Anatomy of the Kidney


The kidneys are two bean-shaped organs that are approximately the size of a fist. They are located just below the rib cage and in the back. There are two kidneys on the right and left, with the spine in the center. In the anatomy of the kidney, there is also an adrenal gland located on top of each kidney. Although humans are normally born with two kidneys, a single kidney is also enough to maintain vital functions.

General Information

Each kidney weighs approximately 200 grams. At the same time, each kidney is approximately 10 to 12 cm long and 5 to 7 cm wide. An adult kidney has a bean shape and connects with the renal artery, renal vein and ureter from the center. Blood enters the kidney through the renal artery and exits through the renal vein. The urine produced in the kidney is transported from the kidney to the bladder via the ureter.

For more information about the kidney, you can read:
Kidney Cancer Basics: What is the Kidney?


A healthy kidney filters about half a cup of blood every minute. Thus, it removes wastes such as urea or salt and excess water in the body and provides the formation of urine. The urine is transported to the bladder via two thin tubes called ureters on both sides. All of these organs, kidney, ureter and bladder form your urinary system.

Anatomy of the Kidney

The kidney is mainly composed of nephron, renal cortex, renal medulla, renal pelvis and ureters. These parts work together and synchronously to ensure the functions which are very important for the body and continuity of life.

1. Nephrons

Nephrons are the main and most important functional unit of the kidney. Each healthy kidney contains approximately 1 million nephrons. With their unique structure, they take blood, metabolize nutrients and filter the waste from the blood.
The blood comes to the nephron is filtered after passing through the renal corpuscle and renal tubules parts respectively.

a. Renal corpuscule

Once blood enters the nephron, it goes through the renal corpuscule. Renal corpuscule is also called as the Malpighian body.
It has a cluster of capillaries which named as the glomerulus. Proteins are absorbed from the blood passing through this cluster.
After the proteins are absorbed, the remaining fluid, which called capsular urine, passes into the Bowman Capsule and then proceeds into the renal tubules.

b. Renal tubules

Renal tubules are a series of tubes starting after the Bowman Capsule. They end with the collecting ducts.
The fluid that reaches the collecting ducts is dilated and becomes rich from urea which is the end product of protein metabolism.

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They have several parts such as Proximal Convoluted Tubule, loop of Henle and Proximal Convoluted Tubule. Different functions are performed in each of these parts.

  • Proximal Convoluted Tubule: The main function performed in this section is the reabsorption of water. Besides water, important components such as sodium and glucose are also absorbed back into the blood.
  • Loop of Henle: In this section, mainly, minerals such as potassium, chloride and sodium are reabsorbed into the blood.
  • Distal Convoluted Tubule: In this section, further reabsorption of sodium back to blood is achieved, and potassium and acid excretion to the urine are also provided.

Renal Cortex

The outer part of the kidney is called as the renal cortex. Glomerulus and convoluted tubules are located in the renal cortex.
The renal cortex is surrounded by a renal capsule on the outside. Renal capsule composed of a layer of fatty tissue and it is the most outer part of the anatomy of the kidney.
The renal capsule and the renal cortex together provide a solid roof to the structures located inside the kidney.

Renal Medulla

The renal medulla is the soft tissue on the inside of the kidney. The renal cortex has glomerulus and convoluted tubules in its structure, while the renal medulla contains loop of Henle and renal pyramids.

a. Renal pyramids

Renal pyramids contain strings of nephrons and tubules. The tubules contained here in allow fluids to be transported to the kidney. These liquids are then transported by tubules from the nephrons to the inner structures. These inner structures collect and carry away the urine out of the kidney.

b. Collecting ducts

At the end of each nephron structure is a collecting duct. These ducts are located in the renal medulla and the filtered fluid leaves the nephron from this part. Every fluid that entered the collecting duct reaches the last stop, the renal pelvis.

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Renal Pelvis

Renal pelvis is the funnel-shaped part of the kidney which located at inner mostly. Its function is to create a pathway to the fluid, which is formed in the nephrons, in order to allow the passage to the bladder.

a. Renal calyces

The first structure of the renal pelvis is calyces. Calyces are small cup shaped structures. Here, the urine accumulated before proceeding to the bladder. At the same time, this is the part where waste and extra liquid are converted to the final urine.

b. Renal hilum

The hilum is a small opening in the center of the kidney. In the hilum, the renal artery enters the kidney, while the renal vein and ureters exit the kidney. Renal arteries bring oxygenated blood which needed to filtered to the kidney, while the renal vein carries the filtered blood out of the kidney. Ureters carry urine to the bladder.

Ureters

The ureters are the last part of the anatomy of the kidney.
They are tubular structures with muscles on the walls that push urine into the bladder.
Two ureters on each side enter the bladder and transfer the urine here.

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