Tissue blood capillaries connect the arterioles to the venules. These are the smallest blood vessels in the body. Arterioles are connected to arteries of more average caliber. And they represent the arterial circulation from the heart to the tissues (in red). So they provide the cells of the tissues with the nutrients and oxygen necessary for their functioning. The venules represent the venous circulation, from the tissues to the heart (in blue). And they are connected to medium caliber veins. So they recover the waste and the CO2 for their disposal. Thus, these tissue capillaries are organized in tree networks. They are also called capillary beds. And they come together and intertwine in the tissues and therefore interact closely with them. It is also at their level that blood pressure is lowest. (Photo by: JACOPIN/BSIP/UIG)