I am so confused. I do not understand the physiology behind filtration and absor

Question

I am so confused. I do not understand the physiology behind filtration and absorption at the capillary level. This is the information my professor has on his powerpoint:

Filtration is pressure-driven movement of fluid and solutes from the blood capillaries into interstitial fluid. Blood Hydrostatic Pressure and Interstitial Fluid Osmotic Pressure promote filtration.

Reabsorption is pressure-driven movement of fluid and solutes from the interstital fluid into blood capillaries. Interstitial Fluid Hydrostatic Pressure and Blood Colloid Osmotic Pressure promote reabsorption.

I understand that substances move from the capillaries to the interstitial fluid at the arterial end, and substances from the interstitial fluid enter the capillaries at the venous end, but I am not understanding the physiology behind this. Can you please walk me through this and make it easier to understand. Analogies always help!

Explanation / Answer

At the arterial end the sum of blood hydrostatic pressure of the artery and the interstitial fluid Osmotic pressure of the interstitium surrounding the arterial capillaries is greater than the sum of blood oncotic pressure and the hydrostatic pressure by interstitial fluid therefore the net flow of substances from blood vessel to the interstitium.

Vice versa occurs in case of Venus end of capillaries. Here the sum of blood hydrostatic pressure of the vein and interstitial fluid Osmotic pressure of the interstitium surrounding the Venus capilaries is lesser than the sum of Blood oncotic pressure and the hydrostatic pressure by the interstitial fluid therefore the netflow of substance is from interstitium to the blood vessel.

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