IGCSE Biology glossary
Glomerulus
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Definition
A tight knot of blood capillaries inside the Bowman's capsule of a nephron in the kidney. Blood enters under high pressure through the afferent arteriole. Small molecules (water, glucose, urea, ions) are forced out of the blood into the Bowman's capsule by ultrafiltration.
What to include in an exam answer
The glomerulus is the site of ultrafiltration. The high pressure forces small molecules through, while large molecules (proteins and blood cells) remain in the blood. Protein in urine suggests kidney damage.
Example in context
Explain why protein molecules are not found in the filtrate in Bowman's capsule (2 marks): Protein molecules are too large to pass through the pores in the capillary walls of the glomerulus and the Bowman's capsule wall, so they remain in the blood.
Related syllabus topic
Excretion in humans