Birds

The structure of the heart and circulatory system of birds

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Birds are a unique group of homeoy organisms whose lifestyle is associated with such ability as flying. It is possible under the condition of hard work of the muscles of the sternum and forelimbs - wings. This process, in turn, is ensured by the continuous supply of myocytes with oxygen and nutrients, especially glucose.

Blood is a substance that transports them throughout the body, and its movement depends on the intense activity of the heart, the pump that tirelessly pumps fluid connective tissue. The transfer of oxyhemoglobin and organic matter is carried out by the circulatory system of birds. The heart is the main organ that provides blood circulation. Features of its structure and functions will be discussed in this article.

Features of the circulatory system

Intensive metabolism in birds is possible for two reasons. The first is high blood pressure, which causes a high rate of blood flow in arteries and even veins. The second is the specificity of the blood supply to the lungs. The heart of the birds is four-chamber, the left and right parts of it are not communicated (there is a complete septum), so the blood does not mix: the arterial moves in the left, and the venous in the right. Birds metabolism is influenced by such factors as the passage through the kidneys of not only arterial (as in mammals), but also venous blood through the portal system of blood vessels, therefore uric acid is formed in their liquid metabolites instead of urea. Further: the blood cells, the red blood cells, in the representatives of the Aves class have nuclei, which increases the lifespan of these cells. From the left ventricle of the heart comes the largest arterial vessel - the aorta. It has a right arc, the bifurcation of which leads to the formation of the left and right nameless arteries, which provide the head and wings of birds with nutrients and oxygen.

Heart anatomy

Being a hollow muscular organ, it is located on the right side of the chest and is covered with a pericardium, the pericardium. In front of the sternum, the birds' heart is partially covered by additional respiratory organs - the airway bags. It has the shape of a cone, the tip of which is intermediate between the stomach and the liver.

Depending on the species of bird, the shape of the heart can vary from round conic to ellipsoid-elongated. This circulatory organ consists of three membranes: the outer - the serous (epicardium), the middle (myocardium) and the inner (endocardium). The most important of them is the middle shell, on the structure of which high activity and cardiac performance depend.

It is formed by striated muscular tissue of a special structure, which distinguishes the heart in birds from all other internal organs containing only smooth muscles. The internal location of the cardiomyocytes provides strength and evenly distributes the load during their reduction. Another major feature of the heart muscle is the independence of systole and diastole chambers: atria and ventricles. Myocardial cells are intertwined with each other, so the nerve impulses irradiately radiating along the cardiomyocytes, and the entire membrane is instantly reduced.

Heart chambers

Two atria - the left and right, as well as the two ventricles have several features associated with the anatomy of the myocardium. Its wall is much stronger and thicker in the left half of the heart, since arterial blood from its ventricle is released into the aorta under pressure and then enters the systemic circulation. In the heart, blood always moves in one direction: from the atria to the ventricles and then from the right to the pulmonary arteries, and from the left to the right aortic arch. At the boundary between the chambers are located atrioventral valves consisting of connective tissue: muscular and membranous. They do not allow portions of blood to return from the ventricle to the atrium. The bird's heart, the structure of its chambers and valves depends on which systematic group it belongs to.

In the new-born (real birds), the front left and right, as well as the back veins flow into the right atrium independently, while in the ancient, the hollow veins merge to form a sinus. Two muscular valves are formed between it and the right atrium. The first group includes birds of the pigeon-like, anseriformes, passerines, woodpeckers, etc. The second group is formed by casuaridae, kiwiforms, and nandoobs, also called killer-like birds (non-flying).

Circles of blood circulation

As we have already mentioned, the birds have a four-chamber heart. Its structure causes two circles of blood circulation. The small circle (pulmonary) begins in the right ventricle, and ends in the left atrium. The big circle originates in the left ventricle. From the right aortic arch, arteries branch out and bring oxygen and nutrients into the cells of all organs and tissues of the bird. Venous blood is collected in the hollow veins, which are included in the right atrium, this ends a large circle of blood circulation.

