The Heart: The Intricate Engine of Life and the Root of "Civilization Diseases" in the Circulatory System [i]

Heart disease is damage to the heart, that has been the saying for a long time. Heart disease is the leading cause of death. Although the human heart appears to be just an ordinary muscle, it is actually a highly efficient machine. It begins its enormous work as early as three weeks after the embryo is formed. Based on the average human lifespan, it will beat for 2.5 billion times before finally ceasing function. The human heart weighs approximately 280–310 grams. To estimate its size, the so-called "fist rule" can be used, meaning that the human heart is roughly the size of a clenched fist. A newborn's heart beats 130–160 times per minute, while an adult's beats 60–80 times per minute. During systole, the heart pumps approximately 75 milliliters of blood in just one-quarter of a second. An adult's total blood volume is about 8% of their body weight. The role of blood is to supply all organs and tissues with oxygen and nutrients throughout a person's life. To fulfill this transport task, the heart bears an unimaginable burden, pumping approximately 4.5 liters of blood throughout the body every minute, which equates to 7,200 liters per day, and a total of 182 million liters over a 70-year lifespan. Its operation is similar to a pump, but the heart must operate continuously and without maintenance throughout its life. There is only a brief interval for rest between the systolic phase (when the heart muscle contracts to expel blood) and the diastolic phase (when blood returns to the heart). Throughout history, people have praised the heart's unique functions and roles. In many cultures, the heart is considered the source of love, courage, and compassion. Anatomically, the heart is a system composed of four spaces: the left and right ventricles, each containing an atrium. The blood vessels connected to the heart function like a transportation system: the left ventricle carries oxygen-rich blood through the aorta, a "highway," through increasingly finer branching vessels (arteries and arterioles), transporting the blood to the farthest corners of the body, and then through capillaries to deliver oxygen and nutrients to the cells. During return flow, blood flows in the opposite direction, passing through veins and vena cava back to the right atrium and then into the right ventricle. To ensure blood flows in one direction throughout the vessels, the heart has valves-actually valves. These valves function like check valves. When the heart contracts, they are opened by the pressure of the pumped blood; during diastole, they close automatically under the pressure of the returning blood. Here are some essential facts about the heart: Arteries are the blood vessels that carry blood from the heart to the rest of the body. Arterial blood is oxygenated after gas exchange in the lungs. Veins are the blood vessels that return blood to the heart. Venous blood has been supplied with oxygen and nutrients to the cells and has had carbon dioxide and other metabolic waste products removed. Systole is the period when the heart pumps blood out. Diastole is the period when blood returns to the heart. Arrhythmia refers to an irregular heart rate; bradycardia refers to a heart rate that is too slow (less than 60 beats per minute); tachycardia refers to a heart rate that is too fast (more than 100 beats per minute). We must understand that, aside from metabolic factors, most heart disease is caused by lifestyle factors such as psychological and physical stress, alcohol and nicotine abuse, lack of exercise, and improper diet. These lifestyle-related diseases are major killers of modern health and quality of life. [i]