Cardio Vascular System Histo Speciale PDF

Cardio vascular system 2ème année bac+6 ISV Saad Dahlab Blida Pr.Boumahdi Merad Z The function of the cardiovascular system is : Supplying oxygen and nutrients to all tissues and organs. Carrying waste products of metabolism to the lungs and kidneys for elimination. It is...

Cardio vascular system 2ème année bac+6 ISV Saad Dahlab Blida Pr.Boumahdi Merad Z The function of the cardiovascular system is : Supplying oxygen and nutrients to all tissues and organs. Carrying waste products of metabolism to the lungs and kidneys for elimination. It is also involved in temperature regulation, hormone distribution, and immune function. The circulatory system consists of: Heart - It is a hollow muscular organ located in the thoracic cavity , behind the sternum between the lungs and above the diaphragm. Arteries - vessels that carry blood to tissues away the heart. Veins - vessels that carry blood towards the heart. Capillaries - networks of small vessels that perfuse tissues.  1. ANATOMICAL DATA ❖The heart is a muscular organ, which is subdivided into four chambers and four valves. ❖The left atrium and the right atrium are separated by the interatrial septum. ❖ The left ventricle and the right ventricle are separated by the interventricular septum. ❖The transition between the atrium and the ventricle is through the atrioventricular orifice or atrioventricular valve. ❖Each orifice is made up of a valve : the tricuspid valve on the right and the mitral valve on the left. ❖The right atrium receives venous blood brought by the superior vena cava and inferior vena cava. ❖The blood passes into the right ventricle and is propelled via the pulmonary artery into the lungs. ❖Oxygenated blood from the lungs arrives via the four pulmonary veins in the left atrium; it reaches the left ventricle from where it is returned to the body via the aorta. SHEEP HEART View of the valves of the heart  Cardiac valves 1) Tricuspid valve: Between the RA and RV Also called the right AV valve 3 cusps: anterior, posterior, and septal 2) Mitral valve: Between LA and LV Also called the left AV valve Bicuspid = 2 cusps: anterior and posterior 3) Pulmonary valve: Between RV and pulmonary trunk Semilunar in shape, with 3 cusps: right, left, and anterior 4) Aortic valve: Between left ventricle and aorta Semilunar in shape, with 3 cusps: right, left, and posterior An echocardiogram of heart valves The tricuspid valve and bicuspid valve (mitral valve) are attached to the right and left ventricle respectably by strong, elastic threads known as chordae tendineae. The four valves of the heart during ventricular systole Atrioventricular Valves (Bicuspid and Tricuspid Valves) The atrioventricular valves (bicuspid and tricuspid) have two or three leaflets (“cusps”) which are flaps of connective tissue that project into the ventricles. When the ventricles contract, the force of the blood flow pushes the cusps up toward the atrium, closing off the path between the atrium and ventricle and preventing blood from flowing “backwards.” Instead, blood flows from the ventricles into the pulmonary trunk or aorta. Each of the cusps of the tricuspid and bicuspid valves are attached to papillary muscles in the ventricle by chordae tendineae. When the ventricles contract, the papillary muscles also contract, putting tension on the chordae tendineae and preventing the valve cusps from everting into the atria.  Aortic valve Pulmonary valve REMEMBER: Blood pressure is significantly higher in the systemic circulation, thus explaining a greater thickness of the free wall of the left ventricle compared to that of the right ventricle.  The cardiac Valves Valves open as blood is pumped through. Each leaflet(cusp) is formed by a core of dense connective tissue. This core is covered by endocardium. Held in place by chordae tendineae (“heart strings”) Close to prevent backflow General structure and flow of blood through the heart: Blue denotes the path of deoxygenated blood, while red indicates the path of oxygenated blood.. The heart functions as a pump generating a contraction phase, systole, and a relaxation phase, diastole, allowing the circulation of blood throughout the body. The left heart is responsible for the systemic circulation, or large circulation, whose function is to collect oxygen-rich blood, leaving the lungs through the pulmonary veins, and to transport it to all the organs of the body, via the aorta. The pulmonary circulation or small circulation is ensured by the right heart whose role is to receive oxygen-poor blood from the whole body, entering through the venae cavae, and to bring it into contact with the pulmonary alveoli, via the pulmonary artery. Once re-oxygenated, the blood returns to the systemic circulation 2. HISTOLOGICAL STRUCTURE OF THE HEART WALL The walls of the atria and ventricles are similar in organization, although the walls are thicker in the ventricles. The heart walls contain three distinct