Similar to all other cells, thrombocytes originate in the bone marrow. A healthy adult aged between 30 and 70, weighing 70 kg, has about 1,300-1,500 g of thrombocytes; 40% in the spinal bone marrow, 25% in the ribs and sternum, 15% in the pelvis, 10% in the skull, and 10% in other bones.
Progenitor cells of the thrombocytic lineage develop in the same way as other immature cells of bloodlines in the bone marrow. When immature cells differentiate into directed stem cells of thrombocytopoiesis, they are morphologically recognizable as the progenitor cells of thrombocytic lineage.
The stem cell is megakaryoblast, 21-50 mm in diameter. It gives rise to the promegakaryocyte and then the megakaryocyte - the largest cell in the bone marrow, 70-100 mm in diameter. There are 1/3 immature and 2/3 mature elements of megakaryocyte lineage in the bone marrow.
Thrombocytes are formed by the breaking off of small fragments of the megakaryocyte cytoplasm.
Each megakaryocyte gives rise to 3,000 to 4,000 thrombocytes.
The development of the megakaryocyte from the megakaryoblast takes 4-5 days, and their life-span is 7-10 days.
The number of thrombocytes in the peripheral blood is 150-350 x 109/L.
The organism can tolerate a large decrease in thrombocyte number because spontaneous bleeding appears just when their number falls below 20-30 x 109/L. Normal daily “consumption” of thrombocytes is about 15 x 109/L. |
