Blood Platelets

Platelets, or thrombocytes, the smallest formed elements in the blood histology , are disklike cell fragments that vary in diameter from 2 to 5 um. In humans, they lack nuclei and originate by budding from large cells in the bone marrow called megakaryocytes. They range in number from 200,000 to 400,000 mm3 of blood and have a lifespan of about 8 days. In blood smears they appear in clumps. Each platelet has a peripheral hyalomere region that stains a faint blue and a dense central granulomere that contains a few mitochondria and glycogen granules and a variety of purple granules. Platelets have an important physical role in plugging wounds, and they contribute to the cascade of molecular interactions among the various clotting factors dissolved in the plasma blood histology