layers. a. Inner layer = Endocardium b. Middle layer = Myocardium c. Outer layer = Pericardium or (epicardium formed by the visceral layer of the pericardium). Endocardium Myocardium pericardium Heart Wall 1.The endocardium: surrounds the lumen of the heart, is itself composed of three sub layers: ▪ Innermost layer :Endothelium of a simple squamous epithelium that covers the luminal surface of the heart and valves comes in contact with blood. The endothelial cells rest on a basal lamina. ▪Middle subendothelial layer (subendothelium) loose connective tissue and smooth muscle cells (like lamina propria). ▪Deep subendocardial layer (sub endocardium): a thicker layer of more loose fibrous connective tissue in contact with cardiac muscle. Separates the delicate endocardium from the vigorous pumping action of the myocardium.Vascularized containing nerve fibers, blood vessels and it is limited only to specific regions of the heart ( we see it more in the ventricular wall) were we find the ramifications of the nodal tissue of the Purkinje fibres. These are non-contractile ventricular myocytes specialized in rapid conduction. The Purkinje fibers extend the branches of the bundle of His in the subendocardium of each ventricle, activating the contractile myocytes. They are much larger than normal cardiac muscle cells and more lightly stained. endocardium of a cow's heart: the nucleus, in 1, is rounded and protrudes into the lumen. In 2, the cytoplasmic border remains thin. cardiac conduction system Terminal branches of the atrio ventriculo (AV) bundle branches located in the subendocardial connective tissue. ENDOCARDIUM MYOCARDIUM  CLUSTERS OF LARGE CELLS PURKINJE FIBERS ENDOCARDIUM MYOCARDIUM  ENDOTHELIAL CELLS SUB ENDOTHELIAL LAYER MYOCARDIUM SUB ENDOCARDIAL LAYER PURKINJE FIBERS: higher content of glycogen and poor on myofibrills INNER VENTRICUL WALL  Purkinje Fibers ▪Purkinje fibers are the structures present in the inner walls of the right and left ventricles of the heart. Large modified muscle cells. Cell Cluster in groups together. ▪1 to 2 nuclei and stain pale due to fewer myofibrils. ▪Impulse conducting fibers allowing the contraction of the cavities of the heart. 2. The myocardium : It represents the thickest tunic of the heart wall ▪ Because strong force is required to pump blood through the systemic and pulmonary circulations, the myocardium is much thicker in the walls of the ventricles, particularly the left, than in the atrial walls. It is organized with its fibers arranged spirally around each heart chamber valve in the form of myocardial trabeculae made up of rectangular striated cardiomyocyte contractil cells anastomosing by linking to each other via the intercalated discs. The cardiomyocyte contractil cells contain one or two nuclei in their center, numerous mitochondria and especially myofibrils. Between these trabeculae, interfascicular partitions of loose connective tissue and blood capillaries. Orientation of the myocardium, allowing the heart to pump blood effectively  Location and orientation of the heart Located in the mediastinum in the thoracic cavity, between the lungs. Sits in its own space called the pericardial cavity. The heart is slightly rotated so that: Right side is more anterior Left side is more posterior Base of the heart Apex of the heart  CARDIOMYOCYTE ▪Cylindrical in shape. ▪ Intermediate in diameter between skeletal and smooth muscle fibers. ▪Branch and anastomose. ▪ Covered by a thin sarcolemma. ▪ Mononucleated. Nuclei are oval and central. ▪ Sarcoplasm is acidophilic and shows non-clear striations (fewer myofibrils). ▪ Divided into short segments (cells) by the intercalated discs.  Intercalated disks Junctional complexes that contain fascia adherens, desmosomes, and gap junction to provide connection and connect the ends of cardiac muscle fibers to one another. Allow muscle action potentials to spread from one cardiac muscle fiber to another. Longitudinal section, cardiac striated muscle cells have the shape of long cylinders which present, at the level of the arrows, numerous anastomosing branches with neighboring cells.  the Pericardium The pericardium is a sero-fibrous sac. It is inside this sac that the heart will beat and that the vessels will allow blood circulation to pass: Like the pleural cavity around the lungs and the peritoneal cavity inside the abdomen, the pericardial cavity around the heart is enclosed in a double layer of fibroelastic connective tissue known as pericardium. ❑Layers of the pericardium: It is made up of two parts: 1) Outer layer: Defines outer layer of pericardial cavity it is made up of: ▪Fibrous pericardium: dense fibrous tissue ▪Serous parietal pericardium: thin, smooth, inner serous layer The fibrous and serous parietal pericardial layers are in direct contact with one another. They anchors the heart to: Diaphragm below Great vessels above 2) Visceral pericardium: Directly covers the surface of the heart is the serous visceral layer of pericardium is made of : ❖Simple squamous epithelium ❖Areolar tissue (Contains adipose tissue ). Relationship Between the Heart and Pericardial Sac.  