The circulatory system includes blood vessels and the central organ of blood circulation – the heart .
The heart works like a pump. This pump pumps blood. Blood moves in a circle in tubes called blood vessels. The heart pressurizes blood into large blood vessels called arteries. Arteries carry blood away from the heart to smaller vessels. The smallest vessels are called capillaries. Their diameter is about 7 microns (0.007 mm). Capillaries are connected to each other, and at the same time form vessels of ever larger diameter. These vessels are called veins . Veins carry blood from the capillaries to the heart.
The heart consists of four cavities:
the left ventricle.
The right atrium and right ventricle of the heart are separated from the left atrium and left ventricle by a septum . Thus, the right and left heart are distinguished. Each atrium communicates with the corresponding ventricle of the heart. Each ventricle of the heart communicates with its atrium through the atrioventricular orifice. There are two such openings in the heart:
one – between the right atrium and the right ventricle, right atrioventricular orifice ,
Other – between the left atrium and the left ventricle, the left atrioventricular orifice .
Each of these openings has a valve that controls the direction of blood flow from the atrium to the ventricle of the heart.
Venous blood from the whole body enters through the veins into the right atrium , from there through the right atrioventricular opening into the right ventricle of the heart. From the right ventricle, blood enters a large artery called the pulmonary trunk. The pulmonary trunk divides into two pulmonary arteries, the right pulmonary artery and the left pulmonary artery, which carry blood to the right and left lungs. Here the branches of the pulmonary arteries branch into tiny vessels – pulmonary capillaries .
In the pulmonary capillaries with venous blood, the following occurs:
It is saturated with oxygen
· It is released from carbon dioxide and water.
Thus, the blood in the pulmonary capillaries becomes arterial and, through the four pulmonary veins , is sent to the left atrium.
From the left atrium, blood passes through the left atrioventricular orifice into the left ventricle of the heart. From the left ventricle of the heart, blood enters the largest arterial highway – the aorta. The branches of the aorta carry blood throughout the body. The terminal branches of the aorta break up in the tissues of the body to capillaries .. In the capillaries, blood gives oxygen to the tissues and takes carbon dioxide from them. In this case, the blood becomes venous. Capillaries, again connecting with each other, form larger vessels – veins.
All veins of the body are collected in two large trunks – the superior vena cava , and the inferior vena cava . The superior vena cava collects blood from areas and organs of the head and neck, upper limbs, and some parts of the body walls. The inferior vena cava collects blood from the lower extremities, walls and organs of the pelvic and abdominal cavities.
Both vena cava bring blood to the right atrium, where the venous blood of the heart itself is also collected (see “Venas of the heart”). Thus, a vicious circle of blood circulation is obtained. This blood path is called the general circulation . In the general circle of blood circulation, a small circle of blood circulation and a large circle of blood circulation are distinguished.
The small circle of blood circulation , or the pulmonary circulation, is called its area, starting from the right ventricle of the heart, through the pulmonary trunk, its branches, the capillary network of the lungs, the pulmonary veins and ending with the left atrium.
The systemic circulation , or circulation of the body, is its area, starting from the left ventricle of the heart, through the aorta, its branches, capillary network and veins of organs and tissues of the whole body and ending with the right atrium.
Consequently, blood circulation takes place in two circles of blood circulation connected to each other in the cavities of the heart.
The heart is an approximately cone-shaped hollow organ with well-developed muscular walls. It is located in the lower part of the anterior mediastinum on the tendon center of the diaphragm, between the right and left pleural sacs, is enclosed in the pericardium, and is fixed to the back wall of the chest on large blood vessels. The heart is sometimes shorter, rounded, sometimes more elongated, sharp; in the filled state, in size it is approximately equal to the fist of the person being examined. In men, the size and mass of the heart are generally larger than in women, and its walls are somewhat thicker.
The long axis of the heart runs from top to bottom, from back to front and from left to right.
The posterior-upper expanded part of the heart is called the base of the heart. The structure of the base includes the atria and large vessels – arteries and veins. The anteroinferior, free-lying part of the heart is called the apex of the heart . The apex of the heart consists entirely of the ventricles.
The heart has two surfaces – diaphragmatic and sternocostal. Of the two surfaces of the heart, the posterior inferior, flattened, diaphragmatic surface is adjacent to the diaphragm. Anterior superior, more convex, thoracic-costal surface, facing the sternum and costal cartilages. Both surfaces merge into one another with rounded edges; while the right edge is longer and sharper, the left one is shorter and rounded.
