The circulatory system of reptiles is closed or open. Circulatory system

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 may 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.

). 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 mollusks, 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 and ever? – 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.

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 all useful substances and heat are delivered to all organs of our body, a person could not live even 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 distinctive feature, namely, compared with such a large volume of blood, the speed of its movement is too low. As for the closed circulatory system, it can consist of one or two circles - small and large. An interesting fact is that circulating in a small and large circle, 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 pulmonary respiration. Both closed and open circulatory systems have characteristic features that every person needs to know about, even if only 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. You should not listen to the opinion of relatives who do not have a medical education, the most ideal option would be to simply consult with your therapist about this.

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 a closed circulatory system is more dynamic, through an extensive network of capillaries it contacts with a larger 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 tissue gaps (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 a hole 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.

On this page, material on the topics:

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) circle of blood 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 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. 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.