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).
There are also two semilunar valves; one between the right ventricle and the lungs (pulmonary semilunar valve) and one between the left ventricle and the aorta (aortic semilunar valve). The main purpose of the valves is to prevent backflow of blood in the heart. There are things called the chordae tendinae and papillary muscle that help control the opening and closing of the valves as blood flows through them. There are also valves in the veins.