What circulatory system is usually called a closed one? Which animals have an open circulatory system Representatives of the type have a closed circulatory system.

Many invertebrates have well-developed circulatory systems (circulatory systems). Two types are known: open (open) and closed.

With an open system, which we see in molluscs, arthropods and echinoderms, circulation occurs in the body cavity (whole, or hemocele). In animals with a closed circulation system, blood flows through vessels with walls and does not exit them into the body cavity. For both systems, we need propulsor organs - muscle pumps, usually called hearts or heart tubes.

It is not easy to answer the question which type of circulatory system is more efficient. With an open system, blood flows more slowly, but it comes into direct contact with the cells of the surrounding tissues, since the walls of the vessels do not separate them. But closed circulatory system more dynamic, through an extensive network of capillaries, it contacts with a large number of cells than an open one. The latter has another important function: it plays the role of a hydrostatic skeleton.

Closed circulatory system

AT closed circulatory system earthworm, which can be taken as an example (Fig. 9), there are two large vessels - dorsal and abdominal, passing above and below the intestine. In the dorsal vessel, blood moves from back to front, in the abdominal - from front to back. In each segment of the worm, the longitudinal vessels are connected by annular vessels. All vessels, except for the abdominal one, are capable of contracting their walls due to the muscles that dress them. These pulsating vessels are called hearts. They contract sequentially, and this process resembles the peristalsis of the intestines through which food passes. Large vessels with thick muscular walls are called arteries. They branch dichotomously, dividing into smaller and smaller vessels with thin walls. In the end, branching leads to the formation of tiny capillaries, the walls of which consist of a single layer of cells. Through the capillaries, diffusion of small molecules and the release of cellular elements of the blood are carried out, which can then return to the bloodstream in the same way. The total surface of the capillaries is huge. The terminal vessels-capillaries, uniting with each other, form small vessels-venules, and those, in turn, are larger veins. These veins enter the heart vessel and connect there with the arterial trunks. Thus, the blood flows in circles. A rich plexus of blood vessels covers the outside of the intestine in the form of a clutch. This allows the products of digestion to freely enter the bloodstream and spread throughout the body of the animal. Blood moves due to the contractility of individual sections of the dorsal, and in the earthworm - and annular vessels. In this case, there is no single heart.

Open (open) circulatory system

Many invertebrates have a different type of circulatory system - open or open. It is characteristic of arthropods, mollusks (except cephalopods), echinoderms. Mollusks have a heart, usually consisting of a ventricle and an atrium, there are large vessels, but no capillaries. The terminal ramifications of the vessels open into the body cavity - slit-like gaps in the tissue (sinuses and lacunae), and from them the blood, or, more precisely, the hemolymph, is sucked in by the terminal ramifications of the venous vessels. There is a definite correlation between the complexity of the circulatory system and the size of the body.

In arthropods, with their open circulatory system, blood, or hemolymph, fills the body cavity and the spaces between the organs that it washes, and is only partially enclosed in the propulsor organ - the dorsal vessel. This is a tube dressed with muscles and suspended on short cords to the dorsal wall of the body. The vessel is subdivided into the back part - the heart, consisting of chambers capable of pulsation, and the anterior part - the tubular aorta, in which there are no chambers. The chambers of the heart have a pair of lateral openings - ostia, equipped with valves that open inward. Through the ostia, blood from the body cavity is sucked into the chambers. There are also valves between the chambers. The posterior end of the heart is usually closed, the anterior end of the aorta is open. Special pterygoid muscles are connected with the lower wall of the heart (Fig. 10). They are located in segments, and their fibers are attached to the wall of the heart. material from the site

Blood moves through the dorsal vessel from back to front due to the successive pulsation of the heart chambers and the work of the muscles. When the chamber expands (diastole stage), blood enters it through the ostia, and when it contracts (systole stage), the resulting blood pressure opens the anterior valves, closes the posterior ones and moves the blood forward. The aorta reaches the head, where it breaks off with an opening through which blood flows into the body cavity. Here it moves from front to back and then enters the heart again. Additional "hearts" in the form of ampoules are often located in the appendages of the body of insects - antennae, legs and wings.

Only in insects, an open circulatory system is not used to transport oxygen. Instead, they have formed a tracheal respiratory system, which allows gaseous oxygen to be delivered to all tissues in which metabolic processes take place.

