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, so that, if necessary, we can compare the indicators when a pathology of the heart muscle occurs.
What are the functions of the heart muscle?
First you need to understand what the functions of the heart are, 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 the blood flow of kinetic energy. Many people associate myocardium with a pump. Only, unlike this mechanism, the heart is characterized by high performance and speed, smooth transition processes and safety margin. The heart is constantly updated tissue.
Blood circulation, its components
To understand the physiology of the blood circulation of the heart, you should understand what are the components of blood circulation.
The circulatory system consists of four elements: the heart muscle, blood vessels, the regulatory mechanism, and the organs that are the blood depots. This system is an integral component of the cardiovascular system (the lymphatic system also enters the cardiovascular system).
Due to the presence of the latter system, 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 prevent blood from flowing back, and also the closure influence it. In addition, the elasticity of the walls of the vessels, the negative intrapleural pressure, due to which the blood “sucks” and more easily returns to the heart through the veins, as well as the force of gravity of the blood, have an effect. Due to the contraction 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 proprioreceptors increases, increasing the excitability in the central nervous system and the frequency of contractions of the heart muscle.
Circulatory Circles
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, it should be understood how the blood circulates through them.
As early as 1553, M. Servet described the pulmonary 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 is exchanged, then blood passes through the veins of the lung and arrives in the left atrium. Due to this, blood enriches with oxygen. Further, saturated with oxygen, it flows into the left ventricle, in which a large circle originates.
Humanity became aware of a large circle of blood circulation in 1685, and it was discovered by W. Harvey. According to the basics of the physiology of the heart and circulatory system, 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 takes place in them.
Also in the human body there is an upper and lower vena cava that flows into the right atrium. Venous blood moves along them, which contains a little oxygen. It should also be noted that in a large circle, arterial blood passes through the arteries, and venous blood passes through the veins. In a small circle, the opposite is true.
Physiology of the heart and its conducting system
Now let's look at the physiology of the heart in more detail. Myocardium is a striated muscle tissue that consists of special single cells called cardiomyocytes. These cells are connected by nexuses and form a muscle fiber of the heart. The myocardium is not an anatomically holistic organ, but works like syncytium. Nexuses quickly carry out excitement 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 the features of functioning, and this is the atypical muscles and the acting myocardium, which consists of muscle fibers characterized by a fairly developed striated-transverse striation.
The main 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 muscles. The cells of the acting myocardium are characterized by a large value of the membrane potential, which causes their reaction only to significant irritation.
The physiology of the cardiac system is such that due to the fact that the conductive excitation rate is small, the atria and ventricles begin to contract alternately.
Refractoriness, 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 contracts in a single type, and also according to the law "either all or nothing."
Atypical muscle fibers have mild contractility properties, but at the same time, these fibers have a high level of metabolic processes. Here mitichondria come to the rescue, whose function is close to the functions of nerve fibers. Mitichondria conduct nerve impulses and provide generation. The conduction system of the heart is formed precisely thanks to the atypical myocardium.
Atypical myocardium and its main properties
- The level of excitability of the atypical myocardium is less than that of the skeleton muscles, but it is more 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 skeleton muscles, but at the same time, on the contrary, is higher than that of the contractile myocardium.
- In the long refractory period, the action potential and calcium ions arise here.
- Atypical myocardium is characterized by a small lability and a small ability to contract.
- Cells independently generate a nerve impulse (automatic).
Conducting system of atypical muscles
Studying the physiology of the work of the heart, it should be mentioned that the conduction system of the atypical muscles consists of the sinoatrial node located on the right side on the back wall, at the border separating the superior and inferior vena cava, the atrioventricular node that sends impulses to the ventricles (located below the atrial septum), Gisa (passes through the atrio-gastric septum into the ventricle). Another component of the atypical muscle is the Purkinje fiber, whose branches are given to cardiomyocytes.
There are also other structures here: Kent and Meigail bundles (the first go along the lateral edge of the heart muscle and connect the ventricles and atrium, and the second is located at the bottom of the atrioventricular node and transmits signals to the ventricles without affecting the bundles of His). It is thanks to these structures, in the event that the atrioventricular node is turned off, the transmission of impulses is provided, which entail the arrival of unnecessary information in case of illness and cause additional contraction of the heart muscle.
What is the heart cycle?
The physiology of heart functions is such that contraction of the heart muscle can be called a well-organized periodic process. The conduction system of the heart helps to organize this process.
Since the heart is rhythmically contracting, the 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 systoles of the ventricles and atria, as well as a pause. With atrial systole, the pressure rises from 1-2 millimeters of mercury to 6-9 and up to 8-9 millimeters of mercury 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 closing of the lunar valves. When the pressure in the ventricles drops to zero, the valves of the casement type will open, and the phase will begin in which 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. Only one thing can be said: their duration is a variable variable. Here, the decisive factor is the frequency of the heart muscle rhythm. If the functions of the heart are upset, then with the same rhythm, the duration of the phase can vary.
External signs of heart activity
The cardiac muscle is characterized by external signs of its work. These include:
- The tip is apical.
- 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 the initial ellipsoidal shape to round. 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. So there is an apical impulse.
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 - it is also systolic - which is characteristic for atrioventricular valves. The second tone - diastolic - occurs at the time of closing of the valves of the pulmonary trunk and aorta. The first tone is long, dull and below the second. The second tone is high and short.
The 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 the more stretched the muscle fiber, the stronger its further contraction. The amount of blood accumulated in the heart during the diastole period affects the level of stretching. The larger the volume, the more vigorous the contraction during systole will be.
The second (F. Bainbridge) says that when blood pressure rises in the vena cava (at the mouth), an increase in the frequency and strength of muscle contractions at a reflex level is observed.
Both of these laws work simultaneously. They are referred to the self-regulation mechanism, which 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 salts (electrolytes) also influence the work of this organ. For example, acetylchopin (a mediator) and an excess of potassium ions weaken cardiac activity, making the rhythm rare, as a result of which even cardiac arrest can occur. A large number of calcium ions, adrenaline and norepinephrine, on the contrary, contribute to increased cardiac activity and its increased frequency. Adrenaline, in addition, dilates the coronary vessels, which improves myocardial nutrition.
Cardiac regulation mechanisms
In accordance with the needs of the body 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 mechanisms for regulating activity. Some of them are directly related to the properties that myocardial fibers possess. Here, there is a relationship between the force of contraction of the fiber and the rhythm of the heart muscle, as well as the dependence of the energy of contraction and the degree of stretching of the fiber during the diastole.
The elastic property of myocardial fibers, which is not manifested in the process of active conjugation, is called passive. Carriers of elastic properties are considered to be the trophic skeleton, as well as actomyosin bridges, which are located in the inactive muscle. The skeleton has a very positive effect on myocardial elasticity when sclerotic processes occur.
If a person has ischemic contracture or inflammatory myocardial diseases, then the bridge stiffness increases.
The work of the cardiovascular system is a complex process. Any failure can lead to negative consequences. See your doctor regularly and do not neglect his recommendations. After all, preventing the disease is much easier than treating it, spending money on expensive medications.