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.
Whenever there is a difference in pressure between two locations fluid flows from the region of high pressure to that of low by bulk flow. The heart causes blood to flow by creating a mean arterial pressure that is greater than the pressure in the veins.Hence, a pressure gradient drives the blood from the arteries to the veins. As blood flows from the arteries to the veins the pressure decreases. This decrease in pressure is called a pressure drop.The pressure drop is greatest in the arterioles and greater in the systemic compared to the pulmonary circuit.his is because the pressure at the other end is the central venous pressure which is approximately 2-8 mm Hg and very close to 0 mm Hg. In a similar way the pressure gradient in the pulmonary circuit is about 15 mm Hg which is about equal to the mean pulmonary arterial pressure.