Ultrafiltration
- ICSE Class 10, Unit 3 Human Anatomy and Physiology
Ultrafiltration is the filtering of the liquid part of blood, under high pressure, from the glomerulus into Bowman's capsule of a nephron.
It is the first step in making urine. Blood enters the glomerulus by a wide vessel, the afferent arteriole. It leaves by a narrower one, the efferent arteriole. More blood comes in than can get out easily, so the pressure inside rises.
That pressure pushes water and small dissolved things through the thin capillary walls into Bowman's capsule. This liquid is called the filtrate.
- Passes into the filtrate: water, glucose, urea, salts.
- Stays in the blood: blood cells and large proteins, which are too big to pass.
A small example
Think of a garden hose with a finger over its end. The water inside is pushed hard against the opening. The narrow efferent arteriole works like that finger. Useful glucose is filtered out too, but it is taken back into the blood further along the tube.
Where marks go
The 2024 ICSE Biology paper asked for a definition of ultrafiltration. The marking scheme needs two key words: the glomerulus, and high pressure. CISCE's 2024 Biology report notes answers that left one of them out.
The same paper asked how the two arterioles differ in width. The error the report names is the reverse: afferent narrow, efferent wide. The wide one brings blood in. For the drawing, see the nephron and value points.
Sources
Facts last checked against these sources on 30 September 2026.
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