Three furrows are distinguished on the surfaces of the heart:
1. Coronal sulcus . Separates the atria from the ventricles.
2. anterior interventricular sulcus of the heart . Separates the right and left ventricles.
3. posterior interventricular sulcus of the heart Separates the right and left ventricles.
As stated above, the cavity of the heart is divided into four chambers:
· right atrium,
the left ventricle
The atrial cavities are separated from one another by the interatrial septum , the cavity of the ventricles of the heart – by the interventricular septum , the direction of the latter is marked on the surface of the heart by the position of the anterior and posterior interventricular sulci.
The atria, as indicated, communicate with the corresponding ventricles of the heart through openings between the atria and ventricles – the atrioventricular openings: the right atrium with the right ventricle of the heart – the right atrioventricular opening, the left atrium with the left ventricle of the heart – the left atrioventricular opening.
Right atrium , located in the region of the right side of the base of the heart, has the shape of an irregular cube.
The bottom wall is missing; here is the right atrioventricular opening , which communicates the right atrium with the right ventricle.
The more expanded posterior part of the right atrium is the confluence of large venous vessels, called the sinus of the vena cava . The narrowed part of the atrium anteriorly passes into the right ear,
Two empty vena cava and inferior vena cava and coronary sinus flow into the right atrium.
a) The superior hollow collects blood from:
upper limbs and
body walls and
the superior vena cava opens into the right atrium through the opening of the superior vena cava .
b) Inferior vena cava , collects blood from:
walls. Pelvic and abdominal cavities
organs of the pelvic and abdominal cavities
It opens at the border of the superior and posterior wall of the right atrium with an opening of the inferior vena cava,
c) Coronary sinus , – a common collector of the heart’s own veins. The confluence of the coronary sinus is located on the border between the medial and posterior wall of the right atrium,
The right ventricle is separated from the left ventricle by the anterior and posterior interventricular sulci on the surface of the heart; the coronal groove separates it from the right atrium. The outer (right) edge of the right ventricle is pointed and is called the right edge.
The right ventricle has the shape of an irregular three-sided pyramid, the base of which is directed upwards. side of the right atrium, top – down and to the left. The anterior wall of the right ventricle is convex, the posterior wall is flattened. The left, internal, wall of the right ventricle is an interventricular septum, it is concave from the side of the left ventricle, i.e., convex towards the right ventricle.
The posterior part of the ventricular cavity, through the right atrioventricular orifice, which is located on the right and behind, communicates with the cavity of the right atrium. The described hole from the side of the right atrium has an oblong-rounded shape. The formed right atrioventricular valve is attached around the circumference of this hole. It has a second name – the tricuspid valve. Three of its valves are formed by a duplication of the inner lining of the heart – the endocardium. These three valves with their free edges protrude into the cavity of the right ventricle. Tendon filaments – chords – are attached to the edges of the valve. These chordae connect the edges of the valve to the papillary muscles . They prevent the eversion of the valves into the atrial cavity with an increase in blood pressure in the ventricle, which in turn prevents the reverse flow of blood from the cavity of the right ventricle into the cavity of the right atrium.
The anterior part of the ventricular cavity is called the conus arteriosus. This one has a cylindrical shape and smooth walls. Its cavity ends with an opening of the pulmonary trunk . The opening of the pulmonary trunk leads to the pulmonary trunk. Attached to the edge of this hole are three semi- lunar flaps – front, right and left. Their free edges protrude into the pulmonary trunk. All three of these flaps together form the pulmonary valve . This valve prevents the backflow of blood from the pulmonary trunk into the cavity of the right ventricle.
The left atrium , like the right one, has an irregularly cuboidal shape. Its walls are thinner than those of the right atrium.
It distinguishes between the upper, anterior, posterior and outer (left) walls. The inner (right) wall is the interatrial septum . The left ear departs from the anteroposterior wall of the atrium . It bends anteriorly, covering the beginning of the pulmonary trunk.
In the posterior section of the upper wall of the atrium, four openings of the pulmonary veins open , bringing arterial blood from the lungs into the cavity of the left atrium.
The lower wall of the left atrium is pierced by the left atrioventricular orifice , through which the cavity of the left atrium communicates with the cavity of the left ventricle.
