Platelet
Chapter: 2
Platelets cirrculate in the blood and are derived from megakaryocytes in the marrow. Like erythrocytes, they are anucleate. However, unlike erythrocytes, they contain numerous intracytoplasmic granules and are the source of numerous proinflammatory mediators. In fact, they are quantitatively the greatest single source of vasoactive amines in the body. They also are a rich source of thromboxane A2. It is their activation that, in part, initiates the vascular phase of the acute inflammatory response (see Fig. 2-13 in text). To have them play this role makes imminently good sense, because they are present in large numbers throughout the circulation, i.e., some are always in close proximity to an inciting stimulus.
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