PLATELETS

INTRODUCTION: Platelets are the smallest formed elements in the blood. They are fragments of larger, multinucleated cells, which are the largest discrete constituents of the bone marrow known as megakaryocytes, but platelets have no nuclei of their own. Most platelets remain in the circulation, but a substantial minority is trapped in the spleen; this phenomenon becomes important in a variety of immune-mediated decreases in platelet count known as thrombocytopenia.

LIFE SPAN OF PLATELETS: In the setting of a normal platelet count, they have a circulatory half-life of about 10 days. In cases of thrombocytopenia, their half-life decreases, as they are consumed in the routine maintenance of vascular integrity.

ROLE OF PLATELETS IN CIRCULATION: Platelets are integral components of the coagulation system. Their membranes provide an important source of phospholipids (PLs), which are required for the function of the coagulation system proteins, and contain important receptors that allow attachment to endothelial cells (platelet adhesion) so that a platelet plug can be formed in response to blood vessel injury. This prevents further blood loss after trauma and limits the coagulation response to the site of injury rather than letting coagulation proceed inappropriately.

The cytoplasm is also important for platelet function, particularly the intracellular dense granules and alpha granules. The phenomenon of platelet activation is also called “degranulation” and can be initiated by exposure of platelets to the activated blood coagulation factor thrombin, adenosine 5′-diphosphate (ADP), or collagen. This last reaction is probably the most important, occurring when collagen, normally in the basement membrane below the endothelial cells, is exposed to the blood after injury.

APPEARANCE AND SHAPE: On examination of the blood smear, platelets are small, irregularly shaped blue or purple granular bodies. In conditions in which platelet numbers are rising as a result of increased marrow activity, the more immature platelets can be identified by their larger size.

RELATED;

1. RED BLOOD CELLS  

2.  LEUKOCYTES

3.  THROMBOCYTOPENIA

REFERENCES