Large and small circles of blood circulation. Arteries of the systemic circulation
Arterial blood- This is blood saturated with oxygen.
Deoxygenated blood- saturated with carbon dioxide.
Arteries- These are vessels that carry blood from the heart.
Vienna- These are vessels that carry blood to the heart.
(In the pulmonary circulation, venous blood flows through the arteries, and arterial blood flows through the veins.)
In humans, in all other mammals, as well as in birds four-chambered heart, consists of two atria and two ventricles (in the left half of the heart there is arterial blood, in the right - venous, mixing does not occur due to a complete septum in the ventricle).
Between the ventricles and atria are flap valves, and between the arteries and ventricles - semilunar. The valves prevent blood from flowing backwards (from the ventricle to the atrium, from the aorta to the ventricle).
The thickest wall is at the left ventricle, because it pushes blood through the systemic circulation. When the left ventricle contracts, a pulse wave is created, as well as maximum blood pressure.
Blood pressure: in the arteries the largest, in the capillaries the average, in the veins the smallest. Blood speed: in the arteries the largest, in the capillaries the smallest, in the veins the average.
Big circle blood circulation: from the left ventricle, arterial blood flows through the arteries to all organs of the body. Gas exchange occurs in the capillaries of a large circle: oxygen passes from the blood into the tissues, and carbon dioxide passes from the tissues into the blood. The blood becomes venous, flows through the vena cava into the right atrium, and from there into the right ventricle.
Small circle: From the right ventricle, venous blood flows through the pulmonary arteries to the lungs. Gas exchange occurs in the capillaries of the lungs: carbon dioxide passes from the blood into the air, and oxygen from the air into the blood, the blood becomes arterial and flows through the pulmonary veins into the left atrium, and from there into the left ventricle.
Establish a correspondence between the sections of the circulatory system and the circle of blood circulation to which they belong: 1) Systemic circulation, 2) Pulmonary circulation. Write numbers 1 and 2 in the correct order.
A) Right ventricle
B) Carotid artery
B) Pulmonary artery
D) Superior vena cava
D) Left atrium
E) Left ventricle
Answer
Choose three correct answers out of six and write down the numbers under which they are indicated. Large circle of blood circulation in the human body
1) begins in the left ventricle
2) originates in the right ventricle
3) is saturated with oxygen in the alveoli of the lungs
4) supplies organs and tissues with oxygen and nutrients
5) ends in the right atrium
6) brings blood to the left side of the heart
Answer
1. Establish the sequence of human blood vessels in order of decreasing blood pressure in them. Write down the corresponding sequence of numbers.
1) inferior vena cava
2) aorta
3) pulmonary capillaries
4) pulmonary artery
Answer
2. Establish the order in which the blood vessels should be arranged in order of decreasing blood pressure in them
1) Veins
2) Aorta
3) Arteries
4) Capillaries
Answer
Establish a correspondence between the vessels and human circulatory circles: 1) pulmonary circulation, 2) systemic circulation. Write numbers 1 and 2 in the correct order.
A) aorta
B) pulmonary veins
B) carotid arteries
D) capillaries in the lungs
D) pulmonary arteries
E) hepatic artery
Answer
Choose one, the most correct option. Why can't blood get from the aorta to the left ventricle of the heart?
1) the ventricle contracts with great force and creates high pressure
2) semilunar valves fill with blood and close tightly
3) leaflet valves are pressed against the walls of the aorta
4) leaflet valves are closed and semilunar valves are open
Answer
Choose one, the most correct option. Blood enters the pulmonary circulation from the right ventricle through
1) pulmonary veins
2) pulmonary arteries
3) carotid arteries
4) aorta
Answer
Choose one, the most correct option. Arterial blood flows through the human body
1) renal veins
2) pulmonary veins
3) vena cava
4) pulmonary arteries
Answer
Choose one, the most correct option. In mammals, blood is enriched with oxygen in
1) arteries of the pulmonary circulation
2) capillaries of the great circle
3) arteries of the great circle
4) capillaries of the small circle
Answer
1. Establish the sequence of blood movement through the vessels of the systemic circulation. Write down the corresponding sequence of numbers.
1) portal vein of the liver
2) aorta
3) gastric artery
4) left ventricle
5) right atrium
6) inferior vena cava
Answer
2. Determine the correct sequence of blood circulation in the systemic circulation, starting with the left ventricle. Write down the corresponding sequence of numbers.
1) Aorta
2) Superior and inferior vena cava
3) Right atrium
4) Left ventricle
5) Right ventricle
6) Tissue fluid
Answer
3. Establish the correct sequence of blood passage through the systemic circulation. Write down the corresponding sequence of numbers in the table.
1) right atrium
2) left ventricle
3) arteries of the head, limbs and torso
4) aorta
5) inferior and superior vena cava
6) capillaries
Answer
4. Establish the sequence of blood movement in the human body, starting with the left ventricle. Write down the corresponding sequence of numbers.
1) left ventricle
2) vena cava
3) aorta
4) pulmonary veins
5) right atrium
Answer
5. Establish the sequence of passage of a portion of blood in a person, starting with the left ventricle of the heart. Write down the corresponding sequence of numbers.
1) right atrium
2) aorta
3) left ventricle
4) lungs
5) left atrium
6) right ventricle
Answer
Arrange the blood vessels in order of decreasing speed of blood movement in them
1) superior vena cava
2) aorta
3) brachial artery
4) capillaries
Answer
Choose one, the most correct option. The vena cava in the human body drains into
1) left atrium
2) right ventricle
3) left ventricle
4) right atrium
Answer
Choose one, the most correct option. Valves prevent blood from flowing back from the pulmonary artery and aorta into the ventricles.
1) tricuspid
2) venous
3) double-leaf
4) semilunar
Answer
1. Establish the sequence of blood movement in a person through the pulmonary circulation. Write down the corresponding sequence of numbers.
