Help the development of the site, sharing the article with friends!

VERIFIED CONTENTAuthor: lek. Piotr Podwysocki

The circulatory system is a closed system of blood and lymph vessels that constantly transport blood and lymph through the body. Blood, set in motion by the heart, reaches every corner of the body as it flows through arteries, capillaries and veins. How is the small circulation different from the great circulation? And what is the role of lymph vessels and lymph? Learn about the structure of the circulatory system.

The circulatory system(Latinsistema sanguiferum hominis ) consists of the heart, blood vessels and lymph vessels, and its main function is blood distribution throughout the body. It provides tissues with oxygen and nutrients, removes metabolic products and carbon dioxide, participates in the regulation of the activities of individual organs and the entire body, and helps to maintain a proper body temperature. In addition, it regulates the acid-base balance, inflammatory and immune processes in the body, and prevents hemorrhages by producing a clot.

Structure of the circulatory system: blood

Blood is a type of connective tissue that consists of liquid plasma and morphotic elements. It accounts for about 7-8% of the body weight.

Plasma takes up 55% of its volume, while the rest - morphotic elements. Plasma consists of 91% water and 9% of compounds such as amino acids, proteins, fats and inorganic compounds. Among the plasma proteins, the most important role is played by albumin, globulins and fibrinogen.

The morphotic elements of blood are:

  • red blood cells (erythrocytes): from 4.5-5.4 million in 1mm3blood
  • white blood cells (leukocytes) in the number from 4,000 to 10,000 in 1mm3blood, including basophils (basophils), eosinophils, granulocytes neutrophils, lymphocytes and monocytes
  • platelets (thrombocytes): from 150-400 thousand in 1 mm3blood

Structure of the circulatory system: lymph

Lymph is an alkaline substance, slightly yellowish in color. It is formed from tissue fluid that penetrates the blind capillaries that begin in the tissues.

The total amount of lymph produced per day is 1-2 liters. Characteristic is the concentration of electrolytes in itis the same as in the blood plasma, but the protein concentration is lower.

Structure of the circulatory system: heart

The heart is the main organof the circulatory systemand acts as a suction and pressure pump. Its regular, contractile activity allows it to collect blood circulating in the body from the main veins and pulmonary veins, and then transport it to the capillary network of the entire body.

In one minute, the heart performs an average of 70-75 contractions and ejects about 70 ml of blood into the bloodstream during one contraction, which gives a minute volume of about 5 l / min. in peace. The size of the heart changes with age - in relation to body weight it is greatest in newborns and young children.

The heart can be divided into two halves - right and left. Venous blood, rich in carbon dioxide, circulates in the right heart, while in the left heart, arterial blood enriched with oxygen.

The inside of the heart is divided into four cavities - two atria and two chambers. The right atrium enters the superior and inferior vena cava and the coronary sinus, which drains most of the venous blood from the heart walls. Two right pulmonary veins and two left pulmonary veins enter the left atrium. Each of the atria is connected to the corresponding ventricle by a wide atrioventricular outlet, while each ventricle connects to the beginning of the great arteries - the right ventricle with the pulmonary trunk, and the left ventricle with the aorta.

The heart is divided by a longitudinal septum, which at the atrial level is called the atrial septum, and at the ventricular level - the interventricular septum.

Valves are present on the border of the atria and ventricles, as well as within the arterial openings. They are made of doubled endocardium, are divided into petals, and most importantly - they condition unidirectional blood flow. There is a right atrio-ventricular (tricuspid) valve between the right atrium and the right ventricle, while the left atrio-ventricular (mitral) valve is located between the left atrium and the left ventricle. In addition, arterial (crescent) valves - the pulmonary valve and the aortic valve - are present in the arterial openings.

The heart is located in the anterior mediastinum and is covered by the pericardial sac (pericardium). The pericardium is a system of serous membranes and is composed of the serous pericardium (inner part) and the fibrous pericardium (outer part). The visceral lamina of the serous pericardium is the epicardium.

