Thrombopoiesis is a fascinating process in our body in which blood platelets, also known as thrombocytes, are formed. These small cells play a crucial role in blood clotting and help us to close wounds and stop bleeding. +

It all starts in the bone marrow, the soft tissue inside our bones. Not only red and white blood cells are produced here, but also the precursors of thrombocytes. The main players in this process are the so-called megakaryocytes – huge cells that develop from stem cells in the bone marrow. These stem cells are like all-rounders: they can transform into different types of blood cells, depending on what the body needs at the time.

In order for a stem cell to become a megakaryocyte, a certain messenger substance is required: the hormone thrombopoietin, or TPO for short. This hormone is mainly produced in the liver and to a lesser extent in the kidneys. It works like a signal transmitter that tells the bone marrow: “Hey, we need more platelets!” Especially when the number of thrombocytes in the blood drops – for example after an injury or illness – the production of thrombopoietin increases in order to replenish the supply.

As soon as the thrombopoietin has done its job, the megakaryocytes begin to grow and change. Not only do they become larger, they also develop a very special nucleus: it multiplies several times without the cell dividing. The result is a huge cell with a so-called polyploid nucleus that contains a lot of DNA. This is important because the megakaryocytes soon have a lot of work ahead of them.

Now comes the exciting part: the megakaryocytes begin to cut off small pieces of themselves. These pieces are the thrombocytes! You can imagine it like a factory that pushes small packages off the assembly line. The megakaryocytes form long, thread-like extensions, the so-called proplatelets, and the finished platelets are then formed from these extensions. This process takes place directly in the bone marrow, and the freshly formed thrombocytes then enter the bloodstream.

A single megakaryocyte can produce thousands of thrombocytes – an impressive feat! Once the platelets are in the blood, they remain active for about 7 to 10 days. They are then broken down by the spleen and liver and the body restarts the process to maintain the supply. In total, around 150,000 to 450,000 thrombocytes per microliter of blood circulate in a healthy person – a number that is constantly adjusted by thrombopoiesis.

Thrombopoiesis is therefore a perfectly coordinated interplay between bone marrow, hormones and special cells. It usually takes place unnoticed, but without it we could not survive. If this process is disrupted, for example by diseases such as leukemia or medication, it can lead to problems such as bleeding or thrombosis. Fortunately, our body has a clever system to keep the balance – and thrombopoiesis is a central part of it.

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