November 20, 2023

What is the Functional Unit of the Kidney?

The kidneys filter blood, extract waste and control water and salt levels to maintain body fluid balance. Each kidney contains over a million microscopic structures called nephrons that carry out these essential functions.

Each nephron consists of a renal corpuscle and a renal tubule. The renal corpuscle consists of a tuft of capillaries and a cup-like structure called Bowman’s capsule where the glomerulus sits. The Bowman’s capsule opens into a coiled region of tube called the proximal convoluted tubule.

From the proximal convoluted tubule, the filtrate passes through another coiled region of tubule called the loop of Henle. In this step, the filtrate exchanges solutes and water with the vascular network of peritubular capillaries in a process known as tubular reabsorption. The reabsorbed solutes are then secreted into urine in the final step of the nephron, the distal convoluted tubule.

The urine formed in the nephrons drains into cuplike structures called ducts. There are 8-18 minor calyces and 2-3 major calyces in each kidney. The major calyces are lined with nephrons and receive a mixture of urine from all the minor calyces. Then, the urine is funneled into the collecting duct system, a system of tubes that drains urine into a large container called the renal pelvis. From here, the urine travels down the ureters to the bladder.

Like a network of motorways linking the UK’s key cities, each of our vital organs work closely together. Problems with one organ often affect other areas of the body, and this is especially true for our kidneys. For example, if a person’s kidneys are not functioning properly, the heart can get overworked and begin to malfunction. This is why doctors often perform kidney function tests, such as blood tests for creatinine and BUN to look at the level of waste and protein in the urine.


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