Answer:
The “lub” is the first heart sound, commonly termed S1, and is caused by turbulence caused by the closure of mitral and tricuspid valves at the start of systole. The second sound,” dub” or S2, is caused by the closure of aortic and pulmonic valves, marking the end of systole.
The pancreas and gland cells of the small intestine secrete digestive enzymes that chemically break down complex food molecules into simpler ones.
answer is digestive enzymes
