Describe the pathway of an oxygen molecule from when it enters the bloodstream to reaching the site of the muscle. Ensure you make reference to  the following structures in your response - different chambers of the heart, major arteries and veins involved in the transportation.

Sure, let's describe the pathway of an oxygen molecule from when it enters the bloodstream to reaching the site of the muscle, step by step:

1. Inhalation and Alveoli: The oxygen molecule is inhaled into the lungs and reaches the alveoli, tiny air sacs where gas exchange occurs.

2. Diffusion into Bloodstream: The oxygen molecule diffuses across the alveolar membrane into the pulmonary capillaries, where it binds to hemoglobin in red blood cells.

3. Pulmonary Veins: The oxygen-rich blood is then transported via the pulmonary veins to the left atrium of the heart.

4. Left Atrium: The left atrium receives the oxygenated blood and contracts, pushing the blood through the mitral valve into the left ventricle.

5. Left Ventricle: The left ventricle, which is the main pumping chamber of the heart, contracts and sends the oxygenated blood through the aortic valve into the aorta.

6. Aorta and Arteries: The aorta, the largest artery in the body, distributes the oxygen-rich blood into various systemic arteries that branch off to supply different parts of the body.

7. Arterioles and Capillaries: The blood travels through progressively smaller arteries and arterioles until it reaches the capillary networks in the muscle tissue.

8. Oxygen Delivery to Muscle Cells: In the capillaries, the oxygen molecule diffuses from the red blood cells into the muscle cells, where it is used for cellular respiration to produce energy.

9. Deoxygenated Blood Return: After delivering oxygen, the now deoxygenated blood collects carbon dioxide and other waste products from the muscle cells and is transported back through venules and veins.

10. Major Veins and Right Atrium: The deoxygenated blood is carried by major veins, such as the superior and inferior vena cava, back to the right atrium of the heart.

11. Right Atrium to Right Ventricle: The right atrium contracts, pushing the deoxygenated blood through the tricuspid valve into the right ventricle.

12. Right Ventricle to Lungs: The right ventricle contracts, sending the deoxygenated blood through the pulmonary valve into the pulmonary arteries, which carry it back to the lungs for reoxygenation.

This cycle repeats continuously, ensuring that oxygen is delivered to the muscles and other tissues throughout the body.