Hematology: Hemostasis

Platelet development, also known as thrombopoiesis, is the process by which platelets, small cell fragments found in the blood, are produced in the bone marrow. Platelets play a crucial role in the blood clotting process and are essential for wound healing and preventing excessive bleeding. Here is an overview of platelet development: Hematopoietic Stem Cells: The process of platelet development begins with hematopoietic stem cells in the bone marrow. These multipotent stem cells have the potential to differentiate into various blood cell types, including platelets. Commitment to the Megakaryocytic Lineage: Hematopoietic stem cells commit to the megakaryocytic lineage, which is a specialized lineage of blood cell development dedicated to producing platelets. This commitment is regulated by various growth factors and hormones, including thrombopoietin (TPO). Formation of Megakaryocytes: Megakaryocytes are large, multinucleated cells that are the precursors of platelets. They are unique in that they do not fully divide like typical cells. Instead, they undergo a process known as endomitosis, in which their nuclei replicate without cell division, resulting in a single megakaryocyte with multiple nuclei. Maturation and Development: Within the bone marrow, megakaryocytes mature and develop. They extend long, branching projections called proplatelets into the blood vessels of the bone marrow, reaching into the sinusoidal spaces where blood flows. Platelet Formation: Proplatelets fragment into smaller, disc-shaped structures called platelets as they enter the bloodstream. These platelets are released into circulation, where they are carried throughout the body. Circulation and Function: Circulating platelets are involved in maintaining hemostasis, the process of preventing excessive bleeding when blood vessels are injured. They adhere to the site of vascular injury, aggregate to form a plug, and release clotting factors to initiate the coagulation cascade.

Collagen: from endothelial cells ADP: Released from activated platelets (autocrine and paracrine) Thromboxane A2 (TXA2): Diffuses out of platelets (autocrine and paracrine) Thrombin: Part of coagulation cascade can activate platelets