1) pulmonary artery
2) right ventricle
3) capillaries
4) left atrium
5) veins
Answer
2. Establish the sequence of circulatory processes, starting from the moment when blood moves from the lungs to the heart. Write down the corresponding sequence of numbers.
1) blood from the right ventricle enters the pulmonary artery
2) blood moves through the pulmonary vein
3) blood moves through the pulmonary artery
4) oxygen comes from the alveoli to the capillaries
5) blood enters the left atrium
6) blood enters the right atrium
Answer
3. Establish the sequence of movement of arterial blood in a person, starting from the moment it is saturated with oxygen in the capillaries of the pulmonary circle. Write down the corresponding sequence of numbers.
1) left ventricle
2) left atrium
3) veins of the small circle
4) small circle capillaries
5) arteries of the great circle
Answer
4. Establish the sequence of movement of arterial blood in the human body, starting with the capillaries of the lungs. Write down the corresponding sequence of numbers.
1) left atrium
2) left ventricle
3) aorta
4) pulmonary veins
5) capillaries of the lungs
Answer
5. Establish the correct sequence of passage of a portion of blood from the right ventricle to the right atrium. Write down the corresponding sequence of numbers.
1) pulmonary vein
2) left ventricle
3) pulmonary artery
4) right ventricle
5) right atrium
6) aorta
Answer
Establish the sequence of events that occur in the cardiac cycle after blood enters the heart. Write down the corresponding sequence of numbers.
1) contraction of the ventricles
2) general relaxation of the ventricles and atria
3) blood flow into the aorta and artery
4) blood flow into the ventricles
5) atrial contraction
Answer
Establish a correspondence between human blood vessels and the direction of blood movement in them: 1) from the heart, 2) to the heart
A) veins of the pulmonary circulation
B) veins of the systemic circulation
B) arteries of the pulmonary circulation
D) arteries of the systemic circulation
Answer
Choose three options. A person has blood from the left ventricle of the heart
1) when it contracts, it enters the aorta
2) when it contracts, it enters the left atrium
3) supplies body cells with oxygen
4) enters the pulmonary artery
5) under high pressure enters the large circulation circle
6) under slight pressure enters the pulmonary circulation
Answer
Choose three options. Blood flows through the arteries of the pulmonary circulation in humans
1) from the heart
2) to the heart
4) oxygenated
5) faster than in the pulmonary capillaries
6) slower than in the pulmonary capillaries
Answer
Choose three options. Veins are blood vessels through which blood flows
1) from the heart
2) to the heart
3) under greater pressure than in the arteries
4) under less pressure than in the arteries
5) faster than in capillaries
6) slower than in capillaries
Answer
Choose three options. Blood flows through the arteries of the systemic circulation in humans
1) from the heart
2) to the heart
3) saturated with carbon dioxide
4) oxygenated
5) faster than in other blood vessels
6) slower than in other blood vessels
Answer
1. Establish a correspondence between the type of human blood vessels and the type of blood they contain: 1) arterial, 2) venous
A) pulmonary arteries
B) veins of the pulmonary circulation
B) aorta and arteries of the systemic circulation
D) superior and inferior vena cava
Answer
2. Establish a correspondence between a vessel of the human circulatory system and the type of blood that flows through it: 1) arterial, 2) venous. Write numbers 1 and 2 in the order corresponding to the letters.
A) femoral vein
B) brachial artery
B) pulmonary vein
D) subclavian artery
D) pulmonary artery
E) aorta
Answer
Choose three options. In mammals and humans, venous blood, unlike arterial,
1) poor in oxygen
2) flows in a small circle through the veins
3) fills the right half of the heart
4) saturated with carbon dioxide
5) enters the left atrium
6) provides body cells with nutrients
Answer
Choose three correct answers out of six and write down the numbers under which they are indicated. Veins, as opposed to arteries
1) have valves in the walls
2) may fall off
3) have walls made of one layer of cells
4) carry blood from organs to the heart
5) withstand high blood pressure
6) always carry blood that is not saturated with oxygen
Answer
Analyze the table “The work of the human heart.” For each cell indicated by a letter, select the corresponding term from the list provided.
1) Arterial
2) Superior vena cava
3) Mixed
4) Left atrium
5) Carotid artery
6) Right ventricle
7) Inferior vena cava
8) Pulmonary vein
Answer
Choose three correct answers out of six and write down the numbers under which they are indicated. Elements of the human circulatory system containing venous blood are
1) pulmonary artery
2) aorta
3) vena cava
4) right atrium and right ventricle
5) left atrium and left ventricle
6) pulmonary veins
Answer
Choose three correct answers out of six and write down the numbers under which they are indicated. Blood leaks from the right ventricle
1) arterial
2) venous
3) through the arteries
4) through the veins
5) towards the lungs
6) towards the cells of the body
Answer
Establish a correspondence between the processes and the circles of blood circulation for which they are characteristic: 1) small, 2) large. Write numbers 1 and 2 in the order corresponding to the letters.
A) Arterial blood flows through the veins.
B) The circle ends in the left atrium.
B) Arterial blood flows through the arteries.
D) The circle begins in the left ventricle.
D) Gas exchange occurs in the capillaries of the alveoli.
E) Venous blood is formed from arterial blood.
Answer
Find three errors in the given text. Indicate the numbers of the proposals in which they are made.(1) The walls of arteries and veins have a three-layer structure. (2) The walls of the arteries are very elastic and elastic; The walls of the veins, on the contrary, are inelastic. (3) When the atria contract, blood is pushed into the aorta and pulmonary artery. (4) The blood pressure in the aorta and vena cava is the same. (5) The speed of blood movement in the vessels is not the same; in the aorta it is maximum. (6) The speed of blood movement in capillaries is higher than in veins. (7) Blood in the human body moves through two circulation circles.
