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What Do The Kidneys Do? A Simple Explanation.

Updated on July 19, 2014

The Kidneys

Humans have two kidneys. Without at least one functioning kidney, the body is unable to survive.

Kidneys are complex, bean-shaped organs located on either side of the spine just below the ribcage, and above the lower back. Each kidney is approximately 2.5" (6cm) wide, 4-6" (11-14cm) long and 1.5" (4cm) thick.

Their main function is to regulate and remove waste from the blood.

"Renal" means "of the kidney" and is found in the names of many of kidney's components.

How Kidneys Work

The outer part of the kidney is fibrous tissue called the renal capsule (9). Inside the capsule are three major structures. The outer part is called the renal cortex, and the deeper part is called the renal medulla. Below that is the renal pelvis. The renal cortex is formed around sections of the renal medulla, creating renal pyramids (1) with renal columns(17) made of renal cortex anchoring the structure.

Blood flows into the kidney from the renal artery (3). This artery divides and branches into smaller arteries called interlobar arteries (2) which go into the renal capsule, and then through the renal columns between the renal pyramids.

Between the renal cortex and the renal medulla are units called nephrons (13). A normal human kidney can contain up to one and half million nephrons. Nephrons are made up of a filtering device called a glomerulus, and tubules to collect filtered blood.

As the blood passes through the nephrons, it is filtered and regulated, and hormones and enzymes secreted by the kidneys are added. The nephrons reabsorb water, glucose, amino acids and salts, controlling the amount of blood, blood pressure, pH balance, and levels of essential chemical compounds.

Waste products are excreted as the fluid we all know as urine, which passes through renal tubules into a collecting duct, and deep into the renal medulla, eventually emptying into the renal pelvis (6), which becomes the ureter (7) leading to the bladder.

This essential function of balancing and regulating the blood is called "homeostasis".

Once the blood has been filtered, it flows into veins which join to flow into the renal vein (4) leaving the kidney.

Every hour the blood is circulated through the kidneys about twelve times. The kidneys generate about 380 pints (180 litres) of liquid called filtrate each day. Almost all of that is reabsorbed, and the average human only excretes approximately 4 pints (2 litres) of urine.

Kidney Structure and Function

Location of the Kidneys

Did You Know ... ?

  • Humans can survive perfectly well with only one kidney.
  • The left kidney is usually slightly larger than the right kidney.
  • The right kidney sits slightly lower than the left kidney.
  • Kidney stones are a very painful build up of solid minerals in the kidneys.
  • A kidney can be transplanted.
  • Dialysis is the method by which a machine helps or replaces the kidneys by cleaning the blood. It is used when there is a severe reduction or failure of the kidneys to carry out their function.

What To Know More?

Janice VanCleave's The Human Body for Every Kid: Easy Activities that Make Learning Science Fun
Janice VanCleave's The Human Body for Every Kid: Easy Activities that Make Learning Science Fun

Finding out how your body works is fun with this interactive book full of super cool experiments. Heaps of activities for kids of all ages.



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    • donabhatt profile image

      donabhatt 5 years ago from Hyderabad

      Very informative...

    • mwilliams66 profile image

      mwilliams66 5 years ago from Left Coast, USA

      Interesting, informative and well structured hub. My understanding of the kidneys has greatly increased.

    • fridayonmymind profile image

      fridayonmymind 5 years ago

      That's really interesting. I can see how that would increase the risks of infections. I hope it doesn't cause you too much trouble.

    • justateacher profile image

      LaDena Campbell 5 years ago from Somewhere Over The Rainbow - Near Oz...

      Great info on kidneys. I have had kidney issues since I was born. I have a horseshoe kidney - which means sometime before I was born my kidneys grew together in the shape of a horseshoe. Because of that it is harder for my kidney to get rid of the waste, which causes infections.

    • fridayonmymind profile image

      fridayonmymind 5 years ago

      Thank you!

    • dmop profile image

      dmop 5 years ago from Cambridge City, IN

      I had some idea of what the kidneys do, but have a better understanding after reading your article. Thanks for sharing, voted up and useful.