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The glomerulus in nephrons are just a ball of capillaries, so why can't it allow the white blood cells to squeeze though the epithelial cells into Bowman's capsule just like the formation of tissue fluid in other capillaries by filtration?

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Red blood cells, White blood cells, platelets and proteins with large molecular weight cannot pass through the podocyte and fenestrations in glomerular capillary, but small molecules like water, salts and sugars are filtered out as part of urine.

As these cells and proteins are large to cross through this filter, they remain in the capillary and create osmotic pressure within the capillary. Bowman’s space has osmotic pressure approximately zero. So, only hydrostatic pressure works in this state and help in movement of fluid across the capillary wall.

Via: https://opentextbc.ca/anatomyandphysiology/chapter/25-5-physiology-of-urine-formation/

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    $\begingroup$ So it means that the epithelial cells (podocyte) in the glomerulus are more closely packed so they don't allow the filtration of white blood cells like other capillaries in the human body? Thank you very much $\endgroup$ – Tony1300 Nov 14 at 1:53
  • $\begingroup$ Yes, in association with endothelial capillaries and basement membrane they form filtration barrier in glomerulus. $\endgroup$ – Twinkle Sheen Nov 14 at 2:00

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