Biology · Excretion. The idea in plain words, the rules to remember, the mistake to avoid and a worked example, written and checked by Mega Lecture.
The two kidneys remove urea, excess salts and excess water from the blood as urine. Urine flows down a ureter from each kidney to the bladder, where it is stored. It leaves the body through the urethra.
Each kidney contains many nephrons. Blood is filtered in the glomerulus, a knot of capillaries inside the Bowman's capsule. Water, glucose, urea and ions pass into the capsule. Blood cells and proteins are too large and stay in the blood. Along the tubule and loop of Henle, all of the glucose, some ions and most of the water are reabsorbed into the blood. What is left flows down the collecting duct as urine.
The liver makes proteins from amino acids and removes the nitrogen from excess ones to form urea.
Ureter and urethra are easy to confuse. There are two ureters, from the kidneys to the bladder, and one urethra, from the bladder to the outside.
Answer: About 99% of the filtrate is reabsorbed into the blood, which is why most of the water is not lost.
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