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Just organized animals such as coelenterates and flatworms, there are no 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 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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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 substances and heat are transported for metabolic processes that also affect 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 a small and large 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 the warm-bloodedness of higher animal species is possible, which allows you to have a constant body temperature, regardless of conditions. environment. Peculiar to birds and mammals and high efficiency of metabolism.

Circulation in human body provided by the contractions of the heart, which works like a pump. Among other factors that promote the movement of blood - respiratory movements, reducing 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 open and closed circulatory system has very characteristic features, which every erudite, and not only, person must know.

Even from the school biology course, many remember that the circulatory system can be closed and open, but not everyone will remember what their difference is. It is thanks to the circulatory system that the coordinated movement of blood through the body is carried out, which in itself indicates the provision of a full life. Without normal blood circulation, due to which the delivery of all useful substances and warmth to all the organs of our body, a person could not live a day. In addition, without blood circulation, there would be no metabolic processes that have an impact on the metabolic rate.

An open circulatory system is found in invertebrates, including the lancelet.. This type of circulation has one distinguishing feature, namely, compared with such a large volume of blood, the speed of its movement is too small. As for the closed circulatory system, it can consist of one or two circles - small and large. Interesting fact- circulating in a small and large circle, the blood can periodically change its composition and be either arterial or venous.

An open circulatory system is characteristic of arthropods, such as mollusks, and for such a simple invertebrate as the lancelet. In these species, the delivery of useful and vital substances, including oxygen, is carried out from the place of their perception to parts of the body by means of diffuse currents. It also happens that in some animals there are ways through which blood passes - in fact, this is how vessels appear, which have a rather primitive appearance.

Not everyone knows that evolutionary processes took place in the circulatory system, which, one way or another, influenced its development. For the first time you could hear this at school, from the one who taught you biology. For the first time, the circulatory system appeared in annelids - it has a vicious circle.

It should be noted that chordates and invertebrates have different theories of evolution, each of which has its own characteristics.

First, there was a significant increase in the function responsible for transportation, which is the most important, due to the formation of the heart and large arteries. Secondly, the number of so-called functions performed, which include thermoregulation and protective reactions, has expanded. Thirdly, there have been changes in the change of habitat, lifestyle, as well as lung breathing. Both closed and not closed system blood circulation have characteristic features that every person needs to know about, even in general terms.

Key Features

It is believed that the open circulatory system is somewhat imperfect, which cannot be said about birds and mammals, which have a closed circulatory system. In all representatives of this type, the system consists of a heart with four chambers and two circles of blood circulation, which are divided into small and large. Under normal conditions, the circulating blood in such a system never mixes with each other.

A closed circulatory system has the following advantages:

• Such a system is characterized by a fairly high pressure.
• The rate of blood circulation through the vessels. An interesting fact is that the time it takes for one circulation of blood is different for everyone, for example, for small bugs, the passage of one circle takes at least twenty minutes, and for a dog - sixteen seconds.

In the human body, blood circulates through the veins, vessels and arteries due to the contraction of the muscles of the heart, the work of which can be compared to a pump. Among other things, there are several other factors that contribute to the movement of blood through the body, which a person may not know about, and hear about them for the first time in his life.

These factors are commonly referred to as:

• Movements made during breathing.
• Contraction of skeletal muscles.
• The pressure that exists in the vessels and the difference between them.

One of the main characteristics of the heart is the pulse rate. What is it? The pulse is a phenomenon in which there is an expansion of the arteries, despite the fact that it occurs periodically and coincides with the contraction of the heart muscle. The pulse rate can depend on many reasons, each person has its own. So, even extra pounds, temperature and stress, both physical and emotional, can affect the pulse. There are generally accepted norms, for example, in an adult, the pulse rate can range from sixty to eighty beats per minute.

If any deviation was revealed during the measurement of the pulse rate, there is reason to think about it and make an appointment with a specialist, as this may indicate the presence of any deviation. Do not listen to the opinion of relatives who do not have medical education, the most ideal option would be to simply consult with your therapist about this.

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 big circle arterial blood goes to the head, to all organs and tissues of the body, 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.)

(the cardiovascular system), designed to carry blood (in arthropods - hemolymphs). 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 drain into the dorsal aorta, which carries blood to the trunk, tail, and internal organs, and in front of 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.
A small (pulmonary) circle starts from the right ventricle of the heart with a trunk 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 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 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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