An open circulatory system is characteristic of representatives of the type. The circulatory system is open and closed

circulatory system, a set of organs and structures of animals and humans involved in blood circulation. In the course of evolution, the circulatory system was formed (independently in different groups of animals) from slit-like cavities in the parenchyma, which filled the primary body cavity in lower multicellular organisms (for example, flatworms). Distinguish between open and closed circulatory system. The first is formed by various vessels, which are interrupted by cavities deprived of their own walls - lacunae or sinuses; at the same time, the blood, called in this case hemolymph, comes into direct contact with all tissues of the body (including those of brachiopods, echinoderms, arthropods, hemichordates, and tunicates). In a closed circulatory system, blood circulates in vessels that have their own walls.

In primitive worms, the movement of blood is provided by contractions of the muscles of the body wall (the so-called skin-muscle sac); in other groups, in various vessels equipped with muscular walls, pulsating areas ("hearts") are differentiated. On the basis of one of these areas, the most highly organized animals form a special pulsating organ - the heart. In different groups of invertebrates, it develops on the dorsal side of the body, in vertebrates - on the ventral side. The blood vessels that carry blood away from the heart are called arteries, and those that carry blood to the heart are called veins. In a closed circulatory system, large arteries are successively divided into smaller and smaller ones, up to thin arterioles, which break up into capillaries that form an extensive network in various tissues. From it, blood enters thin venules; connecting with each other, they gradually form larger veins. Blood is called arterial if it is enriched with O 2 in the respiratory organs, depleted in oxygen after passing through the capillary networks of other organs - venous.

Nemerteans have the simplest type of closed circulatory system (2 or 3 longitudinal blood vessels are connected to each other by bridges). In many of them, the blood circulation is not ordered: the blood moves through the vessels back and forth with contractions of the muscles of the body. In the so-called hoplonemertins, the walls of the vessels acquired contractility; blood flows forward through the median dorsal vessel, and back through the two lateral vessels. In the closed circulatory system of annelids, the dorsal and abdominal longitudinal vessels are connected by vascular arches that run in septa between body segments. Arteries depart from them to the lateral appendages of the body (parapodia) and gills; the movement of blood is provided by the pulsation of the walls of some vessels; blood flows forward through the dorsal vessel, back through the abdominal vessel.

Arthropods, brachiopods and mollusks develop a heart. In the course of evolution, the circulatory system in arthropods loses its closedness: the hemolymph from the arteries enters the system of lacunae and sinuses and returns to the heart through holes in its walls (ostia), equipped with valves that prevent its reverse movement. This is most pronounced in insects, which is associated with the increased development of their tracheal system, which transports O 2 and CO 2. In mollusks, all transitions from an open to an almost closed (cephalopod) circulatory system are observed, there is an increase in the function of the heart; it has atria, into which, in some groups, veins flow, collecting hemolymph from the peripheral sinuses. In cephalopods, a circulatory system is formed, including capillary networks, and the heart is supplemented by pulsating vessels at the bases of the gills (the so-called gill hearts).

The circulatory system reaches considerable perfection during the evolution of chordates. In non-cranial (lancelets), the role of the heart is performed by a pulsating longitudinal vessel passing under the pharynx - the abdominal aorta. Branchial arteries depart from it, located in the partitions between the gill slits. Enriched with O 2 blood enters the dorsal aorta and arteries extending from it to various organs. To the head end of the body, blood enters from the anterior branchial arteries through the carotid arteries. From the capillary networks, blood is collected into veins, the most important of which are the longitudinal paired anterior (from the head end of the body) and posterior (from the area behind the pharynx) cardinal veins that flow into the Cuvier ducts (through which blood enters the abdominal aorta). The hepatic vein also flows there, carrying blood from the capillary network of the portal system of the liver. In vertebrates, the heart is formed from the posterior part of the abdominal aorta, which in cyclostomes and fish includes the venous sinus, atrium, ventricle, and arterial cone. In cyclostomes, the circulatory system is not yet closed: the gills are surrounded by paragill sinuses. All other vertebrates have a closed circulatory system; it is complemented by an open lymphatic system. In most fish, arterial blood from the gills enters the carotid arteries and dorsal aorta, while the heart receives venous blood from the capillary networks of the head and body organs.

Ancient lobe-finned fish developed additional respiratory organs - lungs, which allow breathing atmospheric air with a deficiency of O 2 dissolved in water. An additional small (pulmonary) circulation appears: the lungs receive venous blood through the pulmonary arteries (originated from the posterior pair of branchial arteries) and return arterial blood saturated with O 2 through the pulmonary veins to the isolated left atrium. The left side of the heart becomes arterial, while the right side still receives venous blood from the rest of the body. A system of internal partitions and valves is formed in the heart, distributing blood in such a way that arterial blood from the left atrium (from the lungs) enters mainly into the carotid arteries and goes to the head (the brain is most sensitive to oxygen deficiency), and venous blood - from the right atrium to gills and lungs.

