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. During 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 animals (for example, flatworms). There are open and closed circulatory systems. The first is formed by various vessels, which are interrupted by cavities without their own walls - lacunae or sinuses; in this case, the blood, called in this case hemolymph, comes into direct contact with all tissues of the body (including brachiopods, echinoderms, hemichordate arthropods, tunicates). In a closed circulatory system, blood circulates in vessels with their own walls.

In primitive worms, blood movement is ensured by contractions of the muscles of the body wall (the so-called musculocutaneous sac); in other groups, pulsating areas (“hearts”) are differentiated in various vessels equipped with muscular walls. On the basis of one of these areas, in the most highly organized animals, a special pulsating organ is formed - 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 from the heart are called arteries, and the blood vessels that carry blood to the heart are called veins. In a closed circulatory system, large arteries are successively divided into smaller and smaller ones, down to thin arterioles, which break up into capillaries, forming an extensive network in various tissues. From it, blood flows into thin venules; connecting with each other, they gradually form larger veins. Blood is called arterial if it is enriched with O2 in the respiratory organs, and 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 connected to each other by jumpers). In many of them, blood circulation is not ordered: blood moves back and forth through the vessels when the muscles of the body contract. In the so-called hoplonemertines, the walls of blood vessels acquired contractility; blood flows forward through the median dorsal vessel, and backward through the two lateral vessels. In the closed circulatory system of annelids, the dorsal and abdominal longitudinal vessels are connected by vascular arches passing in the septa between the body segments. Arteries extend from them to the lateral appendages of the body (parapodia) and gills; blood movement is ensured by the pulsation of the walls of some vessels; Blood flows forward through the spinal vessel, and backward through the abdominal vessel.

Arthropods, brachiopods and mollusks develop a heart. During evolution, the circulatory system in arthropods loses its closedness: 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 enhanced 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, and the function of the heart increases; 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 significant perfection during the evolution of chordates. In skullless animals (lancelets), the role of the heart is played 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. Blood enriched with O2 enters the dorsal aorta and the arteries extending from it to various organs. To the head end of the body, blood flows from the anterior branchial arteries through the carotid arteries. From the capillary networks, blood collects into veins, the most important of which are longitudinal paired anterior (from the head end of the body) and posterior (from the area behind the pharynx) cardinal veins, flowing into the Cuvier ducts (through them 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 sinus venosus, atrium, ventricle and conus arteriosus. In cyclostomes, the circulatory system is not yet closed: the gills are surrounded by circumbranchial sinuses. All other vertebrates have a closed circulatory system; it is supplemented by an open lymphatic system. In most fish, arterial blood from the gills enters the carotid arteries and dorsal aorta, and 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 allowed them to breathe atmospheric air with a deficiency of O 2 dissolved in water. An additional pulmonary (pulmonary) circulation appears: the lungs receive venous blood through the pulmonary arteries (arising from the posterior pair of branchial arteries) and return O2-saturated arterial blood through the pulmonary veins to the isolated left atrium. The left half of the heart becomes arterial, while the right 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 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.

In terrestrial vertebrates, further rearrangements of the circulatory system occurred. The heart of amphibians is divided into the sinus venosus, which drains into the right atrium, left atrium, common ventricle and conus arteriosus. The loss of gills led to reduction of the abdominal aorta; The branchial arteries became part of the carotid arteries, aortic arches and pulmonary arteries, starting from the conus arteriosus. The aortic arches form the dorsal aorta. In the venous system, the posterior cardinal veins are reduced, functionally replaced by the azygos posterior vena cava. The anterior cardinal veins are called the superior (internal) jugular veins, and the ducts of Cuvier are called the anterior vena cava. In amphibians, an important additional respiratory organ is the skin, arterial blood from which passes 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 has disappeared. In most of them, the venous sinus and conus arteriosus were reduced; the heart consists of two atria and a ventricle, in which there is an internal, usually incomplete (except in crocodiles) septum, which allows partial separation of the flow of arterial and venous blood coming from the left and right atria and redistribution of them in accordance with physiological needs. Reptiles retain 2 aortic arches, from which the right one receives arterial blood, and the left one receives mixed blood; Venous blood enters the pulmonary artery.

In birds and mammals, complete division of the ventricle of the heart led to the formation of four chambers: the left and right atria and 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 begins from the right ventricle. The renal portal system, which was present in most primitive vertebrates (except cyclostomes), is being reduced. All these changes in the circulatory system contributed to a significant increase in the overall level of metabolism of the body in birds and mammals.

