Define the term- Ultrafiltration

Ultrafiltration occurs when the flow of a substance across a cell membrane is increased by a hydrostatic pressure. This process was initially believed to be responsible for the majority of aqueous humour formation. The capillary wall is made up of tubes of flattened blood cells and plasma proteins of higher molecular weight. According to the ultrafiltration theory, the capillary wall behaves as a semi-permeable membrane. This membrane functions to block the entrance of small to medium sized particles that are dissolved in the plasma.