Inside the human body are the organs of digestion, circulation, hearing, etc. All of them are involved in ensuring the normal functioning of the body. However, it is believed that the circulatory system performs the key tasks. Consider it in more detail.
General information
Circulation is the continuous movement of blood through a closed system. It provides oxygen to tissues and cells. However, this is not all the functions of the circulatory organs. Due to their activity, nutrients, vitamins, s alts, water, hormones enter the cells and tissues. They are also involved in the removal of end products of metabolic processes, maintain a constant body temperature.
Biology, Grade 8: circulatory organs
The first acquaintance with the internal structure of the body occurs at school. Students don't just learn that there are circulatory organs. Grade 8 involves the study of their features, interaction with other elements of the human body. For a better understanding of the subject, children are offeredsimple diagrams. They clearly show what circulatory organs a person has. The diagrams simulate the internal structure of the body.
What is the circulatory system?
First of all, it is the heart. It is considered the main organ of the system. However, its activity would be useless in the absence of vessels present in all tissues of the body. It is through them that nutrients and other necessary substances are transported with blood. Vessels vary in size and diameter. There are large ones - veins and arteries, and there are small ones - capillaries.
Heart
It is represented by a hollow muscular organ. There are four chambers in the heart: two atria (left and right) and the same number of ventricles. All these spaces are separated from each other by partitions. The right atrium and ventricle communicate with each other through the tricuspid valve, and the left through the bicuspid valve. The weight of an adult heart is on average about 250 g (for women) and 330 g (for men). The length of the organ is about 10-15 cm, and its transverse size is 8-11 cm, the distance from the front to the back wall is about 6-8.5 cm. The average volume of a man's heart is 700-900 cm3, women - 500-600 cm3.
Specific activity of the heart
The outer walls of the organ are formed by muscle. Its structure is similar to the structure of striated muscles. The heart muscle, however, is able to contract rhythmically, regardless of external influences. This happens due to impulses that occur in the organ itself.
Cycle
The task of the heart is to pump arterial blood through the veins. The organ contracts approximately 70-75 times / min. at rest. This is approximately once every 0.8 sec. Continuous work of the body consists of cycles. Each of them involves contraction (systole) and relaxation (diastole). In total, there are three phases of the activity of the heart:
- Atrial systole. It lasts 0.1 seconds.
- Ventricular contraction. It lasts 0.3 seconds.
- General relaxation - diastole. It lasts 0.4 seconds.
Throughout the entire cycle, thus, the work of the atria lasts 0.1 sec., and their relaxation - 0.7 sec. The ventricles contract for 0.3 seconds and rest for 0.5 seconds. This determines the ability of the muscle to work throughout life.
Vessels
High performance of the heart is associated with its increased blood supply. It occurs due to the vessels extending from it. Approximately 10% of the blood entering the aorta from the left ventricle enters the arteries that feed the heart. Almost all of them carry oxygen to tissues and other elements of the body. Venous blood is carried only by the pulmonary artery. The vessel wall consists of three layers:
- Outer connective tissue sheath.
- Medium, which is formed by smooth muscles and elastic fibers.
- Internal, formed by connective tissue and endothelium.
The diameter of human arteries is in the range of 0.4-2.5 cm. On average, the total volume of blood in them is 950 ml. Arteries branch into smaller arterioles. They, in turn,pass into the capillaries. These circulatory organs are considered the smallest. The diameter of the capillaries is not more than 0.005 mm. They permeate all tissues and organs. Capillaries connect arterioles to venules. The walls of the smallest vessels are made up of endothelial cells. Through them, the exchange of gases and other substances is carried out. Veins carry blood enriched with carbon dioxide, containing metabolic products, hormones and other elements from the organs to the heart. The walls of these vessels are thin and elastic. Medium and small veins have valves. They prevent backflow of blood.
Circles
Blood and circulatory organs were described as early as 1628. The cardiovascular scheme of mammals and humans was studied at that time by the English physician W. Harvey. He found out that the circulatory organs form two circles - small and large. They differ from each other in their tasks. In addition, there is a third circle, the so-called heart. It serves directly the heart. The circle begins with the coronary arteries extending from the aorta. The third circle ends with cardiac veins. They converge into the coronary sinus, which flows into the right atrium. Other veins enter his cavity directly.
