final summary of excretion

THE FINAL SUMMARY OF EXCRETION

How the kidney works

·      Step 1 – Ultrafiltration: this happens in the glomerulus where the walls are porous and only let smaller molecules like urea, water, salts, ions etc go through. Blood passes through the capillary at the start of the nephron and then small molecules passe into the nephron tubule. Small molecules end up in the Bowman’s capsule. Large molecules exit through the capillary/blood vessel

·      Step 2 – Selective reabsorption: this is when the kidney re-absorbs all the molecules that are needed. The rest are excreted as urine. Among the molecules/substances that are re-absorbed are: all of the glucose, as much water as needed to maintain water levels normal and as many ions as needed to maintain a balance of water and mineral ions in the plasma. The reabsorption takes place by osmosis. The reabsorption of glucose and mineral ions takes place by active transport.

·      Step 3 - The formation of urine: Molecules that are not selectively absorbed continue along the nephron tubule as urine, which eventually passes down to the bladder through the ureter.

Nephrons are a very important part of the kidney. They have 6 main parts:

·      The glomerulus

·      The Bowman’s capsule

·      The proximal convoluted tubule

·      The loop of Henlé

·      The distal convoluted tubule

·      The collecting duct(s)

 How filtration of blood works J

·      In the glomerulus, small molecules are forced out at high pressure through porous walls into the Bowman’s capsule.

·      In the proximal tubule, most of the materials required are re-absorbed. This includes salts, ions, water…