Kidney Anatomy: External and Internal Structures

Kidney anatomy includes all the internal and external tissue-components that collectively form the structure of the kidney.  The structure of the kidney is uniquely designed to enable it to effectively discharge its critical functions in the body.

External Kidney Anatomy

Kidneys have a very distinct shape and color. They are bean-shaped and dark-red in color. In fact, they look very similar to red kidney beans.

One side bulges outward (convex) and the other side is indented (concave).  The indented or concave section is known as the hilum. This is where the renal artery, the renal vein and the ureter enter/ exit the kidney.

Each Kidney is enclosed in a semi-transparent membrane called the renal capsule. It is the container or sac in which the other components of the internal kidney anatomy are stored.

The renal capsule is not only a storage container for internal components of the kidneys but it also protects against infections and trauma.


Internal Kidney Anatomy

If a human kidney, is sliced vertically (from top to bottom), the intricate structure of the internal anatomy will be revealed. These internal components are responsible for performing the many essential functions of the kidney.

Some of these components can be seen with the naked eye and are known as the gross anatomy.  Others are very tiny and can only be observed with a microscope.  These are referred to as the microscopic anatomy.

Nephrons are the most basic structures of kidney's anatomy.  Inside each kidney there are about one million of these microscopic structures. They are responsible for filtering the blood... removing waste products.

The internal structure of the kidney is divided into two main areas... a light outer area called the renal cortex, and a darker inner area called the renal medulla. (Please refer to diagram on right).


Within the medulla there are eight (8) or more cone-shaped sections known as renal pyramids. The renal papilla is located at the smaller end of the cone-shaped renal pyramids. The areas between the pyramids are called renal columns.

Each renal papilla is attached to a cup, or a small tube, called the minor calyx (CAY-lix), which collects urine for removal from the kidney, and eventually from the body. Two or three of these minor calices (plural of minor calyx) merge into what is called a major calyx.


Kidney Location and Kidney Size

Typically, the kidneys are located on the flanks at the back of the abdominal cavity. Although this is the normal kidney location, this is not always the case.  Sometimes, one or both kidneys can be located much lower in the abdomen.

Most humans are born with two kidneys, although one kidney is capable of performing the normal functions of both kidneys.

Some people are born with one kidney. Others may lose a kidney through injury, disease or surgery (for example when someone donates a kidney).   Amazingly, most people with a single healthy kidney are still able to lead normal lives, without any adverse effects to their health.

Kidney size varies and is predominantly determined by age and body size.   The normal size of an adult human kidney is about the size of a fist. Some diseases may, however, cause the kidneys to shrink (atrophy) or expand (distension) beyond their normal size.

Kidney anatomy is a fascinating topic, especially to an inquisitive mind.  It provides an understanding of how the kidneys work and the various components that make it such an efficient, effective and resilient organ.