Yes it is a Blood Vessel
The vena cava carries deoxygenated blood into the left atrium.
Pulmonary Vein
pulmonary veins
The Pulmonary Vein carries oxygenated blood from the lungs to the Left Atrium.
Blood that comes in to the right atrium comes from the pulmonary vein.
Right atrium and Left atrium
The left ventricle.
vena cava
There isn't one. The pulmonary artery flows from the lungs to the Left atrium, to the left ventricle, and then to the aorta
Lowest carbon dioxide content would be the vessel right after the lungs, pulmonary vein to the left atrium.
the size of the right atrium is smaller that the left atrium.