Answer
Choose three correctly labeled captions for the picture that depicts the internal structure of the heart. Write down the numbers under which they are indicated.
1) superior vena cava
2) aorta
3) pulmonary vein
4) left atrium
5) right atrium
6) inferior vena cava
Answer
Choose three correctly labeled captions for the picture that depicts the structure of the human heart. Write down the numbers under which they are indicated.
1) superior vena cava
2) flap valves
3) right ventricle
4) semilunar valves
5) left ventricle
6) pulmonary artery
Answer
© D.V. Pozdnyakov, 2009-2019
In medicine, blood is usually divided into arterial and venous. It would be logical to think that the first flows in the arteries, and the second in the veins, but this is not entirely true. The fact is that in the systemic circulation, arterial blood (a.k.) actually flows through the arteries, and venous blood (v.k.) through the veins, but in the small circle the opposite happens: c. It enters from the heart into the lungs through the pulmonary arteries, releases carbon dioxide to the outside, is enriched with oxygen, becomes arterial, and returns from the lungs through the pulmonary veins.
How does venous blood differ from arterial blood? A.K. is saturated with O 2 and nutrients; it flows from the heart to organs and tissues. V. k. - “spent”, it gives O 2 and nutrition to the cells, takes CO 2 and metabolic products from them and returns from the periphery back to the heart.
Human venous blood differs from arterial blood in color, composition and functions.
By color
A.K. has a bright red or scarlet tint. This color is given to it by hemoglobin, which added O 2 and became oxyhemoglobin. V.K. contains CO 2, so its color is dark red, with a bluish tint.
By composition
In addition to gases, oxygen and carbon dioxide, the blood also contains other elements. In a. k. a lot of nutrients, and c. to. - mainly metabolic products, which are then processed by the liver and kidneys and excreted from the body. The pH level also differs: in a. k. it is higher (7.4) than that of v. k. (7.35).
By movement
Blood circulation in the arterial and venous systems is significantly different. A. k. moves from the heart to the periphery, and v. k. - in the opposite direction. When the heart contracts, blood is ejected from it under a pressure of approximately 120 mmHg. pillar As it passes through the capillary system, its pressure decreases significantly and is approximately 10 mmHg. pillar Thus, a. k. moves under pressure at high speed, and c. It flows slowly under low pressure, overcoming the force of gravity, and its reverse flow is prevented by valves.
How the transformation of venous blood into arterial blood and vice versa occurs can be understood if we consider the movement in the pulmonary and systemic circulation.
Blood saturated with CO 2 enters the lungs through the pulmonary artery, from where CO 2 is excreted. Then saturation with O 2 occurs, and the blood already enriched with it enters the heart through the pulmonary veins. This is how movement occurs in the pulmonary circulation. After this, the blood makes a large circle: a. It carries oxygen and nutrition through the arteries to the cells of the body. Giving up O 2 and nutrients, it is saturated with carbon dioxide and metabolic products, becomes venous and returns through the veins to the heart. This completes the large circle of blood circulation.
By functions performed
Main function a. k. – transfer of nutrition and oxygen to cells through the arteries of the systemic circulation and the veins of the small circulation. Passing through all organs, it gives off O 2, gradually takes up carbon dioxide and turns into venous.
The veins carry out the outflow of blood, which has taken away cell waste products and CO 2 . In addition, it contains nutrients that are absorbed by the digestive organs and hormones produced by the endocrine glands.
By bleeding
Due to the characteristics of movement, bleeding will also differ. With arterial bleeding, the blood flows in full swing; such bleeding is dangerous and requires prompt first aid and medical attention. With venous flow, it calmly flows out in a stream and can stop on its own.
Other differences
- A.K. is located on the left side of the heart, in. k. – in the right, blood mixing does not occur.
- Venous blood, unlike arterial blood, is warmer.
- V. k. flows closer to the surface of the skin.
- A.K. in some places comes close to the surface and here the pulse can be measured.
- The veins through which the v. flows. to., much more than arteries, and their walls are thinner.
- Movement a.k. is ensured by a sharp release during contraction of the heart, outflow into the. the valve system helps.
- The use of veins and arteries in medicine also differs - medications are injected into the vein, and it is from it that biological fluid is taken for analysis.
Instead of a conclusion
Main differences a. k. and v. consist in the fact that the first is bright red, the second is burgundy, the first is saturated with oxygen, the second is saturated with carbon dioxide, the first moves from the heart to the organs, the second - from the organs to the heart.
Blood circulation is a continuous flow of blood that moves through the vessels and cavities of the heart. This system is responsible for metabolic processes in the organs and tissues of the human body. Circulating blood transports oxygen and nutrients to the cells, taking carbon dioxide and metabolites from there. That is why any circulatory disorders threaten with dangerous consequences.
The blood circulation consists of a large (systemic) and a small (pulmonary) circle. Each turn has a complex structure and functions. The systemic circle originates from the left ventricle and ends in the right atrium, and the pulmonary circle originates from the right ventricle and ends in the left atrium.
Blood circulation is a complex system that consists of the heart and blood vessels. The heart constantly contracts, pushing blood through the vessels to all organs and tissues. The circulatory system consists of arteries, veins, and capillaries.
The circulatory system is formed by arteries, veins and capillaries
The arteries of the systemic circulation are the largest vessels; they have a cylindrical shape and transport blood from the heart to the organs.
Structure of the walls of arterial vessels:
- outer connective tissue membrane;
- middle layer of smooth muscle fibers with elastic veins;
- strong elastic inner endothelial membrane.
Arteries have elastic walls that constantly contract, allowing blood to move evenly.
With the help of the veins of the systemic circulation, blood moves from the capillaries to the heart. Veins have the same structure as arteries, but they are less strong, since their middle layer contains less smooth muscle and elastic fibers. That is why the speed of blood movement in the venous vessels is largely influenced by nearby tissues, especially skeletal muscles. All veins, except the vena cava, are equipped with valves that prevent the backflow of blood.