Lit.: Tatarinov L.P. Evolution of the apparatus for separating blood currents in the heart of vertebrates // Zoological Journal. 1960. T. 39. Issue. 8; Beklemishev V.N. Fundamentals of comparative anatomy of invertebrates. 3rd ed. M., 1964. T. 2; Romer A., ​​Parsons T. Anatomy of vertebrates. M., 1992. T. 2.

U just organized animals worms, 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 metabolic rate at this evolutionary stage is low. The distances that substances travel inside the body are also small, so they can easily move by diffusion or with the flow of the cytoplasm.

As the size increases and complexity of animal organization the amounts of substances entering the body and being removed from it increase. The distances these substances must travel within the body are also increasing, creating a need for a more efficient way to transport them. This method involves transferring them with a flow of liquid, or transferring them through a volumetric flow mechanism. There are two circulatory systems that provide 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 rapid volumetric flow of substances between parts of the body over distances too large for transport by the diffusion mechanism. Upon reaching their destination, the substances must be able to penetrate through the walls of blood vessels into the corresponding organs or tissues. Likewise, substances produced by these organs or tissues must also enter the circulatory system. In other words, specialized metabolic systems are associated with the system of substance transport using the volume 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 the heart;
3) tubes or vessels through which liquid moves.

Animals have two types of circulatory systems - open (lacunar) and closed.

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

CLOSED CIRCULATORY SYSTEM(in echinoderms, most cephalopods, annelids, vertebrates, including humans). The circulatory system of this type is characterized by the following features.
1. The 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 under 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 occurs only through the walls of blood vessels.

Blood vessels are called differently depending on their structure and function. The vessels through which blood flows from the heart are called arteries. The arteries branch into smaller arterioles, and they, in turn, branch repeatedly, forming a dense network of microscopic capillaries that penetrates almost all tissues of the body. This is where the exchange of substances between blood and other tissues occurs.

Connecting inside an organ or tissue, capillaries form venules, from which the path of blood to the heart begins; merging with each other, the venules form increasingly larger veins. Ultimately, all the blood returns to the heart through the main veins. 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 about the closed and open circulatory system. But it is to her that living beings owe the coordinated movement of blood throughout the body, which thereby ensures full functioning. The delivery of heat and nutrients 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.

Unclosed circulatory system

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

They deliver oxygen and vital elements using diffuse currents. Some living beings develop pathways for blood to pass through. This is exactly how vessels with a rather primitive appearance arise, interrupted by slit-like spaces, which are called sinuses or lacunae.

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

In arthropods, the open circulatory system is designed to transport nutrients to the organs, as well as remove waste products. The movement of blood is ensured by contractions of the heart, which is located in the posterior part of the aorta (dorsal vessel). It, in turn, branches into arteries, the blood from which flows into the internal organs and open cavities being washed. This blood flow system 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 contained in them does not come into contact with the tissues of the body. This type is characteristic of humans, other vertebrates, some other groups of animals and annelids. In the former, blood flow occurs thanks to a well-developed muscular heart. Its contractions are carried out automatically, but it can also be regulated by the central nervous system.

Advantages of a closed blood system

This type is characterized by fairly high blood 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 is different for all organisms - for some it is twenty minutes, while for others the blood makes a revolution in sixteen seconds.

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

Pulse

It is one of the main characteristics of the heart. With this phenomenon, the periodic dilation 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 pulsation frequency of an adult should not exceed eighty beats per minute.

If any deviations are revealed during the measurement, this is a reason 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 K. with: open, or lacunar (echinoderms, arthropods, brachiopods, mollusks, hemichordates, tunicates, etc.), and closed (nemerteans, annelids and all vertebrates). In animals with unclosed K. s. the vessels are interrupted by slit-like spaces (lacunae, sinuses) that do not have their own. walls Blood (called hemolymph in this case) 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. In some arthropods K. s. simplified, because it means that part of the breath. functions transferred from K. s. to the tracheas, delivering O2 directly to the tissues. In mollusks, all transitions from open-loop c. are observed. to almost closed (cephalopods). K. s. in all vertebrates mainly is constructed in the same way: they all have a heart and an aorta, arteries, arterioles, capillaries, venules and veins, organized according to a single principle. IN closed K. s. the 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 flows first into small vessels - venules, and then into increasingly larger ones - veins. Cyclostomes and fish (except lungfishes) have one circulation. Lungfishes and terrestrial vertebrates have 2 circulations. In a small circle, venous blood from the heart is directed through the pulmonary arteries to the lungs and returns to the heart through the pulmonary veins. In a large circle, arterial blood is directed 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 the pulmonary circulation during the evolution of vertebrates, progressive differentiation of the parts of the heart occurs. In birds and mammals, this led to the emergence of a four-chambered heart and to the complete separation of arterial and venous blood flows in it. (see CIRCULATION, HEART), (see 53_TABLE_53).