Terrestrial vertebrates have undergone further rearrangements of the circulatory system. The heart of amphibians is divided into the venous sinus, which flows into the right atrium, left atrium, common ventricle and conus arteriosus. The loss of the gills led to the reduction of the abdominal aorta; gill arteries became part of the carotid arteries, aortic arches and pulmonary arteries, starting from the arterial cone. The aortic arches form the dorsal aorta. In the venous system, the posterior cardinal veins are reduced, functionally replaced by the unpaired posterior vena cava. The anterior cardinal veins are called the superior (internal) jugular veins, and the Cuvier ducts are called the anterior vena cava. In amphibians, an important additional respiratory organ is the skin, arterial blood from which enters through the vena cava into the venous sinus and then into the right atrium, and arterial blood from the lungs through the pulmonary veins into the left atrium. Arterial blood from both respiratory organs mixes with venous blood in the common ventricle of the heart.

In reptiles, with the improvement of the lung ventilation mechanism, the need for skin respiration disappeared. In most of them, the venous sinus and arterial cone were reduced; the heart consists of two atria and a ventricle, in which there is an internal, usually incomplete (with the exception of crocodiles) septum, which allows you to partially separate the flows of arterial and venous blood coming from the left and right atria, and redistribute them in accordance with physiological needs. Reptiles retain 2 aortic arches, from which the right one receives arterial blood, and the left one - mixed; venous blood enters the pulmonary artery.

In birds and mammals, the complete separation of the ventricle of the heart resulted in the formation of four chambers: the left and right atria and the ventricles. The only surviving aortic arch (right in birds, left in mammals and humans) starts from the left ventricle, passes into the carotid and subclavian arteries and into the dorsal aorta. The common pulmonary artery originates from the right ventricle. The portal system of the kidneys, which was present in most primitive vertebrates (except cyclostomes), is reduced. All these changes in the circulatory system contributed to a significant increase in the overall level of metabolism in birds and mammals.

Lit .: Tatarinov L.P. Evolution of the apparatus for dividing blood currents in the heart of vertebrates // Zoological Journal. 1960. T. 39. Issue. eight; Beklemishev VN Fundamentals of comparative anatomy of invertebrates. 3rd ed. M., 1964. T. 2; Romer A., ​​Parsons T. Vertebrate Anatomy. M., 1992. T. 2.

Just organized animals, such as coelenterates and flatworms, lack specialized systems for internal transport and distribution of substances. These animals are characterized by a high ratio of body surface area to its volume, and gas exchange through the outer integument fully meets their needs, especially since the intensity of metabolism at this evolutionary stage is low. The distances that substances travel inside the body are also small, so they can easily move with the help of diffusion or with the current of the cytoplasm.

As the size increases and complexity of animal organization the amount of substances entering the body and subject to removal from it increases. The distances that these substances must travel within the body are also increasing, and therefore there is a need for a more efficient method of transporting them. In this way, their transfer with a liquid current, or transfer by a volumetric flow mechanism, becomes. There are two circulatory systems that ensure the transport of substances between different parts of the body, namely the circulatory (cardiovascular) and lymphatic. These systems are called vascular because blood or lymph passes at least part of its path inside specialized tubular structures - vessels.

General features of the circulatory system

Function of the circulatory system- maintaining a fast volumetric flow of substances between body parts at distances too large for transport by the diffusion mechanism. Upon reaching their destination, the substances must be able to penetrate through the walls of the vessels into the corresponding organs or tissues. Similarly, substances produced by these organs or tissues must also enter the circulatory system. In other words, specialized exchange systems are associated with the system of transport of substances by the volumetric flow mechanism.

Any circulatory system consists of three main components:
1) circulating fluid (blood);
2) a contractile organ that functions as a pump and pumps fluid throughout the body; this role is played either by specialized vessels or by the heart;
3) tubes or vessels through which fluid moves.

Two types of circulatory systems are known in animals - open (lacunar) and closed.

OPEN CIRCULATION SYSTEM(in most arthropods, in some cephalopods, etc.). The heart pushes blood into the aorta, which branches into several arteries. They open in the cavity between the internal organs, collectively called the hemocoel. Thus, the blood does not remain permanently in the vessels, hence the very name of the system - open. Blood slowly moves along the hemocoel at low pressure, washing around the surrounding tissues, and gradually collects back into the heart directly through holes in it or open veins at the ends. The distribution of blood to different parts of the body is poorly regulated.

