18 March 2019 Author : José Ferreira Santos This system contributes in various ways to maintaining the body’s balance - homeostasis , in particular by performing the following functions: Carrying oxygen from the lungs to the entire organism, and carrying carbon dioxide in the opposite direction to be eliminated; Transporting absorbed nutrients to the places they are needed in the body; Transporting the residue of cell metabolism to the sites from which they are eliminated; Transporting substances produced in certain places in the body (e.g. hormones and antibodies) to other places where they are needed; Participating in the regulation of body temperature. The elements of the cardiovascular system The cardiovascular system consists of several elements. Find out more about them and learn about their functions. 1. Heart The heart is located in the chest cavity, slightly to the left. It is the central organ of the cardiovascular system and its main function is to propel blood through the vessels. The heart is a hollow organ , the wall of which consists of three layers: The outermost, known as the epicardium; The middle one, known as the myocardium; The inner layer, endocardium, which has direct contact with the blood. The heart is wrapped on the outside in the pericardium , a bag-like membrane that protects it and which has 2 layers: The visceral pericardium, which adheres to the surface of the heart; The outer layer or parietal pericardium. Between the 2 layers is the pericardial cavity , this contains a small amount of fluid that lubricates the surfaces of the layers to prevent friction during the heart’s movements. How is the heart divided? Inside, the heart is divided into four chambers: 2 atria; 2 ventricles. The right atrium communicates with the right ventricle through the right atrioventricular orifice, which has a valve known as the tricuspid . The left atrium communicates with the left ventricle through the left atrioventricular orifice which has a valve known as the mitral . The right and left atria receive blood from the vena cava and pulmonary veins , respectively. How does blood move around the heart? The movement of blood in the heart is made from the atria to the ventricles . From the right ventricle and the left ventricle, the blood is moved to the pulmonary artery and to the aorta , respectively. The pulmonary valve is at a point on the transition from the right ventricle to the pulmonary artery. The aortic valve is at a point on the transition from the left ventricle to the aorta . What do the heart valves do? The function of the heart valves (tricuspid, mitral, pulmonary and aortic) is to ensure blood circulates in one direction only and prevent reflux (when they close). In cardiac auscultation , sounds associated with the closure of cardiac valves are audible. Therefore, this technique enables us to: Identify the frequency of cardiac beats; Detect the presence of abnormal sounds. When heart valves wear out due to a natural process or due to illness, they may fail to perform their function correctly; in this case, we are in the presence of a valve disease or valvopathy . How does circulation take place in the heart? Circulation of the heart is not done by the blood present in its cavities. It is carried out by means of the coronary circulation , which starts in 2 coronary arteries leading out from the starting point of the aorta. The oxygen and nutrients needed by the cardiac muscle cells originate in the blood coming from the coronary arteries. Therefore, any problem with this circulation can impair heart function . How does the heart rate vary? The innervation of the heart is the responsibility of the autonomic (or involuntary) nervous system and its sympathetic and parasympathetic divisions. Sympathetic stimulation increases the heart rate (number of heartbeats per minute), and parasympathetic stimulation decreases it. 2. Blood Vessels There are basically 3 types of blood vessels: Arteries; Veins; Capillaries. Arteries The blood vessels that carry the blood out of the heart are the arteries . The artery wall consists of 3 layers: The inner layer, made up of a layer of cells; The intermediate layer, made up of muscle tissue; The external layer, which is made up of essentially elastic fibres. The elasticity of the artery wall allows the arteries to transport blood at high pressure. As they travel through the organism, moving away from the heart, the arteries branch off into progressively thinner vessels until they form arterioles . Capillaries The arterioles are followed by a network of small vessels and a thin wall - the capillaries , where the necessary exchanges of oxygen and nutrients with the cells take place. Carbon dioxide and the products of cell metabolism are present in the liquid that surrounds them (extracellular fluid) and which, for the most part, is reabsorbed by the capillaries and integrated into the blood that returns to the heart The capillary wall has a single layer corresponding to the inner layer of the veins and arteries. Veins As they return to the heart, the capillaries follow the venules that join together to form progressively larger vessels, ending up in the veins that carry the blood back to the heart . The vein wall also has 3 layers , but the muscular layer and the elastic layer are thinner than those corresponding to the arteries. The veins have valves inside them that ensure that the blood circulates in a single direction . How does blood circulation take place? Circulation is the movement of blood through the heart and the blood vessels. Two circuits can be distinguished in the circulatory system: Small circulation The small circulation, or pulmonary circulation, carries the venous blood to the lungs in order to be oxygenated, and returns the oxygenated blood to the left heart. In summary, the pathway of the blood in the small circulation is as follows: Right ventricle - pulmonary artery - lungs - pulmonary vein - left atrium. Large circulation The large circulation, systemic circulation or peripheral circulation, distributes the oxygenated blood throughout the body and takes back the venous blood in the direction of the right heart. In summary, the pathway of blood in the large circulation is as follows: Left ventricle - aortic artery - body organs and tissues - vena cava - right atrium. The blood circulates in a sense of lowering pressure ; that is, the pressure is higher in the arteries than in the veins. How do the heart movements work? The mechanical functioning of the heart , pumping blood through the cardiovascular system, results from the contraction and relaxation of the muscle that surrounds the cavities . In order for the cardiac cavities to fill with blood, they need to relax. However, for them to pump blood out, they need to contract. Cardiac muscle cells need an initial stimulus to make them contract. This electrical stimulus originates from the sinoatrial or sinus node , also known as the cardiac pacemaker, located in the right atrium. The impulses from the sinoatrial node then hit another structure - the atrioventricular node. From here, they are carried to the whole heart via the bundle of Hiss and finally the Purkinje network , rigorously controlling the activity of the cardiac muscle. What happens when there are irregularities in the heart eletric activation? When there are changes in the integrity of this system for electric control of cardiac movements, whatever the reason, arrhythmia arises. In some situations, it is necessary to implant an electronic pacemaker to perform the functions of the sinoatrial node. As the body is a good conductor of electricity, cardiac electrical activity can be recorded on the body surface. This is achieved by placing electrodes in specific positions and obtaining a graphic record of that activity, known as an electrocardiogram (ECG) . Blood pressure: cardiac systole and cardiac diastole The contraction of the atria and the ventricles is not simultaneous . When the atria contract (to push the blood out to the ventricles), the ventricles relax (to receive the blood from the atria). Conversely, when the ventricles contract (to push the blood out to the arteries), the atria relax (to receive the blood from the veins). Therefore, the cardiac systole is the heart contraction that refers to the ventricles. The cardiac diastole is the cardiac relaxation (or dilation), which also refers to the ventricles. During a cardiac systole and diastole cycle , the following events take place: Changes in the volume and internal pressure of the heart cavities; Movement of the heart valves; Changes to the blood pressure in the vessels. The pressure exerted by the blood onto the wall of the arteries is called blood pressure . It is at its maximum in ventricular systole and minimal in ventricular diastole and can be measured in the arteries of the arms. Meet the cardiology team from Hospital da Luz network. The content published in the Health Guide is intended for the general public and is provided for informational and educational purposes only. It does not replace individual medical assessment, diagnosis, or personalized clinical advice from a qualified healthcare professional. The content is produced or reviewed by physicians and other healthcare professionals at Hospital da Luz and is based on the knowledge available at the time of publication or the most recent update, as indicated at the beginning of each item.
