Pets care

Kidneys

Anatomy of the Kidney

The kidneys of mammals are round or bean-shaped organs. They are located outside of the peritoneum – the membrane that encloses the organs of the abdominal cavity. Because of this position, they are referred to as 'retroperitoneal.' They are surrounded by fat tissue known as 'perirenal fat.' A fibrous capsule covers the kidney. The indentation of the bean shape is called the 'hilum.' The hilum is the site where the renal artery enters the kidney and both the renal vein and ureter exit.

The kidney can be divided into two distinct regions – the outer cortex and the inner medulla. The cortex is where blood is actually filtered through small structures called 'glomeruli'. The medulla is where the urine is concentrated through a complex system of tubules. They accomplish this by absorbing the water and electrolytes while preventing waste products from being reabsorbed. One glomerulus and its corresponding set of tubules are called a 'nephron' – the microscopic functional unit of the kidney. The anatomy and function of the nephron will be discussed in detail below.

The tubules of multiple nephrons are grouped into larger visible portions of the kidney called 'pyramids’. The renal columns are spaces between the renal pyramids that provide a route for blood vessels traveling to the cortex. The tips of the pyramids are called 'papillae,' and they drain urine from nephron tubules into larger vessels called 'minor calyxes.' The minor calyxes converge into still larger vessels called the 'major calyxes'. These lead to the enlarged opening of the ureter. This collecting chamber is called the 'renal pelvis.'