the renal stones
stay usually.

These constrictions are:
① Superior stricture: At the junction
of the ureter and the renal pelvis,
② Middle stricture: At the point
where ureter crosses the superior
aperture of the lesser pelvis,
③ Inferior stricture: The intramural
part.
Section 3 The Urinary Bladder
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
The urinary bladder is a hollow, muscular organ
which stores the urine.
It varies in size, shape, position and relations
according to the amount of urine that it contains.
In the adult the volume of the urinary bladder
averages 300～500 ml, with the largest volume of
800 ml. In the babaies the volume is 1/10 of the
adult’s volume. In old age the volume is volume
is larger than in the adult, because the tension of
the muscles of the urinary bladder is reduced. In
female its volume is less than in the male.
Ⅰ. The Features of Urinary Bladder
The empty urinary bladder is in the
form of a triangular pyramid. It may
be divided into four portions:
 apex,
 body,
 fundus
 neck.
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The apex of bladder is directed
ventrally toward the posterior
surface of the upper part of the pubic
symphysis.
The fundus of bladder is triangular
and directed posteriorly and
inferiorly
The body of bladder is between the
apex and fundus.
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The neck of bladder is the lowest and
also the most fixed part. It is pierced by
the internal urethral orifice. In the male
the neck rests upon the prostate gland.
When the bladder is filled up with urine, it
is oval in shape, the boundaries between
the surfaces are not clear, and the
mucosal folds become disappeared.
Ⅱ. The Location and Relations of
the Urinary Bladder
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The urinary bladder rests in front against
the pubis symphysis. There are loose
connective tissue and venous plexus
between the bladder and the pubic
symphysis.
In males, the bladder is in front of the
rectum.
In females, it lies just anterior to the
uterus and the superior portion of the
vagina.
The fundus of the bladder:
 In the male the fundus of bladder is
anterior to the seminal vesicles, ampullae
ductus deferentes and rectum.
 In the female it (the fundus) is attached
posteriorly to the upper portion of the
vagina and cervix of uterus by the loose
connective tissue containing the venous
plexus.
The neck of the bladder:
 In the male the neck of bladder is firmly
attached to the prostate gland, and in the
female to the urogenital diaphragm.
 In the adult the empty urinary bladder is
entirely within the lesser pelvis, but as it
becomes distended it expands upwards
and forwards into the abdominal cavity.

The urinary bladder is a
interperitoneal organ, only the
superior surface and upper portion of
the inferolateral surfaces are covered
by peritoneum, which is reflected
from the lateral wall of the pelvis and
from the anterior abdominal wall just
above the level of the pubic
symphysis when the bladder is
empty.

As the bladder fills, the superior surface of
the bladder enlarges and bulges upward
into the abdominal cavity, the peritoneal
covering is peeled off away from the lower
part of the anterior abdominal wall, and
the reflection of the peritoneum becomes
higher. So that the bladder comes into
direct contact with the anterior abdominal
wall. Therefore the puncture of bladder
can be performed just above the pubic
symphysis without injuring the peritoneum.
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In the male the peritoneum covering
on the superior surface of the
bladder reflects to the rectum to
form the rectovesical pouch.
In the female it continues to the
uterus to form the vesicouterine
pouch.
Ⅲ. The Interior Structure of the
Urinary Bladder

It is lined by mucous membrane.
When empty, the mucous membrane
lie in folds except over the trigone
ofbladder where it is smooth.
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Trigone of bladder:
The trigone of bladder is on the interior of the
fundus of bladder. When the bladder is empty
there are many folds on the mucosa of its
internal surface, but on the fundus of bladder
there is a smooth triangular area are called the
trigone of bladder. The anteroinferior angle of
the trigone is formed by the internal urethral
orifice, the two posterolateral angles by the
ureteric orifices. The area of this trigone is said
to be susceptible to tuberculosis, tumor and
inflammation.
A ridge, the interureteric fold, connects the two
ureteric orifices at the upper border of the trigone.
Secton 4 The Urethra
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The urethra extends from the urinary
bladder to the exterior. It is very different
in males and females.
The female urethra is a membranous
canal, about 5 cm long, extending from
the urinary bladder to the external
urethral orifice in the vaginal vestibule.
It is wider, shorter, straighter than the
male urethra.