CLOSED CIRCULATION SYSTEM(in echinoderms, most of the cephalopods, annelids, vertebrates, including humans). The circulatory system of this type is characterized by the following features.
1. Blood remains inside the heart and blood vessels and does not come into direct contact with body tissues.
2. Blood flows quickly and flows to all parts of the body and back to the heart at a relatively high pressure.
3. The distribution of blood to different organs is regulated depending on their needs.
4. The entry of substances into the system and their exit from it is carried out only through the walls of the vessels.

Blood vessels called differently depending on their structure and function. The vessels that carry blood away from the heart are called arteries. Arteries branch into smaller arterioles, which, in turn, branch many times, form a dense network of microscopic capillaries that penetrates almost all tissues of the body. This is where the exchange of substances between the blood and other tissues takes place.

Connecting within an organ or tissue, capillaries form venules from which the path of blood to the heart begins; merging with each other, venules form ever larger veins. Ultimately, all the blood returns through the main veins to the heart. The structure of vessels of each of these types is discussed in detail in the article.

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It is from the biology course that we remember the closed and open circulatory system. But it is precisely to her that living beings owe the coordinated movement of blood through the body, which thereby ensures a full-fledged life activity. The delivery of heat and useful substances to all organs of the human body, without which existence is impossible, is also a merit of normally circulating blood. Without it, there would be no metabolic processes affecting the metabolic rate.

open circulatory system

This type of circulation is characteristic of protozoan invertebrates, echinoderms, arthropods, and brachiopods, as well as hemichordates.

In them, the delivery of oxygen and vital elements is carried out using diffuse currents. Some living beings have ways for the passage of blood. This is exactly how the rather primitive-looking vessels arise, interrupted by slit-like spaces, which are called sinuses or lacunae.

A distinctive feature of an open circulatory system is the too low speed of movement in relation to a large volume of blood. It slowly, under low pressure, moves between the tissues, and then, through the open ends of the venous vessels, it again gathers to the heart. Slow hemolymph circulation leads to passive breathing and poor oxygen supply to the body.

In arthropods, an open circulatory system is designed to transport nutrients to the organs, as well as remove waste products. The movement of blood is provided by contractions of the heart, which is located in the posterior portion of the aorta (spinal vessel). It, in turn, branches into arteries, the blood from which flows into the internal organs washed and open cavities. This system of blood flow is believed to be imperfect, unlike that of mammals and birds.

Closed circulatory system

This type of blood flow can consist of one or two circles - large and small. Circulating through them, the blood can periodically change its composition and become either venous or arterial.

In this system, metabolism passes only through the vascular walls, and the blood enclosed in them does not come into contact with body tissues. This type is typical for humans, other vertebrates, some other groups of animals and annelids. In the former, blood flow occurs due to a well-developed muscular heart. Its contractions are carried out automatically, but regulation by the central nervous system is also possible.

Benefits of a Closed Blood System

This type is characterized by rather high pressure. Unlike an open circulatory system, the speed of blood movement through the vessels is much faster here. At the same time, the time of one revolution for all organisms is different - for someone it takes twenty minutes, and for someone the blood makes a revolution in sixteen seconds.

There are several factors that promote blood circulation throughout the body. These include the pressure in the vessels and the difference between them, movements made during breathing, contractions of the muscles of the skeleton.

Pulse

It is one of the main characteristics of the heart. With this phenomenon, the periodic expansion of the arteries coincides with the contraction of the heart muscle. The pulse rate depends on a large number of reasons: emotional and physical stress, body temperature, excess kilograms. According to generally accepted standards, the frequency of the pulsation of an adult should not exceed eighty beats per minute.

In the event that any deviations were revealed during the measurement, this is an occasion to think about the presence of heart disease and pay a visit to a specialist. And the opinion of incompetent relatives and neighbors in this case must be ignored.