Capillaries are small vessels that consist of endothelium (a single layer of flat cells). They are quite thin (about 1 micron) and short (from 0.2 to 0.7 mm). Due to their structure, microvessels saturate tissues with oxygen and useful substances, carrying away carbon dioxide, as well as metabolic products. Blood moves slowly through them; in the arterial part of the capillaries, water is removed into the intercellular space. In the venous part, blood pressure decreases and water flows back into the capillaries.
Structure of the systemic circulation
The aorta is the largest vessel of the great circle, with a diameter of 2.5 cm. This is a kind of source from which all other arteries emerge. The vessels branch, their size decreases, they go to the periphery, where they give oxygen to organs and tissues.
The largest vessel of the systemic circulation is the aorta
The aorta is divided into the following sections:
- ascending;
- descending;
- the arc that connects them.
The ascending section is the shortest, its length is no more than 6 cm. The coronary arteries emanate from it, which supply oxygen-rich blood to the myocardial tissues. Sometimes the term “cardiac circulation” is used to name the ascending section. From the most convex surface of the aortic arch, arterial branches depart that supply blood to the arms, neck, and head: on the right side there is the brachiocephalic trunk, divided in two, and on the left there is the common carotid, subclavian artery.
The descending aorta is divided into 2 groups of branches:
- Parietal arteries that supply blood to the chest, spinal column, and spinal cord.
- Visceral (splanchnic) arteries that transport blood and nutrients to the bronchi, lungs, esophagus, etc.
Under the diaphragm is the abdominal aorta, the parietal branches of which supply the abdominal cavity, the lower surface of the diaphragm, and the spine.
The internal branches of the abdominal aorta are divided into paired and unpaired. The vessels that extend from the unpaired trunks transport oxygen to the liver, spleen, stomach, intestines, and pancreas. The unpaired branches include the celiac trunk, as well as the superior and inferior mesenteric arteries.
There are only two paired trunks: renal, ovarian or testicular. These arterial vessels are adjacent to the organs of the same name.
The aorta ends with the left and right iliac arteries. Their branches extend to the pelvic organs and legs.
Many people are interested in the question of how the systemic circulatory system works. In the lungs, the blood is saturated with oxygen, after which it is transported to the left atrium, and then to the left ventricle. The iliac arteries supply blood to the legs, and the remaining branches supply blood to the chest, arms, and organs of the upper half of the body.
The veins of the systemic circulation carry oxygen-poor blood. The systemic circle ends with the superior and inferior vena cava.
The diagram of the veins of the systemic circle is quite clear. The femoral veins in the legs unite to form the iliac vein, which becomes the inferior vena cava. In the head, venous blood collects in the jugular veins, and in the arms - in the subclavian veins. The jugular as well as the subclavian vessels unite to form the innominate vein, which gives rise to the superior vena cava.
Blood supply to the head
The circulatory system of the head is the most complex structure of the body. The carotid artery, which is divided into 2 branches, is responsible for the blood supply to the parts of the head. The external carotid arterial vessel saturates the face, temporal region, oral cavity, nose, thyroid gland, etc. with oxygen and useful substances.
The main vessel supplying blood to the head is the carotid artery
The internal branch of the carotid artery goes deeper, forming the Circle of Wallisian, which transports blood to the brain. In the cranium, the internal carotid artery branches into the ophthalmic, anterior, middle cerebral, and communicating arteries.
This is how only ⅔ of the systemic circle is formed, which ends with the posterior cerebral arterial vessel. It has a different origin, the scheme of its formation is as follows: subclavian artery - vertebral - basilar - posterior cerebral. In this case, the brain is supplied with blood by the carotid and subclavian arteries, which are connected to each other. Thanks to anastomoses (vascular anastomoses), the brain survives minor disturbances in blood flow.
Principle of placement of arteries
The circulatory system of each body structure is approximately similar to that described above. Arterial vessels always approach organs along the shortest path. The vessels in the limbs pass precisely along the flexion side, since the extensor part is longer. Each artery originates at the site of the embryonic anlage of the organ, and not at its actual location. For example, the arterial vessel of the testicle emerges from the abdominal aorta. Thus, all vessels are connected to their organs from the inside.
The arrangement of blood vessels resembles the structure of the skeleton
The placement of arteries is also related to the structure of the skeleton. For example, the brachial branch runs along the upper limb, which corresponds to the humerus; the ulnar and radial arteries also pass next to the bones of the same name. And in the skull there are openings through which arterial vessels transport blood to the brain.
Arterial vessels of the systemic circulation form networks in the joint area using anastomoses. Thanks to this scheme, the joints are continuously supplied with blood during movement. The size of the vessels and their number depend not on the dimensions of the organ, but on its functional activity. Organs that work more intensively are saturated with a large number of arteries. Their placement around the organ depends on its structure. For example, the diagram of the vessels of parenchymal organs (liver, kidneys, lungs, spleen) corresponds to their shape.
Structure and functions of the pulmonary circulation
The pulmonary circulation originates from the right ventricle, from which several pulmonary arterial vessels emerge. A small circle closes in the left atrium, to which the pulmonary veins adjoin.
The pulmonary circulation is so called because it is responsible for gas exchange between the pulmonary capillaries and the alveoli of the same name. It consists of the common pulmonary artery, right and left branches with branches, pulmonary vessels, which unite into 2 right and 2 left veins and enter the left atrium.
The common pulmonary artery (diameter from 26 to 30 mm) emerges from the right ventricle; it runs diagonally (up and to the left), dividing into 2 branches that approach the lungs. The right pulmonary arterial vessel goes to the right to the medial surface of the lung, where it divides into 3 branches, which also have branches. The left vessel is shorter and thinner, it passes from the point of division of the common pulmonary artery to the medial part of the left lung in the transverse direction. Near the middle part of the lung, the left artery is divided into 2 branches, which in turn are divided into segmental branches.
