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The kidney and ultrafiltration
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The kidneys remove urea and control the water content of the blood. Each kidney contains about a million tiny filters called nephrons.
Two jobs and the urinary system
Excretion: removing urea from the blood. Osmoregulation: controlling the water content of the blood.
The renal artery brings blood to each kidney. Urine passes down a ureter to the bladder, where it is stored, then out through the urethra.
The renal artery brings blood to each kidney. Urine passes down a ureter to the bladder, where it is stored, then out through the urethra.
The nephron
Blood enters a knot of capillaries called the glomerulus, inside a cup called the Bowman's capsule.
The filtrate then flows along the proximal convoluted tubule, the loop of Henle, the distal convoluted tubule and into the collecting duct.
The filtrate then flows along the proximal convoluted tubule, the loop of Henle, the distal convoluted tubule and into the collecting duct.
Ultrafiltration
Blood in the glomerulus is at high pressure, because the vessel leading out is narrower than the one leading in.
Small molecules are forced out of the blood into the Bowman's capsule: water, glucose, urea and ions. This liquid is the glomerular filtrate.
Large molecules (proteins) and blood cells are too big, so they stay in the blood.
Small molecules are forced out of the blood into the Bowman's capsule: water, glucose, urea and ions. This liquid is the glomerular filtrate.
Large molecules (proteins) and blood cells are too big, so they stay in the blood.
Which of these are found in the glomerular filtrate: glucose, red blood cells, urea, protein?
- Small molecules pass through: glucose and urea.
- Blood cells and proteins are too large.
Answer: Glucose and urea
The kidneys excrete urea and osmoregulate. Urine goes ureter, bladder, urethra. Nephron: glomerulus in Bowman's capsule, proximal tubule, loop of Henle, distal tubule, collecting duct. High pressure forces water, glucose, urea and ions into the capsule; proteins and cells stay in the blood.
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