i believe the answer is to cope with negative emotions.
Caffeine increases action in the central nervous system
The walls of arteries and veins have three layers or tunics: An outer layer (tunica adventitia) of connective tissue with collagen fibers. An inner layer (tunica intima), consisting of a specialized simple squamous epithelium, often called the endothelium, that lines all blood vessels and the endocardium of the heart.
The blood pressure on veins is less than that in the arteries because they are draining blood from the capillary bed. As a consequence of lower pressure in veins, they contain internal flaps which act as one way valves to prevent blood from flowing in the wrong direction. Veins return blood to the heart.