.(Source: “Biological Encyclopedic Dictionary.” Editor-in-chief 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 transport 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 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 body tissues is carried out using the smallest vessels - capillaries, penetrating organs and most tissues.
The circulatory system in which blood circulates through arteries, capillaries and veins is called closed. It is characteristic of annelids and most chordates. In an open circulatory system, the vessels are interrupted by slit-like spaces that do not have their own walls. Entering them from the arterial system, hemolymph washes all 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, mollusks, 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, which branches into paired gill afferent arteries, then into capillaries in which gas exchange occurs. The efferent branchial arteries flow into the dorsal aorta, which carries blood to the body, 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 one carries arterial blood, and the pulmonary artery carries venous blood.
The venous system of aquatic vertebrates consists of paired anterior and posterior cardinal veins, which drain into the venous sinus of the tail vein, two renal portal veins, the hepatic portal vein, and the hepatic vein, which drains into the sinus venosus. In terrestrial vertebrates, the veins of the head and forelimbs form the anterior vena cava system, and the veins of the organs of the trunk and hind limbs form the posterior vena cava.
Humans have a closed circulatory system. Blood circulating through the blood vessels ensures the exchange of substances between the body and the external environment (it delivers oxygen and nutrients to the tissues and removes metabolic products and carbon dioxide). 2 circles extend 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 gives off carbon dioxide, is saturated with oxygen, turning into arterial blood. From the lungs, arterial blood flows through the four pulmonary veins into the left atrium and, as a result of contraction, through the atrioventricular orifice into the left ventricle. Thus, venous blood flows in the arteries of the pulmonary 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 different sizes. The right and left coronary (coronary) arteries, which supply blood to the heart, depart directly from the aorta. 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 releasing oxygen and nutrients and being saturated with carbon dioxide and other dissimilation products, collects into venules, then into 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 they, in turn, into the right atrium. The superior vena cava receives blood from the venous system of the head, neck, upper extremities 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, passing between the liver cells, where the blood is released from toxins (antitoxic, or barrier, function) and the deposition of nutrients (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 response of the circulatory system to internal and external stimuli by changing vascular tone, redistributing blood supply, etc.

.(Source: “Biology. Modern illustrated encyclopedia.” Chief editor A. P. Gorkin; M.: Rosman, 2006.)

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Any circulatory system must include a circulating fluid (blood, lymph, hemolymph), vessels through which the fluid is transported (or parts of the body cavity) and a pulsating organ that ensures the movement of fluid throughout the body (this organ is usually the heart). Blood vessels are divided into arteries, through which blood flows from the heart, and veins, through which blood returns to the heart. The walls of blood vessels in mammals consist 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 these, in turn, branch into microscopic capillaries passing between the cells of almost all tissues. In the described system, the blood is enclosed in vessels along its entire path and does not come into contact with body tissues; metabolism occurs only through the walls of the vessels. Such a system is called closed; it is found in annelids, vertebrates and some other groups of animals.

In an open circulatory system, arteries open into a system of cavities that form the hemocoel. Blood moves slowly between tissues under low pressure and is collected again towards 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 dorsal vessel drive blood to the anterior end of the animal; a series of valves prevent blood from flowing in the opposite direction. 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; it eventually reassembles in the dorsal vessel. The blood of annelids carries oxygen and nutrients throughout the body, and takes away carbon dioxide and metabolic waste.

The circulatory system of arthropods is not closed. It is designed to transport nutrients to the organs and remove waste products (remember that gas exchange in this type of animal occurs through the trachea). Blood flows through the spinal vessel - the aorta; movement is ensured 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, blood flow is ensured 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, 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 epibranchial arteries, and from there 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.