The vessels in the human body form two closed circulatory systems. There are large and small circles of blood circulation. The vessels of the great circle supply blood to the organs, the vessels of the small circle provide gas exchange in the lungs.
Systemic circulation: arterial (oxygenated) blood flows from the left ventricle of the heart through the aorta, then through the arteries, arterial capillaries to all organs; from the organs, venous blood (saturated with carbon dioxide) flows through the venous capillaries into the veins, from there through the superior vena cava (from the head, neck and arms) and the inferior vena cava (from the torso and legs) into the right atrium.
Pulmonary circulation: venous blood flows from the right ventricle of the heart through pulmonary artery into a dense network of capillaries entwining the pulmonary vesicles, where the blood is saturated with oxygen, then arterial blood flows through the pulmonary veins into the left atrium. In the pulmonary circulation, arterial blood flows through the veins, venous blood through the arteries. It begins in the right ventricle and ends in the left atrium. The pulmonary trunk emerges from the right ventricle, carrying venous blood to the lungs. Here the pulmonary arteries break up into vessels of smaller diameter, which turn into capillaries. Oxygenated blood flows through the four pulmonary veins into the left atrium.
Blood moves through the vessels due to the rhythmic work of the heart. During ventricular contraction, blood is forced under pressure into the aorta and pulmonary trunk. The highest pressure develops here - 150 mm Hg. Art. As blood moves through the arteries, the pressure drops to 120 mmHg. Art., and in capillaries - up to 22 mm. Lowest venous pressure; in large veins it is below atmospheric.
Blood is ejected from the ventricles in portions, and the continuity of its flow is ensured by the elasticity of the artery walls. At the moment of contraction of the ventricles of the heart, the walls of the arteries stretch, and then, due to elastic elasticity, return to their original state even before the next flow of blood from the ventricles. Thanks to this, the blood moves forward. Rhythmic fluctuations in the diameter of arterial vessels caused by the work of the heart are called pulse. It can be easily palpated in places where the arteries lie on the bone (radial, dorsal artery of the foot). By counting the pulse, you can determine the frequency of heart contractions and their strength. In a healthy adult, the pulse rate at rest is 60-70 beats per minute. With various heart diseases, arrhythmia is possible - interruptions in the pulse.
Blood flows at the highest speed in the aorta - about 0.5 m/s. Subsequently, the speed of movement drops and in the arteries reaches 0.25 m/s, and in the capillaries - approximately 0.5 mm/s. The slow flow of blood in the capillaries and the large extent of the latter favor metabolism (the total length of capillaries in the human body reaches 100 thousand km, and the total surface of all capillaries in the body is 6300 m2). The large difference in the speed of blood flow in the aorta, capillaries and veins is due to the unequal width of the overall cross-section bloodstream in its various parts. The narrowest such section is the aorta, and the total lumen of the capillaries is 600-800 times greater than the lumen of the aorta. This explains the slowdown in blood flow in the capillaries.
The movement of blood through the vessels is regulated by neurohumoral factors. Impulses sent along nerve endings can cause either a narrowing or expansion of the lumen of blood vessels. Two types of vasomotor nerves approach the smooth muscles of the walls of blood vessels: vasodilators and vasoconstrictors.
The impulses traveling along these nerve fibers arise in the vasomotor center of the medulla oblongata. In the normal state of the body, the walls of the arteries are somewhat tense and their lumen is narrowed. From the vasomotor center, impulses continuously flow through the vasomotor nerves, which determine constant tone. Nerve endings in the walls of blood vessels react to changes in pressure and chemical composition of the blood, causing excitement in them. This excitation enters the central nervous system, resulting in a reflex change in the activity of the cardiovascular system. Thus, an increase and decrease in the diameters of blood vessels occurs in a reflex way, but the same effect can also occur under the influence of humoral factors - chemical substances that are in the blood and come here with food and from various internal organs. Among them, vasodilators and vasoconstrictors are important. For example, the pituitary hormone - vasopressin, the thyroid hormone - thyroxine, the adrenal gland hormone - adrenaline constricts blood vessels, enhances all functions of the heart, and histamine formed in the walls digestive tract and in any working organ, it acts in the opposite way: it expands the capillaries without affecting other vessels. A significant effect on the functioning of the heart is exerted by changes in the content of potassium and calcium in the blood. An increase in calcium content increases the frequency and strength of contractions, increases the excitability and conductivity of the heart. Potassium causes exactly the opposite effect.
