The urinary system consists of the kidneys, ureters, bladder, and urethra. The kidneys filter the blood and remove waste, which is transported through the ureters to the bladder. The bladder stores urine until it is released through the urethra. Key functions include filtering waste from the blood and maintaining water and electrolyte balance. The kidneys receive blood from the renal arteries and produce urine that is collected in the renal pelvis before exiting through the ureters.

1. Urinary System
By
Dr. Luay Obed Hamza

2. Urinary System
 The urinary system is made up of the
kidneys, ureters, bladder and urethra
which filter the blood and dispose of
waste products
– All the blood in the body passes though
the two kidneys more than 400 times per
day and is filtered of nitrogenous wastes
each time

4. Function
 It gets rid of the waste products that are created
when food is transformed into energy.
 It also maintains the correct balance of water
and electrolytes (salts) within the body’s cells.
 Another key function is the production of
hormones called erythropoietin and renin,
which are important in maintaining healthy
blood pressure, producing blood cells, and
absorbing salt correctly.
 Finally, the urinary system processes vitamin D.

5. Location of the kidney
 The kidney is paired structures lying
retroperitoneal passed against the
dorsal abdominal wall on either side of
the vertebral column. They are
predominantly in the lumber region,
but extend cranially under the last ribs
into the intrathoracic part of the
abdomen. Their position changes by
the half of the length of a vertebra with
the movement of the diaphragm.

6.  The right kidney is located further
cranial than that of the left and its
cranial extremity lies in contact with
the caudate process of the liver and
the right lobe of the liver. It lies in a
fossa of liver (renal impression) which
help to limit its movement. The left
kidney is more mobile, which is
suspended in the abdominal cavity.

8. Shape of the kidney
 The kidney are reddish brown organs,
the shape varies among animal. The
left kidney is bean shaped in most
animals, while in horse has bean to
pyramidal shape. The right kidney has
bean shape but in the horse has a
valentine heart shape.

9.  The kidney has smooth surface, which
descried to be having dorsal and
ventral surfaces, lateral and medial
borders and cranial and caudal
extremities or poles. The medial
border is indented to form the renal
hilus through which the dilatator origin
of the ureter, the renal pelvis exits and
the renal vessels and nerves enter the
kidney.

11. Structure of the kidney
 • The renal parenchyma is enclosed
within a tough fibrous capsule, which
passes inward at the medial aspect of
the kidney to line the walls of renal
sinus. This capsule can be easily
removed from a healthy kidney during
post-mortem examination, but adheres
the tissue is scarred by disease.

12. The parenchyma of the kidney is divided
into:
Renal cortex
(peripheral zone and
juxtamedullar zone).
Renal medulla
(external and internal zone).

13.  The renal cortex is reddish brown in
color and has finely granular
appearance. The cortex is delineated
into cortical lobules by radial lines,
which identify the path of the radiate
arteries.
 The renal medulla consists of a dark
outer zone and a paler inner zone
which is radially striated and extends
to the renal sinus.

14.  The kidney has a multilobular
structure during embryonic
development, then all the lobes
fuse finally to form a single
medullary mass surrounded by a
continuous cortical shell (Unilobar
kidney). The fusion joins the
papillae in a common renal crest,
which collecting the urine into the
renal pelvis.

15. Renal pelvis
 The proximal ureter begins with a
common expansion, the renal pelvis, into
which all the papillary ducts open. The
renal pelvis is located within the renal
sinus, but is fused with the renal tissue
around the papillae only.
 The renal pelvis in horse consists of a
central cavity and two large recesses
that are directed toward the poles of the
kidney. Most the papillary ducts open
into the recesses (Terminal recess)

17. The functional units of the kidney
 The functional units are the nephrons
or the tubules. The nephrons are
responsible for urine production, while
the subsequent collecting tubules
convey the urine to the renal pelvis.
They form a system of continuous
convoluted tubules within the kidney,
the number of it in horse up to 2.7
million nephrons, which varies in
number among the different domestic
animals.

18.  The renal tubules are supported by a
connective tissue, through which blood
vessels and nerves pass. Each
nephron is composed of several
segments:
 Glomerular capsule
 Proximal convoluted tubules
 Lobe of Henle (descending limb, U-
turn and ascending limb)
 Distal convoluted tubules

20. Blood supply
 Each kidney is supplied by a renal artery, a
branch of the abdominal aorta. The renal
artery divides into several interlobar
arteries at the hilus of the kidney. These
follow the divisions between the different
renal lobes to the corticomedullary
junction and where they branch into
arcuate arteries. The arcuate arteries curve
over the bases of the medullary pyramids
and give rise to the interlobular arteries,
which radiate in the cortex to supply the
lobules.

22. Innervation
 The kidneys receive sympathetic and
parasympathetic fibers from the solar
plexus, which reach the organ along
the renal arteries. Sympathetic fiber
from synapses in the celiac ganglion in
the cranial mesenteric ganglion and in
smaller ganglia of the renal plexus.
The dorsal branch, the vagus,
contributes the parasympathetic fiber.

23. Ureter
 The paired fibro muscular tubes carrying
urine from the kidneys to the urinary
bladder. Located retroperitoneal along
the dorsal abdominal wall, each ureter
runs caudally to the pelvis. They pass
ventral to the ductus deferens, loop
around the rectum to reach the urinary
bladder dorsal surface. The ureters pass
through the urinary bladder wall at an
acute angle, preventing backflow and
still allowing urine to empty into a full
bladder by peristaltic action.

24. Urinary bladder
 It is greatly distensible pouch receiving
and storing urine from the kidneys for
release out the urethra. The empty
bladder lies almost entirely within the
pelvic cavity, but with distention
extends into the abdominal cavity. The
bladder has a free apex, body and
neck.

25. Ligament of urinary bladder
There are three connecting peritoneal
folds reflected from the urinary bladder
onto the abdominal and pelvis wall.
The median ligament
The tow lateral ligament
The round ligament of the bladder

26. Urethra
In female animal the urethra
exclusively serves to convey
urine, while in the male animal
it carries urine, semen and
seminal secretions.

27.  The female urethra extends caudally
on the pelvic floor ventral to
reproductive tract. It passes obliquely
through the wall of the vagina then
open by the external urethral opening
ventral at the junction between vagina
and vestibule. The length and
diameter varies among animal, which
is short and wide in horse and opens
on a small elevation flank by two
grooves.

29. The male urethra extends from an
internal opening at the bladder neck to
an external opening at the end penis. It
divided into:
 Pelvic part (pre prostatic and prostatic
portion)
 Penile part

31. Thank you