Human Heart Anatomy: The structure of the Heart, Anatomy of Tissues and Cells, Chambers and Valves
The heart is one of the most romantic and sensual organs of the human body. In many cultures, it is considered the seat of the soul, the place where attachment and love originate. However, from an anatomical point of view, the picture looks more prosaic. A healthy heart is a strong muscular organ about the size of its owner’s fist. The work of the heart muscle does not stop for a second from the moment a person is born and until death. By pumping blood, the heart supplies oxygen to all organs and tissues helps to remove decay products and performs part of the body’s cleansing functions. Let’s talk about the features of the anatomical structure of this amazing organ.
Human Heart Anatomy: Historical and Medical Excursion
Cardiology – the science that studies the structure of the heart and blood vessels – was singled out as a separate branch of anatomy back in 1628, when Harvey identified and presented the laws of human blood circulation to the medical community. He demonstrated how the heart, like a pump, pushes blood along the vascular bed in a strictly defined direction, supplying organs with nutrients and oxygen.
The heart is located in the thoracic region of a person, slightly to the left of the central axis. The shape of the organ can vary depending on the individual characteristics of the structure of the body, age, constitution, sex, and other factors. So, in stout, short people, the heart is more rounded than in thin and tall people. It is believed that its shape roughly matches the circumference of a tightly clenched fist, and its weight ranges from 210 grams for women to 380 grams for men.
The volume of blood pumped by the heart muscle per day is approximately 7-10 thousand liters, and this work is carried out continuously! The amount of blood can vary due to physical and psychological conditions. Under stress, when the body needs oxygen, the load on the heart increases significantly: at such moments it can move blood at a speed of up to 30 liters per minute, restoring the body’s reserves. Nevertheless, the organ is not able to constantly work for wear and tear: at rest moments, the blood flow slows down to 5 liters per minute, and the muscle cells that form the heart rest and recover.
The structure of the heart: anatomy of tissues and cells
The heart is classified as a muscle, however, it is erroneous to believe that it consists of only muscle fibers. The wall of the heart includes three layers, each of which has its own characteristics:
1. The endocardium is the inner membrane that lines the surface of the chambers. It is represented by a balanced symbiosis of elastic connective and smooth muscle cells. It is almost impossible to outline the clear boundaries of the endocardium: when it becomes thinner, it smoothly passes into the adjacent blood vessels, and in especially thin places of the atria it grows together directly with the epicardium, bypassing the middle, most extensive layer – the myocardium.
2. The myocardium is the muscle frame of the heart. Several layers of striated muscle tissue are connected in such a way as to quickly and purposefully respond to arousal that occurs in one area and passes through the entire organ, pushing blood into the vascular bed. In addition to muscle cells, the myocardium contains P-cells that is capable of transmitting a nerve impulse. The degree of development of the myocardium in certain areas depends on the volume of functions assigned to it. For example, the myocardium in the atrium is much thinner than the ventricular.
In the same layer is the annulus fibrosus, which anatomically separates the atria and ventricles. This feature allows the chambers to contract alternately, pushing blood in a strictly defined direction.
3. Epicardium – the superficial layer of the heart wall. The serous membrane, formed by the epithelial and connective tissue, is an intermediate link between the organ and the heart sac – the pericardium. The thin transparent structure protects the heart from increased friction and facilitates the interaction of the muscle layer with adjacent tissues.
Outside, the heart is surrounded by the pericardium – a mucous membrane, which is otherwise called a heart bag. It consists of two sheets – the outer one, facing the diaphragm, and the inner one, tightly fitting to the heart. Between them is a fluid-filled cavity that reduces friction during heartbeats.
Chambers and valves
The heart cavity is divided into 4 sections:
the right atrium and ventricle filled with venous blood;
left atrium and ventricle with arterial blood.
The right and left halves are separated by a dense septum, which prevents the two types of blood from mixing and maintains unilateral blood flow. True, this feature has one small exception: in children in the womb, there is an oval window in the septum, through which blood is mixed in the heart cavity. Normally, at birth, this hole is overgrown and the cardiovascular system functions as in an adult. Incomplete closure of the oval window is considered a serious pathology and requires surgical intervention.
