Our language contains hints scattered like signposts. “Get to the heart of the matter,” “he wears his heart on his sleeve,” “she leads with the heart and not the head,” “he has a good heart…” All these expressions allude to our metaphorical conviction that the heart is the seat of emotion, compassion, love, sacrifice, instinctive wisdom, and other positive emotions. The brain is all about reason and intellect, but the heart is the true seat of human emotion.
The Pump at the Center of the Circulatory System
Of course, all these romantic notions aside, the heart is actually just a specialized organ that arguably works harder than any other in the body. Composed of powerful, resilient muscle cells, some nerve cells, and connective tissues, the heart is a muscular organ centered in the chest, just below the sternum. Consisting of four chambers that are demarcated by valves to prevent the back flow of blood, the heart is the pump at the center of the circulatory system.
It serves a singular purpose: to rhythmically contract, squeezing blood through the various chambers and sending wave after wave of blood throughout the miles of blood vessels in the human body, under high pressure—and then back again—in an endless cycle. The vessels—the arteries, veins, and their smaller counterparts all the way down to the level of microscopic capillaries—comprise the remainder of the cardiovascular system.
It’s a closed, continuous loop of refreshed and oxygen-depleted blood, endlessly circulating. The heart sends blood to the lungs for re-oxygenation, and for the removal of gaseous wastes. This re-oxygenated blood is then pumped throughout the body to every far-flung tissue and organ of the body. The body’s trillions of cells require a constantly renewed supply of oxygen and nutrients to survive and thrive.
Some organs, such as the brain—and the heart itself—use up more of these resources than other organs. The brain, for example, requires a great deal of energy in the form of blood sugar (glucose) to perform at peak capacity. All of which explains why the heart never, ever rests, other than in the scant moments between heart beats. Rather, the heart beats continuously, at a rate of about once per second, for our entire lifetimes.
But even that’s a bit misleading. In reality, the not-yet-fully-formed heart begins rhythmically contracting very early during gestation, in the embryo, within the womb. This remarkable event, occurring many months before the fetus will be viable outside the womb, underscores the extreme importance of this organ.
The Circulatory System
Of course, without the blood vessels, the heart would have no purpose. There’s a natural tendency to simplistically view the heart as a pump, and the blood vessels as simple pipes, delivering liquid to distant places. But this simple plumbing analogy risks missing some of the finer points regarding the complexity, elegance—and vulnerability—of the cardiovascular system. The blood vessels themselves, for example, are lined with specialized cells called the endothelium. Arteries are also enrobed in a thin layer of involuntary muscle cells. These muscle cells can be instructed to contract (adrenalin has this effect, for example) which causes the interior diameter of a given vessel to shrink, forcing blood to flow under still-greater pressure.
Rapidly raising the blood pressure is one way the body prepares us for fight or flight, which is a very good thing. But when the stressor that prompted the alarm is never really resolved (as in the case of unresolved psychological distress), a state of chronically high blood pressure may result.
Hypertension is a chief risk factor for heart disease, and is clearly not beneficial for long-term health. Fortunately, a healthful diet, and adequate exercise, can both work to relieve this kind of stress, and to coax blood vessels to relax, allowing blood pressure to return to normal.