CIRCULATORY SYSTEM CIRCULATORY SYSTEM

(systema vasorum), a system of vessels and cavities, through which blood or hemolymph circulates. There are 2 types of C. with: open, or lacunar (echinoderms, arthropods, brachiopods, molluscs, hemichordates, tunicates, etc.), and closed (nemerteans, annelids and all vertebrates). In animals with open K. with. vessels are interrupted by slit-like spaces (lacunae, sinuses) that do not have their own. walls. Blood (called in this case hemolymph) enters directly. contact with all tissues of the body. In arthropods, brachiopods and mollusks, a heart appears (a pulsating section of a vessel or a muscular organ not divided into chambers) located on the dorsal side of the body. At nek-ry arthropods To. simplified, because it means that part of the breathing. functions passed from K. with. to the tracheae, delivering O2 directly to the tissues. In mollusks, all transitions from open K. with. to almost closed (cephalopods). K. s. in all vertebrates in the main. built the same way: they all have a heart and aorta, arteries, arterioles, capillaries, venules and veins, organized according to a single principle. AT closed K. with. arteries are divided into vessels of ever smaller diameter and, finally, pass into arterioles, from which blood enters the capillaries. The latter form a complex network, from which blood enters first into small vessels - venules, and then into increasingly larger ones - veins. In cyclostomes and fish (except lungfish) there is one circle of blood circulation. Lung-breathing fish and terrestrial vertebrates have 2 circles of blood circulation. In a small circle, venous blood from the heart through the pulmonary arteries is sent to the lungs and returns to the heart through the pulmonary veins. In a large circle, arterial blood is sent to the head, to all organs and tissues of the body, and returns through the cardinal or vena cava. All vertebrates have portal systems. With the formation of a small circle of blood circulation in the process of evolution of vertebrates, a progressive differentiation of the heart departments is carried out. In birds and mammals, this led to the emergence of a four-chambered heart and complete separation of arterial and venous blood flows in it. (see BLOOD CIRCULATION, HEART), (see 53_TABLE_53).

.(Source: "Biological Encyclopedic Dictionary." Chief editor M. S. Gilyarov; Editorial board: A. A. Babaev, G. G. Vinberg, G. A. Zavarzin and others - 2nd ed., corrected . - M .: Sov. Encyclopedia, 1986.)

(cardiovascular system), designed to carry blood (in arthropods - hemolymph). Carries out the transport of oxygen and carbon dioxide, nutrients and metabolic products excreted through the kidneys, skin, lungs, and other organs, as well as thermoregulation in warm-blooded animals. The central link of the circulatory system is usually heart- a pulsating organ or section of the abdominal aorta with a thickening of the muscular walls that provide blood flow in the system. The blood vessels through which blood flows from the heart form the arterial system, and the vessels that collect blood and carry it to the heart form the venous system. The exchange of substances between the blood and tissues of the body is carried out with the help of the smallest vessels - capillaries penetrating organs and most tissues.
The circulatory system, in which blood circulates through arteries, capillaries and veins, is called a closed system. It is inherent in annelids and most chordates. In an open circulatory system, the vessels are interrupted by slit-like spaces that do not have their own walls. Getting into them from the arterial system, the hemolymph washes all the internal organs and collects in the heart (a pulsating vessel) through paired openings - ostia, which have valves. An open circulatory system is characteristic of arthropods, molluscs, and echinoderms. In insects, it is poorly developed, and the hemolymph does not carry oxygen, since these animals have a well-branched system trachea.
In vertebrates, the pulsating organ - the heart - is located on the ventral side of the body under the notochord and the digestive tract. Aquatic vertebrates (cyclostomes, fish and amphibian larvae) have one circulation and a two-chambered heart with venous blood. Terrestrial vertebrates have two circles of blood circulation and a three-chambered heart with mixed blood or a four-chambered heart with separate blood - arterial and venous.
The arterial system of aquatic vertebrates consists of the abdominal aorta, branching into paired branchial afferent arteries, then into capillaries in which gas exchange occurs. The efferent branchial arteries flow into the dorsal aorta, which carries blood to the trunk, tail and internal organs, and in front through the carotid arteries to the head. In amphibians, one of the pairs of gill arteries forms the pulmonary circle, but there is also a large cutaneous artery. Reptiles have two aortic arches (right and left), carrying mixed blood and merging into the dorsal aorta, and a pulmonary artery with a predominance of venous blood. In birds, the right aortic arch, and in mammals, the left aortic arch carries arterial blood, and the pulmonary artery carries venous blood.
The venous system of aquatic vertebrates consists of paired anterior and posterior cardinal veins draining into the venous sinus of the tail vein, two renal portal veins, the portal vein of the liver, and the hepatic vein, which flows into the venous sinus. In terrestrial vertebrates, the veins of the head and forelimbs form a system of anterior vena cava, and the veins of the trunk and hind limbs form the posterior vena cava.
Humans have a closed circulatory system. The blood circulating through the blood vessels ensures the exchange of substances between the body and the external environment (delivers oxygen and nutrients to the tissues and removes metabolic products and carbon dioxide). 2 circles depart from the heart blood circulation- big and small.
The small (pulmonary) circle begins from the right ventricle of the heart with the trunk of the pulmonary artery, through which venous blood flows, delivered to the pulmonary capillaries, where it releases carbon dioxide, is saturated with oxygen, turning into arterial blood. From the lungs, arterial blood through four pulmonary veins enters the left atrium and, as a result of contraction through the atrioventricular opening, into the left ventricle. Thus, venous blood flows in the arteries of the small circle, and arterial blood flows in the veins. The systemic circulation begins from the left ventricle with the largest vessel - aorta. It branches into numerous arteries of various sizes. Directly from the aorta depart the right and left coronary (coronary) arteries, supplying blood to the heart. Small arteries branch into thousands of arterioles, which form a network of capillaries that supply blood to the entire body. From the capillaries, the blood, after the release of oxygen and nutrients and saturation with carbon dioxide and other dissimilation products, is collected in venules, then in veins. The veins of the great circle collect blood from all parts of the body, gradually merging into large venous trunks, which flow into the superior and inferior vena cava, and those, in turn, into the right atrium. The superior vena cava receives blood from the venous system of the head, neck, upper limbs and chest cavity; inferior vena cava - from the lower extremities, abdominal cavity and pelvis. Of particular importance in the circulatory system is the so-called. portal (portal) system of the liver (gate, or port). The portal vein collects blood from the stomach, pancreas, spleen, and intestines and drains it to the liver. It branches into hepatic capillaries that pass between the liver cells, where the blood is released from toxins (antitoxic or barrier function) and nutrients are deposited (depot function). Connecting, the capillaries form the hepatic vein, which drains blood into the inferior vena cava. The presence of sensitive and vasomotor receptors in the walls of blood vessels ensures the reaction of the circulatory system to internal and external stimuli by changing vascular tone, redistributing blood supply, etc.

