The heart is the main organ of the blood supply and lymph formation in the body. It is presented in the form of a large muscle with several hollow chambers. Due to its ability to contract, it sets the blood in motion. In total, three heart membranes are presented: epicardium, endocardium and myocardium. The structure, purpose and functions of each of them will be considered in this material.
Human Heart Structure - Anatomy
The heart muscle consists of 4 chambers - 2 atria and 2 ventricles. The left ventricle and the left atrium form the so-called arterial part of the organ, based on the nature of the blood here. On the contrary, the right ventricle and the right atrium make up the venous part of the heart.
The blood organ is presented in the form of a flattened cone. It distinguishes the base, apex, lower and anteroposterior surfaces, as well as two edges - left and right. The top of the heart has a rounded shape and is entirely formed by the left ventricle. Atria are located in the base area, and the pulmonary trunk and aorta lie in its front.
Heart sizes
It is believed that in an adult, a formed human individual, the size of the heart muscle is equal to the size of a clenched fist. In fact, on average, the length of this organ in a mature person is 12-13 cm. In diameter, the heart is 9-11 cm.
The mass of the heart of an adult man is about 300 g. In women, the heart weighs an average of about 220 g.
Phases of the heart
There are several separate phases of contraction of the heart muscle:
- Atrial contraction occurs at the beginning. Then, with some slowdown, ventricular contraction starts. During this process, the blood naturally tends to fill the chambers with reduced pressure. Why doesn’t the outflow back to the atria occur after this? The fact is that blood blocks the path of the gastric valves. Therefore, she can only move in the direction of the aorta, as well as the vessels of the pulmonary trunk.
- The second phase is relaxation of the ventricles and atria. The process is characterized by a short-term decrease in the tone of the muscle structures from which these chambers are formed. The process causes a decrease in pressure in the ventricles. Thus, the blood begins to move in the opposite direction. However, this is prevented by closure of pulmonary and arterial valves. During relaxation, the ventricles are filled with blood that comes from the atria. On the contrary, the atria are filled with bodily fluid from the large and small circle of blood circulation.
What is responsible for the work of the heart?
As you know, the functioning of the heart muscle is not an arbitrary act. The organ remains active continuously, even when a person is in a state of deep sleep. It is unlikely that there are people who pay attention to the heart rate in the process of activity. But this is achieved due to the special structure built into the heart muscle itself - the system of generating biological impulses. It is noteworthy that the formation of this mechanism occurs in the first weeks of fetal birth. Subsequently, the pulse generation system does not allow the heart to stop throughout life.
Interesting facts about the work of the heart
In a calm state, the number of contractions of the heart muscle for a minute is about 70 beats. Within one hour, the number reaches 4200 beats. Given that during one contraction, the heart ejects 70 ml of fluid into the circulatory system, it is easy to guess that up to 300 l of blood passes through it in an hour. How much does this body pump blood for a lifetime? This figure averages 175 million liters. Therefore, it is not surprising that the heart is called the ideal engine, which practically does not fail.
Heart shell
In total, 3 separate shells of the heart muscle are distinguished:
- The endocardium is the inner lining of the heart.
- Myocardium is an internal muscle complex formed by a thick layer of filamentary fibers.
- Epicardium is the thin outer membrane of the heart.
- Pericardium is an auxiliary heart membrane, which is a kind of bag in which the whole heart is contained.
Next, let's talk about the above shells of the heart in order, consider their anatomy.
Myocardium
Myocardium is a multi-tissue muscle membrane of the heart, which is formed by striated fibers, loose connective structures, nerve processes, as well as an extensive network of capillaries. Here are P-cells that form and conduct nerve impulses. In addition, myocytes and cardiomyocytes are present in the myocardium, which are responsible for the contraction of the blood organ.
The myocardium consists of several layers: internal, middle and external. The internal structure consists of muscle bundles that are arranged longitudinally with respect to each other. In the outer layer, the bundles of muscle tissue are oblique. The latter go to the very top of the heart, where they form the so-called curl. The middle layer consists of circular muscle bundles, separate for each of the ventricles of the heart.
Epicardium
The presented membrane of the heart muscle has the smoothest, thinest and somewhat transparent structure. The epicardium forms the external tissues of the organ. In fact, the shell acts as the inner layer of the pericardium - the so-called heart bag.
The surface of the epicardium is formed from mesothelial cells, under which there is a connective, loose structure represented by connective fibers. In the region of the apex of the heart and in its furrows, the membrane in question includes adipose tissue. The epicardium fuses with the myocardium at the sites of the smallest accumulation of fat cells.
Endocardium
Continuing to examine the lining of the heart, let's talk about the endocardium. The presented structure is formed by elastic fibers, which consist of smooth muscle and connective cells. Endocardial tissue lining all the inner chambers of the heart. Elements departing from the blood organ: aorta, pulmonary veins, pulmonary trunk endocardial tissue pass smoothly, without clearly distinguishable boundaries. In the thinnest areas of the atria, the endocardium fuses with the epicardium.
Pericardium
Pericardium is the outer mucous membrane of the heart, which is also called the pericardial sac. The specified structure is presented in the form of a slanted slanting cone. The lower base of the pericardium is located on the diaphragm. To the top, the shell goes more to the left than to the right. This peculiar bag surrounds not only the heart muscle, but also the aorta, the mouth of the pulmonary trunk and adjacent veins.
The pericardium is formed in human individuals in the early stages of fetal development. This happens about 3-4 weeks after the formation of the embryo. Violations of the structure of this membrane, its partial or complete absence often leads to congenital heart defects.
Finally
In the presented material, we examined the structure of the human heart, the anatomy of its chambers and shells. As you can see, the heart muscle has an extremely complex structure. Surprisingly, despite its intricate structure, this organ continuously functions throughout life, giving failures only in case of development of serious pathologies.