Kidney tissue is surrounded on the outside by a tough membrane called the renal capsule. The kidneys are also surrounded by fatty tissue, which protects the kidneys from trauma.

There are ‘adrenal glands’ above each kidney. The right kidney is attached to the liver and part of the duodenum, while the left kidney is attached to the pancreas, vessels, stomach, and spleen. Each kidney has an artery and a vein.

A longitudinal section of the kidney shows two major regions. These regions are called the outer part (cortex) and the inner part (medulla). The outer part is darker in color and has round vascular structures called glomeruli. These vascular tangles are embedded in a structure called Bowman’s capsule. This structure continues with straight and curved tubules. This structure of glomerulus and tubules is called a nephron. Nephrons are the basic structural unit of the kidneys and are responsible for urination. There are about 1 million of them in each kidney. Many nephrons first pass urine through common opening channels to a structure called the renal papilla. The urine is then collected in the calyxes. All the calyces come together to form a large pool of urine called the pelvis renalis. The collected urine then travels through a tube called the ureter to the bladder.