Kidney Anatomy

Kidney anatomy encompasses all the tissue-components that collectively form the structure of the kidney.

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.

The kidneys are the main organs of the urinary system and are primarily responsible for removing toxins and other metabolic wastes from the blood.

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.

External Kidney Anatomy

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 anatomy of the kidneys 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 is 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.

Kidney Anatomy Diagram

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. 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.

The major calices then converge into a funnel-like cavity called the renal pelvis. The renal pelvis, which is attached to the indented side of the kidney anatomy (hilum), extends into the ureter. The ureter is a long narrow duct (tube) that conveys urine from the kidneys to the urinary bladder.

Kidney Anatomy and Excretion


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

The renal artery delivers blood to the kidneys each day. Over 180 liters (50 gallons) of blood pass through the kidneys every day. When this blood enters the kidneys it is filtered and returned to the heart via the renal vein.

The kidneys are full of blood vessels. Blood vessels are integral to efficient kidney function. Every function of the kidney involves blood. It, therefore, requires a lot of blood vessels to facilitate these functions. Together, the two kidneys contain approximately 160 km of blood vessels.

The process of separating wastes from the body's fluids and eliminating them is known as excretion. The body has four organ systems that are responsible for excretion:

  • The respiratory system - responsible for excretion of carbon dioxide and small amounts of water and other gases;

  • The integumentary system - excretes water, lactic acid, inorganic salts and urea in the sweat;

  • The digestive system - excretes water, salts, bile pigments, cholesterol, and other metabolic wastes;

  • The urinary system.

The urinary system is one of the main organ systems responsible for excretion. It excretes a broad variety of metabolic wastes, toxins, drugs, hormones, salts, hydrogen irons and water. The kidneys are the main organs of the urinary system.

Kidney Anatomy At Work

Urinary Tract

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.

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.

The location, size and other unique elements of the kidney anatomy facilitates the efficient and effective performance of its crucial functions, on a continuous basis.

Some of these functions include the removal of toxic waste products from the body, regulating blood pressure and the production of certain hormones.

The kidneys, therefore, play an essential role in achieving and maintaining optimum health.