The wall of the heart consists of three layers - endocardium, endocardium and epicardium. The endocardium covers the inner surface of the atria and ventricles, as well as the surface of the valves, chords andpapillary muscles. The endocardium is the thickest layer of the heart wall and consists of the heart muscle proper, the skeleton of the heart, and the heart's conductive system.

The heart skeleton consists of four fibrous rings surrounding the arterial and venous openings and separating the muscle of the ventricles and atria, as well as two fibrous triangles and the membranous part of the interventricular septum. The heart's conducting system is necessary because it determines the correct sequence of contractions of individual parts of the heart, and also ensures the right rhythm of its work.

It consists of the sinoatrial node, the atrioventricular node and the atrioventricular bundle. The cells that build it are characterized by slow resting depolarization, which brings their membrane potential closer to the threshold potential, which is necessary for the rhythmic generation of impulses - and consequently inducing a contraction.

Structure of the circulatory system: blood vessels

Blood vessels are a closed system of tubes and include arteries, arterioles, capillaries, veins and veins. Arterial vessels, due to the high blood pressure prevailing in them, are characterized by high elasticity and wall tension. Capillaries have a special structure of the endothelium, which enables them to exchange molecules between blood and tissues.

The veins, on the other hand, have walls with less developed muscles and fewer elastic fibers.

Remember that an artery, regardless of the type of blood flowing in it, is a blood vessel that carries blood from the heart to the periphery. Therefore, an artery is said to divide or give off branches, or sometimes as an extension (depending on its location).

A vein is a blood vessel that carries blood to the heart - so veins are joined together, receive tributaries, or extend (depending on location). Deep veins accompany arteries and have the same names, and small and medium-sized arteries are usually accompanied by two veins.

Structure of the circulatory system: arteries

The wall of the arteries is made up of three layers - the inner, middle and outer (adventitious) layers.

The inner layer consists of endothelial cells and subendothelial collagen fibers. Outside of them, there may be an elastic inner membrane made of elastic fibers.

The middle layer is made of smooth muscle cells and elastic fibers in a circular arrangement. The outer layer (adventitia) consists mainly of flaccid connective tissue, which contains numerous collagen and elastic fibers with longitudinal course. Sometimes they occur between the middle and outer layerselastic fibers arranged in a circular pattern, forming an outer elastic membrane.

Arteries can be divided on the basis of their lumen diameter and detailed structure. It is distinguished by:

  • Large, flexible arteries (so-called conductive arteries)

Their wall contains a considerable amount of elastic tissue, but less muscle fibers. Thanks to this, these vessels ensure constant blood pressure during the heart's work, which determines its continuous flow. Examples of this type of vessel are the aorta, brachiocephalic trunk, common carotid artery, subclavian artery, vertebral artery or common iliac artery

  • Medium muscle arteries (so-called distributing arteries)

They are branches or extensions of the above-described arteries. They contain relatively many muscle fibers, which gives them the ability to change their diameter while the heart beats. As a result, it is possible to distribute the blood depending on the needs of the specific organ. These types of arteries include the axillary artery, the brachial artery, the intercostal arteries, and the mesenteric arteries.

  • Arteries

They have a diameter of less than 100 micrometers and have relatively thick walls, with a ratio of lumen diameter to vessel wall thickness of approximately 1: 2. They contain a lot of circular muscle fibers that regulate blood flow depending on the needs.

Circulatory system: capillaries

Capillaries are the extension of arterioles from 4 to 15 micrometers in diameter and form a branching network within tissues and organs. Their main task is to mediate the exchange of fluids, molecules and various compounds between the blood flowing through them and the surrounding tissues.

Their wall consists of endothelial cells that are flattened and overlap. These cells are arranged on the basement membrane, which is made of collagen and reticular fibers embedded in the mucopolysaccharide matrix. On the outside of the vessel there are cells called pericytes.

A special type of capillary are the sinus vessels (so-called csinoids), the diameter of which can be up to 30 micrometers. They are found in organs such as the liver, spleen, bone marrow and endocrine glands.