The expansion and contraction of blood vessels in various organs significantly affects the redistribution of blood in the body. More blood is sent to a working organ, where the vessels are dilated, and to a non-working organ - \ less. The depositing organs are the spleen, liver, and subcutaneous fat.
IN circulatory system There are two circles of blood circulation: large and small. They begin in the ventricles of the heart and end in the atria (Fig. 232).
Systemic circulation begins with the aorta from the left ventricle of the heart. Through it, arterial vessels bring blood rich in oxygen and nutrients to the capillary system of all organs and tissues.
Venous blood from the capillaries of organs and tissues enters small, then larger veins and ultimately, through the superior and inferior vena cava, collects in the right atrium, where it ends big circle blood circulation
Pulmonary circulation begins in the right ventricle with the pulmonary trunk. Through it, venous blood reaches the capillary bed of the lungs, where it is freed from excess carbon dioxide, enriched with oxygen and returns to the left atrium through four pulmonary veins (two veins from each lung). The pulmonary circulation ends in the left atrium.
Vessels of the pulmonary circulation. The pulmonary trunk (truncus pulmonalis) begins from the right ventricle on the anterior superior surface of the heart. It rises up and to the left and crosses the aorta lying behind it. The length of the pulmonary trunk is 5-6 cm. Under the aortic arch (at level IV thoracic vertebra) it is divided into two branches: the right pulmonary artery (a. pulmonalis dextra) and the left pulmonary artery (a. pulmonalis sinistra). From the terminal part of the pulmonary trunk to the concave surface of the aorta there is a ligament (arterial ligament) *. The pulmonary arteries are divided into lobar, segmental and subsegmental branches. The latter, accompanying the branches of the bronchi, form a capillary network that densely entwines the alveoli of the lungs, in the area of which gas exchange occurs between the blood and the air in the alveoli. Due to the difference in partial pressure, carbon dioxide passes from the blood into the alveolar air, and oxygen enters the blood from the alveolar air. Hemoglobin contained in red blood cells plays an important role in this gas exchange.
* (The ligament arteriosus is a remnant of the overgrown ductus arteriosus of the fetus. During the period of embryonic development, when the lungs do not function, most of blood from the pulmonary trunk is transferred through the ductus botallus to the aorta and thus bypasses the pulmonary circulation. During this period, only small vessels - the rudiments of the pulmonary arteries - go to the non-breathing lungs from the pulmonary trunk.)
From the capillary bed of the lungs, oxygenated blood passes sequentially into the subsegmental, segmental and then lobar veins. The latter in the area of the gate of each lung form two right and two left pulmonary veins (vv. pulmonales dextra et sinistra). Each of the pulmonary veins usually drains separately into the left atrium. Unlike veins in other areas of the body, the pulmonary veins contain arterial blood and do not have valves.
Vessels of the systemic circulation. The main trunk of the systemic circulation is the aorta (aorta) (see Fig. 232). It starts from the left ventricle. It distinguishes between the ascending part, the arc and the descending part. The ascending aorta in primary department forms a significant expansion - an onion. The length of the ascending part of the aorta is 5-6 cm. At the level of the lower edge of the manubrium of the sternum, the ascending part passes into the aortic arch, which goes back and to the left, spreads through the left bronchus and at the level of the IV thoracic vertebra passes into the descending part of the aorta.
The right and left coronary arteries of the heart depart from the ascending aorta in the region of the bulb. From the convex surface of the aortic arch, the brachiocephalic trunk (innominate artery) departs successively from right to left, then the left common carotid artery and left subclavian artery.
