Everybody knows that some organs in the human body are necessary for survival: you need your brain, your heart, your lungs, your kidneys... Show
KIDNEYS? Absolutely. Even though you won't find a Valentine's Day card with a kidney on the cover, the kidneys are every bit as important as the heart. You need at least one kidney to live! What Are Kidneys?Kidneys normally come in pairs. If you've ever seen a kidney bean, then you have a pretty good idea what the kidneys look like. Each kidney is about 5 inches (about 13 centimeters) long and about 3 inches (about 8 centimeters) wide — about the size of a computer mouse. To locate your kidneys, put your hands on your hips, then slide your hands up until you can feel your ribs. Now if you put your thumbs on your back, you will know where your kidneys are. You can't feel them, but they are there. Read on to find out more about the cool kidneys. What Do Kidneys Do?One of the main jobs of the kidneys is to filter the waste out of the blood. How does the waste get in your blood? Well, your blood delivers nutrients to your body. Chemical reactions in the cells of your body break down the nutrients. Some of the waste is the result of these chemical reactions. Some is just stuff your body doesn't need because it already has enough. The waste has to go somewhere; this is where the kidneys come in.
First, blood is carried into the kidneys by the renal artery (anything in the body related to the kidneys is called "renal"). The average person has 1 to 1½ gallons of blood circulating through his or her body. The kidneys filter that blood about 40 times a day! More than 1 million tiny filters inside the kidneys remove the waste. These filters, called nephrons (say: NEH-fronz), are so small you can see them only with a high-powered microscope. Page 1The Path of PeeThe waste that is collected combines with water (which is also filtered out of the kidneys) to make urine (pee). As each kidney makes urine, the urine slides down a long tube called the ureter (say: yu-REE-ter) and collects in the bladder, a storage sac that holds the pee. When the bladder is about halfway full, your body tells you to go to the bathroom. When you pee, the urine goes from the bladder down another tube called the urethra (say: yu-REE-thruh) and out of your body. The kidneys, the bladder, and their tubes are called the urinary system. Here's a list of all of the parts of the urinary system:
Keeping a BalanceThe kidneys also balance the volume of fluids and minerals in the body. This balance in the body is called homeostasis (say: hoh-mee-oh-STAY-sus). If you put all of the water that you take in on one side of a scale and all of the water your body gets rid of on the other side of a scale, the sides of the scale would be balanced. Your body gets water when you drink it or other liquids. You also get water from some foods, like fruits and vegetables. Water leaves your body in several ways. It comes out of your skin when you sweat, out of your mouth when you breathe, and out of your urethra in urine when you go to the bathroom. There is also water in your bowel movements (poop). When you feel thirsty, your brain is telling you to get more fluids to keep your body as balanced as possible. If you don't have enough fluids in your body, the brain communicates with the kidneys by sending out a hormone that tells the kidneys to hold on to some fluids. When you drink more, this hormone level goes down, and the kidneys will let go of more fluids. You might notice that sometimes your pee is darker in color than other times. Remember, pee is made up of water plus the waste that is filtered out of the blood. If you don't take in a lot of fluids or if you're exercising and sweating a lot, your pee has less water in it and it looks darker. If you're drinking lots of fluids, the extra fluid comes out in your pee, and it will be lighter. What Else Do Kidneys Do?Kidneys are always busy. Besides filtering the blood and balancing fluids every second during the day, the kidneys constantly react to hormones that the brain sends them. Kidneys even make some of their own hormones. For example, the kidneys produce a hormone that tells the body to make red blood cells. Now you know what the kidneys do and how important they are. Maybe next Valentine's Day, instead of the same old heart, you can give your parents a special card featuring the kidneys! The kidneys are a pair of bean-shaped organs present in all vertebrates. They remove waste products from the body, maintain balanced electrolyte levels, and regulate blood pressure. The kidneys are some of the most important organs in the body. The ancient Egyptians left only the brain and kidneys in position before embalming a body, inferring that they held a higher value than other organs. In this article, we look at the structure and function of the kidneys, the diseases that affect them, and how to keep them healthy. The positioning of the kidneys is just below the rib cage, with one on each side of the spine. The right kidney is generally slightly lower than the left kidney to make space for the liver. Each kidney is approximately 3 centimeters (cm) thick, 6 cm wide, and 12 cm long. In males, the average weight of the kidneys is roughly 129 grams (g) for the right one and 137 g for the left. In females, the average weight of these organs is 108 g for the right kidney and 116 g for the left kidney. Click on the BodyMap above to interact with a 3D model of the kidneys. The kidneys are two bean-shaped organs that are roughly the size of a fist. A tough, fibrous renal capsule surrounds each kidney and provides support for the soft tissue inside. Beyond that, two layers of fat serve as further protection. The adrenal glands lie on top of the kidneys. Inside the kidneys are a number of pyramid-shaped lobes. Each consists of an outer renal cortex and an inner renal medulla. Nephrons flow between these sections. Each nephron includes a filter, called the glomerulus, and a tubule. The glomerulus filters blood, which enters the kidneys through the renal arteries and leaves through the renal veins. The kidneys are relatively small organs, but they receive 20–25% of the heart’s output. The tubule returns necessary substances to the blood and removes waste that then becomes urine. The kidneys excrete urine through the ureter, a tube that leads to the bladder. What does a kidney look like?The main role of the kidneys is maintaining homeostasis. They manage fluid levels, electrolyte balance, and other factors that keep the internal environment of the body consistent and comfortable. These organs carry out a wide range of bodily functions. Waste excretionThe kidneys remove various waste products and get rid of them in the urine. Some major compounds that the kidneys remove are:
