San Bernardino County Sheriff's Department Infographic Thursday, November 16, 2017 The San Bernardino County Sheriffâs Department is the law enforcement agency for the largest geographical county in the nation. The department serves over 2.1 million residents with 15 patrol stations and 3800 employees to ensure the quality and safety of those we serve...
Veins branch at their beginnings into tiny venules which join capillaries.  Veins have valves which stop the blood from flowing backward. Compared to the arteries, pressure in the veins is very low. The blood is being pushed through the arteries as the heart squeezes the blood out. This is not true for the veins. Blood is pushed through the veins when body muscles contract and squeeze the veins.
The vena cava has a thinner wall and a wider lumen than the aorta because of the lower blood pressures it has to deal with . Arterial blood pressure will be higher than venous blood pressure. The force generated by the heart as it pushes blood out requires thick vessel wall so it does not rupture. The vena cava simply carries blood back to the heart, there is much less force/pressure in the vena cava.