The US in now ranked 46th on the RWB list, in between Romania and Haiti. It was ranked 32nd in the 2013 index. The press freedom group was blunt in its explanation. It cited increased efforts to track down whistleblowers and the sources of leaks, mentioning Chelsea Manning and Edward Snowden in particular.
The heart has four valves-one for each chamber of the heart. The valves keep blood moving through the heart in the right direction. The mitral valve and tricuspid valve are located between the between the atria (upper heart chambers) and the ventricles (lower heart chambers).
Many veins, particularly those in the upper and lower limbs, have flaplike valves, which project inward from their linings. Valves are usually composed of two leaflets that close if blood begins to backup in the vein. These valves aid in returning blood to the heart, but close if it is in the opposite direction. Arteries do not contain valves.