The final vessels of the systemic circulation are the superior and inferior vena cava (vv. cavae superior et inferior) (see Fig. 232).
The superior vena cava is a large but short trunk, its length is 5-6 cm. It lies to the right and somewhat posterior to the ascending aorta. The superior vena cava is formed by the confluence of the right and left brachiocephalic veins. The confluence of these veins is projected at the level of the connection of the first right rib with the sternum. The superior vena cava collects blood from the head, neck, upper limbs, organs and walls chest cavity, from the venous plexuses of the spinal canal and partially from the walls abdominal cavity.
The inferior vena cava (Fig. 232) is the largest venous trunk. It is formed at the level of the IV lumbar vertebra by the confluence of the right and left common iliac veins. The inferior vena cava, rising upward, reaches the opening of the same name in the tendon center of the diaphragm, passes through it into the chest cavity and immediately flows into the right atrium, which in this place is adjacent to the diaphragm.
In the abdominal cavity, the inferior vena cava lies on the anterior surface of the right psoas major muscle, to the right of the lumbar vertebral bodies and the aorta. The inferior vena cava collects blood from the paired organs of the abdominal cavity and the walls of the abdominal cavity, the venous plexuses of the spinal canal and the lower extremities.
A person has a closed circulatory system, the central place in it is occupied by a four-chambered heart. Regardless of the composition of the blood, all vessels coming to the heart are considered to be veins, and those leaving it are considered to be arteries. Blood in the human body moves through the large, small and cardiac circulation circles.
Pulmonary circulation (pulmonary). Venous blood from the right atrium passes through the right atrioventricular orifice into the right ventricle, which contracts and pushes blood into the pulmonary trunk. The latter is divided into the right and left pulmonary arteries, passing through the hilum of the lungs. In the lung tissue, the arteries divide into capillaries surrounding each alveolus. After red blood cells release carbon dioxide and enrich them with oxygen, venous blood turns into arterial blood. Arterial blood flows through four pulmonary veins (there are two veins in each lung) into the left atrium, and then passes through the left atrioventricular orifice into the left ventricle. The systemic circulation begins from the left ventricle.
Systemic circulation. Arterial blood from the left ventricle is ejected into the aorta during its contraction. The aorta breaks up into arteries that supply blood to the head, neck, limbs, torso and all internal organs, in which they end in capillaries. From the blood capillaries into the tissues come nutrients, water, salts and oxygen, metabolic products and carbon dioxide are resorbed. The capillaries gather into venules, where the venous system of vessels begins, representing the roots of the superior and inferior vena cava. Venous blood through these veins enters the right atrium, where the systemic circulation ends.
Cardiac circulation. This circle of blood circulation begins from the aorta with two coronary cardiac arteries, through which blood enters all layers and parts of the heart, and then collects through small veins into the coronary sinus. This vessel opens with a wide mouth into the right atrium of the heart. Some of the small veins of the heart wall open into the cavity of the right atrium and ventricle of the heart independently.
Thus, only after passing through the small circle of blood circulation does the blood enter the large circle, and it moves through a closed system. The speed of blood circulation in a small circle is 4-5 seconds, in a large circle - 22 seconds.
Criteria for assessing the activity of the cardiovascular system.
To evaluate the work of the cardiovascular system, its following characteristics are examined - pressure, pulse, electrical work of the heart.
ECG. Electrical phenomena observed in tissues during excitation are called action currents. They also arise in the beating heart, since the excited area becomes electronegative relative to the non-excited one. They can be recorded using an electrocardiograph.
Our body is a liquid conductor, i.e. a conductor of the second kind, the so-called ionic one, therefore the biocurrents of the heart are conducted throughout the body and can be recorded from the surface of the skin. To avoid interfering with the currents of the skeletal muscles, the person is placed on a couch, asked to lie still, and electrodes are applied.
To record three standard bipolar leads from the limbs, electrodes are applied to the skin of the right and left arms - lead I, right hand and the left leg - II lead and the left arm and left leg - III lead.
