The Circulatory System PDF

The Circulatory system  The circulatory system include the: - Cardiovascular system or blood vascular system -Lymphatic vascular system Figure 1-2(f) 1 The cardiovascular system is transport system...

The Circulatory system  The circulatory system include the: - Cardiovascular system or blood vascular system -Lymphatic vascular system Figure 1-2(f) 1 The cardiovascular system is transport system of body It comprises blood, heart and blood vessels. The system supplies nutrients to and remove waste products from various tissue of body. The conveying media is liquid in form of blood which flows in close tubular system. 2  FUNCTION OF CARDIOVASCULAR SYSTEM  Transport nutrients, hormones  Remove waste products  Gaseous exchange  Immunity  Blood vessels transport blood ◦ Carries oxygen and carbon dioxide ◦ Also carries nutrients and wastes  Heart pumps blood through blood vessels 3  The cardiovascular system consists of: - the heart—a muscular pump—and closed vessels through which blood circulates in the body. -Arteries leave the heart, branch repeatedly, and have smaller diameters as they course toward the periphery. -They deliver blood to capillaries, which are the thinnest vessels and are closest to body cells. -Blood in capillaries is returned to the heart via veins. 4  BLOOD The Blood: Blood cells & Plasma Blood cells 1- Erythrocytes - Red Blood Cells 2- Leucocytes 3- Thrombocytes Plasma is fluid portion 5  HEART Heart is a four chambered, hollow muscular organ approximately the size of your fist Location: – Superior surface of diaphragm – Left of the midline – Anterior to the vertebral column, posterior to the sternum 6 HEART 7 The walls of all four heart chambers consist of three major layers: the internal endocardium; the middle myocardium; and the external epicardium 8  The endocardium Inner layer of the heart lines the atria and ventricles and covers the heart valves vessels, has three sublayers: 1- Endothelium - innermost portion a simple squamous epithelium. 2- Middle layer of the endocardium is mix of connective tissue and smooth muscle. 3- Subendocardial Layer - outer layer of the endocardium is loose connective tissue joining the endocardium and myocardium. The myocardium Is the middle layer (thickest layer) of the heart wall consist of the cardiac muscle with its fibers arranged spirally around each heart chamber. The cardiac muscle cells joined together by intercalated discs, and encased by collagen fibers and other substances that form the extracellular matrix. 9 10  The epicardium Is the outer layer of the heart wall ( simple squamous mesothelium) supported by a layer of loose connective tissue containing blood vessels and nerves. The epicardium corresponds to the visceral layer of the pericardium (the membrane surrounding the heart). ----pericardium is a two layered sac that surrounds the heart. The fibrous pericardium is the outside layer of the pericardium, made up of dense and loose connective tissue, is lined by a double inner membrane called the serous pericardium that produces pericardial fluid to lubricate the surface of the heart. The part of the serous membrane attached to the fibrous membrane is called the parietal pericardium, while the part of the serous membrane attached to the heart is the visceral pericardium (epicardium) The space between the two layers is the pericardial cavity, that contains serous fluid. 11  Tissues of the vascular wall Walls of all blood vessels except capillaries contain smooth muscle and connective tissue in addition to the endothelial lining. The amount and arrangement of these tissues in vessels are influenced by mechanical factors, blood pressure, and metabolic factors reflecting the local needs of tissues 12 1- The endothelium is a specialized epithelium that acts as semipermeable barrier. Besides their key role in metabolite exchanges between blood and tissues, endothelial cells have several other functions: -The endothelium presents a nonthrombogenic surface on which blood will not clot and actively secretes agents that control local clot formation. -The cells regulate local vascular tone and blood flow by secreting various factors that stimulate smooth muscle contraction or relaxation. - Endothelium has several roles in inflammation and local immune responses. - Endothelial cells formation of new blood vessels (angiogenesis) 13 2- Smooth muscle fibers occur in the walls of all vessels larger than capillaries and are arranged helically in layers. In arterioles and small arteries, the smooth muscle cells are connected by many more gap junctions and permit vasoconstriction and vasodilation which are of key importance in regulating the blood pressure. 3- Connective tissue components are present in vascular walls in variable amounts and proportions based on local functional requirements. - Collagen fibers are found in the subendothelial layer, between the smooth muscle layers, and in the outer covering. - Elastic fibers provide the resiliency required for the vascular wall to expand under pressure. 14 All walls of larger vessels have three concentric layers, or tunics : 1- Tunica Intima : consists of one layer of endothelial cells supported by a subendothelial layer of loose connective tissue containing smooth muscle cells. In arteries, the intima is separated from the media by an internal elastic lamina, This lamina, composed of elastin, has gaps (fenestrae) that allow the diffusion of substances to nourish cells deep in the vessel wall. 15 2- Tunica Media : consists of concentric layers of helically arranged smooth muscle cells. Interposed among these cells are variable amounts of elastic fibers, reticular fibers and lamellae. In arteries, the media has a thinner external elastica lamina, which separates it from the tunica adventitia 16 3- Tunica Adventitia: The adventitia consists of collagen and elastic fibers. The arterial blood vessels are classified , based on their diameter into arterioles , arteries of medium diameter ( muscular arteries) and large arteries ( elastic arteries ) : - Elastic Arteries are the aorta, the pulmonary artery, and their largest branches; these large vessels are also called conducting arteries because their major role is to carry blood to smaller arteries. The most prominent feature of elastic arteries is: -The intima is well developed, with many smooth muscle cells in the subendothelial connective tissue. -The internal elastic lamina is not easily discerned because it is similar to the elastic laminae of the next layer. -The thick media in which elastic lamellae, alternate with layers of smooth muscle fibers. The adventitia is much thinner than the media. The numerous elastic laminae of these arteries contribute to their important function of making blood flow more uniform. 