When you tutor Biology 12, you need to discuss the heart.

As is commonly known, the heart is a muscular pump.  Its beat pushes the blood through the vessels to every part of the body.

The human heart has two sides.  The pulmonary side receives oxygen-depleted blood from the vena cava (the big, final veins), then pumps it through the pulmonary artery to the lungs to get re-oxygenated.  The systemic side receives oxygenated blood from the lungs (via the pulmonary vein), then pumps it through the aorta which divides to service every part of the body.

Each side of the heart has two chambers:  a reception chamber and an output chamber. The reception chamber is called the atrium or the auricle.  The output chamber is called the ventricle.

One practical problem every plumbing system needs to prevent is backflow.  The heart prevents backflow using valves.  Each side of the heart has two valves:  one between the atrium and the ventricle, then one between the ventricle and the outgoing artery.

The valve between a ventricle and its outgoing artery is called a semilunar valve.  The left semilunar valve prevents blood flowing backward from the aorta into the left ventricle.  The right semilunar valve prevents backflow from the pulmonary artery into the right ventricle.

The valve between an atrium and a ventricle has several possible names.  It can be known, generally, as an atrioventricular valve.  However, each atrioventricular valve has its own unique name(s) as well.  For instance, the right atrioventricular valve is also known as the tricuspid.  The left atrioventricular valve has two specific names:  it can be called the bicuspid or the mitral valve.

The heart’s pace is ultimately decided by the medulla oblongata, located in the brain stem. However, when the medulla oblongata chooses not to interfere, the heartbeat is self-governed from the SA node, which is set to around 70 bpm.  If the SA node is damaged, the AV node can step in, but it creates a heartbeat of only 40-60 bpm. Hence, a pacemaker might be needed.

Hope you enjoyed this heartfelt discussion,

Jack of Oracle Tutoring by Jack and Diane, Campbell River, BC.

Source:  Inquiry into Life, Eleventh Edition, Sylvia S. Mader.  McGraw-Hill:  2006.