When registering chest (pericardial) unipolar leads, designated by the letter V, one electrode, which is inactive (indifferent), is applied to the skin of the left leg, and the second, active, is placed on certain points on the anterior surface of the chest (V1, V2, V3, V4, v5, V6). These leads help determine the location of damage to the heart muscle. The recording curve of the biocurrents of the heart is called an electrocardiogram (ECG). The ECG of a healthy person has five waves: P, Q, R, S, T. The P, R and T waves are usually directed upward (positive waves), Q and S are directed downwards (negative waves). The P wave reflects atrial excitation. At the time when excitation reaches the muscles of the ventricles and spreads through them, a QRS wave appears. The T wave reflects the process of cessation of excitation (repolarization) in the ventricles. Thus, the P wave makes up the atrial part of the ECG, and the complex of Q, R, S, T waves makes up the ventricular part.
Electrocardiography makes it possible to study changes in detail heart rate, disruption of the conduction of excitation through the conduction system of the heart, the appearance of an additional focus of excitation when extrasystoles appear, ischemia, cardiac infarction.
Blood pressure. The value of blood pressure is an important characteristic of the activity of the cardiovascular system. An indispensable condition for the movement of blood through the system of blood vessels is the difference in blood pressure in the arteries and veins, which is created and maintained by the heart. With each systole of the heart, a certain volume of blood is pumped into the artery. Due to the high resistance in the arterioles and capillaries, until the next systole only part of the blood has time to pass into the veins and the pressure in the arteries does not drop to zero.
The level of pressure in the arteries should be determined by the size of the systolic volume of the heart and the resistance indicator in the peripheral vessels: the more forcefully the heart contracts and the more narrowed the arterioles and capillaries, the higher the blood pressure. In addition to these two factors: cardiac work and peripheral resistance, the volume of circulating blood and its viscosity influence the value of blood pressure.
The highest pressure observed during systole is called maximum, or systolic, pressure. The lowest pressure during diastole is called minimum, or diastolic. The amount of pressure depends on age. In children, the arterial walls are more elastic, so their blood pressure is lower than in adults. In healthy adults, the normal maximum pressure is 110 - 120 mmHg. Art., and the minimum is 70 - 80 mm Hg. Art. In old age, when the elasticity of the vascular walls as a result of sclerotic changes decreases, the level of blood pressure increases.
The difference between the maximum and minimum pressure is called pulse pressure. It is equal to 40 - 50 mm Hg. Art.
Blood pressure can be measured by two methods - direct and indirect. When measuring using the direct, or bloody, method, a glass cannula is tied into the central end of the artery or a hollow needle is inserted, which is connected with a rubber tube to a measuring device, such as a mercury manometer. In the direct method, a person’s blood pressure is recorded during major operations, for example on the heart, when It is necessary to continuously monitor the pressure level.
To determine pressure, the indirect, or indirect, method is used to find the external pressure that is sufficient to compress the artery. In medical practice, blood pressure in the brachial artery is usually measured using the indirect sound Korotkoff method using a Riva-Rocci mercury sphygmomanometer or a spring tonometer. A hollow rubber cuff is placed on the shoulder, which is connected to a rubber pressure bulb and a pressure gauge indicating the pressure in the cuff. When air is pumped into the cuff, it puts pressure on the tissues of the shoulder and compresses the brachial artery, and the pressure gauge shows the amount of this pressure. Vascular sounds are listened to with a phonendoscope above the ulnar artery, below the cuff.N. S. Korotkov established that in an uncompressed artery there are no sounds during blood movement. If you raise the pressure above the systolic level, the cuff will completely compress the lumen of the artery and the blood flow in it will stop. There are also no sounds. If you now gradually release air from the cuff and reduce the pressure in it, then at the moment when it becomes slightly below systolic, blood during systole will break through the compressed area with great force and a vascular tone will be heard below the cuff in the ulnar artery. The pressure in the cuff at which the first vascular sounds appear corresponds to the maximum, or systolic, pressure. With further release of air from the cuff, i.e., a decrease in pressure in it, the sounds intensify, and then either sharply weaken or disappear. This moment corresponds to diastolic pressure.