Small circle
With its help, the respiratory and circulatory organs interact. The small circle is also called the pulmonary. It ensures the enrichment of blood in the lungs with oxygen. The circle starts from the right ventricle. Venous blood moves to the pulmonary trunk. It is divided into two branches. Each of them carries blood, respectively, toright and left lung. Inside them, the arteries diverge into capillaries. In the vascular networks that braid the pulmonary vesicles, the blood gives off carbon dioxide and receives oxygen. It becomes scarlet and goes through the capillaries into the veins. Then they join into four pulmonary vessels and flow into the left atrium. Here, in fact, the small circle ends. The blood entering the atrium flows through the atrioventricular orifice into the left ventricle. This is where the big circle starts. Thus, the pulmonary arteries carry venous blood, and the veins carry arterial blood.
Great Circle
It involves all the circulatory organs, except for the pulmonary vessels. A large circle is also called a corporeal circle. It collects blood from the veins of the upper and lower body and distributes the arterial. The circle starts from the left ventricle. From it, blood flows into the aorta. It is considered the largest vessel. Arterial blood contains all the substances necessary for the life of the body, as well as oxygen. The aorta diverges into arteries. They go to all tissues of the body, pass into the arterioles and then into the capillaries. The latter, in turn, are connected into venules and then into veins. The exchange of gases and substances occurs through the capillary walls. Arterial blood gives off oxygen and takes away metabolic products and carbon dioxide. The venous fluid is dark red in color. Vessels are connected to the vena cava - large trunks. They enter the right atrium. This is where the big circle ends.
Movement through vessels
The flow of any liquid occurs due to the differencepressure. The larger it is, the higher the speed. Similarly, blood moves through the vessels of the small and large circles. The pressure in this case is created by contractions of the heart. In the aorta and left ventricle, it is higher than in the right atrium and vena cava. Due to this, the liquid moves through the vessels of a large circle. The pressure in the pulmonary artery and right ventricle is high, while that in the left atrium and pulmonary veins is low. Due to the difference, movement occurs in a small circle. The greatest pressure is in the large arteries and the aorta. This indicator is not constant. In the course of blood flow, part of the energy from pressure is spent on reducing the friction of blood on the vascular walls. In this regard, it begins to gradually decline. Especially clearly this process occurs in the capillaries and small arteries. This is due to the fact that these vessels provide the greatest resistance. In the veins, the pressure continues to decrease and in the hollow vessels it becomes like atmospheric pressure or even lower.
Movement speed
Features of the circulatory organs are in their internal structure and size. For example, if we talk about vessels, then the speed of fluid movement will depend on the width of their channel. The largest, as mentioned above, is the aorta. This is the only vessel with the widest channel. All the blood leaving the left ventricle passes through it. This also determines the maximum speed in this vessel - 500 mm/sec. Arteries branch into smaller ones. Accordingly, the speed in them is reduced to 0.5 mm/sec. in capillaries. Due to this, the blood has time to give up nutrients and oxygen and pick up metabolic products. The movement of fluid through the capillaries is caused by a change in the lumen of small arteries. When they expand, the current increases, when they narrow, it weakens. The smallest organs of blood circulation - capillaries - are represented in large numbers. In humans, there are about 40 billion of them. At the same time, their total lumen is 800 times larger than the aortic one. However, the speed of fluid movement through them is very low. The veins, approaching the heart, become larger and merge. Their total lumen decreases, but the blood flow velocity increases in comparison with capillaries. The movement in the veins is due to the pressure difference. The blood flow is directed towards the heart, which is facilitated by the contraction of skeletal muscles and the activity of the chest. So, when you inhale, the pressure difference at the beginning and end of the venous system increases. When the skeletal muscles contract, the veins contract. It also promotes blood flow to the heart.
Pathological conditions
Diseases of the circulatory system today occupy one of the first places in statistics. Often, pathological conditions lead to complete disability. The reasons for which these violations occur are very diverse. Lesions can appear in various parts of the heart and in the vessels. Diseases of the circulatory organs are diagnosed in people of different ages and gender. According to statistics, however, some pathological conditions may occur more often in women, while others in men.
