Final answer:
Thrombopoietin (TPO) is a hormone produced mainly in the liver and to a lesser extent in the kidneys, which functions to stimulate the development of megakaryocytes into platelets.
Step-by-step explanation:
Thrombopoietin (TPO) is a glycoprotein hormone responsible for the regulation of platelet production. It is primarily produced by the liver, with a smaller amount also being secreted by the kidneys. TPO's key role is to stimulate the development of megakaryocytes into platelets, which play a critical role in blood clotting. Understanding the production of TPO is essential in medical conditions relating to both excessive bleeding and clotting, known as thrombocytopenia and thrombocytosis, respectively.