Question 4: the correct answer is 4. Got it right? Award yourself 1 point.
Question 5 of 10
Which is the longest bone in the human body?
Why, in question 4: How many chambers does the human heart have?
The answer is 4: two atria, at the top, which receive blood, and two ventricles, at the bottom, which pump it out. The right side sends blood to the lungs, and the left side sends it to the rest of the body.
A pump that never stops
At rest, an adult's heart beats 60 to 100 times per minute. Over the course of a day, that adds up to roughly 100,000 beats, without a single pause.
The rhythm is controlled by a natural pacemaker, a small group of cells in the right atrium that generates electrical impulses on its own. That is why the heart keeps beating without needing a command from the brain.
The valves between the chambers work like one-way doors and prevent blood from flowing back. The heartbeat sound a doctor hears through the stethoscope is precisely the closing of these valves.
The heart muscle, the myocardium, is different from the other muscles in the body: it works its whole life without the fatigue of a leg muscle and receives blood through its own arteries, the coronary arteries.
