Define the term ultrafiltration.
Topic: Ultrafiltration
Answer
ULTRAFILTRATION is the filtration of blood under HIGH PRESSURE in the MALPIGHIAN CAPSULE of the nephron, in which water, glucose, amino acids, urea and salts are forced out of the glomerulus into Bowman’s capsule, while the blood cells and the large plasma PROTEINS are held back.
Three elements make a complete definition: HIGH PRESSURE, WHERE it happens (glomerulus into Bowman’s capsule), and WHAT IS LEFT BEHIND (blood cells and proteins).
The prefix ULTRA- means the filtration is unusually fine — fine enough to separate small molecules from large ones.
WHERE THE PRESSURE COMES FROM, which links to Question 3(iii) of this paper: the AFFERENT arteriole is WIDER than the EFFERENT one, so blood enters faster than it can leave and pressure builds inside the glomerulus. Without that difference in diameter there would be no ultrafiltration.
Finding PROTEIN in the urine (albuminuria) therefore means the filtering membrane has been damaged — proteins should never get through.