How does ultrafiltration happen?
Reveal answer
Efferent narrower than afferent → high pressure → small molecules forced into Bowman's capsule.
Key words: pressure
3(i) EXCRETION · RECALL
3.25B Ultrafiltration
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Name four substances in glomerular filtrate.
Reveal answer
Water, glucose, urea, salts (also amino acids).
Key words: urea · glucose
What is NOT filtered?
Reveal answer
Blood cells and proteins.
Key words: proteins
What is meant by the term ultrafiltration?
Reveal answer
Pressure-driven filtration of small substances from glomerular blood.
Key words: ultrafiltration
What is meant by the term hydrostatic pressure?
Reveal answer
Pressure exerted by a fluid against a surface.
Key words: hydrostatic pressure
What is meant by the term podocyte?
Reveal answer
Specialised Bowman’s-capsule cell forming filtration slits.
Key words: podocyte
What is meant by the term glomerular filtrate?
Reveal answer
Fluid entering Bowman’s capsule after ultrafiltration.
Key words: glomerular filtrate
Blood, filtrate and urine: for Blood cells, give the glomerular filtrate and the normal final urine.
Reveal answer
Glomerular filtrate: Absent. Normal final urine: Absent.
Key words: Blood cells
Blood, filtrate and urine: for Large plasma proteins, give the glomerular filtrate and the normal final urine.
Reveal answer
Glomerular filtrate: Mostly absent. Normal final urine: Absent/trace.
Key words: Large plasma proteins
Blood, filtrate and urine: for Glucose, give the glomerular filtrate and the normal final urine.
Reveal answer
Glomerular filtrate: Present. Normal final urine: Normally absent.
Key words: Glucose
Blood, filtrate and urine: for Urea, give the glomerular filtrate and the normal final urine.
Reveal answer
Glomerular filtrate: Present. Normal final urine: Present and concentrated.
Key words: Urea
Blood, filtrate and urine: for Water and ions, give the glomerular filtrate and the normal final urine.
Reveal answer
Glomerular filtrate: Present. Normal final urine: Present in variable amounts.
Key words: Water and ions
True or false, and why? “The glomerulus actively chooses useful molecules.”
Reveal answer
False. Initial filtration is mainly size/pressure based; selective recovery happens in tubules.
True or false, and why? “Normal filtrate contains no glucose.”
Reveal answer
False. Glucose is small enough to filter and is later reabsorbed.
True or false, and why? “High pressure forces blood cells into the capsule.”
Reveal answer
False. The intact filtration barrier retains cells and large proteins.