​KIDNEY

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The kidney is a vital organ that plays several critical roles in maintaining the body's overall health. It’s a pair of bean-shaped organs located in the lower back, one on each side of the spine. Kidneys are involved in many essential functions that help regulate homeostasis, the body's internal balance.

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Functions of the Kidneys

1. Filtration of Blood:

   • Blood filtration happens in the nephrons. The kidneys filter waste products, excess substances (like water, salts, and glucose), and toxins from the bloodstream.

   • The blood enters the kidneys through the renal artery, which branches into smaller vessels leading to the nephrons. The filtration process removes waste products, which then become part of the urine.

2. Regulation of Blood Pressure:

   • Kidneys help regulate blood pressure through the renin-angiotensin-aldosterone system (RAAS). When blood pressure drops, the kidneys release renin, which triggers a chain reaction to constrict blood vessels and retain sodium, both of which raise blood pressure.

3. Electrolyte Balance:

   • Kidneys maintain the balance of electrolytes (e.g., sodium, potassium, calcium, magnesium, and phosphate) in the body. They regulate the excretion or reabsorption of these electrolytes based on the body's needs.

4. Acid-Base Balance:

   • The kidneys help regulate the body's pH by excreting hydrogen ions (acid) and reabsorbing bicarbonate ions (base). This maintains a stable blood pH, which is essential for enzyme function and overall metabolism.

5. Excretion of Waste:

   • The kidneys remove waste products, including urea, creatinine, and uric acid, which are byproducts of protein metabolism. These are excreted in the urine.

6. Hormone Production:

   • The kidneys produce several important hormones:

     • Erythropoietin (EPO): Stimulates the production of red blood cells in the bone marrow when oxygen levels are low.

     • Renin: Part of the RAAS, it helps regulate blood pressure.

     • Calcitriol: The active form of vitamin D, important for calcium absorption in the gut and bone health.

7. Detoxification:

   • Kidneys also play a role in detoxifying the body by filtering out toxins and harmful substances from the blood.

8. Fluid Balance:

   • Kidneys maintain the balance of fluids in the body by regulating the amount of water excreted in the urine. This is important for hydration and the proper function of organs.

 

Urine Formation Process

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The process of urine formation involves three key steps:

1. Filtration: Blood enters the glomerulus (a network of capillaries) within the nephron, where water, ions, and small molecules are filtered out into the Bowman's capsule.

2. Reabsorption: As the filtrate moves through the proximal tubule, loop of Henle, distal tubule, and collecting duct, essential substances like water, glucose, and salts are reabsorbed back into the bloodstream.

3. Secretion: Waste products and excess ions are secreted into the filtrate, ensuring that harmful substances are eliminated in the urine.

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