FIBROUS PERICARDE PERICARDAL CAVITY ENDOCARDIUM SEROUS PERICARDE VISCERAL PARIETAL MYOCARDIUM Fibrous pericardium PARIETAL VISCERAL MYOCARDIUM PERICARDIAL CAVITY VISCERAL MESOTHELIUM Visceral pericardium includes a mesothelium and a thin layer of loose connective tissue that is adjacent to the myocardium and the adipose tissue that surrounds it. Parietal pericardium includes a mesothelium and a thin layer of loose connective tissue that is adjacent to the fibrous pericardium (a thick layer of dense connective tissue). Myocardial cells are divided into two groups: 1. Contraction ( Ordinary fibers) 2. Conduction ( Conducting System) 1. Myocardial contractil cells: have a cylindrical shape whose ends have bifurcations, to which they enter into connection with adjacent myocardial cells to form a complex three-dimensional network. 2. Myocardial conducting cells:they are generally much smaller than the contractile cells and have few of the myofibrils. The main parts of the system are the sino atrial (SA) node, atrio ventricular (AV) node, bundle of HIS, bundle branches, and Purkinje fibers. There are two basic types of cardiac myocytes, those specialized for contraction and those specialized for impulse conduction( initiate and propagate the action potential (the electrical impulse) that travels throughout the heart and triggers the contractions that propel the blood) All these things need to be precisely coordinated and regulated.How this is achieved ? What are the steps of the heart conduction pathway? Our heart is a pump that sends blood throught our body. For each heartbeat, electrical signals travel through the conduction pathway of our heart. It starts when the sinoatrial (SA) node creates an excitation signal). The excitation signal travels to: Our atria (top heart chambers), telling them to contract the atrioventricular (AV) node, delaying the signal until atria our are empty of blood. The bundle of His (center bundle of nerve fibers), carrying the signal to the Purkinje fibers. The Purkinje fibers to our ventricles (bottom heart chambers), causing them to contract. The myocardial conducting cells is represented by 04 formations: ❑KEITH and FLACK‘ Sino atrial (SA) node or the natural pacemaker. Is located in the wall of the right atrium near the mouth of the superior vena cava. ❑ASCHOFF-TAWARA' Atrial ventricle (AV) node Is located in the postero-inferior part of the interatrial septum. ❑ His bundle: From the ASchoff-Tawara node, it crosses the interventricular septum and divides into 02 branches. ❑ Purkinje network: The Purkinje fibers come from the branches of the His bundle. They are spread under the ventricular endocardium. Conduction of electrical activity : Before any cardiac contraction, the heart generates an electrical impulse that will propagate along a precise path in order to have a synchronized contraction. The electrical wave is initiated within the sino atrial (SA) node ,a specialized clump of myocardial conducting cells located in the superior and posterior walls of the right atrium in close proximity to the orifice of the superior vena cava. The SA node is known as the pacemaker of the heart. It initiates the sinus rhythm, or normal electrical pattern followed by contraction of the heart and propagates to all the atria, causing them to contract. The signal converges towards the atrioventricular node (AV) node, and pushes the blood into the ventricles. The signal descends along the bundle of His and reaches its left and right branches, located in the ventricles, causing the ventricle to contract, before dividing into a very dense network of Purkinje fibers. Purkinje fibers lie in the deepest layer of the endocardium and supply the papillary muscles. Hence the apex of the heart contracts first, followed by the papillary muscles, and then the wave of depolarisation spreads up the walls of the ventricles from the base upwards.. STEPS OF HEART ELECTRICAL CONDUCTION What tissue is responsible for the electrical activity of the heart? Specialized tissue or nodal tissue. What is an electrical impulse? An electrical impulse refers to the flow of electricity generated by specific cells of the heart's electrical system, which triggers the contraction of the heart muscles. These cells, called pacemaker cells, have the ability to spontaneously generate electrical signals, thus triggering the rhythmic activity of the heart. What parts of the heart’s electrical conducting system play a role in ventricular contraction? The SA node starts the sequence by causing the atrial muscles to contract. Then the signal travels to the AV node, through the bundle of His, along the bundle branches, and through the Purkinje fibers, causing the ventricles to contract. Where does the transmission of electrical impulses begin in the heart? In order for the