Circulatory system: veins

The wall of the veins, as in the case of arteries, is made of three layers, but within it there are a smaller number of elastic and muscle fibers, which makes it lax. Interestingly, the outer membrane of the veins consists of numerous, longitudinal bundles of smooth muscle fibers. It is a characteristic feature that distinguishes between veins and arteriesthe presence of valves in the wall of the veins that prevent the backflow of blood Depending on the diameter of the veins, the following are distinguished:

  • 20-30 micrometer lines
  • small and medium-sized veins, which are muscle-type veins, characterized by a thick outer membrane made of longitudinally arranged bundles of collagen fibers and smooth muscles
  • large veins, which include the superior and inferior vena cava, portal vein, and the direct tributaries to them

It is worth knowing that there are also direct connections between the artery and the vein, bypassing the capillary system. They are the so-calledarteriovenous anastomoses , which include simple and glomerular arteriovenous anastomoses. Their task is to regulate blood flow through tissues and organs.

Arteriovenous connections appear in the form of a strange network. These types of connections occur in the kidney, where arterial capillaries combine to form arterial vessels.

Strange venous network occurs when venous capillaries pass into veins, e.g. in the liver or pituitary gland. An example of a strange venous network is also the portal circulation.

Circulatory system: lymphatic vessels

Lymph vessels begin as blind capillaries that are similar in structure to capillaries but are slightly larger in diameter. The capillaries then extend into small lymph vessels that contain valves and individual smooth muscle cells.

Small lymph vessels form medium lymph vessels, which have a three-layer wall - they are the so-called absorbent trunks. They come from the regional lymph nodes - the intestine, lumbar, axillary and deep cervical lymph nodes and enter into 2 lymphatic ducts - the thoracic duct, which is the main lymphatic duct, and the right lymphatic duct.

Both lines go into the main venous trunks - the thoracic duct opens in the left venous corner into the left brachiocephalic vein, and the right lymphatic duct in the right venous corner into the right brachiocephalic vein.

Circulatory system: vessel innervation

The wall of vessels, and arteries in particular, has a rich innervation in the form of vascular nerves, which contain sympathetic, parasympathetic and sensory fibers - they form plexuses. Interestingly, in the aortic arch and carotid arteries, nerve endings sensitive to changes in blood pressure (so-called baroreceptors) and carbon dioxide content (so-called chemoreceptors) are present.

Circulatory system: small (pulmonary) circulation

This circulation is located between the right ventricle and the left atrium. FROMThe pulmonary trunk comes out of the right ventricle, which then divides into the right and left pulmonary arteries - these go to the lung cavity.

There, they divide again into the lobar and segmental arteries of the lungs, and finally into the alveolar capillaries, where the blood undergoes oxygenation.

Oxygenated blood returns to the left atrium through interlobular and intersegmental veins, which join into four pulmonary veins.

Circulatory system: great (systemic) circulation

Begins in the left ventricle, from which the aorta emerges in the extension of the left ventricular arterial cone. In the initial section, the aorta goes upwards as the ascending aorta - the coronary arteries that supply the heart depart from it.

Then the ascending aorta passes into the aortic arch, from which the brachiocephalic trunk, left common carotid artery and left subclavian artery depart - these vessels supply the area of ​​the head, neck and upper limbs.

In the next episode, the aortic arch passes into the descending aorta, which at the chest level is called the descending aorta - it supplies blood to the chest wall and organs.

After passing through the diaphragm, the thoracic aorta is called the abdominal aorta - it supplies the walls and organs of the abdominal cavity. At the level of the fourth lumbar vertebra, it ends with a bifurcation of the common iliac arteries. The common iliac artery is divided into the internal iliac artery - supplies the walls and organs of the pelvis and the external iliac artery - supplies mainly blood to the lower limb.

The veins of the great circulation are composed of the following vein systems - the cardiac vein system, the superior and inferior vena cava system, and the portal vein system. The veins of the head and neck, upper limb, thorax and thoracic spine enter the superior vena cava system. The veins of the abdomen, pelvis and lower limbs enter the inferior vena cava system. The portal vein system, on the other hand, collects blood from the odd viscera of the abdominal cavity (except the liver).

Help the development of the site, sharing the article with friends!

Category:

Cardiology