Kidney

You have two kidneys in your body.

They are shaped like little beans. They sit on both sides of your spine.

These organs work hard to clean your blood. They act like a filter. They take out bad things from your blood. This helps keep you healthy.

Your kidneys also help make pee. They move the pee through a small tube. This tube goes to your bladder.

Inside each kidney, there are tiny parts. There are about one million of these parts. They work together to clean everything.

Your kidneys help keep your body in balance. They make sure you have the right amount of water. It is amazing how they work!

You have two bean-shaped organs in your body.

These are your kidneys. They sit on both sides of your spine. Each kidney has about one million tiny parts. We call these parts nephrons.

Nephrons work to clean your blood. First, blood enters a tiny part called a glomerulus. This part acts like a sieve. It lets small things through but keeps big things in the blood. This first step is called filtration. Next, the kidney uses reabsorption. This means it takes good things back into the blood. It keeps water, sugar, and salt. Then, the kidney uses secretion. This is when it lets out extra waste.

All these steps make urine, or pee. The urine travels through a tube called a ureter. This tube carries the liquid to your bladder. Your kidneys also do other jobs. They help make vitamin D. They also make hormones to help your body work right. They keep your body fluids in balance.

Your kidneys are two reddish-brown organs shaped like beans. They sit on both sides of your spine in a space called the retroperitoneal space.

One kidney is on the left and one is on the right. The right kidney is often slightly smaller and lower than the left. This happens because the liver sits near it. Your kidneys are very important for keeping your body healthy. They help balance your fluids and remove toxins from your blood. They also help control your blood pressure and acid levels.

Inside each kidney, a tiny part called a nephron does the hard work. Each human kidney has about 1 million of these units.

The process of making urine happens in four main steps. First, blood enters a tiny filter called a glomerulus. This part performs filtration by letting small things through while keeping large proteins in the blood. Next, the kidney uses reabsorption to take good things back. It keeps water, sugar, and salt in your body. Then, the kidney uses secretion to move extra waste out.

Finally, the liquid becomes urine and travels through a tube called a ureter.

Scientists study how these organs work through a field called renal physiology. They also study kidney diseases through a specialty called nephrology.

Doctors use many tools to check if kidneys are working well. They might perform a urinalysis to look at urine under a microscope. They can also use a CT scan to see the anatomy. If someone has kidney failure, they may need dialysis. This is a treatment that helps clean the blood. Some people might even need a kidney transplantation to stay healthy.

There are many specific facts about how kidneys function. An adult kidney makes about 180 liters of filtrate every single day. Most of that liquid is reabsorbed back into the body. A healthy person might produce between 800 and 2,000 milliliters of urine in 24 hours.

A mouse has a much smaller kidney with only 12,500 nephrons. The kidneys also make important things like the hormone erythropoietin. They even help turn vitamin D into its active form, called calcitriol.

You can think of your kidneys like a very smart water treatment plant. Just as a plant cleans water for a city, your kidneys clean your blood. They decide what stays in your body and what goes away. They also act like a control center for your body's chemistry. They make sure you have the right amount of salt and water. This helps your whole body run smoothly every day. Without them, the waste in our blood would build up quickly.

The kidneys are two reddish-brown, bean-shaped organs essential for human life. They function as sophisticated biological filters that maintain the body's internal balance, or homeostasis. These organs are located in the retroperitoneal space, which is the area behind the abdominal lining. Each kidney sits on opposite sides of the spine at the vertebral level of T12 to L3.

Because of the liver's position, the right kidney is typically smaller and sits slightly lower than the left. The kidneys play a vital role in regulating fluid volume, acid-base balance, and electrolyte concentrations. They also remove toxins and metabolic wastes from the bloodstream.

The primary functional unit of the kidney is the nephron. Each adult human kidney contains approximately 1 million nephrons.

These microscopic structures perform the complex work of processing blood. The kidney receives about 20% to 25% of the total cardiac output through the renal arteries. Within the nephron, the process of urine formation begins at the glomerulus. The glomerulus acts as a filter where one-fifth of the blood volume entering the kidney is processed. This stage is called filtration, where small molecules pass through while large proteins and blood cells are retained.

After filtration, the kidney performs two critical steps: reabsorption and secretion. During reabsorption, the nephron pulls useful substances back into the blood. These include glucose, amino acids, sodium, bicarbonate, and solute-free water.

This step is crucial because the kidney generates about 180 liters of filtrate every day. Without reabsorption, the body would lose too much vital material. In the next step, called secretion, the kidney moves specific wastes from the blood into the tubules. Examples of secreted substances include hydrogen, potassium, ammonium, and uric acid. The remaining liquid, now called urine, travels through the renal pelvis and into the ureter.

Structurally, the kidney is divided into two main regions: the outer renal cortex and the inner renal medulla. The cortex surrounds the medulla, which contains cone-shaped structures called renal pyramids. Between these pyramids are extensions of the cortex known as renal columns. The tips of the pyramids, called the renal papilla, empty urine into a series of collecting structures. These include the minor calyces, which merge into major calyces, and finally into the renal pelvis. This entire system is protected by a tough fibrous layer called the renal capsule. Surrounding the kidney are layers of fat, including perirenal and pararenal fat, which provide cushioning.

Beyond filtration, the kidneys perform important endocrine functions. They synthesize specific hormones that regulate other body systems. For instance, they produce renin, which helps manage blood pressure. They also produce erythropoietin, a hormone involved in blood cell production. Additionally, the kidneys play a role in bone health by converting a vitamin D precursor into its active form, calcitriol. This shows that the kidneys are not just filters, but active chemical factories that communicate with the rest of the body.

Kidney health is a major global concern due to chronic kidney disease (CKD). The estimated global prevalence of CKD is 13.4%. Currently, between 5 and 7 million people require renal replacement therapy due to kidney failure. When renal function drops below 15%, doctors often use dialysis or kidney transplantation. Dialysis is a medical procedure that performs the cleaning work the kidneys can no longer do. Doctors monitor kidney health using tools like urinalysis, CT scans, and the estimated glomerular filtration rate (eGFR). The eGFR is calculated using serum creatinine levels to measure how well the kidneys are filtering.

Medical science divides the study of the kidneys into two distinct specialties. Nephrology is the branch of medicine that focuses on kidney diseases and functions. This includes managing conditions like acute kidney injury or nephritic syndromes. Urology, however, focuses on the anatomy of the urinary tract. Urologists treat physical issues such as kidney stones, renal cysts, or cancers. Understanding both the microscopic function of the nephron and the gross anatomy of the organ is essential for treating these complex conditions.