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No. 14 1. Introduction of the Cardiovascular System 2. Heart (1) The location of heart The external features of heart The chambers of heart The Structure of heart PART Ⅳ ANGIOLOGY Introduction: Physico-chemical properties and composition of the micro-environment of the cells comprising the various tissues of the body remain relatively constant, by the operation of a complex series of homeostatic control mechanisms, which depend for effectiveness upon adequate circulatory system The circulatory system can be separated into two divisions: the cardiovascular system consisting the heart and blood vessels through which the blood circulates, and the lymphatic system consisting of lymph nodes and vessels which conduct the lymph fluid. The cardiovascular system includes the heart, which serves as a pump for the blood, and the blood vessels, which transport the blood throughout the body. The lymphatic system consists of organs that play a role in specific immune responses (tonsils, thymus, spleen, lymph nodes, and lymphatic nodules) and vessels that collect tissue fluid from between the cells of the body and transport it to the cardiovascular system. Chapter 1 The Cardiovascular System Section 1 Introduction The cardiovascular system is a closed circular system. Confined to the heart and the numerous vessels, blood continuously travels a circular route through the heart, into arteries, then to capillaries, into veins, and back to the heart. Normally, blood does not leave this system, although some of the fluid part of the blood does pass through the walls of the capillaries to join the tissue fluid between the cells. However, even this fluid is returned to the cardiovascular system directly or by way of the lymphatic system Ⅰ. Organization of the Cardiovascular System The Cardiovascular system comprises the heart and blood vessels. The blood vessels consist of arteries, veins and capillaries. Ⅰ) Heart The heart is a hollow, muscular organ situated within the thorax. Its contraction expels blood to all parts of the body through a complicated series of tubes, termed arteries. In order to function as a pump, the heart must have both receiving and delivery chambers, valves to direct the flow of blood through the heart, a wall that is strongly compressible and thus provides the force to propel blood, and vessels to deliver blood to and from the heart. The heart consists of four chambers: right and left atria and right and left ventricles, of which two are receiving and two are distributing chambers. The right and left atria receive the blood from the great veins and expel it into the right and left ventricles. From the ventricles the blood is pumped into the arterial system and carried to the various organs of the body. Each atrium communicates with the corresponding ventricle through atrioventricular orifices, but the right and left chambers of the heart are separated from one another by partitions, called septa. Ⅱ) Arteries The arteries carry blood away from the heart. They transport blood to the various body tissues under high pressure exerted by the pumping action of the heart. It is, therefore, imperative that they possess strong, elastic walls to insure fast, efficient blood flow to the tissues. Compared to the other types of blood vessels, arteries must be able to withstand the greatest internal pressrue. Arteries are classified according to size as large, medium, and small ones. The wall of an artery consists of three layers, which are named from within outwards: the tunica intima, the tunica media, and the tunica adventitia. The arteries ramify extensively in their course throughout the body, and end in minute vessels, called arterioles, which open into a close-meshed network, capillaries. Ⅲ) Capillary They are simply thin endothelial tubes with a layer of basement membrane. They have an average diameter of 7~8μ. They have extremely thin walls. As a consequence, they are sites at which the exchange of materials between the blood and the interstitial fluid takes place. Across their walls the fluids, oxygen, carbon dioxide, nutrients, vitamins, hormones, metabolic products and immune substances are exchanged between the blood and tissue fluid. In the body they anastomose with each other to form capillary networks except for in the cartilage, hair, cornea and lens. Ⅳ) Veins After the blood has passed through the capillaries, it is collected into a series of minute vessels, called venules, which join with one another to form veins. The major veins return blood to the atria of the heart. The veins unite with one another, and ultimately two large venous trunks, named the superior and inferior venae cavae, are formed, which convey the blood to the heart. After the blood leaves the capillaries, its