"We should remember, too, that the human body is an acid-consuming, acid-manufacturing, and acid-eliminating machine, and that the blood is always alkaline
because of the presence in it of sodium bicarbonate, commonly called baking soda. The blood may be more alkaline (hyperalkaline) or it may be less (hypoalkaline).
The normal reaction is faintly alkaline.
There is a slight difference between the alkaline reaction of the blood that flows in the veins and in the arteries. Blood in the veins is a little less alkaline because it
contains carbonic acid, resulting from cell activity, which it is carrying to the lungs. The blood in the arteries is a little more alkaline because the carbonic acid leaves the blood as it passes through the lungs."