Left ventricle , in relation to other parts of the heart, is located to the left, backwards and downwards. It has an oblong-oval shape.
The narrowed anteroinferior section of the left ventricle corresponds to the apex of the heart . The boundary between the left and right ventricles on the surface of the heart corresponds to the anterior and posterior interventricular sulci of the heart.
The cavity of the left ventricle is divided into two sections:
wider posterior, representing the own cavity of the left ventricle, and
narrower anterior right, which is, as it were, an upward continuation of the cavity of the left ventricle.
The proper cavity of the left ventricle communicates with the cavity of the left atrium through the left atrioventricular orifice. The left atrioventricular (mitral, or bicuspid) valve is attached around the circumference of the left atrioventricular orifice. The free edges of its valves protrude into the cavity of the ventricle. Like the tricuspid valve, they are formed by duplication of the innermost layer of the heart, the endocardium. This valve, when the left ventricle contracts, prevents the passage of blood from its cavity back into the cavity of the left atrium.
The valve is divided into an anterior leaflet and a rear leaflet.
The free edges of the valves are fixed by tendon chords to the papillary muscleslocated on the walls of the ventricle.
From the side of the inner surface, the wall of the posterior part of the left ventricle is covered with a large number of protrusions and bridges – fleshy trabeculae . Repeatedly splitting and reconnecting, these fleshy trabeculae intertwine and form a network. There are especially many trabeculae at the apex of the heart in the region of the interventricular septum.
The anterior right part of the cavity of the left ventricle is called the conus arteriosus. It communicates through the aortic orifice with the aorta. Three semilunar valves of the aorta are fixed along the circumference of the aortic opening. Together, these flaps form the aortic valve . The aortic valve prevents backflow from the aorta to the left ventricle at the time of diastole.
SHELLS OF THE HEART
The wall of the heart consists of three layers:
external – epicardium
middle – myocardium
internal – endocardium.
The epicardium is a thin epithelial serous membrane.
Myocardium – represented by striated muscle cells. These cells have four properties:
Excitability – able to be excited when exposed to a stimulus
contractility – when excited, the cells contract – their length decreases
conduction – an excited cell transmits excitation to other cells with which it is in contact. This means that no matter what myocardial cell is brought into an excited state, this excitation will be transmitted to the entire myocardium.
Automatism – each cell is capable of self-excitation after a certain time.
The muscle layer has a different thickness in different parts of the heart. In the atria, its thickness is 1-2 mm, in the right ventricle – 2-5 mm, in the left ventricle -1.5-2 cm.
The ventricular myocardium is isolated from the atrial myocardium. Those. excitation of the atrial myocardium is not transmitted directly to the ventricular myocardium. For this purpose, there is a conducting system of the heart .
The structure of the myocardium is different in different parts of the heart.
Two muscle layers are distinguished in the atria – superficial and deep . The surface layer is common to both atria and consists of muscle bundles running in the transverse direction. The deep layer of the muscles of the right and left atria is not common to both atria: it distinguishes between ring-shaped or circular and loop-shaped muscle fibers.
There are three muscle layers in the myocardium of the ventricles. The outer layer is common to both ventricles. The direction of the fibers in it is oblique. In the region of the apex of the heart, the fibers of the outer layer form a curl of the heart and pass into the deeper layers.
The deep layer consists of cylindrical bars rising from the apex of the heart to its base. They branch many times and join again to form a network. The shorter of these bundles do not reach the base of the heart, they are directed obliquely from one wall of the heart to another in the form of fleshy trabeculae. Trabeculae are located in large numbers along the entire inner surface of both ventricles and have different sizes in different areas. Only the inner wall (septum) of the ventricles, immediately below the arterial openings, is devoid of these crossbars.
A number of such short, but more powerful muscle bundles protrude freely into the cavity of the ventricles, forming papillary muscles of various sizes.
There are three papillary muscles in the cavity of the right ventricle, and two in the cavity of the left. From the top of each of the papillary muscles, tendon chords begin, through which the papillary muscles are connected to the free edge of the cusps of the tricuspid and mitral valves.
Papillary muscles with tendon chords keep the valve leaflets from eversion into the atrial cavity during systole (ventricular contraction). This is necessary so that at this time the blood does not flow in the opposite direction (from the ventricles to the atria).
The interventricular septum is formed by all three muscular layers of both ventricles.