Final answer:
The inverting of tubes in coagulation studies promotes mixing of blood with anticoagulants, preserving coagulation factors for accurate testing. The endothelium prevents coagulation in healthy blood vessels by inhibiting platelet adhesion.
Step-by-step explanation:
When a tube used for coagulation studies is inverted 3-4 times, it is to ensure proper mixing of blood with an anticoagulant present in the tube. This prevents clotting within the tube itself and preserves the coagulation factors for accurate testing. The citrate-based anticoagulant in the tube chelates calcium ions, which are essential for blood clotting, and thus, prevents the blood from clotting while it is in the tube. The preservation of coagulation factors is crucial for the validity of coagulation tests, such as the Prothrombin Time (PT) or International Normalized Ratio (INR), which assess the integrity of the coagulation pathways and the liver's ability to produce these factors.
The endothelium of blood vessel walls plays a key role in maintaining a balance between hemorrhage and thrombosis. It secretes substances that prevent platelet adhesion and aggregation, thus keeping blood fluid within the vascular system.