The human heart is a vital organ, without which the life is not possible. Many of us wonder how the human heart is created, how it functions and what are some of the most known medical conditions that affect it? In general, various medical conditions that affect the structures of the heart are serious, sometimes even life threatening and require proper medical diagnosis and immediate medical treatment.
What is the anatomy and structure of the human heart?
The human heart is a muscular organ located on the left side of the body inside of the rib cage. It has the size of a fist and the main role of the heart is to circulate the blood. This means that it works as a pump that pumps the blood into the circulatory system. The hart located just posterior the sternum, has its base located along the body’s midline, while its apex is pointing toward the left side. It has the shape of an upside down pear, with a weight between 7-15 ounces. The heart continues to beat from the time we are born, until the time we die approximately 72 times per minute.
The human heart consists of four chambers: two ventricles and two atria. There are the left and right ventricle and the left and right atrium. The ventricles are located in the lower part of the heart, while the atria are located in the upper part of the heart.
The blood rich with carbon dioxide enters the heart through the right atria, from where it travels into the right ventricle and then to the lungs through the pulmonary artery. The blood rich with oxygen from the lungs enters the heart through the left ventricle, from where it travels into the aorta and then into the circulatory system, which distributes it all over the body.
The human heart has four valves, which have the function to stop the blood from traveling backwards. These valves are:
• Pulmonary valve – has the function of allowing the blood travel from the right ventricle to the pulmonary artery. It is located between these two structures of the human heart.
• Tricuspid valve – has the function of allowing the blood travel from the right atrium to the right ventricle. It is located between these two structures of the human heart.
• Mitral valve – has the function of allowing the blood travel from the left atrium to the left ventricle. It is located between these two structures of the human heart.
• Aortic valve – has the function of allowing the blood to travel from the left ventricle to the aorta. It is located between these two structures of the human heart.
Conductive System of the Heart
The human heart has also a conduction system, which allows her to have her own rhythm and conduct signal which are necessary to maintain and coordinate its rhythm. 1% of all the muscle cells found in the heart are responsible for the formation of the conduction system. The conduction system of the heart is also known as a pacemaker. The signal starts in the sinoatrial SA node, from where it travels to the atrioventricular AV node, and later on to the atrioventricular bundle. The atrioventricular bundle consists of strands of conductive tissue which splits into the left and right branches. These branches continue to run and conduct the signal through the septum, until it reaches the apex of the heart. The sinoatrial node is located in the wall of the right atrium, just below the superior vena cava, while the atrioventricular node is located in the right atrium, in the inferior portion of the interatrial septum. The signal conducted into the ventricle walls, stimulate the cardiac muscle cells to contract and pump out blood in a rhythmic way.
Blood Vessels of the Heart
The human heart and the circulatory system also consist from different blood vessels: the arteries and the veins. The function of the arteries is to take oxygenated blood from the heart and transport it all over the human body to the capillaries. The function of the veins is to take the blood which is rich in carbon dioxide from the capillaries and transport in to the heart, and later to the lungs where it gets oxygenated again, through the gas exchange in the lungs while breathing air in and out of the lungs.
The wall of the human heart consists of three layers:
• Endocardium, and
Myocardium is the middle layer of the heart’s wall which contains all the cardiac muscle tissue. It is a thick mass of muscle cells, which plays a great role in the process of pumping blood from the heart to the circulatory system.
Epicardium is the outer layer of the heart’s wall. Basically it is a very thin layer of serous membrane which lubricates the heart and protects it from the outer side of the heart.
Endocardium is the layer on the inner surface of the heart’s wall, just beneath the myocardium. It is usually a very smooth layer, and the main role of it is to prevent the blood from sticking to its walls. Endocardium plays also a great role in the process of preventing blood clots to from.
The Cardiac Cycle
The human heart functions in a cyclic rhythm. At any given time the human heart and its chambers could be either in systole or diastole. During systole the cardiac muscle tissue gets contracted and pushed the blood out of the chamber, while during diastole the cardiac muscle tissue gets relaxed and allows the blood to get into the chambers.
The cardiac cycle is characterized by three phases:
• atrial systole,
• ventricular systole, and
During atrial systole the atria are contracted and the blood gets pushed into the ventricles. The atrioventricular valves are open during atrial systole, while the semilunar valves are closed in order to prevent the blood flow backwards. During ventricular systole the ventricles are contracted and the blood gets pushed into the aorta and pulmonary trunk. The semilunar valves are open due to pressure, while the atrioventricular valves remain closed. When the atria are in systole, the ventricles are in diastole. The relaxation phase is characterized by a relaxation of all four chambers of the heart, which are in diastole, allowing the blood to enter the heart from the veins. During repolarization the cardiac muscle cells are repolarized and they prepare for the next cardiac cycle.
Medical Conditions and Diseases that affect the Heart
The human heart is affected by various medical conditions and diseases. These medical conditions and diseases include:
• Arrhythmia – is an abnormal or irregular rhythm of the heart due to a change in the conduction system. They vary from non – harmful to life threatening arrhythmias.
• Heart Murmur – is an abnormal sound of the heart, heard by your doctor with the help of a stethoscope. They are usually benign. However, in some cases a heart murmur is a sign of a heart disease.
• Heart Valve Disease – any of the four valves of the heart can be affected. Impaired function of the heart valves will interfere with its ability to pump up blood correctly. During each cardiac cycle, the heart valves that do not function normally, allow the blood to flow backwards. If not diagnosed and treated on time, heart valve disease leads to congestive heart failure.
• Myocarditis – is the inflammation of myocard. Myocarditis is usually caused by a viral infection.
• Coronary Artery Disease – is a condition characterized by a formation of cholesterol plaques in the arteries that supply the heart with blood. These plaques are formed due to the cholesterol being clogged and buildup. Narrow arteries may lead to a development of blood clots, a condition known as heart attack.
• Myocardial Infarction – is also known as heart attack. It is a condition when there is a sudden blockage of the coronary arteries which supply the heart with blood. Due to the blockage the amount of oxygen in the heart drops, leading to infarction and death of the heart muscle. Depending from the amount of the artery blocked, from its location and from the collateral arteries, myocardial infarction can be fatal.
• Congestive Heart Failure – is characterized by a stiff and weak heart, which is not able to pump enough blood into the rest of the body.
• Cardiac Arrest – is a heart failure characterized by a sudden loss of the heart’s function.
• Sudden Cardiac Death – is considered when there is a sudden loss of the heart function.