The Kidneys

Functions of the kidney

The two main functions of the kidney are:

– Removal of metabolic waste (excretion)

– Osmoregulation, which involves regulating water and salt concentration in the blood.

Structure of the kidney

There is one pair of kidneys located in the abdominal cavity in the region of the lower back. They are dark red organs shaped liked kidney beans. Each kidney is supplied with oxygen rich blood from the renal artery. Deoxygenated blood is returned to the circulatory system from the kidneys by the renal vein.  Blood entering the kidneys from the renal artery are rich in waste materials, and blood exiting the kidneys from the renal vein is deficient in these waste materials.

Internal structure of the kidney

A kidney has several layers, as shown in the diagram below. There is a thin outer fibrous layer called the renal capsule, which is the protective layer. Beneath this layer lies the cortex, a smooth textured area. Under the cortex lies the inner region called the medulla. Within the medulla are the triangular structures called pyramids, which appear striated in structure. These striations are due to the presence of tubules and blood vessels. These tubules drain into the renal pelvis situated on the concave side of each kidney. The renal pelvis then drains into the ureter. The functional unit of the kidney is the nephron.

A LONGITUDINAL SECTION THROUGH A KIDNEY