Which of the following statements is/are correct in a healthy human?
- During inspiration, the pressure within the chest cavity is lower than outside the body.
- During ventricular systole, the pressure in the atrium is lower than in the ventricles.
- During ventricular systole, the pressure in the aorta is lower than the pressure in the atrium.
A. 1 only
B. 3 only
C. 2 and 3 only
D. 2 only
E. 1 and 2 only
The correct answer is E.
Let’s tackle this question by reviewing each item one by one :
- During inspiration, intercostal muscles contract and the lung capacity is augmented by the lowering of the diaphragm. This causes the pressure inside the chest to lower than the pressure outside of the body, making inspiration possible. It is the opposite mechanism for expiration.
Item 1 is correct.
Ventricular systole is when both ventricles are contracted and full of blood ; it occurs while the atrium are relaxed. Because the ventricle is full of blood and contracted while the atrium is not, the pressure in the atrium is lower than in the ventricles.
Item 2 is correct.
- During ventricular systole, and due to the pressure exerted by the blood, the following events occur :
the tricuspid and mitral valves close up ;
the semi-lunar, aortic and pulmonary valves open up ;
the blood goes into the aorta and pulmonary arteries ;
We’ve already established that the pressure inside the atrium is lower than the one in the ventricles. In addition to that, because the blood flows through the aorta from the ventricle, its pressure raises, making it higher than the one in the atrium.
Item 3 is incorrect.
Because the items 1 and 2 only are correct, the right answer is E.