pressure continues to drop; it is lowest near the right atrium of the heart in the superior and inferior venae cavae. With the progressive change from capillaries to venules to veins, the diameters of individual vessels and the thickness of their walls steadily increase, whereas the total cross-sectional area of parallel vessels decreases. Venous pressure is always lower than arterial pressure, and the walls of the veins are never as thick as the walls of the corresponding arteries. The walls of veins, like those of the arteries, are composed of three coats: the internal being endothelial, the middle muscular and the external connective tissue. Ⅱ. The Cardiovascular Circuits The superior and inferior venae cavae bring to the right atrium the blood which has become deoxygenated and taken up carbon dioxide during its circulation through the tissues of the body. From the right atrium this venous blood passes into the right ventricle, by which it is expelled into the pulmonary trunk to be conveyed to the lungs. As it circulates through the pulmonary capillaries the blood is brought into close relationship with the inspired air and it gives off some of its carbon dioxide and acquires a fresh supply of oxygen. This oxygenated blood is returned by the pulmonary veins to the left atrium and thence passes into left ventricle. With each beat of the heart the left ventricle pumps its contents into the aorta, which distributes blood through its numerous branches to all the tissues and organs of the body. Greater or systemic circulation and lesser or pulmonary circulation: The course of the blood from the left ventricle through the whole body finally to the right atrium of the heart constitutes the greater or systemic circulation. While the passage from the right ventricle through the lung to the left atrium of the heart is termed the lesser or pulmonary circulation. Ⅲ Anastomoses 1. Anastomoses between arteries: Arteries do not always end in capillaries; in many cases they unite with one another, forming what are called anastomoses. Anastomosis between arterial trunks of nearly equal size is found in the brain and in the abdomen. In the limbs, the anastomoses are largest and most numerous around the joints; these anastomoses may be so numerous that they constitute a close network. Arteries often join end to end, forming the arterial arch (e.g. the palmar and plantar arches). 2. Anastomoses between veins: Veins join with one another to from the venous plexus or network. 3. Anastomoses between arteries and veins: In a number of situations in the body direct connections exist between the small arteries and corresponding veins, they are called the arteriovenous anastomoses. The connecting vessel can conduct blood directly from the artery to the vein and so partially or completely exclude the capillary bed from the circulation for the time being. Arteriovenous anastomoses are found in the skin of the nose, lips, hands and feet. They function to regulate the local blood flow and temperature. 4. Collateral anastomoses: Each region or organ of the body is usually supplied by several vessels. One of them, the largest in diameter, is called the main vessel, while the smaller ones are called the accessory or collateral vessels; they communicate with one another through anastomotic channels. If a vessel is occluded by thrombosis, embolism or by ligation, the flow of blood through the collateral and anastomotic channels will increase. The anastomotic channels may become so enlarged as to replace the normal and constitute an aberrant supply to a part. The blood circulation is thus partially restored and the collateral circulation is established. Sudden occlusion of a vessel may be followed in some situations by necrosis of the part supplied, while gradual occlusion may allow time for the dilatation of the anastomosing channels and the establishment of the collateral circulation. Section 2 The Heart The heart is the pump that provides the force necessary to keep the blood flowing through the system of vessels. It is a hollow, muscular organ of a somewhat conical form, about the size of a person’s fist and weighs about 260g in Chinese adult. Ⅰ. The Location of Heart The heart is located in the middle mediastinum between the lungs, and is enclosed in the pericardium. It is obliquely in the chest behind the body of the sternum and adjoining parts of the costal cartilages, onethird of it on the right of the median plane and two-thirds on the left. Ⅱ. The External Features of Heart The heart is described as having a base, an apex, two surfaces (diaphragmatic and sternocostal surfaces), three borders and four grooves. Ⅰ) Cardiac base The cardiac base faces backwards and to the right. It consists mainly of the left atrium, part of the right atrium. The four pulmonary veins, two on each side, open into the left atrium, while the superior vena cava opens into the upper part, and the inferior vena cava into the lower part, of the right atrium. Ⅱ) The cardiac apex The cardiac apex, formed by the left ventricle, is directed downwards, forwards and to the left, and is overlapped by left lung and pleura. It is situated in the 5th left intercostal space 1~2 cm to the right of the left mid-clavicular plane. Here the apex beat is palpable. Ⅲ) The two surfaces 1. The sternocostal surface, or called the anterior surface, is directed forwards, upwards and to the left. It consists of an atrial and a ventricular portion. 