Question

Arrange the following events in the correct sequence, starting immediately after deoxygen blood has entered the heart.
a. The right atrium contracts
b. The semilunar valves open
c. The right ventricle contracts
d. The tricuspid valves close

Answer 1

Among the most essential organs responsible for maintaining life of humans is the human heart. It is a four-chambered muscular organ. The organ is about the size of a clenched fist. In any organism, the purpose of the heart is to maintain a steady flow of blood across the body. This replenishes oxygen and redistributes cells and tissues with nutrients.

Complete answer:
Inside the body, there are two different types of circulation: pulmonary circulation (carries the deoxygenated blood to the lungs and then returns oxygenated blood to the heart) and systemic circulation (pumps oxygenated blood throughout the body and brings deoxygenated blood to the heart).

The chambers of the heart which receive blood are the atria and ventricles are the chambers that pump blood.The right atrium receives deoxygenated blood from the inferior and superior vena cava veins. This deoxygenated blood is then passed on to the right ventricle, via the atrioventricular valve or the tricuspid valve . After it has been filled, the right ventricle pumps the blood via the pulmonary arteries, by-passing through the semilunar valve (or pulmonic valve) to the lungs for the purpose of re-oxygenation of blood. The semilunar valves close after the blood passes via the pulmonary arteries, preventing the blood from flowing back into the right ventricle. The left atrium then receives oxygen-rich blood from the lungs, via the pulmonary vein. This blood passes into the left ventricle, and the blood is pumped out through aorta, delivering oxygenated blood to the body's organs and muscles. This pumping pattern is called double circulation and is present in all mammals.

So, the correct sequence of events is – A, followed by D then C and last B.

Note: The pericardium is a heart-enveloping fibrous membrane. By creating a serous fluid that lubricates the heart and reduces friction between the surrounding organs, it also performs a protective role. In addition, the pericardium keeps the heart in its place and provides the heart with a hollow room to expand and contract.