Questions one through four

The blood entering the right atrium is venous and is returning from the vena cava. The blood entering the left atrium is arterial and is returning from the lungs. The blood entering the right ventricle is venous and is sent out to the lungs by way of the the pulmonary arteries. The blood entering the left ventricle is arterial and is sent out  to the body through the aortic artery.

Explanation:

The human heart has four chambers, responsible for the distribution of blood in the circuits known as major circulation and minor circulation.

Major circulation implies the route made by the blood, pumped by the heart, through the whole body, carrying oxygenated blood —arterial— through the arteries, to later return as non-oxygenated or venous blood through the veins, reaching the heart again. Minor circulation goes from the heart to the lungs and from these to the heart. The right ventricle sends venous blood through the pulmonary arteries to the lungs, and returns through the pulmonary veins to the heart.

A summary of the complete pathway of the blood in the body is:

The blood reaches the right atrium through the cava vein, goes into the right ventricle and from there goes to the lungs, through the pulmonary arteries, the only arteries that carry venous blood. The lungs send the blood to the left atrium, through the pulmonary veins —the only ones that carry arterial blood— it passes to the left ventricle and from there it is pumped to the entire body through the aorta artery, which distributes it throughout the arterial tree.

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