The specifics of cardiac activity

Studying the main part of the circulatory system - the heart of the bird, the structure and functions of its chambers - we note that this organ has a sufficiently large size and mass relative to the weight of the organism itself. For example, in birds such as bullfinch, crows, ducks about 1 - 1.3% of body weight, and in species with high speed and maneuverability of flight - up to 2%.

For example, in birds of prey — the white-tailed eagle and falcon — the heart index is about 1.8%. In addition, the birds have high blood pressure, and the pulse rate ranges from 200 to 600 beats per minute, and during the flight it reaches 1200 heartbeats.

In this paper, we answered the question of which heart is in birds, having studied the characteristics of the myocardium and characterizing the specificity of their cardiovascular activity.

Pressure and pulse in birds

All birds have a special structure of organs and vital systems:

  • The heart of birds has an impressive size - up to 1% of the total weight of the individual.
  • The faster the feathers fly, the larger its heart. The fact is that during the flight takes a lot of energy, due to which the body requires more oxygen.
  • When compared with human parameters, the pulse of birds in 60 seconds reaches 300 beats, and during the flight even more - 500 beats per minute.
  • The smaller the bird, the more often its heart beats (more than a thousand beats per minute).
  • The pressure of birds is always high - 220 mm Hg.
  • The blood is rich in oxygen, and the number of blood cells is four times the value in mammals. That is why the birds are perfectly developed thermoregulation.

The heart of the birds: where located, the structure

The feathered heart muscle is empty inside and is located on the right side of the chest. From above it is covered with a special bag - pericardium. The front part of the sternum partially overlap the bags. The shape of the heart of birds resembles an inverted cone, the base of which is located between the stomach and the liver.

The heart consists of four chambers separated by a dense wall. Thanks to her, venous blood is not mixed with arterial. Due to this, all the molecules of the organs of the birds are fed from the blood from the arteries, containing many useful substances.

Avian lymphatic system

The lymphatic system of birds consists of capillaries, the space between the lymphatic vessels, the nodes and the lymph itself - a colorless fluid that washes the cells and tissues of the body. Its outflow prevents many lymphatic vessels with special pockets with flaps.

Lymphatic fluid moves exclusively from the tail to the head of the birds, along the spine and on both sides. Lymph nodes are venous and cortical. The veins draw blood from the head, neck, trachea and esophagus. The cortical nodes are located in the lower part of the neck of the bird. And also near the sex glands, the aorta, the left side of the kidneys, liver, intestines and lungs.

Heart and circulatory system

The circulatory system in birds consists of several circles in which blood constantly moves. The right aortic arch, which feeds all organs, departs from the large heart valve. It fills the left and right nameless arteries. The blood runs along the bronchi closer to the spine - along the spinal artery. Smaller branches, which are responsible for the nutrition of all other organs, are already moving away from it. They supply oxygen to the wings and legs.

The small circle of the circulatory system of birds is venous blood. It enters the lungs, saturating them with air. It also moves along the left aortic arch, coming out of the heart, passing the way from the head, wings, shoulders and chest of birds. The blood passes through the liver and kidneys, is cleaned and returns back to the atrium.

Skeleton, respiration, digestion and excretion system

The skeleton of the bird is arranged in the most comfortable way for the birds. It creates reliable conditions for flying in the sky. For example, bones are lightweight, and the tail and neck are a series of dense muscles.

The peculiarity of the respiratory system of birds - special air bags. While inhaling, the exhaust air goes into the front bags. From the back comes a new batch of fresh with nutrients.

The lungs are like a sponge. In a sitting position, the birds exhale the air by contracting their muscles; in flight, by waving wings and a special fork.

The digestive tract in birds is completed within an hour. In the beak salivary glands are secreted for swallowing. In front of the esophagus there is a goiter, in which the food eaten accumulates. In feathered two stomachs. The first ventricle is needed for fermentation, the second - for grinding food.

Because of the lack of rectum, food goes out quickly, lightening weight. The main excretory secret is uric acid. After working it goes directly through the skin - the birds do not have a bladder.

Nervous system, vision, hearing and reproductive system of birds

For the quick response and the acquisition of conditioned reflexes in birds are responsible for the frontal hemisphere of the brain and the enlarged cerebellum. Feathers in birds are eyes and ears. They perfectly see in the distance and distinguish colors.

