Here's how to break down the path of a blood cell from the brain to the lungs and determine the number of heart valves it passes through:

1. The Journey:

* Brain: Blood carrying deoxygenated blood from the brain enters the superior vena cava.

* Superior Vena Cava: This large vein carries blood to the right atrium of the heart.

* Right Atrium: The right atrium receives deoxygenated blood.

* Tricuspid Valve: The blood flows through the tricuspid valve into the right ventricle.

* Right Ventricle: The right ventricle pumps deoxygenated blood through the pulmonary valve.

* Pulmonary Valve: This valve controls the flow of blood from the right ventricle into the pulmonary artery.

* Pulmonary Artery: This artery carries deoxygenated blood to the lungs.

2. Heart Valves:

* Tricuspid Valve: Separates the right atrium from the right ventricle.

* Pulmonary Valve: Separates the right ventricle from the pulmonary artery.

3. Answer:

Therefore, a blood cell traveling from the brain to the lungs must pass through two heart valves: the tricuspid valve and the pulmonary valve.