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Cardiovascular System.Pdf cardiovascular system It is a network of tubular passages runs through the connective tissues, through which the more fluid components of the extracellular environment flow. The fluid is either blood forming blood vascular system which is formed of heart,the cardiovascular system consist of heart, arteries ,arterioles, capillaries, venules , and veins The main function of the circulatory system 1-deliver oxygenated blood to cells and tissue and to return venous blood to the lungs for gaseous exchange 2-distributes nutrients, hormones to all parts of the body; collects wastes produced during cellular metabolism. Histological structure of the typical artery and vein The wall of the typical artery and vein consist of three layers (tunics) 1-Inner, tunica intima:- consist of simple squamous epithelium(endothelium)and the underlying subendothelial connective tissue 2-Middle ,tunica media:- composed mainly of smooth muscle fibers Interspersed among the smooth muscle fibers are a variable amount of elastic and reticular fibers 3-Outer, tunica adventitia:- contains primarily collagen (type I) and elastic fibers Muscular artery and vein Types of arteries There are three types of arteries in the body according to the histological structure 1-Elastic arteries :- are the largest vessels in the body include aorta and their branches , the brachiocephalic , common carotid , subclavian ,vertebral ,pulmonary trunk , common iliac artery ,and charactirized by a-Exhibit resilience and flexibility during blood flow b-Walls greatly expand during systole (heart contraction ) and during diastole (heart relaxation) walls recoil and force blood forward histological structures of elastic arteries . Tunica intima consist of endothelium, basement membrane, underlying subendothelial connctive tissue . Tunica media is very thick and composed of predominant elastic fibers with less amount of circular smooth muscle fibers , the wall of elastic artery visible elastic membrane is the internal elastic lamina which located between tunica intima and tunica media. tunica adventitia composed of collagen and elastic fibers Elastic artery . 2-Muscular arteries(distributing arteries) :- Control of blood flow through vasoconstriction or vasodilation of lumina by autonomic nervous system histological structur of muscular arteries . Tunica intima consist of endothelium, basement membrane, underlying subendothelial connctive tissue. Tunica media composed of predominant circular smooth muscle fibers (more than 25 layer) and a less amount of elastic fibers and theirs two elastic membranes, internal elastic membrane between tunica intima and tunica media , external elastic membrane between tunica media and tunica adventitia. tunica adventitia composed of collagen and elastic fibers. 3-Arterioles are the small blood vessels with one to five layers of smooth muscle in tunica media. Note:- . Terminal arterioles deliver blood to smallest blood vessels (capillaries). Capillaries sites of metabolic exchanges between blood and tissues. Capillaries connect arterioles with venules. Capillary wall is two layers ,tunica intima and tunica adventitia. Venules consist of one layer ,tunica intima (there is no tunica media and tunica adventitia) Histological structure of large vein( portal vein) . The tunica intima consist of endothelium , basement membrane , subendotheliual connective tissue. Tunica media is thinner and consist of smooth muscle in circular orientation . The tunica adventitia characterized by thick in which the smooth muscle fibers show longitudinal orientation. Note:- Small and medium size veins particularly in the extremities have valves. Vasa vasorum Small blood vessels supply tunica media and tunica adventitia and found in the walls of large arteries and veins large vein Types of capillaries Capillaries are the smallest blood vessels ,their average diameter is about 8µm which is about the size of erythrocyte (red blood cell) ,there are three types of capillaries 1-Continuous capillaries :-are the most common ,they are found in ,muscle , connective tissue ,nervous tissue , skin ,respiratory organs and exocrine glands . In this capillaries the endothelial cell are joined and form an uninterruptid and solid endothelial lining 2-Fenestrated capillaries:-Are vessels characterized by large openings or fenestration (pores) in the cytoplasm of endothelial cells designed for rapid exchange of molecules between blood and tissue , they are found in endocrine tissues and glands ,small intestine and kidney glomeruli 3-Sinusoidal capillaries :- Are blood vessels that exhibit irregular ,tortuous paths characterized by wider diameter ,slow down the flow of blood and endothelial junction rare in sinusoidal capillaries and wide gaps exist between individual endothelial cell because a basement membrane underlying the endothelium is either incomplete or absent , a direct exchange of molecules occurs between blood and cells ,its found in the liver ,spleen and bone marrow Lymph vascular system . Lymphatic system consists of lymph capillaries and lymph vessels and this system starts as blind-ending . These vessels collect the excess interstitial fluid (lymph) from the tissues to the venous blood via large lymph vessels . The structure of large lymphatic vessels is similar to that of venous except that their walls are much thinner . The contraction of surrounding skeletal muscles forces the lymph to move forward and the lymph vessels contain more valves to prevent a backflow of collected lymph . Lymph vessels are found in the all tissues except the central nervous system ,cartilage , bone and bone marrow , thymus , placenta ,and teeth Heart :- It is a hollow muscular organ consisting of groups of cardiac muscle cells surrounded by highly vascularized connective tissue. These muscle bundles comprise the myocardium, constituting the walls of atria & ventricles. On the inner & outer surfaces the myocardium is lined by the endocardium & epicardium, respectively. Histologicaly ,the wall of the heart consist of three layers 1- an inner, endocardium :-consist of simple squamous endothelium, basement membrane and subendothelial connective tissue ,deeper to the endocardium is the subendocardial layer of connective tissue contain blood vessels and purkinje fibers and this layer attaches to the endomysium of the cardiac muscle 2-A middel layer myocardium:- is the thickest layer and consist cardiac muscle fibers 3-An outer layer epicardium:- consist of simple squamous mesothelium and an underling subepicardial connective tissue which contain coronary blood vessels ,nerves, adipose tissue Heart Pacemaker of the heart :- are specialized or modified cardiac muscle fibers located in the sinoatrial (SA) node and atrioventricular (AV )node in the wall of the right atrium of the heart , because the fibers in the SA nod depolarize and repolarize faster than those in the AV node ,the SA node sets the pace for the heartbeat (Pacemaker) Intercalated disks (gap junction bind all cardiac muscles fibers) and Purkinje fibers are conducted impulses of the heart . Atrial natriuretic hormone (heart as endocrin gland) Cardiac muscles in the atrium exhibit dense granules in their cytoplasm contain atrial natriuretic hormons ,thes hormone release in response to the atrial distension (blood hypertension), which lead to inhibiting the release of renin (by specialized cells in the kidney ) and aldosterone (from the adrenal gland cortex) ,this induces to lose more sodium and water (diuresis) as a result the blood volume and blood pressure reduce heart wall Arteriovenous anastomoses :- are special areas of the skin of the nose , lips and pads where the arteriole opens directly into venule without going through the capillary bed , this provides an alternative channel of blood supply and regulation of heat loss. .
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