heart to pump blood, an electrical impulse, to trigger a heartbeat. The electrical impulse starts on the right side of the upper chamber, in an area called the sinus node. How does the heart conduct electrical impulses? The electrical impulse travels from the sinus node to the atrioventricular node (also called the AV node). There, the impulses are slowed for a very short time and then continue along the conduction pathway via the bundle of His to the ventricles BUNDLE OF HIS AND PURKINJE FIBERS  The sinoatrial (SA) node and the remainder of the conduction system are at rest. (2) The SA node initiates the action potential, which sweeps across the atria. (3) After reaching the atrioventricular node, there is a delay that allows the atria to complete pumping blood before the impulse is transmitted to the atrioventricular bundle. (4) Following the delay, the impulse travels through the atrioventricular bundle and bundle branches to the Purkinje fibers, and also reaches the right papillary muscle via the moderator band. (5) The impulse spreads to the contractile fibers of the ventricle. (6) Ventricular contraction begins. Basic representation of cardiac electrical conduction system  THE ARTERIES: Arteries are efferent blood vessels from the heart that leave it to the organs and tissues. Their constitution and diameter vary as we move away from the heart. Thus, according to their diameter, we can have 4 types of arteries: 1. Large-caliber arteries of large arterial vessels: The aorta, pulmonary arteries. 2. Medium-caliber arteries: femoral, tibial and radial arteries. 3. Transitional arteries. 4. Small-caliber arteries or arterioles: which are the branches that will penetrate the tissues. ARTERY WALL The arteries are formed of 3 layers superimposed on each other and delimiting a lumen where the blood passes. The tunica intima: The innermost layer, is composed of a single layer of flattened, squamous endothelial cells,lining the lumen of the blood vessel rest on a basal lamina (basement membrane, and a subendothelial layer lies immediately beneath the endothelial cells. It is composed of loose connective tissue. Beneath the subendothelial connective tissue layer is an internal elastic lamina that is especially well developed in muscular arteries. Separating the tunica intima from the tunica media. the tunica media, the intermediate layer, thickest layer of the vessel wall, is composed of helically disposed layers of smooth muscle and the external elastic lamina,when present. consists of smooth muscle cells as well as elastic fibers. The media with its elastic fibers plays a role in vasoconstriction and vasodilation during diastole and systole. the tunica adventitia, the outermost layer, is composed mainly of fibroelastic connective tissue arranged longitudinally. Vasa Vasorum (vessels of the vessel) furnish the muscular walls of blood vessels with a blood supply. The deeper cells of the tunica media and tunica adventitia are nourished by the vasa vasorum. The tunica intima houses in its outermost layer the internal elastic lamina, a thin band of elastic fibers that is well developed in medium-sized arteries. The outermost layer of the tunica media houses another band of elastic fibers, the external elastic lamina, although it is not distinguishable in all arteries. The arterial wall has 3 concentric layers: Intima, media, adventitia Lumen Adventitia ARTERIEL WALL  Classification of Arteries Based on their relative size, largest to smallest, they are as follows: ❖Elastic (conducting) arteries. ❖ Muscular (distributing) arteries. ❖Arterioles. 1. Elastic or conducting arteries: (large caliber): They are located near the heart (aorta, pulmonary arteries ensure the collection and propulsion of blood). They have a wide lumen and their walls are made up of 1. Intima: Thick, up to 150µm (as is the case in the aorta). It is formed of endothelial cells that form a squamous epithelium. The intima is separated from the media by a dense elastic membrane called the internal elastic lamina(prevents the obliteration of the lumen), elastic fibers and collagen. They do not have an external elastic lamina. 2. The media: thickness 0.5 – 2mm, in this layer the layers of elastic fibers and collagen alternate with the muscle layers. 3. The adventitia: not very thick, made up of connective tissue. ELASTIC ARTERIES  A thin layer of internal elastique lamina media adventitia ELASTIC ARTERY 2. Muscular or distributing arteries: (medium caliber) (renal arteries) Ensure the distribution of blood. Their diameter varies from 0.3 – 10mm. 1. intima: similar to elastic arteries. 2. media: the thickest, dense layer is mainly formed of several layers of smooth muscle cells ranging from 3 to 40 layers. Between the layers there are elastic fibers. They have a very visible internal and external elastic lamina layer. 