Venules emanate from the capillary vessels of the lungs, which pass into the veins of the small circle. There are 2 veins coming out of each lung (upper and lower). When the common basal vein connects with the superior vein of the lower lobe, the right inferior pulmonary vein is formed.
The superior pulmonary trunk has 3 branches: apical-posterior, anterior, and lingular vein. It takes blood from the upper part of the left lung. The left upper trunk is larger than the lower one; it collects blood from the lower lobe of the organ.
The superior and inferior vena cava transport blood from the upper and lower parts of the body to the right atrium. From there, the blood is sent to the right ventricle, and then through the pulmonary artery to the lungs.
Under the influence of high pressure, blood rushes to the lungs, and under negative pressure, to the left atrium. For this reason, blood always moves slowly through the capillary vessels of the lungs. Thanks to this pace, the cells have time to become saturated with oxygen, and carbon dioxide penetrates into the blood. When a person plays sports or does hard work, the need for oxygen increases, then the heart increases pressure and blood flow accelerates.
Based on the foregoing, blood circulation is a complex system that provides vital functions to the entire body. The heart is a muscular pump, and arteries, veins, capillaries are systems of channels that transport oxygen and nutrients to all organs and tissues. It is important to monitor the state of the cardiovascular system, as any violation can have dangerous consequences.
The continuous movement of blood through a closed system of heart cavities and blood vessels is called circulation. The circulatory system helps ensure all vital functions of the body.
The movement of blood through the blood vessels occurs due to contractions of the heart. In humans, there are large and small circles of blood circulation.
Systemic and pulmonary circulation
Systemic circulation begins with the largest artery - the aorta. Due to the contraction of the left ventricle of the heart, blood is ejected into the aorta, which then breaks up into arteries, arterioles, supplying blood to the upper and lower extremities, head, torso, all internal organs and ending in capillaries.
Passing through the capillaries, the blood gives oxygen and nutrients to the tissues and takes away dissimilation products. From the capillaries, blood collects into small veins, which, merging and increasing their cross-section, form the superior and inferior vena cava.
A large circle of blood circulation ends in the right atrium. Arterial blood flows in all arteries of the systemic circulation, and venous blood flows in the veins.
Pulmonary circulation begins in the right ventricle, where venous blood enters from the right atrium. The right ventricle contracts and pushes blood into the pulmonary trunk, which divides into two pulmonary arteries that carry blood to the right and left lungs. In the lungs they are divided into capillaries surrounding each alveoli. In the alveoli, the blood releases carbon dioxide and is saturated with oxygen.
Through four pulmonary veins (there are two veins in each lung), oxygenated blood enters the left atrium (where the pulmonary circulation ends), and then into the left ventricle. Thus, venous blood flows in the arteries of the pulmonary circulation, and arterial blood flows in its veins.
The pattern of blood movement through the circulation was discovered by the English anatomist and physician W. Harvey in 1628.
Blood vessels: arteries, capillaries and veins
There are three types of blood vessels in humans: arteries, veins and capillaries.
Arteries- cylindrical tubes through which blood moves from the heart to organs and tissues. The walls of the arteries consist of three layers, which give them strength and elasticity:
- Outer connective tissue membrane;
- middle layer formed by smooth muscle fibers, between which elastic fibers lie
- inner endothelial membrane. Thanks to the elasticity of the arteries, the periodic pushing of blood from the heart into the aorta turns into a continuous movement of blood through the vessels.
Capillaries are microscopic vessels whose walls consist of a single layer of endothelial cells. Their thickness is about 1 micron, length 0.2-0.7 mm.
Due to the structural features, it is in the capillaries that blood performs its main functions: it gives oxygen and nutrients to tissues and removes carbon dioxide and other dissimilation products that need to be excreted.
Due to the fact that the blood in the capillaries is under pressure and moves slowly, in the arterial part of it, water and nutrients dissolved in it seep into the intercellular fluid. At the venous end of the capillary, blood pressure decreases and intercellular fluid flows back into the capillaries.
Vienna- vessels that carry blood from capillaries to the heart. Their walls consist of the same membranes as the walls of the aorta, but are much weaker than arterial ones and have fewer smooth muscle and elastic fibers.
Blood in the veins flows under low pressure, so the movement of blood through the veins is more influenced by surrounding tissues, especially skeletal muscles. Unlike arteries, veins (with the exception of hollow veins) have valves in the form of pockets that prevent the reverse flow of blood.
This is the continuous movement of blood through a closed cardiovascular system, ensuring the exchange of gases in the lungs and body tissues.
In addition to providing tissues and organs with oxygen and removing carbon dioxide from them, blood circulation delivers nutrients, water, salts, vitamins, hormones to cells and removes metabolic end products, and also maintains a constant body temperature, ensures humoral regulation and the interconnection of organs and organ systems in body.
The circulatory system consists of the heart and blood vessels that penetrate all organs and tissues of the body.
Blood circulation begins in the tissues where metabolism occurs through the walls of the capillaries. The blood, which has given oxygen to the organs and tissues, enters the right half of the heart and is sent by it to the pulmonary circulation, where the blood is saturated with oxygen, returns to the heart, entering its left half, and is again distributed throughout the body (systemic circulation) .
Heart- the main organ of the circulatory system. It is a hollow muscular organ consisting of four chambers: two atria (right and left), separated by an interatrial septum, and two ventricles (right and left), separated by an interventricular septum. The right atrium communicates with the right ventricle through the tricuspid valve, and the left atrium communicates with the left ventricle through the bicuspid valve. The average weight of an adult human heart is about 250 g in women and about 330 g in men. The length of the heart is 10-15 cm, the transverse size is 8-11 cm and the anteroposterior size is 6-8.5 cm. The heart volume in men is on average 700-900 cm 3, and in women - 500-600 cm 3.