Pulse. The pulse is a rhythmic oscillation in diameter arterial vessels, arising during the work of the heart. When blood is expelled from the heart, the pressure in the aorta rises, and a wave of increased pressure spreads along the arteries to the capillaries. It is easy to feel the pulsation of the arteries that lie on the bone (radial, superficial temporal, dorsal artery of the foot, etc.). Most often, the pulse is examined at the radial artery. By feeling and counting the pulse, you can determine the frequency of heart contractions, their strength, as well as the degree of elasticity of blood vessels. An experienced doctor, by pressing on the artery until the pulsation completely stops, can quite accurately determine the height of blood pressure. In a healthy person, the pulse is rhythmic, i.e. the blows follow at regular intervals. With heart disease, rhythm disturbances - arrhythmia - may occur. In addition, such characteristics of the pulse as tension (the amount of pressure in the vessels), filling (the amount of blood in the bloodstream) are also taken into account.
Blood circulation is the continuous movement of blood along a closed cardiac circuit. vascular system, providing vital important functions body. The cardiovascular system includes organs such as the heart and blood vessels.
Heart
Heart - central authority blood circulation, ensuring the movement of blood through the vessels.
The heart is a hollow four chambered muscular organ, having the shape of a cone, located in the chest cavity, in the mediastinum. It is divided into right and left halves by a continuous partition. Each half consists of two sections: the atrium and the ventricle, connected to each other by an opening that is closed by a leaflet valve. In the left half, the valve consists of two valves, in the right - of three. The valves open towards the ventricles. This is facilitated by tendon filaments, which are attached at one end to the valve leaflets, and at the other to the papillary muscles located on the walls of the ventricles. During ventricular contraction, tendon threads prevent the valves from everting towards the atrium. Blood enters the right atrium from the superior and inferior vena cava and the coronary veins of the heart itself; four pulmonary veins flow into the left atrium.
The ventricles give rise to vessels: the right one - the pulmonary trunk, which is divided into two branches and carries venous blood to the right and left lungs, that is, to the pulmonary circulation; The left ventricle gives rise to the left aortic arch, but through which arterial blood enters the systemic circulation. At the border of the left ventricle and the aorta, the right ventricle and the pulmonary trunk, there are semilunar valves (three cusps in each). They close the lumens of the aorta and pulmonary trunk and allow blood to pass from the ventricles into the vessels, but prevent the reverse flow of blood from the vessels to the ventricles.
The wall of the heart consists of three layers: the inner - endocardium, formed by epithelial cells, the middle - myocardium, muscle and outer - epicardium, consisting of connective tissue.
The heart lies freely in the pericardial sac of connective tissue, where fluid is constantly present, moisturizing the surface of the heart and ensuring its free contraction. The main part of the heart wall is muscular. The greater the force of muscle contraction, the more powerfully developed is the muscular layer of the heart, for example, the greatest thickness of the walls is in the left ventricle (10–15 mm), the walls of the right ventricle are thinner (5–8 mm), and the walls of the atria are even thinner (23 mm).
The structure of the heart muscle is similar to the striated muscles, but differs from them in the ability to automatically contract rhythmically due to impulses arising in the heart itself, regardless of external conditions - cardiac automaticity. This is due to special nerve cells, located in the heart muscle, in which excitations arise rhythmically. The automatic contraction of the heart continues even when it is isolated from the body.
Normal metabolism in the body is ensured by the continuous movement of blood. Blood in the cardiovascular system flows in only one direction: from the left ventricle through the systemic circulation it enters the right atrium, then into the right ventricle and then through the pulmonary circulation it returns to the left atrium, and from there to the left ventricle. This movement of blood is determined by the work of the heart due to the sequential alternation of contractions and relaxations of the heart muscle.