2. The diaphragmatic surface The diaphragmatic surface, or called the inferior surface, is directed downwards and slightly backwards. It is formed by the ventricles (chiefly by the left ventricle), and rests upon the diaphragm. Ⅳ) Three borders 1. The right border The right border of the heart, formed by the right atrium, is almost vertical. 2. The left border The left border, formed mainly by the left ventricle, is rounded. 3. The inferior border The inferior border, formed almost entirely by the right ventricle and the cardiac apex, is nearly horizontal. Ⅴ) Four grooves 1. The coronary groove The coronary groove separates the atria from the ventricles and contains the trunks of the coronary vessels of the heart. It is deficient in front, where it is crossed by the root of the pulmonary trunk. 2. The anterior interventricular groove On the sternocostal surface, the line of separation between the ventricles being marked by the anterior interventricular groove. 3. The posterior interventricular groove The diaphragmatic surface is traversed obliquely by the posterior interventricular groove. 4. The posterior interatrial groove On the diaphragmatic surface, the sulcus between the right atrium and the right superior and inferior pulmonary veins. Cardiac apical incisure: The anterior and posterior interventricular grooves extend from the base of the ventricular portion to a notch, termed the cardiac apical incisure, situated a little to right of the apex of the heart. Crux: The crossing point of the posterior interatrial groove, the posterior interventricular groove and the coronary groove is the crux. Ⅲ. The Chambers of Heart The heart is divided into right and left halves, each half is subdivided into two chambers. The upper chambers, the atria, are separated by the interatrial septum; the lower chambers, the ventricles, are separated by the interventricular septum. The atria serve as receiving chambers for blood from the various parts of the body, the ventricles as pumping chambers. Ⅰ) The Right Atrium It constitutes the right superior portion of the heart. Right auricle: a small, conical, muscular pouch, termed the right auricle, projects towards the left from its upper and anterior part and overlaps the right side of the ascending aorta. The cavity of right atrium is divided into two portions, an anterior (atrium proper) and a posterior (sinus venarum cavarum), by the crista terminalis, a smooth, muscular ridge, which extends from the orifice of the superior vena cava to the orifice of the inferior vena cava. 1. The atrium proper The anterior portion, called the atrium proper, has rough walls. Many nearly parallel muscular ridges, termed the pectinate muscles, run forwards from the crista terminalis towards the auricle. In the auricle they are connected to one another so as to form a muscular network. 2. The sinus venarum cavarum The posterior portion, termed the sinus venarum cavarum, has smooth walls. There are three orifices opens into it: ① Orifice of superior vena cava The superior vena cava returns the blood from the upper half of the body, and opens into the upper part of the sinus venarum cavarum. ② Orifice of inferior vena cava The inferior vena cava returns the blood from the lower half of the body, and opens into the lowest part of the sinus venarum cavarum. The valve of inferior vena cava (Eustachian valve) lies anterior lip of the orifice of inferior vena cava. ③ Orifices of coronary sinus The coronary sinus returns the greater part of the blood from the substance of the heart. Its opening, the orifice of coronary sinus, is placed between the orifice of inferior vena cava and the right atrioventricular orifice. Fossa ovalis: On the lower part of the septal wall of the atrium there is an oval depression, called the fossa ovalis, which is the remnant of the oval foramen of the fetal heart. The anterior inferior part of the right atrium is the right atrioventricular orifice. Blood from the right atrium goes into the right ventricle through this orifice. Ⅱ) The Right Ventricle It constitutes the right inferior portion of the heart. Its anterosuperior surface forms a large part of the sternocostal surface of the heart. The wall of the right ventricle is thinner than that of the left, the proportion between them being as 1:3. The interior of the right ventricle is separated into the inflow and outflow tracts by a muscular ridge, the supraventricular crest, situated between the atrioventricular and pulmonary orifices. 