The physiology of the heart is a concept that any doctor should understand. This knowledge is very important in clinical practice and allows us to understand the normal functioning of the heart, in order, if necessary, to compare the indicators in the event of a pathology of the heart muscle.
What are the functions of the heart muscle?
First you need 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 pump blood from a vein into an artery at a rhythmic pace, 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 the myocardium with a pump. Only, in contrast to this mechanism, the heart is distinguished by high performance and speed, smoothness of transient processes and a margin of safety. The tissues in the heart are constantly being renewed.
Circulation, its components
To understand the physiology of the circulation of the heart, one should understand what components existcirculation.
The circulatory system consists of four elements: the heart muscle, blood vessels, regulation mechanism and organs that are blood depots. This system is a constituent component of the cardiovascular system (the lymphatic system is also included in the cardiovascular system).
Due to the presence of the last system, the blood moves 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 that do not allow blood to flow back, and also the isolation. In addition, the elasticity of the walls of the vessels, the negative intrapleural pressure, due to which the blood "sticks" and more easily returns to the heart through the veins, as well as the gravity of the blood, have an effect. Due to the contraction of the skeletal muscles, the blood is pushed, breathing becomes more frequent and deep, and this leads to the fact that the pleural pressure decreases, the activity of proprioreceptors increases, increasing the excitability in the central nervous system and the frequency of contractions of the heart muscle.
circulation circles
There are two circles of blood circulation in the human body: large and small. Together with the heart, they form a closed system. Understanding the physiology of the heart and blood vessels, one should understand how blood circulates through them.
Back in 1553, M. Servet described the pulmonary circulation. It originates from the right ventricle and passes into the pulmonarytrunk and then to the lungs. It is in the lungs that gas exchange takes place, then the blood passes through the veins of the lung and arrives in the left atrium. Due to this, the blood is enriched with oxygen. Further, saturated with oxygen, it flows into the left ventricle, in which a large circle originates.
The systemic circulation became known to mankind in 1685, and W. Harvey discovered it. According to the basics of the physiology of the heart and circulatory system, oxygen-enriched blood moves through the aorta to small vessels through which it is transported to organs and tissues. Gas exchange takes place in them.
Also in the human body there are superior and inferior vena cava that flow into the right atrium. They move venous blood, which contains little oxygen. It should also be noted that in a large circle, arterial blood passes through the arteries, and venous blood through the veins. In the small circle, the opposite is true.
Physiology of the heart and its conduction system
Now let's look at the physiology of the heart in more detail. The myocardium is a striated muscle tissue that is made up of special individual cells called cardiomyocytes. These cells are interconnected by nexuses and form the muscle fiber of the heart. The myocardium is not an anatomically complete organ, but works like a syncytium. Nexuses quickly conduct excitation from one cell to another.
According to the physiology of the structure of the heart, two types of muscles are distinguished in it according to their characteristicsfunctioning, and this is atypical muscles and an active myocardium, which consists of muscle fibers characterized by a fairly developed striated transverse striation.
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 striated muscles to respond to nerve impulses. It is not as large as that of similar skeletal-type muscles. The cells of the active myocardium have a large membrane potential, which causes them to react only to significant irritation.
The physiology of the conduction system of the heart is such that due to the fact that the conduction velocity of excitation is small, the atria and ventricles begin to contract alternately.
Refractoriness, on the contrary, is characterized by 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 contracts in a single pattern, as well as according to the law of "either all or nothing."
Atypical muscle fibers have weak contractility properties, but at the same time such fibers have a high level of metabolic processes. Here mitochondria come to the rescue, the function of which is close to the functions of nerve fibers. Mitichondria conduct nerve impulses and provide generation. conduction system of the heartis formed precisely due to the atypical myocardium.
Atypical myocardium and its main properties
- The level of excitability of atypical myocardium is less than that of skeletal muscles, but at the same time it is greater than that characteristic of contractile myocardium. Nerve impulses are generated here.
- The conductivity of the atypical myocardium is also lower than that of the skeletal muscles, but at the same time, on the contrary, it is higher than that of the contractile myocardium.
- In the long refractory period, an action potential and calcium ions arise here.
- Atypical myocardium is characterized by little lability and little ability to contract.
- Cells independently generate a nerve impulse (automation).