3. adventitia: is thicker. Light micrograph of a muscular artery with waves of internal elastic lamella (iEL)and elastic extern lamella (xEL).TI(Tunic intima);TM(Tunic media)  x EL adventitia media Wavy i EL intima Muscular artery 3.Arterioles: Arterioles are the terminal arterial vessels that regulate blood flow into capillaries. The intima : Endothelium is supported by a thin subendothelial connective tissue layer. A thin, fenestrated internal elastic lamina is present in larger arterioles but absent in small and terminal arterioles. Arterioles do not have an external elastic lamina. The media is formed of 1 to 2 layers of muscle cells arranged in a helix. The adventitia:formed of elastic fibers and collagen. In small arterioles, the tunica media is composed of a single smooth muscle cell layer that completely encircles the endothelial cells. In larger arterioles, the tunica media consists of two to three layers of smooth muscle cells. Arteries that supply blood to capillary beds are called metarterioles. They are approximately 8 μm in diameter and differ structurally from arterioles in that their smooth muscle layer is not continuous; rather, the individual muscle cells (precapillary sphincters) are spaced apart, and each encircles the endothelium of capillary arising from the metarteriole  VEINS: Veins are vessels that carry blood to the heart and usually accompany the corresponding arteries. They have a thin wall (because of the low pressure). Their structure is quite variable and follows roughly that of the corresponding arteries. There is no limiting. We note above all the presence of valves in the lumen that prevent the backflow of blood. The lumen is wider than that of the arteries. There are two types of veins according to the media: 1. The propulsive veins: located in the lower part of the body, they are more muscular, thick media and provided with valves so that the blood rises in columns; as is the case with the inferior vena cava. For people who are standing all the time, varicose veins can be observed because of the wall of the veins that dilates. 2. The receiving veins: Drain the upper part of the body, they do not need a valve, they have a fibroelastic structure. The media contains very few muscle fibers. DIFFERENCE BETWEEN AN ARTERY (A) AND A VEIN (V) VEIN AND ARTERY  VEINS Blood vessels that carry blood back to the heart are called veins. They have one-way valves which prevent blood from flowing backwards. They carry blood that is high in carbon dioxide known as deoxygenated blood (oxygen poor blood).  CAPILLARIES These are the place of exchange between blood and tissues. They arise from a terminal arteriole and are anastomosed between them and converge towards a post-capillary venule. They are the finest endothelial tubes, more or less regular, anastomosed in networks and whose diameter varies from 5 – 30 µm. The endothelium rests on a basal lamina surrounded by pericytes (peri: around; cyte: cell )which are elongated cells imbeded in the basement membrane of the endothelium. Pericytes have been postulated to regulate capillary blood flow and the clearance and phagocytosis of cellular debris. There is therefore no media or adventitia in the wall of the blood capillaries. They are called pericyte because of their location on the outer surface of blood capillaries and their close interaction with the underlying endothelial cells (ECs), with which they share the basement membrane Pericyte (pc)in the outer surface of endothelial (en)blood capillaries pericyte Pericytes, Scanning electron microscope Scanning electronmicrograph of a capillary displaying a pericyte on its surface.  The smallest blood vessels are capillaries and they connect the arteries and veins. This is where the exchange of nutrients and gases occurs.  Classification of Capillaries There are 3 types of capillaries that have different functions and therefore different locations. 1. Continuous capillaries: have no pores or fenestrae in their walls. The intercellular junctions between their endothelial cells are fasciae occludentes, which prevent passage of many molecules. Their endothelial cells are joined and rest on a continuous basal lamina. Pericytes are numerous and have contractile proteins in their cytoplasm implying a contractility function. They are located at the level of the (muscle, skin, brain, mucous membrane, exocrine glands, lungs). 2. Fenestrated capillaries: Endothelial cells have numerous perforations in the endothelial wall (pores of 10-100nm). The basal lamina is continuous. Pericytes are rare. Located in the (endocrine glands, intestines, renal glomeruli). 3. Discontinuous or sinusoidal capillaries: the endothelial cells are not joined which allows the passage of the formed elements of the blood, the basal lamina is discontinuous or absent, the pericytes are absent wide lumen (liver, spleen, bone marrow  BASAL LAMINA ENDOTHELIALE PERICYTE CELL CONTINUES CAPILLARY BASAL PORES LAMINA LUMEN ENDOTHELIALE CELL PERICYTE FENESTRATED CAPILLARY  FENESTRATION PORES DISCONTINUE BASAL LAMINA SINUSOIDAL CAPILLARY And ABSENCE OF PERICYTE