We label the human sex chromosomes with X's and Y's. For example. A boy's chromosomes are XY. A girls chromosomes are XX. When a child is born, they get an X from their mother, and either an X or Y from their Father, thus determining their sex.
Answer:
Heart valves or the closure of the mitral and tricuspid atrioventricular (AV) valves at the beginning of ventricular systole and the closure of the aortic valve and pulmonary valve at the end of ventricular systole.
Explanation:
The heart tone “lub,” or S1, is caused by the closure of the mitral and tricuspid atrioventricular (AV) valves at the beginning of ventricular systole.
The heart tone “dub,” or S2 ( a combination of A2 and P2), is caused by the closure of the aortic valve and pulmonary valve at the end of ventricular systole.
Why am I always answering people questions when they should answer mine
It is true. hope I helped even though it passed