Atypical muscle conduction system
Studying the physiology of the heart, it should be mentioned that the conductive system of atypical muscles consists of a sinoatrial node, located on the right on the back wall, on the border separating the superior and inferior vena cava, an atrioventricular node that sends impulses to the ventricles (located below interatrial septum), bundle of His (passes through the atriogastric septum into the ventricle). Another component of the atypical muscle is the Purkinje fiber, the branches of which are given to cardiomyocytes.
There are also other structures here: the bundles of Kent and Maygail (the former go along the lateral edge of the heart muscle and connect the ventricles and the atrium, and the second is located below the atrioventricular node and transmits signals to the ventricles without affecting the bundles of His). Thanks to these structures,If the atrioventricular node is turned off, the transmission of impulses is ensured, which entail the receipt of unnecessary information in case of illness and cause additional contraction of the heart muscle.
What is the cardiac 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. The conduction system of the heart helps organize this process.
As the heart beats rhythmically, blood is periodically expelled into the circulatory system. The cardiac cycle is the period when the heart muscle contracts and relaxes. This cycle consists of ventricular and atrial systoles, as well as pauses. With atrial systole, the pressure rises from 1-2 mmHg to 6-9 and up to 8-9 mmHg in the right and left atria, respectively. As a result, blood enters the ventricles through the atrioventricular openings. When the pressure in the left and right ventricles reaches 65 and 5-12 millimeters of mercury, respectively, blood is expelled and ventricular diastole occurs, causing a rapid drop in pressure in the ventricles. This increases the pressure in large vessels, which leads to the slamming of the semilunar valves. When the pressure in the ventricles drops to zero, the cusp-type valves open and the ventricles fill up. This phase completes the diastole.
How long are the phases of the heart muscle cycle? This question is of interest to many people who are interested inphysiology of cardiac regulation. Only one thing can be said: their duration is not constant. Here, the decisive factor is the frequency of the rhythm of the heart muscle. If the functions of the heart are upset, then with the same rhythm, the duration of the phase may vary.
External signs of heart activity
For the heart muscle is characterized by external signs of its work. These include:
- Top push.
- Electrical phenomena.
- Heart sounds.
Minute and systolic volumes of the myocardium are also indicators of its work.
At the time when ventricular systole occurs, the heart makes a turn from left to right, changing from its original ellipsoidal shape to a round 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 is how the apex beat occurs.
As for the physiology of heart sounds, they should be mentioned separately. Tones are sound phenomena that occur during the work of the heart muscle. In total, two tones are distinguished in the work of the heart. The first tone - aka systolic - which is characteristic of the atrioventricular valves. The second tone - diastolic - occurs at the moment of closing the valves of the pulmonary trunk and aorta. The first tone is long, deaf and lower than 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 heart fiber and the law of the rhythm of the heart muscle.
The first (O. Frank - E. Starling) says that whatthe more stretched the muscle fiber, the stronger will be its further contraction. The level of stretch is affected by the amount of blood accumulated in the heart during diastole. The larger the volume, the more vigorous the contraction will be during systole.
The second (F. Bainbridge) says that when blood pressure rises in the vena cava (at the mouths), 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 as a self-regulation mechanism that helps to adapt the work of the heart muscle to various conditions of existence.
Considering the physiology of the heart briefly, one cannot fail to mention that certain hormones, mediators and mineral s alts (electrolytes) also affect the work of this organ. For example, acetylchopine (a mediator) and an excess of potassium ions weaken cardiac activity, making the rhythm rare, as a result of which even cardiac arrest may occur. And a large number of calcium ions, adrenaline and norepinephrine, on the contrary, contribute to increased cardiac activity and its increase. Adrenaline also dilates the coronary vessels, which improves myocardial nutrition.
Mechanisms of regulation of cardiac activity
According to the body's needs for oxygen and nutrition, the frequency and strength of contractions of the heart muscle may vary. The activity of the heart is regulated by special neurohumoral mechanisms.
But the heart also has its own regulation mechanisms. Some of them are directly related toproperties of myocardial fibers. There is a relationship between the force of fiber contraction and the magnitude of the rhythm of the heart muscle, as well as the relationship between the energy of contraction and the degree of stretching of the fiber during diastole.
The elastic property of myocardial fibers, which does not appear in the process of active conjugation, is called passive. The support-trophic skeleton, as well as actomyosin bridges, which are also located in an inactive muscle, are considered to be carriers of elastic properties. 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, then bridging stiffness increases.
The cardiovascular system is a complex process. Any failure can lead to negative consequences. See your doctor regularly and follow his advice. After all, it is much easier to prevent a disease than to treat it by spending money on expensive medicines.