Symptoms of lesions
Diseases of the circulatory organs are accompanied by various complaintspatients. Often the symptoms are common to all pathological conditions and do not refer to any particular disorder. Quite common are cases when, in the early stages of the onset of violations, a person does not make any complaints at all. Some diseases of the circulatory system are diagnosed by chance. However, knowledge of the most common symptoms allows you to identify the pathology in a timely manner and eliminate it at an early stage. Illnesses may be accompanied by:
- Short of breath.
- Pain in the heart.
- Puffiness.
- Cyanosis, etc.
Heartbeat
It is known that he althy people do not feel the contractions of their heart at rest. The heartbeat is not felt even with moderate exercise. However, with its increase, even a he althy person will feel the beating of the heart. His beating can increase when running, excitement, at high temperature. The situation is different for those people who experience problems with the heart or blood vessels. They can feel a strong heartbeat even with a slight load, and in some cases even at rest. The main cause of this condition is considered to be a violation of the contractile function of the organ. Heartbeat in this case is a compensatory mechanism. The fact is that with this violation, in one contraction, the organ ejects into the aorta a smaller volume of blood than necessary. Therefore, the heart goes into intensive mode of operation. This is extremely unfavorable for him, since the relaxation phase is significantly shortened. Thus, the heart rests less than it should. During a shortrelaxation, the biochemical processes necessary for recovery do not have time to go through. A fast heartbeat is called tachycardia.
Pain
This symptom accompanies many illnesses. At the same time, in some cases, pain in the heart may be the main symptom (for example, with ischemia), and in others it may not be of decisive importance. With coronary artery disease, pain is caused by insufficient blood supply to the heart muscle. The manifestation of pathology is quite clear. The pain is compressive in nature, short-term (3-5 minutes), paroxysmal, occurs, as a rule, during exercise, at low air temperature. A similar condition can occur in a dream. Usually a person who feels such pain takes a sitting position, and it is like. This attack is called rest angina. With other diseases, pain does not have such a clear manifestation. Usually they are aching and last for a different time. They are not very intense. At the same time, there is no stopping effect from taking certain medications. Such pains accompany various pathologies. Among them are heart defects, pericarditis, myocarditis, hypertension and so on. Pain in the region of the heart may not be associated with diseases of the circulatory system. For example, they are diagnosed with left-sided pneumonia, osteochondrosis of the cervical and thoracic regions, intercostal neuralgia, myositis, and so on.
Interruptions in the activity of the heart
In this state, a person feels the irregularity of the work of the body. It manifests itself in the form of fading, a strong short blow,stops, etc. For some people, such interruptions are single, for others they are longer and sometimes permanent. As a rule, such sensations are accompanied by tachycardia. In some cases, interruptions are noted even with a rare rhythm. The causes are extrasystoles (extraordinary contractions), atrial fibrillation (loss of the rhythmic function of the heart). In addition, there may be violations of the conduction system and muscles of the organ.
Hygiene of the heart
Normal stable activity of the body is possible only with a well-developed he althy circulatory system. The current velocity determines the degree of supply of tissues with the necessary compounds and the intensity of removal of metabolic products from them. In the process of physical activity, the need for oxygen increases simultaneously with the increase in heart rate. In order to avoid interruptions and violations, it is necessary to train the muscle of the organ. To do this, experts recommend doing exercises in the morning. This is especially important for those people whose activities are not related to physical activity. The greatest effect of the exercises comes if they are done in the fresh air. In general, doctors recommend walking more. Along with this, it should be remembered that excessive psycho-emotional and physical stress can disrupt the normal activity of the heart. In this regard, stress and anxiety should be avoided whenever possible. Being engaged in physical work, it is necessary to choose loads in proportion to the capabilities of the body. Nicotine, alcohol, narcotic substances have an extremely negative effect on the work of the body. They poison the central nervous system andheart, cause serious dysregulation of vascular tone. As a result, severe diseases of the circulatory system can develop, some of which are fatal. People who drink alcohol and smoke are more likely to experience vascular spasms. In this regard, it is necessary to give up bad habits and help your heart in every possible way.
