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Kidneys are super important organs in your body! They do a really important job of filtering your blood and getting rid of waste and toxic materials. This keeps your body healthy and working properly. Your kidneys filter around  litres of blood every day and remove about 2 litres of water and waste materials in urine. That's a lot! Without your kidneys, all those waste materials would build up in your blood and cause damage to your body. So, think of your kidneys like your body's very own sewage treatment plants! But, kidneys do more than just filter your blood. They also help regulate how much water is in your blood and make hormones that your body needs. The waste that comes out of your body is called urine. It's made up of things like water, ions, and urea. Keep your kidneys healthy by drinking enough water and eating a healthy diet.

Kidney Location in the Human Body

Your kidneys are two important organs that are shaped like beans and are about the size of your fist. They sit in the back of your body, below your ribcage, with one kidney on each side of your spine. You'll also find the adrenal glands sitting on top of each kidney. These organs are located in a space called the retroperitoneal area, which is between the T12-L3 vertebrae. The left kidney is slightly higher than the right one because the liver is above the right kidney.'s important to take care of your kidneys by drinking enough water and eating a healthy diet to keep them functioning properly.

Kidney Anatomy

kidneys are made up of three main areas: the outer, inner medulla, and renal pelvis. The cortex extends into the medulla, creating triangular sections called renal pyramids, and the renal pelvis is where blood vessels enter and exit the kidney. Inside each kidney, there are around million tiny filtering units called nephrons. These nephrons are responsible for filtering your blood and helping to remove waste and extra fluids from your body. Adults have about 1.5 million nephrons in each kidney. Each nephron has several parts, including the Bowman's capsule, glomerulus, proximal convoluted tubule, loop of Henle, distal convoluted tubule, and collecting duct. All of these parts work together to filter your blood and selectively reabsorb certain materials.

Kidney Functions

The kidneys play a crucial role in maintaining the body's water balance, which is known as homeostasis. They help regulate the amount of water in the body by filtering excess fluid out of the blood and producing urine. The kidneys can also return water to the blood when necessary, helping to maintain a constant internal environment in the body. In addition to their role in regulating water balance, the kidneys also synthesize essential hormones such as erythropoietin and renin. Erythropoietin is responsible for stimulating the production of red blood cells, and it is synthesized by the kidneys in adults (although in embryos, it is made in the liver). Renin is involved in regulating blood pressure and electrolyte balance in the body. These hormones help to keep the body in good health and functioning properly.

Maintaining Water Balance

The kidneys produce urine to remove excess electrolytes, such as sodium and potassium, from the body. Urine also helps to eliminate metabolic waste products from the blood, which would be harmful if they were allowed to accumulate in the body. The process of producing urine occurs in two stages within the nephrons of the kidneys: the glomerular stage and the tubular stage.

In the glomerular stage, ultrafiltration occurs, and small molecules such as glucose, urea, salts, and water are filtered out of the blood at high pressure. Larger molecules, like proteins and red blood cells, retained the blood vessels supplying the kidneys and are not filtered out.

In the tubular stage, useful substances are reabsorbed back into the blood, including almost all of the glucose, some water, and some salts. This purified blood is then returned to circulation. Any substances that are not reabsorbed travel through the nephron network to the ureter and bladder, where they are stored as urine.

The level of water reabsorption is regulated by the hormone ADH, which is released from the pituitary gland in the brain. When the body detects low water content in the blood, more ADH is released, promoting water reabsorption to return water levels to normal. The process of ultrafiltration occurs within the Bowman's capsule, while selective reabsorption occurs within the tubules, including the proximal and distal convoluted tubules.

Producing Hormones

In addition to their role in maintaining water balance and filtering waste products from the blood, the kidneys also play an endocrine function by producing several hormones, including renin, erythropoietin, and activated vitamin D.

Renin is an important hormone involved in regulating blood pressure. When blood pressure drops, the kidneys release renin, which activates a cascade of other molecules that constrict the capillaries to raise blood pressure. If the kidneys are not functioning correctly, they may secrete too much renin into the blood, leading to hypertension (high blood pressure).

Erythropoietin plays a key role in stimulating the production of red blood cells in the bone marrow. the kidneys are not functioning correctly, an inadequate amount of erythropoietin is produced, leading to a lower number of new red blood cells being produced. This can result in anaemia, a condition in which an individual lacks sufficient numbers of red blood cells in their body.

The kidneys also activate vitamin D into its active hormone form, which is required for calcium absorption in the gut, proper bone formation, and optimal muscular function. If renal function is compromised, there may be low blood calcium and insufficient vitamin D, leading to muscular weakness and diseases of the bone such as rickets.

Overall, the kidneys play a vital role in maintaining the body's overall health and functioning. Dysfunction of the kidneys can lead to a range of issues, including hypertension, anaemia, and bone and muscular disorders.

Kidney Disease

When the kidneys fail, toxic wastes and excess fluid can build up in the body, leading to various symptoms such as ankle oedema, weakness, poor sleep, and shortness of breath. If left untreated, kidney disease can lead to complete kidney failure, which can be life-threatening. Kidney disease is broadly classified into two types: acute kidney injury (AKI) and chronic kidney disease (CKD). AKI is a short-term period of renal damage that is typically triggered by complications of another severe illness, such as kidney stones or kidney inflammation. As a result, excess water and waste products that would have normally been excreted accumulate in the blood, leading to various symptoms. In contrast, CKD is a long-term condition that describes the progressive loss of kidney function over several years. The most common causes of CKD include diabetes, obesity, and high blood pressure. CKD can only be identified after a blood or urine test, and patients may show symptoms such as swollen ankles, shortness of breath, and blood in the urine. Overall, kidney disease can have a significant impact on an individual's health and well-being. It is essential to seek medical attention if you experience any symptoms of kidney disease, as early diagnosis and treatment can help to slow the progression of the disease and improve outcomes.

Kidney Disease Treatments

Individuals should be able to survive with just one healthy kidney, but if both fail, it can ultimately lead to death if left untreated. Those with very poor renal function need to undergo renal replacement therapy, which includes:

Dialysis Kidney transplant

Great summary! To add to your key takeaways, here are a few more points:

  • Haemodialysis involves using a machine to filter the blood outside the body, while peritoneal dialysis involves using the lining of the abdomen to filter the blood. CRRT, on the other hand, is a continuous process used in critically ill patients.
  • Each type of dialysis has its advantages and disadvantages, and the choice of dialysis method will depend on the patient's individual needs and preferences.
  • While dialysis can help to manage the symptoms of kidney disease, it is not a cure, and a kidney transplant remains the best option for those with complete renal failure.
  • It is important to take steps to prevent kidney disease, such as managing underlying conditions like diabetes and high blood pressure, maintaining a healthy lifestyle, and avoiding exposure to toxins and infections that can harm the kidneys.


What are kidneys?

The kidneys are homeostatic bean-shaped organs located in the back of your body, directly below your ribcage.

What is the function of the kidneys?

The kidneys are responsible for maintaining the water balance of the blood by excreting excess salts and metabolic waste products. They also produce important hormones, such as renin and erythropoietin. 

What hormones act on the kidney?

ADH, which is released from the pituitary gland, act on the collecting ducts of the nephron. The presence of more ADH stimulates water reabsorption. 

What is secreted in the kidney?

Two main hormones are secreted in the kidneys: renin and erythropoietin (EPO). Renin helps regulate blood pressure while EPO stimulates the production of red blood cells in the bone marrow.

What are the main part of the kidney?

The kidneys contain three important regions: the outer cortex, inner medulla and renal pelvis.

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