Written by: Liz Paton, MSc

Kidney Anatomy Overview

The kidneys play a very important role in our health, undertaking tasks from regulating your fluid levels and blood pressure to balancing the quantity of minerals in your blood. The kidneys return vitamins, amino acids, glucose and hormones back into the bloodstream. The kidneys are also able to alter their filtering process to excrete more concentrated urine if one has not drunk enough liquid. 

Kidney Anatomy  

The kidneys are reddish-brown, bean-shaped organs that are about the size of a clenched fist. They are located in your abdomen, protected by the last two pairs of ribs as well as perirenal fat and muscle. The left kidney sits slightly higher than the right kidney. 

Structure of the Kidneys 

Each kidney is made up of filtering units called nephrons. A nephron is the functional unit of the kidney, responsible for filtration, excretion and selective resorption of substances such as ions, amino acids and glucose. The nephrons are located in the renal cortex and the renal medulla. The renal cortex makes up the space between the fibrous capsule of the kidney (outer most kidney, also known as the renal capsule) and the renal medulla. It contains the glomerulus and tubules of the nephrons. The renal medulla is a pyramid-shaped structure found in the inner-most region of the kidney, containing the collecting ducts of the nephrons. The renal papilla is where the renal pyramid in the medulla empties urine into the minor calyx of the kidney. The medulla is surrounded by the renal cortex. The renal pelvis is the point where the calyces join together and funnel urine into the ureter. Blood enters the kidney through the renal artery and exits through the renal vein. A duct called the ureter is attached to the kidney through which urine travels down into the bladder. At the inner surface of the kidney is a hilum (concave shape), this is where arteries veins and nerves run through. 

Blood Supply of the Kidneys 

The main blood supply to the kidneys comes from the renal arteries which are a branch of the abdominal artery. When the renal artery reaches the hilum, it branches off into the posterior and anterior branch. The posterior branch supplies the kidneys and the anterior branch gives rise to the segmental arteries. Arterioles (small branches of arteries) supply blood to the glomerulus, a network of small vessels, this allows the kidney to filter blood. The arcuate veins transport deoxygenated blood to the renal veins and back the heart. 

Nerves of the Kidneys 

Nerves branches from the renal plexus enter the kidney at the hilum alongside the renal artery. The kidneys receive innervation from both the sympathetic and parasympathetic nervous systems. 

Function of the Kidneys 

The kidney has several functions, one of their main jobs is to filter waste products from the blood, these waste products are then excreted from our body as urine. Filtering out waste is important to maintain a healthy and functioning body. 

Another function of the kidneys is to maintain balance of blood pressure by releasing hormones and balance of maintaining water and minerals. This balance is known as homeostasis and is important for cells to function and for normal bodily functions to take place. Some other functions of the kidneys include the production of vitamin D, the production of red blood cells in our bone marrow and removing acid from our systems.