Bird hearing is so sensitive (for example, owls) that it is able to catch the slightest sounds made by other animals.

The males have a pair of testes. The bodies of the females have one egg - when conceiving, the pelvis could not miss two eggs at the same time. The sperm matures and passes through the spermaducts into the foul place, after which it is injected into the female. Fertilization occurs first in the oviduct. As the egg moves along the cloaca, it will overgrow with yolk, protein and shells. Usually this process does not exceed a day.

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Rhythm of work

The heart does not get tired because it works rhythmically. When the atria contract, the ventricles are relaxed. Then, with the contraction of the walls of the ventricles, the atria relax.

And the time of work, and the time of relaxation takes less than a second, but this is enough for the muscle tissue to recover and work for many years.

Vessels from the heart

Oxygen-rich (arterial) blood from the lungs always enters the left half of the heart. From the left ventricle, it goes into the aortic arch, which gradually distributes blood to various arteries.

The pulmonary artery leaves the right ventricle, carrying blood to the lungs for oxygen enrichment.

Vessels entering the heart

The pulmonary vein flows into the left atrium.

In the right atrium, blood is poured from the anterior and posterior vena cava, which collect all of the body's venous blood.

Veins are the vessels that go to the heart, and the arteries are from the heart. Blood that is rich in oxygen is called arterial. The pulmonary vein thus contains arterial blood, and the pulmonary artery contains venous blood.

Heart size

The size of the heart in different species varies depending on the activity of metabolism and body size.

Whales have a heart mass of 0.5 - 1% of body weight.

In mole 6 - 7%, and in bat 9 - 15%.

A similar relationship is observed with respect to the pulse:

  • bull 500 kg: 40 - 45 beats per minute,
  • 50 kg sheep: 70 - 80,
  • 25 g mouse: 500 - 600.

A blue whale has only 4 to 8 beats per minute when diving. These impacts are captured by the acoustic instruments of ships at a distance of several tens of kilometers.

Fig. 2. The heart of the whale.

In order for the blood to always flow in one direction, there are valves in the heart. They have the form of flaps opening in one direction. Two of them are located between each atrium and ventricle, and one each in the aorta and the pulmonary artery.

Fig. 3. Valves of the heart.

Background of the appearance of the heart in chordates

For small organisms, there are no problems with the delivery of nutrients and removal of metabolic products from the body (diffusion rate is sufficient). However, as the size increases, the need to ensure that the body needs more and more for energy, nutrition, respiration and timely removal of metabolic products (consumed) increases. As a result, primitive organisms already have so-called “hearts” that provide the necessary functions.

Paleontological finds allow us to say that primitive chordates already have some kind of heart. The heart of all chordates is necessarily surrounded by a heart bag (pericardium) and valve apparatus. The hearts of mollusks can also have valves and a pericardium, which, in gastropods, embraces the posterior intestine. In insects and other arthropods, the organs of the circulatory system may be called hearts in the form of peristaltic expansions of the great vessels. In chordates, the heart is an unpaired organ. In mollusks and arthropods, the number of "hearts" may vary depending on the species. For example, mixins, unlike other chordates, have a second heart (a heart-like structure located in the tail). Concept "a heart" not applicable to worms and similar living organisms. However, a full body is noted in fish. Further, as for all homologous (similar) organs, decrease multiple compartments up to two (in humans, for example, two for each circle of blood circulation).

Fish heart

According to evolutionary theory, for the first time, the heart as a full body is noted in fish: the heart is two-chamber, a valve apparatus and a heart bag appear.

The circulatory system of primitive fish can be conventionally represented as a sequentially located "four-chamber" heart, completely different from the four-chamber heart of birds and mammals:

  1. The “first chamber” is represented by the venous sinus receiving non-oxygenated (poor in oxygen) blood from fish tissue (from the hepatic and cardinal veins),
  2. “The second chamber” is the atrium itself, equipped with valves,
  3. "Third chamber" - actually the ventricle,
  4. The “fourth chamber” is an aortic cone containing several valves and transmitting blood to the abdominal aorta.

