There's two transport proteins, channel/pore protein and carrier protein. Charged/polar molecules or ions need specific transport proteins to pass through across the plasma membrane. Transport proteins allows ions/polar molecules to bind to the specific site and allow them to pass through and enter the cell.
(btw, is this a chemistry question? isn't this a biology ques?)
Always remember blood first flows from atria (remember A comes before V) to ventricles and the right side always carries deoxgenated blood to the lungs which then arrives through the left side when oxygenated
