Circulatory System PDF

Circulatory system It consists of two separate but related components: the cardiovascular system and the lymphatic system. The cardiovascular system is responsible for transporting blood between the heart and tissues, in both directions. The lymphatic system collects the lymph, the excess of tissu...

Circulatory system It consists of two separate but related components: the cardiovascular system and the lymphatic system. The cardiovascular system is responsible for transporting blood between the heart and tissues, in both directions. The lymphatic system collects the lymph, the excess of tissue fluid, and returns it to the cardiovascular system. Cardiovascular system It is made up of blood vessels (that carry blood throughout the body) and the heart (a muscular organ that pumps blood in two separate circuits) - Pulmonary circuit: it carries the blood from the heart to the lungs, where it is oxygenated and returns to the heart. - Systemic circuit: carries oxygenated blood from the heart to the rest of the body and returns without oxygenating. The vessels that make up this system are of three types: - Arteries: carry blood from the heart to the tissues. - Veins: carry blood from the tissues to the heart. - Capillaries: vessels with thin walls, where the exchange of substances between the blood and the tissues takes place, which will be where the arteries end, and the veins are born. Heart It consists of four cavities: two atria, which receive blood, and two ventricles that pump the blood. The blood coming from the systemic circulation reaches the right atrium, passes through the tricuspid valve to the right ventricle and from there it will be impelled into the pulmonary circulation. It returns oxygenated to the left atrium, passes through the mitral valve to the left ventricle and from there goes to the systemic circulation. The heart wall is formed by three layers: - Endocardium: the innermost layer, formed by a simple flat epithelium and a fibroelastic conjunctive. Folds of the endocardium form the valves of the heart, which prevent the backward movement of the blood. - Myocardium: the thicker middle layer formed by cardiac muscle. - Epicardium: the outermost layer, also known as the visceral layer of the pericardium. It is formed by connective tissue and a simple flat epithelium. Next to it is the pericardial cavity filled with fluid and the parietal layer of the pericardium (simple flat epithelium + connective). Conduction system of the heart Sinusal node Bundle A-V Purkinje fibres Internodular pathways Atrioventricular node Among the cardiac muscle cells there are some specialized in generating and transmitting the impulses necessary for the contraction of the heart. Among them, there is a group located at the junction between the right atrium and the superior cava vein that form the sinusal node, which spontaneously depolarize initiating this impulse. That is why this nodule is known as the natural pacemaker of the heart. This impulse then propagates through the walls of the atria through the internodular pathways to the atrioventricular node, located in the wall of the septum just above the tricuspid valve. Then the impulse reaches the bundle of His or atrioventricular and from there it passes to the Purkinje fibers that carry it to all the walls of the ventricles. This way the heartbeat happens continuously, rhythmically and coordinated between the different parts of the heart. The ANS does not initiate the heartbeat, but it is regulating its frequency and stroke volume. Arteries They carry blood from the heart to the capillaries at high pressure, which will help the blood reach remote areas. As we move away from the heart, the diameter of the artery will be smaller to maintain pressure. Its walls are formed by three layers: - Tunica intima: the innermost layer; formed by the endothelium, a simple flat epithelium and loose connective. There is a sheet of elastic fibers called internal elastic lamina. - Tunica media: the thickest layer; formed by smooth muscle and elastic fibers. At the end of this layer, especially in large arteries, an external elastic lamina is distinguished. - Tunica adventitia: composed of dense irregular connective tissue. When the elastic fibers form a thick layer in the tunica media, we say it is an elastic artery. These are usually the larger arteries and the closest to the heart. They are conduction arteries, which have elastic properties to cushion the heart's pumping. If the smooth muscle forms a thicker layer in the tunica media, we speak of muscular arteries. These are smaller arteries that will distribute blood. Thanks to the musculature they can regulate their diameter and therefore the pressure. The last ramifications of the arteries, the smallest ones, are called arterioles and flow into the capillaries. Veins They start from the capillaries as venules and gradually form larger vessels on their way back to the heart. Its walls have the same layers as the arteries, but in general the tunica media is thinner and does not have elastic fibers, since here the pressure is lower. They also tend to have a larger diameter than the arteries and thus carry a greater amount of blood. In addition, the endothelium of the veins, forms folds that give rise to semilunar valves that prevent the backward movement of the blood. Capillaries They arise from the arterioles and end in the venules. They are the smallest vessels, and their wall is formed only by endothelium. They may be of three types: - Continuous: present in muscle tissue, nervous, conjunctive, lungs and exocrine glands. Their endothelial cells have occlusive unions that do not leave spaces between them. The molecules that cross the wall of these capillaries do it through the endothelial cells. - Fenestrated: they have pores in their walls. They appear in the pancreas, intestine, kidneys and endocrine glands. - Sinusoids: large diameter and numerous perforations forming irregular channels for blood transport. They appear in the bone marrow, liver, spleen, lymphoid organs and some endocrine glands. Arteries vs Veins: What’s the Difference? - YouTube Human Circulatory System - YouTube Lymphatic system It is a system of vessels that collects excess tissue fluid and returns it to the cardiovascular system. Unlike the cardiovascular system, it is an open system in which there is no pump to circulate the liquid. This system of vessels begins in the tissues as lymphatic capillaries, with blind ends formed by an endothelium more permeable than that of the blood capillaries. The fluid they collect, which is called lymph, goes through increasingly larger vessels, the lymphatic vessels, very similar in structure to the veins, also with semilunar valves. Finally, they open into two lymphatic ducts, which are: 1. The right lymphatic duct, which collects the lymph in the upper right quadrant of the body and empties where the right subclavian vein and the right internal jugular vein meet. 2. The thoracic duct, which collects the lymph from the rest of the body and ends in the union of the left subclavian vein with the left internal jugular vein. Interposed in the lymphatic circulation, there are the lymphatic nodes, small and rounded organs where lymphocytes and other immune cells abound and are responsible for filtering the lymph. El sistema linfático - YouTube