2. Urinary System
• It removes wastes from the body.
• It also maintains homeostasis or a constant internal
environment within the body.
Components of Urinary System
• The urinary system consists of two kidneys, two ureters, the
urinary bladder and the urethra.
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Urinary System
3. Kidney
• A pair of excretory organs
• Dark brown in color
• Situated with the dorsal wall of the abdominal cavity on each
side of the aorta and caudal vena cava, just ventral to the first
few lumber vertebrae.
• Function
• They remove the waste products of metabolism and excess of
water and salts from the blood and maintains its pH.
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Urinary System
4. Conti…
• Retroperitoneal Organ
• The kidneys are described as retroperitoneal because they
are partly surrounded by fat and are covered only on their
ventral surface by peritoneum.
• Borders
1. Lateral border (convex)
2. Medial border (straight)
• Surfaces
1. Dorsal
2. Ventral
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Urinary System
5. Right Kidney
• Location
• It lies opposite the first three lumbar vertebrae. It is farther
cranial than the left kidney by the length of half a kidney.
• Relation
• It is more extensively related to the liver than to any other
organ. Its cranial third is covered by caudate lobe of the liver.
• The remaining ventral surface is related to duodenum, the
right lobe of the pancreas, the cecum and the colon.
• The caudal vena cava is on the medial border of the right
kidney.
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Urinary System
7. Left Kidney
• Location
• The left kidney lies opposite the second, third and fourth
lumbar vertebrae.
• Relation
• It is related ventrally to the colon and the small intestine.
• The spleen is related to the cranial extremity of the kidney.
• The medial border is close to the aorta.
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Urinary System
8. Gross Features
• Cortex: it is the peripheral part of the renal parenchyma. It
contains the renal corpuscles and convoluted portion of the
tubules.
• Medulla: It is centrally located dense parenchyma of the
kidney. It gives striated appearance due to presence of
numerous collecting ducts in this region.
• Cortico-medullary Junction: it is formed by the joining part
of the cortex and medulla.
• Renal capsule: it is the outermost strong fibrous covering of
the kidney.
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Urinary System
9. Conti…
• Hilus: it is an indention present at the middle of the medial
border of the kidney, where the renal vessels and nerves and
the ureter communicate with the organ.
• Renal Pelvis: it is the expanded portion of the ureter within
the kidney.
• Renal Sinus: it is the fat-filled space that contains the vessels
and surrounds renal pelvis.
• Renal Pyramid: it is formed by the medulla portion of the
kidney; It is also triangular in outline.
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Urinary System
11. Conti…
• Renal Crest: The longitudinal ridge projecting into the renal
pelvis is the renal crest, through which collecting tubules of
the kidney excrete urine into the renal pelvis.
• Arcuate branches: The vessels that are apparent at the
cortico-medullary junction are the arcuate branches of the
renal vessels.
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Urinary System
12. Blood Supply
• Because of its important role in adjusting the composition of
extracellular fluid (including plasma), the blood supply to the
kidney is much more extensive than the size of the organ would
suggest. The two renal arteries may receive as much as one
fourth of the total cardiac output.
• Each renal artery enters the hilus of the kidney and divides into
a number of relatively large branches, the interlobar arteries.
These pass peripherally between pyramids almost to cortex,
where they bend abruptly and become arcuate arteries, which
derived their name from the arched manner by which they
pass along the junction between cortex and medulla.
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Urinary System
13. Conti…
• The arcuate veins drain blood from both the cortex and
medulla, pass through the medulla as interlobar veins, and
enter the renal veins, which emerge from the renal hilus to
empty into the caudal vena cava.
• Nerve supply
• Sympathetic nerves are the primary innervation of the
kidneys.
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Urinary System
14. Ureters
• A pair of narrow, thick walled muscular tubes which convey urine
from the kidneys to the urinary bladder.
• The ureter begins at the renal pelvis and terminates at the
urinary bladder.
• The smooth muscle of the ureter undergoes peristaltic waves of
contraction that encourage the flow of urine to the urinary
bladder.
• Divisions
• (i) Abdominal part of ureter
• (ii) Pelvic part of ureter
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Urinary System
15. Urinary Bladder
• It is a long, narrow pisiform mass which acts as a temporary
store house of urine which gets emptied through the urethra.
• The detrusor muscle of urinary bladder is arranged in whorls
and spirals and is adapted for mass contraction rather than
peristalsis.
• Location
• When empty, it lies on the floor of the pelvic inlet.
• When distended, it lies on the floor of the abdomen and
conforms in shape to the caudal part of the abdominal cavity
because it displaces all freely movable viscera. It frequently
reaches a transverse plane through the umbilicus.
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Urinary System
16. Conti…
• Parts
(i) Vertex: It is the anterior blind part.
(ii) Body: It is the middle rounded part of the bladder.
(iii) Neck: It is the posterior narrower extremity that joins the
urethra.
• Ligaments
• It is fixed in position by the two types of ligaments.
(i) Lateral ligament; two in numbers
(ii) Medial ligaments
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Urinary System
17. Urethra
• The urethra is a tube extending from the urinary bladder to the
outside of the body.
• Male urethra
• The male urethra subserving the functions of urination and
ejaculation i.e. expulsion of semen.
• Female urethra
• The female urethra is for urination only.
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Urinary System
