Your circulating blood is made up of different components: Red Blood Cells (RBC) which carry oxygen to tissues, White Blood Cells (WBC) which help fight infection and foreign material, Platelets which help form blood clots to stop bleeding and promote healing, as well as the protein-rich plasma which is the liquid carrier of these components.
There is a medical procedure that concentrates the platelets and separates them from the RBCs and that platelet-rich elixer - made from your own body's natural healing proteins is call Platelet Rich Plasma (PRP).
Platelets are very small (about 2/1000's of a millimeter in size), but their small size betrays their importance for healing tissues. They contain several healing and growth factors:
Your body responds to direct trauma or repetitive stress injuries
Your body is an amazing and complex set of systems that tries its best to self regulate under extremely varied environmental conditions, nutritional supplies, and must defend itself from countless organisms trying to parasitize or kill us. Your body can selectively attack the invader (the immune system attacking bacteria, virus, fungus, etc.), it can get confused and attack itself (many autoimmune disorders like rheumatoid arthritis, lupus, etc.), it can also have damaging responses to unhealthy foods (gluten, seed oils, etc.) as a few examples.