Final answer:
Blood platelets, also known as thrombocytes, are predominantly made by megakaryocytes in the bone marrow. Thrombopoietin stimulates the development of megakaryocytes, and hematopoiesis continues throughout life as blood elements have short lifespans and need constant replacement.
Step-by-step explanation:
Origin of Blood Platelets
More than half of the body's blood platelets are made by megakaryocytes in the bone marrow. Megakaryocytes, large cells descended from myeloid stem cells, reside within the bone marrow tissue. These megakaryocytes produce platelet-precursor extensions that release thousands of cytoplasmic fragments, each surrounded by a plasma membrane, into the bloodstream. These fragments are known as platelets. Initially, thrombopoietin, a glycoprotein hormone produced by the liver and kidneys, stimulates megakaryoblast proliferation, which then matures into megakaryocytes within the bone marrow.
Following birth, hematopoiesis—the production of blood cells, including platelets—occurs mostly in the red marrow, a type of connective tissue within the spongy bone. Hematopoiesis is a vital process as erythrocytes, leukocytes, and platelets have a relatively short lifespan, necessitating their continuous replenishment. Each megakaryocyte can release 2000-3000 platelets during its lifespan before its remnants are consumed by macrophages.