The abdominal aorta of fish carries blood to the gills where it occurs. oxygenation (oxygen saturation) and blood is delivered to the spinal aorta to the rest of the fish’s body.

In higher fish, the four chambers are not arranged in a straight-line row, but form an S-shaped formation with the last two chambers lying above the first two. This relatively simple pattern is observed in cartilaginous fish and in fin-fin fish. In bony fish, the arterial cone is very small and can be more accurately defined as part of the aorta, and not the heart. The arterial cone is not found in all amniotes — presumably absorbed by the ventricle of the heart during evolution, while the venous sinus is present as a rudimentary structure in some reptiles and birds, later in other species it merges with the right atrium and becomes no longer distinguishable.

The heart of amphibians and reptiles

Amphibians (amphibians) and reptiles (reptiles or reptiles) already have two circles of circulation and their heart is three-chambered (interatrial septum appears). The only modern reptile that has an inferior one (the interatrial septum does not fully separate the atria), but already the four-chamber heart is a crocodile. It is believed that for the first time the four-chamber heart appeared in dinosaurs and primitive mammals. In the future, the direct descendants of dinosaurs - birds and descendants of primitive mammals - modern mammals inherited this structure of the heart.

The heart of birds and mammals

The heart of birds and mammals (animals) - four-chamber. Distinguish (anatomically): right atrium, right ventricle, left atrium and left ventricle. Between the atria and the ventricles are fibrous-muscular valves - to the right is tricuspid (or tricuspid), to the left is bivalve (or mitral). Connective tissue valves (ventricular on the right and aortic on the left) at the exit from the ventricles.

Кровообращение: из одной или двух передних (верхних) и задней (нижней) полых вен кровь поступает в правое предсердие, затем в правый желудочек, затем по малому кругу кровообращения кровь проходит через лёгкие, где обогащается кислородом (оксигенируется), поступает в левое предсердие, затем в левый желудочек и, далее, в основную артерию организма — аорту (птицы имеют правую дугу аорты, млекопитающие — левую).

Регенерация

The muscle tissue of the mammalian heart does not have the ability to recover from damage (except for mammals in the embryonic period, which are capable of regenerating the organ within certain limits), unlike the tissues of some fish and amphibians. However, researchers at the University of Texas Southwestern Medical Center have shown that the heart of a little mouse, which can only recover from birth, but the heart of a seven-day little mouse, no longer exists.

Embryonic development

The heart, like the circulatory and lymphatic systems, is a derivative of the mesoderm. The heart takes its origin from the union of the two rudiments, which, merging, are closed into a heart tube, in which the tissues characteristic of the heart are already represented. The endocardium is formed from the mesenchyme, and the myocardium and epicardium are formed from the visceral sheets of the mesoderm.

Primitive heart tube is divided into several parts:

  • Venous sinus (derived from the sinus vena cava)
  • Common atrium
  • Common ventricle
  • Heart onion (Latinbulbus cordis ).

Further, the heart tube is wrapped as a result of its intensive growth, first S-shaped in the frontal plane, and then U-shaped in the sagittal plane, resulting in finding the arteries in front of the venous gate at the formed heart.

Separation is typical for later stages of development, and the separation of the heart tube by partitions into chambers. Separation does not occur in fish; in the case of amphibians, the wall is formed only between the atria. Atrial wall (lat. septum interatriale ) consists of three components, of which both first grow from top to bottom in the direction of the ventricles:

  • Primary wall,
  • Secondary wall,
  • False wall.

Reptiles have a four-chambered heart, however, the ventricles are united by an interventricular orifice. And only in birds and mammals does a membrane partition develop, which closes the interventricular opening and separates the left ventricle from the right ventricle. The interventricular wall consists of two parts:

  • The muscular part grows from the bottom up and divides the ventricles themselves, in the region of the heart bulb there is a hole - the armor.foramen interventriculare .
  • The membrane part separates the right atrium from the left ventricle, and also closes the interventricular opening.

