as we know..platelet is smaller than any other blood plasma but why it can't pass through the capilarry?

Question

platelet origion from bone marrow and it is fragment of larger cell in bone marrow..even leucocyte can pass the tiny hole in capillary but why the platelet can't?of coz the leucocyte can pass through becoz it can squeeze itself but why this tiny thing can't?

Answer 1

Depends on what you mean by "pass through". Capillary blood samples contain platelets. They have no problems travelling through capillaries. If you are asking about capillary cell wall, then that is a different matter. Leucocytes pass through the cell wall by breaking the adhesion between two connecting epithelial cells and moving through the gap. Platelets don't have the same properties. Either do red cells, for that matter.

Answer 2

Are you talking about passing through the capillary wall, or simpley flow down the capillary?

If you're talking about passing through the capillary wall, then I think your underestimating the size of platelets. On the whole they are about 1-3 microns wide; about 1/10th to 1/3rd the size of a red blood cells.

Leukocytes are able to migrate through cell capillary walls because they squeeze between the endothelial cells that make up the capillary via a complex series of cell adhesion steps. Platelets simply don't have the mechanisms for that.

If you're talking about why can't a platelet pass down a capilarry, they can. They form clots when damage to endothellial cells releases clotting factors like Von Willebrand factor, which then causes platelets to stick together.