The outer walls of the heart are formed by cardiac muscle, which is similar in structure to striated muscles. However, the heart muscle is distinguished by its ability to contract rhythmically automatically due to impulses arising in the heart itself, regardless of external influences (automatic heart).
The function of the heart is to rhythmically pump blood into the arteries, which comes to it through the veins. The heart beats about 70-75 times per minute when the body is at rest (1 time per 0.8 s). More than half of this time it rests - relaxes. The continuous activity of the heart consists of cycles, each of which consists of contraction (systole) and relaxation (diastole).
There are three phases of cardiac activity:
- contraction of the atria - atrial systole - takes 0.1 s
- contraction of the ventricles - ventricular systole - takes 0.3 s
- general pause - diastole (simultaneous relaxation of the atria and ventricles) - takes 0.4 s
Thus, during the entire cycle, the atria work for 0.1 s and rest for 0.7 s, the ventricles work for 0.3 s and rest for 0.5 s. This explains the ability of the heart muscle to work without getting tired throughout life. The high performance of the heart muscle is due to increased blood supply to the heart. Approximately 10% of the blood ejected by the left ventricle into the aorta enters the arteries that branch from it, which supply the heart.
Arteries- blood vessels that carry oxygenated blood from the heart to organs and tissues (only the pulmonary artery carries venous blood).
The artery wall is represented by three layers: the outer connective tissue membrane; middle, consisting of elastic fibers and smooth muscles; internal, formed by endothelium and connective tissue.
In humans, the diameter of the arteries ranges from 0.4 to 2.5 cm. The total volume of blood in the arterial system averages 950 ml. The arteries gradually branch into smaller and smaller vessels - arterioles, which turn into capillaries.
Capillaries(from the Latin “capillus” - hair) - the smallest vessels (average diameter does not exceed 0.005 mm, or 5 microns), penetrating the organs and tissues of animals and humans that have a closed circulatory system. They connect small arteries - arterioles with small veins - venules. Through the walls of capillaries, consisting of endothelial cells, gases and other substances are exchanged between the blood and various tissues.
Vienna- blood vessels carrying blood saturated with carbon dioxide, metabolic products, hormones and other substances from tissues and organs to the heart (with the exception of the pulmonary veins, which carry arterial blood). The wall of a vein is much thinner and more elastic than the wall of an artery. Small and medium-sized veins are equipped with valves that prevent blood from flowing back into these vessels. In humans, the volume of blood in the venous system averages 3200 ml.
Circulation circles
The movement of blood through vessels was first described in 1628 by the English physician W. Harvey.
In humans and mammals, blood moves through a closed cardiovascular system, consisting of the systemic and pulmonary circulation (Fig.).
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The large circle starts from the left ventricle, carries blood throughout the body through the aorta, gives oxygen to tissues in the capillaries, takes up carbon dioxide, turns from arterial to venous and returns through the superior and inferior vena cava to the right atrium. The pulmonary circulation begins from the right ventricle and carries blood through the pulmonary artery to the pulmonary capillaries. Here the blood releases carbon dioxide, is saturated with oxygen and flows through the pulmonary veins to the left atrium. From the left atrium, through the left ventricle, blood again enters the systemic circulation. |
Pulmonary circulation- pulmonary circle - serves to enrich the blood with oxygen in the lungs. It starts from the right ventricle and ends at the left atrium.
From the right ventricle of the heart, venous blood enters the pulmonary trunk (common pulmonary artery), which soon divides into two branches carrying blood to the right and left lungs.
In the lungs, arteries branch into capillaries. In the capillary networks that weave around the pulmonary vesicles, the blood gives up carbon dioxide and receives in return a new supply of oxygen (pulmonary respiration). Blood saturated with oxygen acquires a scarlet color, becomes arterial and flows from the capillaries into the veins, which, merging into four pulmonary veins (two on each side), flow into the left atrium of the heart. The pulmonary circulation ends in the left atrium, and arterial blood entering the atrium passes through the left atrioventricular opening into the left ventricle, where the systemic circulation begins. Consequently, venous blood flows in the arteries of the pulmonary circulation, and arterial blood flows in its veins.
Systemic circulation- bodily - collects venous blood from the upper and lower half of the body and similarly distributes arterial blood; starts from the left ventricle and ends at the right atrium.
From the left ventricle of the heart, blood flows into the largest arterial vessel - the aorta. Arterial blood contains the nutrients and oxygen necessary for the body to function and is bright scarlet in color.
The aorta branches into arteries that go to all organs and tissues of the body and pass through them into arterioles and then into capillaries. The capillaries, in turn, gather into venules and then into veins. Through the capillary wall, metabolism and gas exchange occurs between the blood and body tissues. Arterial blood flowing in the capillaries gives off nutrients and oxygen and in return receives metabolic products and carbon dioxide (tissue respiration). As a result, the blood entering the venous bed is poor in oxygen and rich in carbon dioxide and therefore has a dark color - venous blood; When bleeding, you can determine by the color of the blood which vessel is damaged - an artery or a vein. The veins merge into two large trunks - the superior and inferior vena cava, which flow into the right atrium of the heart. This section of the heart ends the systemic (bodily) circulation.
The complement to the great circle is third (cardiac) circle of blood circulation, serving the heart itself. It begins with the coronary arteries of the heart emerging from the aorta and ends with the veins of the heart. The latter merge into the coronary sinus, which flows into the right atrium, and the remaining veins open directly into the atrium cavity.
Movement of blood through vessels
Any liquid flows from a place where the pressure is higher to where it is lower. The greater the pressure difference, the higher the flow speed. Blood in the vessels of the systemic and pulmonary circulation also moves due to the pressure difference that the heart creates with its contractions.