There are three phases in the work of the heart: the first is contraction of the atria, the second is contraction of the ventricles (systole), the third is the simultaneous relaxation of the atria and ventricles, diastole, or pause. The heart beats rhythmically about 70–75 times per minute when the body is at rest, or 1 time every 0.8 seconds. Of this time, contraction of the atria accounts for 0.1 seconds, contraction of the ventricles accounts for 0.3 seconds, and the total pause of the heart lasts 0.4 seconds.
The period from one atrial contraction to another is called the cardiac cycle. The continuous activity of the heart consists of cycles, each of which consists of contraction (systole) and relaxation (diastole). The heart muscle, the size of a fist and weighing about 300 g, works continuously for decades, contracts about 100 thousand times a day and pumps more than 10 thousand liters of blood. Such high performance of the heart is due to its increased blood supply and high level metabolic processes occurring in it.
The nervous and humoral regulation of the activity of the heart coordinates its work with the needs of the body at any given moment, regardless of our will.
The heart as a working organ is regulated by the nervous system in accordance with the influences of the external and internal environment. Innervation occurs with the participation of the autonomic nervous system. However, a pair of nerves (sympathetic fibers), when irritated, strengthen and speed up heart contractions. When another pair of nerves (parasympathetic, or vagus) is irritated, impulses entering the heart weaken its activity.
The activity of the heart is also influenced humoral regulation. Thus, adrenaline produced by the adrenal glands has the same effect on the heart as the sympathetic nerves, and an increase in potassium in the blood inhibits the heart, just like the parasympathetic (vagus) nerves.
Circulation
The movement of blood through vessels is called circulation. Only by being constantly in motion does the blood carry out its main functions: the delivery of nutrients and gases and the removal of final decay products from tissues and organs.
Blood moves through blood vessels- hollow tubes of various diameters, which, without interruption, pass into others, forming a closed circulatory system.
Three types of vessels of the circulatory system
There are three types of vessels: arteries, veins and capillaries. Arteries called the vessels through which blood flows from the heart to the organs. The largest of them is the aorta. In organs, arteries branch into vessels of smaller diameter - arterioles, which in turn break up into capillaries. Moving through the capillaries, arterial blood gradually turns into venous blood, which flows through veins.
Two circles of blood circulation
All arteries, veins and capillaries in the human body are combined into two circles of blood circulation: large and small. Systemic circulation begins in the left ventricle and ends in the right atrium. Pulmonary circulation begins in the right ventricle and ends in the left atrium.
Blood moves through the vessels due to the rhythmic work of the heart, as well as the difference in pressure in the vessels when blood leaves the heart and in the veins when it returns to the heart. Rhythmic fluctuations in the diameter of arterial vessels caused by the work of the heart are called pulse.
Using your pulse, you can easily determine the number of heartbeats per minute. Spread speed pulse wave about 10 m/s.
The speed of blood flow in the vessels is about 0.5 m/s in the aorta, and only 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 the fact that their number is huge (about 40 billion) and, despite their microscopic size, their total lumen is 800 times larger than the lumen of the aorta. In the veins, with their enlargement as they approach the heart, the total lumen of the bloodstream decreases, and the speed of blood flow increases.
Blood pressure
When the next portion of blood is ejected from the heart into the aorta and into the pulmonary artery, high blood pressure is created in them. Blood pressure rises when the heart pumps faster and harder, pumping more blood into the aorta, and when the arterioles narrow.
If the arteries dilate, blood pressure drops. Blood pressure is also affected by the amount of circulating blood and its viscosity. As you move away from the heart, blood pressure decreases and becomes lowest in the veins. Difference between high pressure blood in the aorta and pulmonary artery and low, even negative pressure in the vena cava and pulmonary veins ensures a continuous flow of blood throughout the entire circulation.
In healthy people, the maximum blood pressure in the brachial artery at rest is normally about 120 mmHg. Art., and the minimum is 70–80 mm Hg. Art.
A persistent increase in blood pressure at rest is called hypertension, and a decrease in blood pressure is called hypotension. In both cases, the blood supply to the organs is disrupted and their working conditions worsen.
First aid for blood loss
First aid for blood loss is determined by the nature of the bleeding, which can be arterial, venous or capillary.
