system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: How does your body produce blood?
gpt
Blood is composed of several components, each produced in/arising from various places. The bone marrow is responsible for the production of most blood cells including platelets and red & white blood cells (although some white blood cells, such as T cells, will mature in the thymus). Plasma (the liquid) is simply made up of the water and salts absorbed from the digestive tract. Hundreds of soluble proteins are also found within the blood which can be produced from almost any organ or tissue!

The process of blood cell production is called haematopoiesis, where progenitor (stem cells) specialise into the various types of red and white cells.