In the left ventricle and aorta, blood pressure is higher than in the vena cava (negative pressure) and in the right atrium. The pressure difference in these areas ensures the movement of blood in the systemic circulation. High pressure in the right ventricle and pulmonary artery and low pressure in the pulmonary veins and left atrium ensure the movement of blood in the pulmonary circulation.
The pressure is highest in the aorta and large arteries (blood pressure). Blood pressure is not constant [show]
Blood pressure- this is the pressure of blood on the walls of the blood vessels and chambers of the heart, resulting from the contraction of the heart, pumping blood into the vascular system, and vascular resistance. The most important medical and physiological indicator of the state of the circulatory system is the pressure in the aorta and large arteries - blood pressure.
Arterial blood pressure is not a constant value. In healthy people at rest, the maximum, or systolic, blood pressure is distinguished - the level of pressure in the arteries during heart systole is about 120 mmHg, and the minimum, or diastolic, is the level of pressure in the arteries during diastole of the heart is about 80 mmHg. Those. arterial blood pressure pulsates in time with the contractions of the heart: at the moment of systole it rises to 120-130 mm Hg. Art., and during diastole it decreases to 80-90 mm Hg. Art. These pulse pressure fluctuations occur simultaneously with pulse fluctuations of the arterial wall.
As blood moves through the arteries, part of the pressure energy is used to overcome the friction of the blood against the walls of the vessels, so the pressure gradually drops. A particularly significant drop in pressure occurs in the smallest arteries and capillaries - they offer the greatest resistance to blood movement. In the veins, blood pressure continues to gradually decrease, and in the vena cava it is equal to or even lower than atmospheric pressure. Blood circulation indicators in different parts of the circulatory system are given in Table. 1.
The speed of blood movement depends not only on the pressure difference, but also on the width of the bloodstream. Although the aorta is the widest vessel, it is the only one in the body and all the blood flows through it, which is pushed out by the left ventricle. Therefore, the maximum speed here is 500 mm/s (see Table 1). As the arteries branch, their diameter decreases, but the total cross-sectional area of all arteries increases and the speed of blood movement decreases, reaching 0.5 mm/s in the capillaries. Due to such a low speed of blood flow in the capillaries, the blood has time to give oxygen and nutrients to the tissues and accept their waste products.
The slowdown in blood flow in the capillaries is explained by their huge number (about 40 billion) and large total lumen (800 times larger than the lumen of the aorta). The movement of blood in the capillaries is carried out due to changes in the lumen of the supplying small arteries: their expansion increases blood flow in the capillaries, and narrowing decreases it.
The veins on the way from the capillaries, as they approach the heart, enlarge and merge, their number and the total lumen of the bloodstream decrease, and the speed of blood movement increases compared to the capillaries. From the table 1 also shows that 3/4 of all blood is in the veins. This is due to the fact that the thin walls of the veins are able to stretch easily, so they can contain significantly more blood than the corresponding arteries.
The main reason for the movement of blood through the veins is the pressure difference at the beginning and end of the venous system, so the movement of blood through the veins occurs in the direction of the heart. This is facilitated by the suction action of the chest ("respiratory pump") and the contraction of skeletal muscles ("muscle pump"). During inhalation, the pressure in the chest decreases. In this case, the pressure difference at the beginning and end of the venous system increases, and blood through the veins is directed to the heart. Skeletal muscles contract and compress the veins, which also helps move blood to the heart.
The relationship between the speed of blood movement, the width of the bloodstream and blood pressure is illustrated in Fig. 3. The amount of blood flowing per unit time through the vessels is equal to the product of the speed of blood movement and the cross-sectional area of the vessels. This value is the same for all parts of the circulatory system: the amount of blood the heart pushes into the aorta, the same amount flows through the arteries, capillaries and veins, and the same amount returns back to the heart, and is equal to the minute volume of blood.
Redistribution of blood in the body
If the artery extending from the aorta to some organ expands due to the relaxation of its smooth muscles, then the organ will receive more blood. At the same time, other organs will receive less blood due to this. This is how blood is redistributed in the body. Due to redistribution, more blood flows to working organs at the expense of organs that are currently at rest.
The redistribution of blood is regulated by the nervous system: simultaneously with the dilation of blood vessels in working organs, the blood vessels of non-working organs narrow and blood pressure remains unchanged. But if all the arteries dilate, this will lead to a drop in blood pressure and a decrease in the speed of blood movement in the vessels.
Blood circulation time
Blood circulation time is the time required for blood to pass through the entire circulation. A number of methods are used to measure blood circulation time [show]
The principle of measuring the time of blood circulation is that a substance that is not usually found in the body is injected into a vein, and it is determined after what period of time it appears in the vein of the same name on the other side or causes its characteristic effect. For example, a solution of the alkaloid lobeline, which acts through the blood on the respiratory center of the medulla oblongata, is injected into the cubital vein, and the time from the moment of administration of the substance to the moment when a short-term breath holding or cough appears is determined. This occurs when lobeline molecules, having circulated in the circulatory system, affect the respiratory center and cause a change in breathing or cough.
In recent years, the rate of blood circulation in both circles of blood circulation (or only in the small, or only in the large circle) is determined using a radioactive sodium isotope and an electron counter. To do this, several such counters are placed on different parts of the body near large vessels and in the heart area. After introducing a radioactive sodium isotope into the cubital vein, the time of appearance of radioactive radiation in the area of the heart and the vessels under study is determined.
The blood circulation time in humans is on average approximately 27 heart systoles. At 70-80 heart beats per minute, complete blood circulation occurs in approximately 20-23 seconds. We must not forget, however, that the speed of blood flow along the axis of the vessel is greater than at its walls, and also that not all vascular areas have the same length. Therefore, not all blood circulates so quickly, and the time indicated above is the shortest.
Studies on dogs have shown that 1/5 of the time of complete blood circulation is in the pulmonary circulation and 4/5 in the systemic circulation.