1. Inflow tract of the right ventricle The inflow tract has rough walls due to the presence of trabeculae carneae. It receives the blood from the right atrium through the right atrioventricular orifice. The right atrioventricular (tricuspid) valve guards the right atrioventricular orifice, and consists of three somewhat triangular cusps, named anterior, posterior, medial or septal cusps. A number of delicate, tendinous cords, termed the chordae tendineae, are attached to the apices, margins and ventricular surfaces of the cusps. The trabeculae carneae are irregular muscular columns which project from the whole of the inner surface of the ventricle. Some of them are merely elevated ridges, others form conical projections, the papillary muscles, which give origin to the chordae tendineae. The chordae tendineae of each papillary muscle are connected with the contiguous margins of two cusps, hence, there are 3 papillary muscles on th eright side. A muscular band termed the moderator band or septomarginal trabecula, which extends from the interventricular septum to the base of the aterior papillary muscle. It serves to convey the right bundle branch of the atrioventricular bundle. Tricuspid valve complex: The rings and apexes of tricuspid valve, chordae tendineae, and papillary muscles constitute the tricuspid valve complex. 2. Outflow tract of the right ventricle, conus arteriosus or infundibulum It has smooth walls and leads upwards to the opening of the pulmonary trunk, termed the pulmonary orifice. The pulmonary valve consists of three semilunar cusps, which are attached to the pulmonary orifice, their free borders being directed upwards into the lumen of the vessel. The semilunar valves are constructed to permit the flow of blood in only one direction. Ⅲ) The Left Atrium It constitutes the most part of the base of the heart. It is divided into two portions, an anterior part (the left auricle), and a posterior part (left atrial sinus or atrium proper). 1. Left auricle A small somewhat conical pouch, termed the left auricle, projects forwards from its upper left corner and overlaps the root of the pulmonary trunk. The pectinate muscles, fewer and smaller than those in the right atrium, are confined to the inner surface of the auricle. 2. left atrial sinus or atrium proper The interior side of left atrial sinus is smooth. The pulmonary veins, four in number, open into the upper part of the posterior surface of the left atrium, two on each side; their orifices are not provided with valves. The left atrioventricular orifice is the aperture between the left atrium and ventricle. Ⅳ) The Left Vertricle It constitutes the left inferior portion and the apex of the heart. Inferiorly, it forms a large part of the diaphragmatic surface of the heart. Inflow tract. Left atrioventricular (or bicuspid, mitral) valve Anterior cusp. Poterior cusp. Mitral valve complex: The rings and apexes of bicuspid valve, chordae tendineae, and papillary muscles constitute the tricuspid valve complex. Outflow tract. Aortic vestibule. Aortic orifice. Aortic sinuses. Ⅳ. The Structure of Heart The wall of the heart comprises three layers, named from within outwards endocardium, myocardium and epicardium. (1) The endocardium is a thin, smooth, glistening membrane which lines the chambers of the heart, and is continuous with the lining of the large blood vessels. The valves are formed by duplications of the lining endocardium of the heart, strengthened by intervening layer of fibrous tissue. (2) The myocardium consists of the ordinary cardiac muscle and specially differentiated cardiac muscle (the conduction system). (3) The epicardium is the visceral layer of the serous pericardium. It consists of a layer of the mesothelium and a delicate layer of connective tissue. The interatrial septum and interventricular septum: The interatrial septum is placed so obliquely that the right atrium lies in front and to the right of the left atrium. It is formed by two layers of the endocardium, strengthened by fibrous tissue and containing a few muscular fibers. The interventricular septum slops obliquely from before backwards and towards the right, and is curved with the convexity towards the right ventricle. Its margins correspond with the anterior and posterior interventricular grooves on the surface of the heart, it is so called the muscular part of the interventricular septum. In its upper part, there is a thin, fibrous area, which is termed the membranous part.