Questions: Describe the function of the chordae tendineae and the papillary muscles. What is the significance of the difference in thickness between the wall of the aorta and the wall of the pulmonary trunk? List the correct pathway through which blood must flow in relation to the region of the heart. Assume blood is currently in a vena cava and will eventually enter the aorta. Include the major blood vessels (arteries and veins) attached directly to a heart chamber, the four heart chambers, and the four heart valves in your list.

The function of the chordae tendineae and the papillary muscles is crucial in the operation of the heart valves, specifically the atrioventricular (AV) valves, which include the tricuspid and mitral valves. The chordae tendineae are strong, fibrous strings that connect the papillary muscles to the leaflets of the AV valves. During ventricular contraction, the papillary muscles contract, pulling on the chordae tendineae. This action prevents the valve leaflets from prolapsing or inverting into the atria, ensuring that the valves close properly and prevent backflow of blood from the ventricles into the atria. This mechanism is essential for maintaining unidirectional blood flow through the heart.

The significance of the difference in thickness between the wall of the aorta and the wall of the pulmonary trunk lies in the different pressures they must withstand. The aorta has a thicker wall compared to the pulmonary trunk because it needs to handle the higher pressure of systemic circulation. The left ventricle pumps oxygenated blood into the aorta, which then distributes it throughout the entire body. This requires a strong, thick-walled vessel to withstand the high pressure. In contrast, the pulmonary trunk carries deoxygenated blood from the right ventricle to the lungs, which is a shorter distance and involves lower pressure. Therefore, the pulmonary trunk has a thinner wall compared to the aorta.

The correct pathway through which blood must flow, starting from the vena cava and eventually entering the aorta, is as follows:

• Blood enters the right atrium from the superior and inferior vena cavae.
• It then flows through the tricuspid valve into the right ventricle.
• From the right ventricle, blood is pumped through the pulmonary valve into the pulmonary trunk and then to the lungs via the pulmonary arteries.
• Oxygenated blood returns from the lungs through the pulmonary veins into the left atrium.
• Blood flows from the left atrium through the mitral valve into the left ventricle.
• Finally, the left ventricle pumps the blood through the aortic valve into the aorta, from where it is distributed to the rest of the body.