Regulation of blood circulation
Innervation of the heart. The heart, like other internal organs, is innervated by the autonomic nervous system and receives double innervation. Sympathetic nerves approach the heart, which strengthen and accelerate its contractions. The second group of nerves - parasympathetic - acts on the heart in the opposite way: it slows down and weakens heart contractions. These nerves regulate the functioning of the heart.
In addition, the functioning of the heart is influenced by the adrenal hormone - adrenaline, which enters the heart with the blood and increases its contractions. The regulation of organ function with the help of substances carried by the blood is called humoral.
The nervous and humoral regulation of the heart in the body act in concert and ensure precise adaptation of the activity of the cardiovascular system to the needs of the body and environmental conditions.
Innervation of blood vessels. Blood vessels are supplied by sympathetic nerves. Excitation spreading through them causes contraction of smooth muscles in the walls of blood vessels and narrows the blood vessels. If you cut the sympathetic nerves going to a certain part of the body, the corresponding vessels will dilate. Consequently, excitation constantly flows through the sympathetic nerves to the blood vessels, which keeps these vessels in a state of some constriction - vascular tone. When excitation intensifies, the frequency of nerve impulses increases and the vessels constrict more strongly - vascular tone increases. On the contrary, when the frequency of nerve impulses decreases due to inhibition of sympathetic neurons, vascular tone decreases and blood vessels dilate. In addition to vasoconstrictors, vasodilator nerves also approach the vessels of some organs (skeletal muscles, salivary glands). These nerves are stimulated and dilate the blood vessels of the organs as they work. The lumen of blood vessels is also affected by substances carried by the blood. Adrenaline constricts blood vessels. Another substance, acetylcholine, secreted by the endings of some nerves, dilates them.
Regulation of the cardiovascular system. The blood supply to organs changes depending on their needs due to the described redistribution of blood. But this redistribution can only be effective if the pressure in the arteries does not change. One of the main functions of the nervous regulation of blood circulation is to maintain constant blood pressure. This function is carried out reflexively.
There are receptors in the wall of the aorta and carotid arteries that become more irritated if blood pressure exceeds normal levels. Excitation from these receptors goes to the vasomotor center located in the medulla oblongata and inhibits its work. From the center along the sympathetic nerves to the vessels and heart, weaker excitation begins to flow than before, and the blood vessels dilate, and the heart weakens its work. Due to these changes, blood pressure decreases. And if the pressure for some reason drops below normal, then the irritation of the receptors stops completely and the vasomotor center, without receiving inhibitory influences from the receptors, increases its activity: it sends more nerve impulses per second to the heart and blood vessels, the vessels narrow, the heart contracts more often and stronger, blood pressure rises.
Cardiac hygiene
Normal activity of the human body is possible only if there is a well-developed cardiovascular system. The speed of blood flow will determine the degree of blood supply to organs and tissues and the rate of removal of waste products. During physical work, the organs' need for oxygen increases simultaneously with the intensification and acceleration of heart contractions. Only a strong heart muscle can provide such work. To be resilient to a variety of work activities, it is important to train the heart and increase the strength of its muscles.
Physical labor and physical education develop the heart muscle. To ensure normal function of the cardiovascular system, a person should start his day with morning exercises, especially people whose professions do not involve physical labor. To enrich the blood with oxygen, it is better to perform physical exercises in the fresh air.
It must be remembered that excessive physical and mental stress can cause disruption of the normal functioning of the heart and its disease. Alcohol, nicotine, and drugs have a particularly harmful effect on the cardiovascular system. Alcohol and nicotine poison the heart muscle and nervous system, causing severe disturbances in the regulation of vascular tone and heart activity. They lead to the development of severe diseases of the cardiovascular system and can cause sudden death. Young people who smoke and drink alcohol are more likely than others to experience heart spasms, which can cause severe heart attacks and sometimes death.
First aid for wounds and bleeding
Injuries are often accompanied by bleeding. There are capillary, venous and arterial bleeding.
Capillary bleeding occurs even with a minor injury and is accompanied by a slow flow of blood from the wound. Such a wound should be treated with a solution of brilliant green (brilliant green) for disinfection and a clean gauze bandage should be applied. The bandage stops bleeding, promotes the formation of a blood clot and prevents germs from entering the wound.
Venous bleeding is characterized by a significantly higher rate of blood flow. The blood that flows out is dark in color. To stop bleeding, it is necessary to apply a tight bandage below the wound, that is, further from the heart. After stopping the bleeding, the wound is treated with a disinfectant (3% hydrogen peroxide solution, vodka), and bandaged with a sterile pressure bandage.
During arterial bleeding, scarlet blood gushes from the wound. This is the most dangerous bleeding. If an artery in a limb is damaged, you need to raise the limb as high as possible, bend it and press the wounded artery with your finger in the place where it comes close to the surface of the body. It is also necessary above the wound site, that is, closer to the heart, to apply a rubber tourniquet (you can use a bandage or rope for this) and tighten it tightly to completely stop the bleeding. The tourniquet should not be kept tight for more than 2 hours. When applying it, you must attach a note in which you should indicate the time of application of the tourniquet.
It should be remembered that venous, and even more so, arterial bleeding can lead to significant blood loss and even death. Therefore, if injured, it is necessary to stop the bleeding as soon as possible, and then take the victim to the hospital. Severe pain or fear can cause a person to lose consciousness. Loss of consciousness (fainting) is a consequence of inhibition of the vasomotor center, a drop in blood pressure and insufficient blood supply to the brain. The person who has lost consciousness should be given a smell of some non-toxic substance with a strong odor (for example, ammonia), moisten his face with cold water, or lightly pat his cheeks. When olfactory or skin receptors are irritated, excitation from them enters the brain and relieves inhibition of the vasomotor center. Blood pressure rises, the brain receives sufficient nutrition, and consciousness returns.
