How much do you know about your kidneys?

They're not that big, but they do a mighty job. Each kidney is about 4-5 inches long. All the blood in your body passes through the kidneys many times each day.

Every day kidneys filter enough fluid to fill a large bathtub. The body takes what it needs, and the kidneys turn the extra water and waste into urine. That's usually about two quarts a day.

Your kidneys are kind of your body's MVPs. Their main job is filtering the waste out of your blood, resulting in urine. But they also keep your blood pressure normal and make a form of vitamin D that helps keep your bones and tissues healthy. In addition, they help with the production of red blood cells and keep levels of salt and potassium under control.

There are many causes of kidney disease, but diabetes and hypertension often top the list. If you have diabetes, high blood sugar can hurt your kidneys. High blood pressure can harm the small blood vessels in your kidneys. If you control your blood sugar levels and high blood pressure, your chances of kidney problems are decreased.

Technically you only need one kidney. The other one is kind of like having a spare. That's why thousands of people are able to donate kidneys ever year without any health problems. Kidneys are the most commonly donated organ in the world. If one kidney is damaged, missing or removed, the other one will grow larger so it can do the job of both.

You can find your kidneys on each side of your spine in a secluded part of your abdomen. Although this can protect them from getting hurt, it also can make it difficult if you need kidney surgery. That's why there are newer techniques such as robotic and laparoscopic surgery, as well as sound wave technology, that make reaching these illusive organs much easier.

Each one of your kidneys has somewhere around 1 million tiny filters. These filters, called nephrons, clean your blood by removing waste your body doesn't need and returning beneficial chemicals that your body can still use.

If your kidneys shut down and stop filtering your blood, toxins start to build up in your body. You need to either get a new kidney or go on dialysis. Dialysis cleans your blood, getting rid of waste and extra water and salt. It also helps control your blood pressure, acting like a stand-in kidney. There are about 450,000 people in the U.S. on dialysis with more than 100,000 waiting for a kidney transplant.

Kidney stones are small, hard rock-like deposits that form when certain substances in your body clump together. They can be as small as a grain of sand or as big as a pearl. They rarely get as big as a golf ball. A kidney stone can stay in your kidney or move down your urinary tract where you'll "pass" it by peeing it out. You're more likely to get kidney stones if you are very overweight, frequently dehydrated, or if other people in your family have had them.

People with kidney disease don't usually have symptoms during the early stages. But gradually, things change and you'll probably notice a change in bathroom habits. You could also have dry, itchy skin, muscle cramps, appetite loss, fatigue and swollen hands or feet.

Heavy or long-term use of some painkillers — such as aspirin, ibuprofen and naproxen — can hurt your kidneys. Never take more than the recommended dosage and drink lots of water, especially when you're taking medication.

The kidneys are mentioned more than 30 times in the Bible. They are written about as the location of emotion, wisdom, prudence, temperament and vigor. Several times, they are cited as the organs God uses to judge a person. The kidneys, it was said, were used by God, along with the heart, as mirrors of the human psyche.

They're tiny, but mighty. These lightweight organs have a big responsibility. They receive 20 percent of the blood pumped by your heart. That blood lets them do all their various important jobs, including regulating blood pressure, stimulating the creation of red blood cells, and regulating the composition of your blood.

When your body doesn't get enough fluid, you can have all kinds of symptoms. The most obvious one is that you'll have to pee less often and when you do, it will likely be a deep yellow color. Drink up! Chronic dehydration can cause kidney stones and kidney damage.

Kidney disease doesn't often make the headlines, and maybe that's why 1 in 3 American adults is at risk for it, reports the National Kidney Foundation. Kidney disease is the ninth leading cause of death in the U.S. In 2013 alone, more than 47,000 Americans died from the disease.