Physiology of the human heart

The physiology of the heart is a concept in which any physician should understand. This knowledge is very important in clinical practice and allows you to understand the work of the heart in the norm, so that if necessary, compare the indicators when the pathology of the cardiac muscle works.

What are the functions of the heart muscle?

To begin with, it is necessary to understand what are the functions of the heart, the physiology of this organ will then be more understandable. So, the main function of the heart muscle is to inject blood from the vein into the artery at a rhythmic rate, at which a pressure gradient is created, which entails its uninterrupted movement. That is, the function of the heart is to provide blood circulation with a blood message of kinetic energy. Many people associate myocardium with a pump. Only, in contrast to this mechanism, the heart is characterized by high productivity and speed, smoothness of transient processes and margin of safety. The tissues are constantly renewed in the heart.

Blood circulation, its components

To understand the physiology of the blood circulation of the heart, it is necessary to understand what are the components of the circulation.

The circulatory system consists of four elements: the heart muscle, the blood vessels, the regulation mechanism and the organs that are blood depots. This system is a component of the cardiovascular system (the cardiovascular system also includes the lymphatic system).

Thanks to the presence of the latter system, blood flows smoothly through the vessels. But here factors such as: the work of the heart muscle as a "pump", the difference in the level of pressure in the cardiovascular system, the valves of the heart and veins, which do not allow blood to flow back, and also closure. In addition, the elasticity of the vessel walls, the negative pressure of the intrapleural, thanks to which the blood "sucks" and more easily returns to the heart through the veins, as well as the gravity of the blood, exert influence. Owing to the reduction of skeletal muscles, blood is pushed, breathing becomes more frequent and deep, and this leads to the fact that pleural pressure decreases, the activity of proprioceptors increases, increasing excitability in the central nervous system and the frequency of contractions of the heart muscle.

Circles of blood circulation

In the human body, there are two circles of blood circulation: large and small. Together with the heart they form a closed-type system. Understanding the physiology of the heart and blood vessels, one should understand how the blood circulates through them.

As far back as 1553 M. Servetus described a small circle of blood circulation. It originates from the right ventricle and passes into the pulmonary trunk and then into the lungs. It is in the lungs that gas exchange takes place, then the blood passes through the veins of the lung and arrives at the left atrium. Thanks to this, oxygen is enriched with blood. Further, saturated with oxygen, it flows into the left ventricle, in which a large circle originates.

About the great circle of blood circulation to mankind became known in 1685, and opened it to W. Garvey. According to the basics of the physiology of the heart and the circulatory system, the blood, which is enriched with oxygen, moves along the aorta, heading for small vessels through which it is transferred to organs and tissues. Gas exchange occurs in them.

Also in the human body is the upper and lower hollow veins that flow into the right atrium. Venous blood moves through them, which contains a little oxygen. It should also be noted that, on a large scale, arterial blood passes through the arteries, and the venous blood passes through the veins. In the small circle, the opposite is true.

The physiology of the heart and its conduction system

Now let's look into the physiology of the heart in more detail. Myocardium is a cross-striated muscle tissue, which consists of special individual cells called cardiomyocytes. These cells are joined together by nexus and form a muscle fiber of the heart. Myocardium is not an anatomically integral organ, but it works as syncytium. Nexus quickly excite from one cell to another.

According to the physiology of the heart structure, two types of muscles are distinguished in it according to the features of functioning, and this is atypical musculature and an active myocardium, which consists of muscle fibers characterized by a fairly developed strip-transverse striation.

The basic physiological properties of the myocardium

The physiology of the heart suggests that this organ has several physiological properties. And this:

• Excitability.
• Conductivity and low lability.
• Contractility and refractoriness.

As for excitability, it is the ability of the striated muscle to respond to nerve impulses. It is not as large as that of similar skeletal muscles. Cells of an active myocardium have a large membrane potential, which causes their reaction only to considerable irritation.

The physiology of the heart system is such that, because the conducting excitation speed is small, the atria and ventricles begin to contract alternately.

Refractory, on the contrary, is inherent in a long period, which has a connection with the period of action. Due to the fact that the refractory period is long, the heart muscle is reduced in a single type, and also according to the law "either all or nothing."

Atypical muscle fibers have weakly expressed contractility properties, but such fibers have a high level of metabolic processes. Here, help comes mitichondria, whose function is close to the functions of nerve fibers. Mitichondria conduct nerve impulses and provide generation. Conductive system of the heart is formed precisely due to atypical myocardium.

Atypical myocardium and its basic properties

• The level of excitability of the atypical myocardium is less than that of the muscles of the skeleton, but it is greater than that characteristic of the contractile myocardium. Nerve impulses are generated here.
• The conductivity of the atypical myocardium is also lower than that of the muscles of the skeleton, but it is, on the contrary, higher than the contractile myocardium.
• In the long refractory period, the action potential and calcium ions appear here.
• Atypical myocardium is characterized by a small lability and a small ability to contract.
• The cells themselves generate a nerve impulse (automata).

