|Posterior view of kidneys and their external vasculature, with adjacent posterior structures labelled.|
|Left: location of kidneys within the body. Right: gross anatomical structures within the kidney (midsagittal cut, left kidney).|
|System||Urinary system and endocrine system|
Kidneys are two organs in the abdomen of vertebrates that are shaped like beans. They make urine and are are part of the urinary system. When medical professionals discuss the kidneys, they typically refer to the word renal. For example, renal failure is when the kidneys are sick and do not work.
The kidney makes hormones. The two most important ones that it makes are erythropoetin and renin. Erythropoetin is made by the kidneys if there is less oxygen in the kidney. Erythropoetin tells the bone marrow to make more red blood cells. So this means there will be more oxygen carried in the blood.
Renin is made by the kidney if there is low blood pressure, low volume of blood, or too low salts in the blood. Renin makes the blood vessels smaller and tells the adrenal gland to make aldosterone (which tells the kidneys to save salts). It also makes a person feel thirsty. All of this makes the blood pressure go up.
The kidney's most important work is keeping homeostasis. Homeostasis means that the body keeps a stable environment inside itself. The body needs to have the consistent and proper amount of water, salt, and acid in the blood. The kidney keeps these things constant.
If there is too much water, the kidney puts more water in the urine. If there is not enough water, the kidney uses less water in the urine. This is why people make less urine when they are dehydrated.
There are many types of kidney diseases. A kidney disease makes the kidneys unable to work perfectly but they do work in part. People can have mild kidney failure and have no symptoms. As long as it does not become worse, people may not even know they have it. Severe kidney failure means very bad failure, the kidneys do not work very much at all. People with severe kidney failure always have symptoms. They may need special care from doctors.
If they have severe kidney failure, they cannot live unless they have a replacement for their kidneys. There are two ways to replace the kidneys: dialysis (when doctors use a machine and medicines to do the work of the kidneys), and transplantation.
A better way to do the kidneys' work is to give the person another kidney. This is called a kidney transplant. Kidney transplants are the most common type of organ transplant. It is the most common because we have two kidneys, but only need one kidney to live. People who are alive can donate a kidney to another person.
Images for kids
Kidney Facts for Kids. Kiddle Encyclopedia.