Circulatory system. An open circulatory system and a closed closed circulatory system are characteristic of which

The circulatory system (open and closed) is the mechanism by which the coordinated movement of blood (hemolymph) through the body is possible, which ensures its full functioning. Its very movement in the system arises in connection with the pulsation or contractions of the thickened walls of the aorta and arteries, or the organs of movement and muscles of the body. It is with the help of blood circulation that the transport of substances and heat occurs for metabolic processes affecting the metabolic rate. Closed and open circulatory system: how do they differ and for whom are they characteristic? The answers to these questions will be presented in the article.

An open circulatory system is found in almost all invertebrates, as well as in lower chordates (in the lancelet). Blood flow in these organisms is determined by the contraction of the heart or "hearts" and, to some extent, by the contraction of the musculature of the body. A characteristic feature is a large volume of blood at a low speed of its movement.

A closed circulatory system can consist of one (fish and cyclostomes) and two - small and large (reptiles, amphibians, birds, mammals). Flowing through the small and big circle, the blood periodically changes its composition, and is either venous or arterial. And in cold-blooded animals, venous and arterial even mix in the aorta or heart, while the blood flow velocity is low. The exchange of substances between body tissues and blood is carried out through the thin walls of capillaries. Filtration of decay products occurs mainly in the kidneys, or in other

An open circulatory system is very imperfect, but among the owners of a closed circulatory system, the most ideal option is in birds and mammals. In representatives of these classes, it consists of a four-chambered heart and two circles of blood circulation. Normally, it never mixes with venous. Quite high pressure is typical. Another advantage is the considerable speed of blood flow through the vessels (for comparison: the time of one blood circulation in insects is approximately 22 minutes, in a dog it is already 16 seconds, and in a rabbit it is 7.5 seconds). It is thanks to these features that warm-bloodedness is possible. higher species animals, which allows you to have a constant body temperature, regardless of conditions environment. Peculiar to birds and mammals and high efficiency of metabolism.

Blood circulation in the human body is provided by contractions of the heart, which works like a pump. Among other factors that contribute to the movement of blood are respiratory movements, reduction of the pressure difference in the vessels. One of the characteristics of cardiac activity is the pulse rate. The pulse is the periodic expansion of the arteries, which coincides with the contractions of the heart muscle. Its frequency depends on many reasons, including body weight, body temperature and condition, physical and emotional stress, and so on. Normal in an adult is 60-80 beats per minute. The speed of blood flow in the vessels is different: from less than 1 mm/s in capillaries to 50 cm/s in large arteries. The time of the entire circulation of blood in the body is about 20-25 seconds. Blood moves in the direction of decreasing pressure, which is greatest in the aorta and large arteries and least, even negative, in the vena cava. The reverse movement of blood is also prevented by valves that close the atrioventricular orifices, the orifices of the pulmonary artery and aorta, and valves located on the walls of large veins. With sufficient contractile blood circulation is not disturbed.

As you can see, the circulatory system is open and closed have a very characteristics, which must be known to every erudite, and not only, person.

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. Delivery of heat and nutrients to all organs human body, without which existence is impossible, is also the 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 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.

). Thus, the exchange of substances between blood and tissues takes place only through the walls of blood vessels.

In an open (lacunar) circulatory system, the vessels are interrupted by spaces that do not have special walls (lacunae, sinuses), and the blood interacts directly with body tissues.

All vertebrates (including humans) and some invertebrates (for example, nemerteans and annelids) have a closed circulatory system. In hemichordates and tunicates it is open. In molluscs, both open and almost closed (in the case of cephalopods) circulatory system, and intermediate variants are found.

A closed circulatory system can be found in all types of animals except mollusks and arthropods.

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An excerpt characterizing the closed circulatory system

She suddenly jumped up on the tub, so that she stood taller than him, hugged him with both arms, so that her thin bare arms bent above his neck, and throwing her hair back with a movement of her head, kissed him on the very lips.
She slipped between the pots to the other side of the flowers and, head down, stopped.
“Natasha,” he said, “you know that I love you, but ...
- Are you in love with me? Natasha interrupted him.
- Yes, I am in love, but please, let's not do what is now ... Four more years ... Then I will ask for your hand.
Natasha thought.
“Thirteen, fourteen, fifteen, sixteen…” she said, counting on her thin fingers. - Good! Is it over?
And a smile of joy and reassurance lit up her lively face.
- It's over! Boris said.
- Forever? – said the girl. - Until death?
And, taking him by the arm, with a happy face she quietly walked beside him into the sofa.

The countess was so tired of the visits that she did not order to receive anyone else, and the porter was only ordered to call everyone who would still come with congratulations to eat without fail. The Countess wanted to talk face to face with her childhood friend, Princess Anna Mikhailovna, whom she had not seen well since her arrival from Petersburg. Anna Mikhailovna, with her tearful and pleasant face, moved closer to the countess's chair.

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. At 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 saturated O 2 arterial blood through the pulmonary veins into 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. V 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 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 makes it possible 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 division 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. From the right ventricle begins the general pulmonary artery. 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 overcome inside the body also increase, and therefore there is a need for more efficient way their transportation. 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 internal organs collectively referred to as 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 penetrating 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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