17 18 - Muscular Arteries The muscular arteries distribute blood to the organs and help regulate blood pressure by contracting or relaxing the smooth muscle in the media. The intima has a very thin subendothelial layer and a prominent internal elastic lamina. The media may contain up to 40 layers of large smooth muscle cells interspersed with a variable number of elastic lamellae (depending on the size of the vessel). An external elastic lamina, the last component of the media, is present only in the larger muscular arteries. The adventitia consists of connective tissue, lymphatic capillaries, vasa vasorum, and nerves are also found in this layer 19  Arterioles The small arteries branch as arterioles: The subendothelial layer is very thin, elastic laminae are absent, The media consists of the circularly arranged smooth muscle cells (only one or two smooth muscle layers), it shows no external elastic lamina. In both small arteries and arterioles, the adventitia is very thin and inconspicuous -The arterioles first branch into smaller vessels called metarterioles (terminal arteriole branches) are encircled by scattered smooth muscle cells, and converge into the thoroughfare channels , lack muscle , which branch further into capillaries. -Capillaries Are composed of a single layer of endothelial cells rolled up as a tube. Capillaries permit and regulate metabolic exchange between blood and surrounding tissues. Capillaries are generally grouped into three histologic types, depending on the continuity of the endothelial cells and the external lamina. 20 1. The continuous or somatic capillaries are characterized by the absence of fenestrae in their wall. They are found in all types of muscle tissue, connective tissue, exocrine glands, and nervous tissue. 2- The fenestrated or visceral capillaries are characterized by the presence of several circular transcellular openings in the endothelium membrane called fenestrae. Fenestrae are limited by the cell membrane. The basal lamina of the fenestrated capillaries is continuous. are found in the kidney, the intestine, and the endocrine glands. 21 3- The discontinuous or sinusoidal capillaries: The endothelial cells form a discontinuous layer and are separated from one another by wide spaces. The basal lamina is discontinuous. Sinusoidal capillary permits maximal exchange of macromolecules as well as cells between tissues and blood are found mainly in the liver , bone marrow and spleen. The transition from capillaries to venules occurs gradully. Postcapillary venules (pericytic venules) are characterized by the presence of pericytes. The tunica intima of these vessels is composed of endothelium and a very thin subendothelial layer. The media may contain only contractile pericytes. Postcapillary venules converge into larger collecting venules. The venules become surrounded by a recognizable tunica media with two or three smooth muscle layers are called muscular venules. Most venules are muscular, with at least a few smooth muscle cells in their walls.The intima usually has a thin subendothelial layer, which may be absent at times. The media consists of small bundles of smooth muscle cells intermixed with reticular fibers and a delicate network of elastic fibers. The collagenous adventitial layer is well developed. A characteristic feature of all venules is the large diameter of the lumen compared to the overall thinness of the wall. 23 The big venous trunks close to the heart, are large veins, have a well-developed tunica intima, but the media is thin, with few layers of smooth muscle cells and abundant connective tissue. The adventitial layer is the thick and best-developed tunic in veins; it contains longitudinal bundles of smooth muscle. These veins have valves in their interior. Valves consist of paired semilunar folds of the tunica intima projecting across part of the lumen. They are rich in elastic fibers and are lined on both sides by endothelium to prevent back-flow of blood. Blood entering veins is under very low pressure and moves toward the heart by contraction of smooth muscle fibers in the media and by external compressions from surrounding muscles and other organs. 24 25  The lymphatic vascular system system of thin-walled endothelial channels that collect excess interstitial fluid from the tissue spaces and return it to the blood. This fluid is called lymph; unlike the blood, it flows in only one direction, toward the heart. 26 The lymphatic vascular system begins with the lymphatic capillaries (lymphatics) , which are closed-ended tubules, that merge to form vessels that conduct lymph between different parts of the body, interposed in the path of these lymphatic vessels are lymph nodes and the larger collecting vessels–the right lymphatic duct and the thoracic duct (the left lymphatic duct) which terminate in the blood vascular system emptying into the large veins near the heart.  lymphatic capillaries are closed-ended vessels consisting of a single layer of very thin endothelial cells on an incomplete basal lamina. Openings between these cells are held open by bundles of anchoring filaments containing elastic fibers that also bind the vessels to the surrounding connective tissue. Folds of the endothelial cells across the openings prevent most backflow of lymph out of the vessels 28 -Lymphatic capillaries converge into larger lymphatic vessels. -The structure of larger lymphatic vessels resembles that of veins except: - Thinner walls and no distinct separation among tunics. - They also have more numerous internal valves than veins. As in veins, lymphatic circulation is aided by external forces (eg, contraction of surrounding skeletal muscle), with the valves responsible for keeping lymph flow unidirectional. -Contraction of smooth muscle in the walls of larger lymphatic vessels also helps propel lymph toward the heart. 29