Valve development occurs parallel to the septic tube of the heart tube. Aortic valve is formed between the arteriosus cone (lat. conus arteriosus ) of the left ventricle and aorta, valve of the pulmonary vein - between the arteriosus cone of the right ventricle and the pulmonary artery. Mitral (bicuspid) and tricuspid (tricuspid) valves form between the atrium and the ventricle. Sinus valves are formed between the atrium and the venous sinus. The left sinus valve is later combined with the septum between the atria, and the right valve forms the inferior vena cava and the valve of the coronary sinus.

Human heart

The human heart consists of four chambers separated by partitions and valves. The blood from the superior and inferior vena cava enters the right atrium, passes through the tricuspid valve (it consists of three petals) into the right ventricle. Then through the pulmonary valve and the pulmonary trunk enters the pulmonary arteries, goes to the lungs, where gas exchange occurs and returns to the left atrium. Then through the mitral (double-leaf) valve (it consists of two petals) enters the left ventricle, then passes through the aortic valve into the aorta.

The right atrium includes hollow, the left atrium - pulmonary veins. The pulmonary artery (pulmonary trunk) and the ascending aorta, respectively, exit from the right and left ventricle. The right ventricle and the left atrium close the small circle of blood circulation, the left ventricle and the right atrium - a large circle. The heart is a part of the organs of the middle mediastinum, most of its front surface is covered with lungs. With flowing areas of the hollow and pulmonary veins, as well as the outgoing aorta and the pulmonary trunk, it is covered with a chemise (heart bag or pericardium). The pericardial cavity contains a small amount of serous fluid. For an adult, its volume and weight average 783 cm³ and 332 g for men, 560 cm³ for women and 253 g.

From 7,000 to 10,000 liters of blood passes through the heart of a person during the day, about 3,150,000 liters a year.

Nervous regulation of the heart

In the cavity of the heart and in the walls of large vessels there are receptors that perceive blood pressure fluctuations. Nerve impulses coming from these receptors cause reflexes that adjust the work of the heart to the needs of the body. The impulse commands to reorganize the work of the heart come from the nerve centers of the medulla oblongata and the spinal cord. Parasympathetic nerves transmit impulses that reduce the heart rate, sympathetic nerves deliver impulses that increase the frequency of contractions. Any physical activity, accompanied by the connection to the work of a large group of muscles, even a simple change in body position, requires correction of the heart and can excite the center, accelerating the activity of the heart. Pain stimuli and emotions can also change the rhythm of the heart.

Cardiac conduction system (PSS) - a complex of anatomical formations of the heart (nodes, bundles and fibers), consisting of atypical muscle fibers (cardiac conductive muscle fibers) and ensure the coordinated work of different parts of the heart (atria and ventricles), aimed at ensuring normal cardiac activity. Atypical cardiomyocytes have the ability spontaneously generate an excitation pulse and conduct it to all parts of the heart, thereby ensuring their coordinated contractions (and this is commonly called heart rate autonomy). The main heart rate driver is sinoatrial knot (Kisa-Vleck knot).

Impacts from the nervous system have only modulating effect on the autonomous work of the conducting system of the heart.

Dextrocardia

Dextrocardia (lat. dextrocardia from lat. dexter - right and other Greek καρδία - heart)) - a rare congenital condition - a variant of the location of the heart in normal anatomy, when due to the reversal of internal organs that occurred during embryonic development, the heart is rotated 180 degrees relative to the vertical axis and takes not the traditional location on the left side of the chest, but right: that is, the apex of the heart is facing right. Marco Aurelio Severino described dextrocardia for the first time in 1643. It can be combined with a full embryonic rotation by 180 degrees of all internal organs of the lat. situs inversus viscerum (verbatim: "Inverted arrangement of internal organs") - then the internal organs have a mirror arrangement compared to their normal position: the apex of the heart is facing to the right (the heart is on the right side), with a three-lobe (Eng. trilobed ) is the left lung, bipartite (eng. bilobed ) - right lung. The blood vessels, nerves, lymph vessels and intestines are also inverted. the liver and gallbladder are on the left (move from the right to the left hypochondrium), the stomach and the spleen are on the right.

In the absence of congenital heart defects, people with a transposition of internal organs can lead a normal life, without any complications associated with the variant of their anatomical structure.

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