Question

Explain the terms ultrafiltration and selective absorption. [5 MARKS]

Answer 1

Each Part: 2.5 Marks

Blood passing through the glomerulus is under high pressure. So the liquid part of the blood is filtered out from the glomerulus into the renal tubule. This filtration under hydrostatic pressure is called ultrafiltration. During this process, almost all the liquid part of the blood plasma along with most organic and inorganic substances including urea, glucose, amino acids etc, is forced through the sieve-like capillaries and into the capsule. This fluid entering the renal tubule is called glomerular filtrate.

The glomerular filtrate is an extremely dilute solution containing a lot of usable materials like water, urea, salts, glucose and other plasma solutes. When the filtrate reaches the proximal convoluted tubule, sodium ions and chloride ions, glucose, amino acids, water and some vitamins move back into the blood. But their re-absorption is only to the extent that the normal concentration of the blond is not disturbed. This is called selective absorption.