Conductive system of atypical muscles

Studying the physiology of the work of the heart, it should be mentioned that the conducting system of atypical muscles consists of a sinoatrial node located on the right at the rear wall, on the border separating the upper and lower hollow veins, the atrioventricular node, sending the impulses to the ventricles (located at the bottom of the interatrial septum) Gisa (passes through the atrioventricular septum into the ventricle). Another component of the atypical muscle is the Purkinje fiber, the branches of which are given to the cardiomyocytes.

Also there are other structures: the bundles of Kent and Meigail (the first go along the lateral edge of the heart muscle and connect the ventricles and the atrium, and the second is located at the bottom of the atrioventricular node and transmits signals to the ventricles without touching the bundles of His). It is thanks to these structures, in the event that the atrioventricular node is turned off, impulses are transmitted, which entail the inflow of unnecessary information in the disease and cause an additional reduction in the cardiac muscle.

What is the heart cycle?

The physiology of the functions of the heart is such that the contraction of the heart muscle can be called a well-organized periodic process. Organizing this process helps the conduction system of the heart.

Since the heart rhythmically contracts, the blood is periodically expelled into the circulatory system. A heart cycle is the period when the heart muscle contracts and relaxes. This cycle consists of ventricular and atrial systole, as well as pauses. With atrial systole, the pressure rises from 1-2 millimeters of mercury to 6-9 and to 8-9 millimeters of mercury in the right and left atriums, respectively. As a result, blood flows to the ventricles through the atrioventricular orifices. When the pressure in the left and right ventricles reaches 65 and 5-12 millimeters of mercury, respectively, the blood is expelled and a ventricular diastole arises that causes a rapid drop in pressure in the ventricles. This increases the pressure in the large vessels, which leads to the collapse of the semilunar valves. When the pressure in the ventricles drops to zero, the valvular type valves will open, and the phase will begin when the ventricles are filled. This phase completes the diastole.

What is the duration of the phases of the heart muscle cycle? This question interests many people who are interested in the physiology of heart regulation. One can say only one thing: their duration is a variable quantity. Here the frequency of the rhythm of the heart muscle is the decisive factor. If the functions of the heart are upset, then with the same rhythm, the duration of the phase may differ.

External signs of heart activity

The heart muscle is characterized by external signs of its work. They include:

• Push the tip.
• Electrical phenomena.
• Heart tones.

Minute and systolic volumes of the myocardium are also indicators of his work.

At the time when the ventricle sits, the heart turns from left to right, changing the original ellipsoidal shape to a rounded one. In this case, the upper part of the heart muscle rises and presses on the chest in the V-shaped intercostal space on the left side. This gives rise to apical push.

As for the physiology of heart sounds, they should be mentioned separately. Tones are sound phenomena that occur during the operation of the heart muscle. In total, two tones are singled out in the work of the heart. The first tone is systolic, which is characteristic of the atrioventricular valves. The second tone - diastolic - occurs when the valves of the pulmonary trunk and aorta are closed. The first tone is long, dull and below the second. The second tone is high and short.

Laws of cardiac activity

In total, two laws of cardiac activity can be distinguished: the law of the cardiac fiber and the law of the rhythm of the heart muscle.

The first (O. Frank - E. Starling) says that the more stretched the muscle fiber, the stronger will be its further reduction. The level of tension is affected by the volume of blood accumulated in the heart during diastole. The larger the volume, the more vigorous the reduction will be during systole.

The second (F. Bainbridge) says that when blood pressure in the hollow veins (in the mouths) increases, there is an increase in the frequency and strength of muscle contractions at the reflex level.

Both of these laws work simultaneously. They are referred to the mechanism of self-regulation, which helps to adapt the work of the heart muscle to various conditions of existence.

Considering the physiology of the heart briefly, one can not help mentioning that some hormones, mediators and mineral salts (electrolytes) also influence the work of this body. For example, acetylchopine (a mediator) and an excess of potassium ions weaken the heart activity, making the rhythm rare, so that even a cardiac arrest can occur. And a large number of calcium ions, adrenaline and norepinephrine, on the contrary, contribute to increased cardiac activity and its frequency. Adrenaline, in addition, expands the coronary vessels, so that myocardial nutrition improves.

Mechanisms of regulation of cardiac activity

In accordance with the needs of the body in oxygen and nutrition, the frequency and strength of the contractions of the heart muscle can vary. The activity of the heart is regulated by special neurohumoral mechanisms.

But the heart has its own mechanisms for regulating activity. Some of them are directly related to the properties that myocardial fibers possess. Here, a relationship is observed between the force of fiber contraction and the magnitude of the rhythm of the heart muscle, as well as the dependence of the energy of contraction and the degree of fiber stretching during diastole.

The elastic property of the fibers of the myocardium, which manifests itself not in the process of active conjugation, is called passive. Bearers of elastic properties are considered the supporting-trophic skeleton, as well as the actomyosin bridges, which are located in the inactive muscle. The skeleton has a very positive effect on the elasticity of the myocardium when sclerotic processes occur.

If a person has ischemic contracture or inflammatory diseases of the myocardium, the bridging rigidity rises.

The work of the cardiovascular system is a complex process. Any failure can lead to negative consequences. Regularly consult a doctor and do not neglect his recommendations. After all, preventing the disease is much easier than treating it, spending money on expensive medications.