The heart is an organ that circulates blood by acting as a pump. It can be a simple tube, like in spiders and annelid worms, or a more complex structure, like in mollusks, with one or more receiving chambers (atria) and a primary pumping chamber (ventricle). The heart of a fish is a folded tube with three or four enlarged portions that correspond to mammalian chambers.
The heart of animals with lungs—amphibians, reptiles, birds, and mammals—has evolved from a single pump to a double pump that circulates blood to the lungs and to the entire body.
The heart is a four-chambered double pump at the center of the circulatory system in humans, other mammals, and birds. It rests on the diaphragm, the muscular wall between the chest and the abdominal cavity, in humans. It is located between the two lungs and somewhat to the left of center, behind the breastbone.
The Human Heart: An Overview
The human heart is one of the most vital organs in the body, as it is responsible for keeping us alive. It is a four-chambered muscular organ. The heart is approximately the size of a clenched hand. The human heart is one of the most powerful and hardest-working muscles in the body, and it functions throughout a person’s life.
The human heart is an organ that pumps blood through the circulatory system’s veins, giving oxygen and nutrition to the tissues while also eliminating carbon dioxide and other pollutants.
Dr. Lawrence Phillips, a cardiologist at NYU Langone Medical Center in New York, said, “The tissues of the body need a steady supply of nutrients in order to be active.” “They will perish if [the heart] is unable to supply blood to the organs and tissues.”
The Heart’s Position in the Human Body
The human heart is in the middle of the chest, just to the left of the sternum (breastbone). It comes from the mesodermal germ layer of the embryo.
According to the Texas Heart Institute, it is wrapped in a double-walled sac called the pericardium that sits between your lungs. The pericardium protects and anchors the heart inside the chest. The outer layer, the parietal pericardium, and the inner layer, the serous pericardium, are lubricated by pericardial fluid. During contractions and movements of the lungs and diaphragm, the fluid lubricates the heart.
How does the Human Heart Appear?
According to the book ‘Anatomy of the Human Body,” the human heart is around the size of a large fist and weighs between 10 and 12 ounces (280 and 340 grams) in males and 8 to 10 ounces (230 and 280 grams) in women.
According to the National Institutes of Health, the human heart contains four chambers: two upper chambers (the atria) and two lower chambers (the ventricles). The “right heart” is made up of the right atrium and right ventricle, whereas the “left heart” is made up of the left atrium and left ventricle. A muscular wall referred to as the septum separates the two sides of the heart.
The Innards of a Human Heart
The outer wall of the heart is made up of three layers. The inner wall of the pericardium is formed by the outermost wall layer, or epicardium. The myocardium, or middle layer, houses the muscle that contracts the heart. According to the British Heart Foundation, the inner layer, or endocardium, borders the heart chambers.
The atrioventricular (AV) valves, which include the tricuspid and mitral valves, connect the upper and lower chambers of the heart. The right ventricle is separated from the pulmonary artery by the pulmonary semi-lunar valve, and the left ventricle is separated from the aorta by the aortic valve. The chordae tendineae, or heartstrings, connect the valves to the heart muscles.
The Heart’s External Structure
The pericardium is one of the first components that can be seen while looking at the exterior structure of the heart.
Pericardium
The pericardial cavity is a fluid-filled cavity that surrounds the human heart, which is located to the left of the chest. The pericardium is a membrane that lines and protects the pericardial cavity’s walls and lining.
The pericardium is a fibrous membrane that surrounds the heart and serves as an exterior covering. It protects the heart by secreting a serous fluid that lubricates the heart and prevents friction between the organs around it.
Apart from lubricating, the pericardium also aids in the stabilization of the heart and the maintenance of a hollow region in which the heart can expand when it is full. There are two distinct layers in the pericardium:
- The visceral layer covers the heart’s exterior.
- The pericardial cavity fluid is contained by the Parietal Layer, which creates a sac around the outside part of the heart.
Structure of the Heart Wall
The three layers of the heart wall are as follows:
- Epicardium – Epicardium is the heart’s outermost layer. It is made up of a thin, multi-layered membrane that lubricates and protects the outer part.
- Myocardium– The myocardium is a layer of muscle tissue that makes up the middle layer of the heart’s wall. It is responsible for the pumping motion and contributes to the thickness.
- Endocardium– The deepest layer of the heart, the endocardium, borders the inner chambers and covers the heart valves. It also stops blood from adhering to the inner walls of the vessels, preventing potentially dangerous blood clots.
How does the Human Heart Function?
The pulmonary circuit and the systemic circuit are the two paths via which the heart pumps blood.
