This pressure is typically 25-30 mmHg. The oncotic pressure increases along the length of the capillary, particularly in capillaries having high net filtration (e.g., in renal glomerular capillaries), because the filtering fluid leaves behind proteins leading to an increase in protein concentration.

What causes increased oncotic pressure?

The plasma oncotic pressure is that part of the total osmotic pressure of the plasma that is due to impermeant proteins. During prolonged water restriction or after water loss due to sweat, the blood becomes more concentrated and its oncotic pressure increases.

What happens when oncotic pressure increases?

Osmotic agents increase the oncotic pressure of the blood; this pulls water from tissues and increases the volume of the blood acutely. The increased blood volume will inhibit renin release, thus increasing renal blood flow.