THE URINARY
SYSYEM
THE URINARY SYSTEM

Paired kidneys


Ureters


that convey the urine from the kidneys to the
bladder
The bladder


form the urine from the blood
where urine is stored until it can be
discharged
The urethra

through which urine finally passes to the
exterior.
The kidney functions

1- Maintenance of the internal
environment.
They do this by filtering the plasma
 initially extracting an enormous volume of
fluid

subjecting the ultra filtrate to further
processing in which
• useful substances selectively reabsorbed
• waste substances are concentrated for elimination

the volume is adjusted by the conservation
of sufficient water to maintain the
composition of the plasma
The kidney functions

In large dogs and animals of similar
size 1000 to 2000 L of blood perfuse
the kidneys daily

the 200 to 300 L of fluid that are
filtered from this volume are later
reduced by reabsorption until only 1 or
2 L of urine remain to be discharged
The kidney functions

2- The endocrine function

consists of the production and release
of two hormones:
• Renin, which plays a vital role in the
regulation of systemic blood pressure
• Erythropoietin, which influences
erythropoiesis.
General morphology
The kidneys are firm, reddish-brown
glands whose appearance varies:
The most familiar “kidneyshaped” to the common
vocabulary, is encountered in the
dog, cat, and small ruminants.
The kidneys of the pig are a
much flattened version, whereas
those of the horse are more
heart-shaped .
In contrast, the bovine kidneys are
deeply fissured to outline many lobes
General morphology

The kidneys are usually found
pressed against the abdominal roof

one to each side of the vertebral
column, and mostly in the lumbar
region
General morphology

They are rarely symmetrical

the right one is about half a kidney-length in
advance of its fellow

The cranial extremity of the right kidney
commonly fits into a fossa of the liver, which
helps fix its position

The left one, lacking this lodgment, is more
mobile and is more likely to sag within the
abdomen (pendulous left kidney)
R
L
General morphology
• The surface of a kidney is generally smoothly
convex except for an indentation of the medial
border
• This indentation leads to a concealed space
occupied by the dilated origin of the ureter
(renal pelvis)
• The vessels and nerves passing to and
from the renal hilus
The internal organization of the
kidney


Longitudinal section will divide the organ
into dorsal and ventral “halves.
Such a section shows that the
parenchyma is enclosed within a tough
fibrous capsule.

The capsule restricts the kidney’s ability to
expand
• the swelling that occurs in certain disease
conditions
• tends to compress the tissue and narrow the
internal passages.
The internal organization of the
kidney

The parenchyma is visibly divided into an
outer cortex and an inner medulla.

The cortex is distinguished by its reddishbrown color and finely granular
appearance.
The medulla consists of:
 a dark, purplish outer zone
 a paler, grayish-red inner zone

The internal organization of the
kidney
In many species the medulla is arranged as several discrete
masses, each roughly pyramidal in form.
The functional units of the
kidney

The functional units are known as renal tubules or
nephrons.

These epithelial tubules are supported by a
connective tissue interstitium
• estimated number several hundred thousand or even a
million in canine kidneys.

Each nephron begins with a blind expansion that is
invaginated by a cluster of capillaries known as a
glomerulus

The glomerulus and its epithelial covering together
constitute renal corpuscle.
The functional units are known as renal tubules or
nephrons.
Estimated number several
hundred thousand or even
a million in canine kidneys.
Each nephron begins with
a blind expansion that is
invaginated by a
cluster of capillaries known
as a glomerulus
The general organization of the
kidney

The remaining part of the nephron
forms a long tubules differentiated
into several successive segments

1- Proximal convoluted tubule
2- A long hairpin loop
3- Distal convoluted part that.
4- Collecting tubule within the
medullary ray.





Each collecting tubule, which
serves many nephrons, runs
through the medulla before
opening into a larger vessel,
5- A papillary duct
Blood supply


Each kidney is
supplied by a renal
artery
The renal artery
divides into several
interlobar arteries

They give rise to
branches known
as Arcuate
arteries
Blood supply



Arcuate arteries in turn
give origin to
numerous interlobular
arteries that supply
the units or lobules
(cortex)
Each interlobular artery
gives rise to many
branches that supply
individual glomeruli
The glomerular
capillaries rejoin in one
emissary vessel at the
distal pole of the
glomerulus
Renal Pelvis and Ureter:

In most domestic species the ureter begins in a common
expansion, the renal pelvis
 All the papillary ducts open

The ureter penetrates the bladder wall very obliquely.

The length of the intramural course guards against reflux of
urine into the ureter when the pressure is raised within the
bladder.

It does not prevent further filling of the bladder since the
resistance is overcome by peristaltic contractions of the
ureter wall.
The Urinary Bladder
The bladder is a distensible storage
organ and thus can have no constant
size, position, or relationships.
 The contracted bladder rests on the
pubic bones

in the larger species it is confined to
the pelvic cavity
 in carnivores extends into the
abdomen

The Urinary Bladder

In the larger species the contracted
bladder is largely retroperitoneal

but most of the surface becomes
intraperitoneal when the organ is even
moderately expanded.
The Urinary Bladder

Three folds continue from
the serosal covering onto the
abdominal and pelvic walls.

Paired lateral vesical folds
convey the round ligaments
of the bladder
•

these vestiges of the
umbilical arteries
The third, median vesical
fold
• is empty in the adult, but
in the fetus it supports the
urachus,
The Female Urethra

The female urethra
runs caudally on
the pelvic floor
below the
reproductive tract.

It passes obliquely
through the vaginal
wall to open
ventrally at the
junction of vagina
and vestibule.