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Briefly describe the mechanism of urine formation.

The 3 main steps in urine formation are- Glomerular filteration, reabsrption and secretion. Glomerular filteration occurs in malphigian corpuscle formed together by glomerulus and its surrounding bowman's capsule. Reabsoption and secretion occurs in highly coiled renal tubule.

URINE FORMATION

Glomerular Filteration- The total volume of blood is filtered through the kidney. The filtration forms an ultra filtrate in the lumen's of the bowman's capsule which contain essentially all constituents of blood except for blood corpuscles and the plasma proteins. Nearly 15-25% of the water and solutes are removed from the plasma that flows through the glomerulus.

Reabsorption- Re-absorption occurs through the epithelial cells of the various segments of the nephrons. The small molecules which are essential for the body must be returned to the interstitial fluid and blood plasma. This selective transport of the substances across the epithelium of the excretory tubule from the ultrafilterate to the interstitial fluid is called reabsorption. The proximal & distal convoluted tubules, henle's loop and collecting duct contribute to reabsorption. Nearly all sugar, vitamins, organic nutrients and most of water is reabsorbed.

Srecretion- Secretion is a selective process involving both active and passive transport. As the filtrate travels through the nephron tubule , tubular cells secrete substances such as H + , K + and ammonia into the filtrate. The proximal & distal convoluted tubules are the main sites of tubular secretion and helps in maintenance of ionic and acid-base balance of body fluids.

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Urine is formed through three processes that occur in the kidney:

 

  • Ultrafiltration, where almost all the blood components are filtered by the kidneys except for the blood cells and the plasma proteins, e.g. urea, water, sodium, glucose, potassium, ...etc.
  • Selective reabsorption, where the essential components are reabsorbed back into the blood vessels, e.g. glucose, water, sodium, ...etc.
  • Secretion, where, e.g. potassium is secreted by cells in exchange for another useful component, e.g. sodium in that case.
  • Then the water reabosprtion content is further regulated before exiting the kidney through a hormone known as ADH.
  • Urine is then formed, collected in the bladder and excreted outside the body later on
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Thnx alot all of u 

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