Between the atria and the ventricles, the mitral and tricuspid valves are located in pairs, which are held in place by tendon threads. Synchronous contraction of the valves allows unilateral blood flow, preventing mixing of arterial and venous flow.
The largest artery of the bloodstream, the aorta, departs from the left ventricle, and the pulmonary trunk originates in the right ventricle. For the blood to move exclusively in one direction, there are semilunar valves between the chambers of the heart and the arteries.
The blood flow is provided by the venous network. The inferior vena cava and one superior vena cava flow into the right atrium, and the pulmonary veins, respectively, into the left.
Anatomical features of the human heart
Since the supply of oxygen and nutrients to other organs directly depends on the normal functioning of the heart, it must ideally adapt to changing environmental conditions, working in a different frequency range. Such variability is possible due to the anatomical and physiological characteristics of the heart muscle:
Autonomy implies complete independence from the central nervous system. The heart contracts from impulses produced by itself, so the work of the central nervous system does not affect the heart rate in any way.
Conduction consists of the transmission of the generated impulse along the chain to other parts and cells of the heart.
Excitability implies an instant response to changes in and out of the body.
Contractility, that is, the force of contraction of the fibers, which is directly proportional to their length.
Refractoriness is the period during which myocardial tissue is not excitable.
Any failure in this system can lead to a sharp and uncontrolled change in heart rate, asynchrony of heart contractions, up to fibrillation, and death.
Phases of the heart
To continuously move blood through the vessels, the heart must contract. Based on the stage of contraction, there are 3 phases of the cardiac cycle:
Atrial systole, during which blood flows from the atria to the ventricles. In order not to interfere with the current, the mitral and tricuspid valves open at this moment, and the semilunar ones, on the contrary, close.
Ventricular systole involves the movement of blood further to the arteries through the open semilunar valves. This closes the flap valves.
Diastole involves filling the atria with venous blood through open leaflet valves.
Each heartbeat lasts about one second, but with active physical work or during stress, the speed of the impulses increases by shortening the duration of diastole. During good rest, sleep, or meditation, heart contractions, on the contrary, slow down, diastole becomes longer, so the body is more actively cleared of metabolites.
Anatomy of the coronary system
To fully perform the assigned functions, the heart must not only pump blood throughout the body but also receive nutrients from the bloodstream itself. The aortic system, which carries blood to the muscle fibers of the heart, is called the coronary system and includes two arteries – left and right. Both of them move away from the aorta and, moving in the opposite direction, saturate the heart cells with useful substances and oxygen contained in the blood.
Cardiac muscle conduction system
Continuous contraction of the heart is achieved due to its autonomous work. An electrical impulse that triggers the process of contraction of muscle fibers is generated in the sinus node of the right atrium at a frequency of 50–80 pulses per minute. Along the nerve fibers of the atrioventricular node, it is transmitted to the interventricular septum, then along with large bundles (His legs) to the walls of the ventricles, and then passes to the smaller nerve fibers of Purkinje. Thanks to this, the heart muscle can progressively contract, pushing blood from the internal cavity into the vascular bed.
Lifestyle and heart health
The state of the whole organism directly depends on the full functioning of the heart, therefore the goal of any sane person is to maintain the health of the cardiovascular system. In order not to face cardiac pathologies, you should try to exclude or at least minimize provoking factors:
smoking, consumption of alcoholic and narcotic substances;
irrational diet, abuse of fatty, fried, salty foods;
high cholesterol levels;
super-intense physical activity;
a state of enduring stress, nervous exhaustion, and overwork.
p style=”background-color: white; box-sizing: border-box; color: #444444; font-family: "PT Serif", Georgia, Cambria, "Times New Roman", Times, serif; font-size: 18px; line-height: var(–line-article); margin: 0px 0px 24px; overflow-wrap: break-word; text-align: justify;”>Knowing a little more about the anatomy of the human heart, try to make an effort on yourself by giving up destructive habits. Change your life for the better, and then your heart will work like a clock.