Kidney

The kidney is a paired, bean-shaped organ located in the dorsal part of the abdominal cavity, the right kidney and the left kidney on each side of the vertebral column. Its main functions include:

• Excretion of metabolic waste products, primarily through urine formation.

• Regulation of fluid and electrolyte balance, acid-base homeostasis, and blood pressure.

• Endocrine roles, such as producing erythropoietin (stimulating red blood cell production) and renin (involved in blood pressure control).

1. General Structure of the kidneys

• The kidneys are paired, bean-shaped organs located retroperitoneally in the lumbar region.

• They have a smooth outer cortex and an inner medulla composed of renal pyramids.

• Each kidney is surrounded by a fibrous capsule, and in some species, there is a significant amount of surrounding fat for protection.

• The functional unit of the kidney is the nephron, which filters blood and produces urine.

3. Internal Structure

• Cortex: Granular and contains glomeruli, proximal and distal convoluted tubules.

• Medulla: Radially striated due to collecting ducts and loops of Henle.

• Renal pelvis (except in ox): Funnel-shaped structure where urine collects before entering the ureter.

• Renal sinus: Contains the pelvis, vessels, and fat.

4. Borders and surfaces

• Lateral border

• Medial border with the renal hilum

• Ventral surface

• Dorsal surface

• Cranial extremity

• Caudal extremity

5. Location and Orientation

• The right kidney is generally more cranial than the left in most species (except pigs).

• In ruminants and carnivores, the kidneys lie asymmetrically due to the rumen or stomach.

• The left kidney in ruminants is often displaced caudally and medially.

6. Blood Supply and Innervation

• Each kidney is supplied by a renal artery branching directly from the abdominal aorta.

• The renal vein drains into the caudal vena cava.

• The kidneys are innervated by sympathetic fibers from the celiac plexus and the renal plexus.