According to the Journal of Biomedical Sciences, deoxygenated blood leaves the right ventricle of the heart via the pulmonary artery and travels to the lungs, while oxygenated blood returns to the left atrium via the pulmonary vein.
The oxygenated blood exits the heart and travels through the left ventricle to the aorta, where it enters the arteries and capillaries to supply oxygen to the body’s tissues. Deoxygenated blood returns to the right atrium of the heart via veins and the venae cavae.
Because the heart is a muscle, it need a constant supply of oxygen and nutrition, according to Phillips.
“Two sets of arteries supply oxygenated blood to feed the heart muscle after blood exits the heart through the aortic valve,” he explained. On one side of the aorta, the left major coronary artery feeds into the left anterior descending artery and the left circumflex artery. On the right side of the aorta, the right coronary artery branches out.
According to Phillips, a blockage of any of these arteries can result in a heart attack or injury to the heart muscle. A heart attack is not to be confused with cardiac arrest, which is a sudden loss of heart function caused by electrical abnormalities in the heart rhythm. He said that a heart attack can lead to cardiac arrest, but that the latter can also be caused by other issues.
The Beating of a Human Heart.
The alternating contractions and relaxations of the myocardium are responsible for the heart’s pumping function, or beating. Electrical impulses from a natural pacemaker, the sinoatrial, or S-A, node, located in the muscle of the right atrium, cause these contractions.
The two atria contract as a result of an impulse from the S-A node, driving blood into the ventricles. The atrioventricular, or A-V, node, located at the confluence of the two atria, controls the contraction of the ventricles. The ventricles relax after a contraction, and the pressure within them decreases. Blood flows into the atria once more, and an impulse from the S-A restarts the cycle. The cardiac cycle is the name for this procedure.
Diastole refers to the interval of relaxation. Systole refers to the duration of contraction. The lengthier of the two stages, diastole, allows the heart to rest between contractions. The rate of heartbeat varies inversely with the animal’s size in general. It averages 25 beats per minute in elephants and 1,000 in canaries.
The rate in humans decreases gradually from birth (when it averages 130) until adolescence, but somewhat increases in old age; the average adult rate is 70 beats per minute at rest. Exercise, emotional excitation, and fever cause a temporary spike in the rate, which then drops during sleep. The apex beat is a rhythmic pulsation felt on the chest that coincides with heartbeat. It is induced by the rounded and hardened ventricular wall exerting pressure on the chest wall at the start of systole.
Your heart will have beaten roughly 100,000 times by the end of the day (around 60 to 80 beats per minute). According to the Cleveland Clinic, this will pump about 1.5 gallons (about 6.8 liters) of blood each minute across the human body’s 60,000 miles (97,000 kilometers) of blood arteries.
The Heart’s Electrical Conduction
Pacemaker cells in the sinoatrial node regulate electrical conduction in the heart in healthy people. Electrical impulses travel from the sinoatrial node to the atrioventricular node and the bundle of His, then into the ventricles through the bundle branches.
Heart sounds are the rhythmic noises that accompany a heartbeat. The stethoscope normally produces two distinct sounds: a low, slightly prolonged “lub” (first sound) at the start of ventricular contraction, or systole, caused by closure of the mitral and tricuspid valves, and a sharper, higher-pitched “dup” (second sound) at the end of systole, caused by closure of the aortic and pulmonary valves.
A third faint, low-pitched sound, which coincides with early diastole and is assumed to be caused by ventricular wall vibrations, is occasionally detectable in normal hearts. Graphic methods indicate a fourth sound that occurs during diastole but is normally inaudible in normal persons; it is thought to be caused by atrial contraction and the impact of blood ejected from the atria against the ventricular wall.
A physician can hear cardiac “murmurs” as subtle swishing or hissing sounds that follow the regular sounds of heart activity. Murmurs can suggest the presence of a significant heart disease by indicating that blood is escaping through an improperly closed valve. Coronary heart disease is a primary cause of death globally, with an insufficient supply of oxygen-rich blood given to the myocardium due to the constriction or blockage of a coronary artery by fatty plaques.
Human Heart Facts
- Every day, the heart pumps approximately 6,000-7,500 liters of blood throughout the body.
- The heart is in the middle of the chest, pointing slightly to the left.
- The heart beats 100,000 times every day on average, equating to about 3 billion beats in a lifetime.
- The typical male heart weighs between 280 and 340 grams (10 to 12 ounces). It weighs roughly 230 to 280 grams in females (8 to 10 ounces).
- An adult’s heart beats 60 to 100 times per minute, whereas a newborn baby’s heart beats 90 to 190 times per minute.