Reabsorption of nutrientsThe kidneys reabsorb nutrients from the blood using tubules and transport them to where they will best support health. They also reabsorb other products to help maintain homeostasis. Reabsorbed products include:
Maintaining pHIn humans, the range of acceptable pH levels is 7.35–7.45. At levels below or above this range, the body enters a state of acidemia or alkalemia, respectively. In these states, proteins and enzymes break down and can no longer function. In extreme cases, this can be fatal. The kidneys and lungs help keep the body’s pH stable. The lungs achieve this by moderating the concentration of carbon dioxide in the blood. The kidneys manage the pH by reabsorbing and producing bicarbonate from urine, which helps neutralize acids. The kidneys can retain bicarbonate if the pH is tolerable and release it if acid levels rise. They can produce new bicarbonate by excreting acid. Osmolality regulationOsmolality is a measure of the body’s electrolyte-water balance, which is the ratio between fluids and minerals in the body. Dehydration is a primary cause of electrolyte imbalance. If osmolality rises in the blood plasma, the hypothalamus in the brain responds by passing a message to the pituitary gland. This gland releases antidiuretic hormone (ADH). In response to ADH, the kidney makes several changes, including:
Regulating blood pressureThe kidneys regulate blood pressure when necessary, but they are responsible for slower adjustments. They adjust long-term pressure in the arteries by causing changes in the fluid outside of cells. The medical term for this fluid is extracellular fluid. These fluid changes occur after the release of a vasoconstrictor called angiotensin II. Vasoconstrictors are hormones that cause blood vessels to narrow. These hormones play a role in increasing the kidneys’ absorption of sodium chloride, or salt. This absorption effectively increases the size of the extracellular fluid compartment and raises blood pressure. Anything that alters blood pressure, including excessive alcohol consumption, smoking, and obesity, can damage the kidneys over time. Secretion of active compoundsThe kidneys release several important compounds, including:
A range of diseases can affect the kidneys. Environmental or medical factors may lead to kidney disease, and they can cause functional and structural problems from birth in some people. Diabetic nephropathyIn people with diabetic nephropathy, damage occurs to the capillaries of the kidney as a result of long-term diabetes. The symptoms may not become apparent until years after the damage starts to develop. They can include:
Kidney stonesStones can form as a solid buildup of minerals in the kidneys. They can cause intense pain and might affect kidney function if they block the ureter. Kidney infectionsKidney infections tend to result from bacteria in the bladder that transfer to the kidneys. The symptoms can include lower back pain, painful urination, and, sometimes, fever. Changes in the urine may include the presence of blood, cloudiness, and an unusual odor. Kidney infections are more common in females than in males and more likely to affect those who are pregnant. The infection often responds well to antibiotics. Renal failureIn people with renal failure, the kidneys become unable to filter out waste products from the blood effectively. If an injury or another factor, such as the overuse of medication, causes kidney failure, the condition may be reversible with treatment. If the cause is a disease, however, kidney failure often does not have a full cure. Kidney hydronephrosisHydronephrosis means “water on the kidney.” It usually occurs when an obstruction prevents urine from leaving the kidney, causing intense pain. In time, untreated hydronephrosis can put pressure on a person’s kidneys and may result in kidney damage. Interstitial nephritisA reaction to medications or infection can cause inflammation of the nephrons. The treatment usually involves addressing the cause of inflammation or changing a course of medication. Kidney tumorThese tumors can be benign or malignant. Benign cancers do not spread or attack tissue, but malignant cancers can be aggressive. The most common malignant kidney cancer is renal cell carcinoma. Nephrotic syndromeWhen damage to the kidney affects its function, this causes protein levels in the urine to increase. This effect leads to a protein shortage throughout the body, which draws water into the tissues. The symptoms of nephrotic syndrome can include:
Lower back pain and changes in urination, especially on one side, may be signs of kidney problems. Some common causes of kidney damage may include:
In the case of severe kidney damage, dialysis might be an option. Doctors only use this treatment for end stage kidney failure involving the loss of 85–90% of kidney function. Kidney dialysis aims to complete some of the functions of a healthy kidney. These include:
The two most common types of kidney dialysis are: HemodialysisAn artificial kidney, or hemodialyzer, removes waste, additional fluids, and chemicals. The treating doctor makes an entry point in the body by connecting an artery and a vein under the skin to create a larger blood vessel. Blood travels into the hemodialyzer, receives treatment, and then returns to the body. This process usually takes place three or four times a week. Peritoneal dialysisThe doctor inserts a sterile cleansing solution into the abdominal cavity around the intestine. This is the peritoneum, and a protective membrane surrounds it. In continuous peritoneal dialysis, the fluid drains through a catheter. The individual discards these fluids four or five times a day. In automated peritoneal dialysis, the fluid also drains through a catheter, and the exchanges usually occur throughout the night while the person sleeps. The following are suggestions for keeping the kidneys healthy and helping avoid kidney disease:
Keeping the kidneys in full working order is essential for overall health. Last medically reviewed on November 28, 2021 Medical News Today has strict sourcing guidelines and draws only from peer-reviewed studies, academic research institutions, and medical journals and associations. We avoid using tertiary references. We link primary sources — including studies, scientific references, and statistics — within each article and also list them in the resources section at the bottom of our articles. You can learn more about how we ensure our content is accurate and current by reading our editorial policy.
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