The most dangerous arterial bleeding occurs when the arteries are injured, and the blood is bright scarlet in color and flows in a strong stream (spring). If an arm or leg is injured, it is necessary to raise the limb, keep it in a bent position, and press the damaged artery with a finger above the wound site (closer to the heart); then you need to apply a tight bandage made of a bandage, towel, or piece of cloth above the wound site (also closer to the heart). A tight bandage should not be left in place for more than an hour and a half, so the victim must be taken to a medical facility as soon as possible.
With venous bleeding, the flowing blood is darker in color; to stop it, the damaged vein is pressed with a finger at the wound site, the arm or leg is bandaged below it (further from the heart).
With a small wound, capillary bleeding appears, to stop which it is enough to apply a tight sterile bandage. The bleeding will stop due to the formation of a blood clot.
Lymph circulation
It's called lymph circulation, moving lymph through the vessels. Lymphatic system promotes additional outflow of fluid from organs. Lymph movement is very slow (03 mm/min). It moves in one direction - from the organs to the heart. Lymphatic capillaries turn into larger vessels, which collect in the right and left thoracic ducts, flowing into large veins. Along the course of the lymphatic vessels there are The lymph nodes: in the groin, popliteal and armpits, under the lower jaw.
The lymph nodes contain cells (lymphocytes) that have a phagocytic function. They neutralize microbes and utilize foreign substances that have entered the lymph, causing the lymph nodes to swell and become painful. Tonsils are lymphoid accumulations in the pharynx area. Sometimes they retain pathogenic microorganisms, the metabolic products of which negatively affect the function of internal organs. Often resort to surgical removal of the tonsils.
Question 1. What kind of blood flows through the arteries of the systemic circle, and what kind of blood flows through the arteries of the small circle?
Arterial blood flows through the arteries of the systemic circle, and venous blood flows through the arteries of the small circle.
Question 2. Where does the systemic circulation begin and end, and where does the pulmonary circulation end?
All vessels form two circles of blood circulation: large and small. The great circle begins in the left ventricle. The aorta departs from it, which forms an arch. Arteries arise from the aortic arch. The coronary vessels depart from the initial part of the aorta, which supply blood to the myocardium. The part of the aorta located in chest, called thoracic aorta, and the part that is located in the abdominal cavity is the abdominal aorta. The aorta branches into arteries, arteries into arterioles, and arterioles into capillaries. Oxygen and nutrients flow from the capillaries of the large circle to all organs and tissues, and from the cells the capillaries receive carbon dioxide and products of exchange. Blood turns from arterial to venous.
Purification of the blood from toxic breakdown products occurs in the vessels of the liver and kidneys. Blood from the digestive tract, pancreas and spleen enters the portal vein of the liver. In the liver, the portal vein branches into capillaries, which then unite again into the common trunk of the hepatic vein. This vein drains into the inferior vena cava. Thus, all blood from the abdominal organs, before entering the systemic circle, passes through two capillary networks: through the capillaries of these organs themselves and through the capillaries of the liver. The portal system of the liver ensures the neutralization of toxic substances that are formed in the large intestine. The kidneys also have two capillary networks: the network of the renal glomeruli, through which the blood plasma containing harmful products metabolism (urea, uric acid), passes into the cavity of the nephron capsule, and the capillary network entwining the convoluted tubules.
Capillaries merge into venules, then into veins. Then, all the blood flows into the superior and inferior vena cava, which drain into the right atrium.
The pulmonary circulation begins in the right ventricle and ends in the left atrium. Venous blood from the right ventricle enters the pulmonary artery, then into the lungs. Gas exchange occurs in the lungs, venous blood turns into arterial blood. The four pulmonary veins carry arterial blood to the left atrium.
Question 3. Is the lymphatic system a closed or open system?
The lymphatic system should be classified as open. It blindly begins in the tissues with lymphatic capillaries, which then unite to form lymphatic vessels, and they, in turn, form lymphatic ducts that flow into the venous system.