.(Source: "Biology. Modern Illustrated Encyclopedia." Editor-in-Chief A.P. Gorkin; M.: Rosmen, 2006.)

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The composition of any circulatory system must include a circulating fluid (blood, lymph, hemolymph), vessels through which the fluid is transferred (or parts of the body cavity) and a pulsating organ that ensures the movement of fluid throughout the body (such an organ is usually the heart). The blood vessels are divided into arteries, which carry blood away from the heart, and veins, which carry blood back to the heart. The walls of blood vessels in mammals are composed of three layers of tissue: squamous endothelium, smooth muscle, and outer collagen fibers. Arteries and veins in organs branch into smaller vessels - arterioles and venules, and those, in turn, branch into microscopic capillariespassing between the cells of almost all tissues. In the described system, the blood is enclosed in vessels all the way and does not come into contact with the tissues of the body, the metabolism is carried out only through the walls of the vessels. Such a system is called closed, it is available in annelids, vertebrates and some other groups of animals.

In an open circulatory system, the arteries open into a system of cavities that form the hemocoel. Blood moves slowly between the tissues at low pressure and is collected back to the heart through the open ends of the venous vessels. Unlike a closed system, here the distribution of blood between tissues is practically not regulated. An open system exists, for example, in arthropods.

Annelids have a well-developed closed circulatory system. Periodic contractions of the spinal vessel drive blood to the anterior end of the animal; a series of valves prevent blood from flowing backwards. Five pairs of pulsating "false" hearts connect the dorsal vessel with the abdominal one; heart valves allow blood to pass only towards the abdominal vessel. After passing through the abdominal vessel, the blood enters the organs of the body; eventually it collects again in the dorsal vessel. The blood of annelids carries oxygen and nutrients throughout the body, takes away carbon dioxide and metabolic waste.

The circulatory system of arthropods is open. It is designed to transport nutrients to organs and remove waste products (recall that gas exchange in this type of animal is carried out through the trachea). Blood flows through the dorsal vessel - the aorta; movement is provided by contractions of the heart located in the posterior portion of the spinal vessel. The aorta branches into arteries, from which blood flows into open cavities and washes the internal organs.

In vertebrates, the blood flow is provided by contractions of a well-developed muscular heart. The backflow of blood is prevented by the heart valve system. Heart contractions occur automatically, but can be regulated by the central nervous system.

In fish, the blood, making a full circle in the body, passes through the heart only once; they say that they have one circle of blood circulation. When the heart contracts, blood is pushed into the abdominal aorta. The gill arteries bring oxygen-poor blood to the gills, where it is saturated with oxygen in the thinnest capillaries. From the efferent branchial arteries, blood enters the supragillary arteries, and from there it passes into the dorsal aorta. The carotid arteries extending forward from the dorsal aorta carry blood to the head; numerous arteries, branching from the dorsal aorta at the back of the body, supply blood to the internal organs.