The cardiovascular system.doc

The cardiovascular systemThe cardiovascular system includes the heart,blood vessels and blood. The heart acts as a musecular pump that continually pumps blood containing oxygen and many other substances to blood vessels.the blood vessels from a closed delivery system that begins and ends at the heart ,the blood acts as the transport meddium that transports nearly everything that must be carried to all parts of the body, blood flows from the hrart to the lungs,where it picks up oxygen j,and then returns to the heart to be pumped throughtout the body, there are two circulatory loops,one short and one long.the short loop is the pumonary circulation which pumps blood from the right side of the heart.the orther is the systemic circulation which pumps blood from the left side of the heart throught the tissues of the body and returns it to the right side of the heart .systemic cirulation delivers oxygen ,nutrients and other needed substances to the body via the arteries while carrying away carbon dioxide and other from the systemic circulation in that oxygen poor blood is carried by the pulmonary arteries from the right ventricle to the alveoil so that gaseous exchange can occur and the pulmonary veins carry oxygen rich blood back to the left atrium so that the heart can pump it throughtout the body.Th e heartThe heart is a muscular organ enclosed in a fibrous sac .the pericardium,and located in the chest.the narrow space between the pericardium and the heart is filled with a watery fluid that serves as a lubricant as the heart moves within the sac.The walls of the heart are composed primarily of cardiac muscle cells and are termed the myocardium.the myocardium .the inner surface of the walls ,that is ,the surface in contact with the blood within the cardiac chambers,is lined by a thin layer of cells known as endothelial cells ,or endothelium.The human heart is divided into right and left havels ,.each consisting of an atrium and a ventricle .lacated between the atrium and ventricle in each half of the heart are the atrioventricular valves,which permit blood to flow atrium to ventricle but not from ventricle to atrium ,the right av valve is called the tricuspid valve,and the left is called the mitral valve.The opening and closing of the av valve is a passive process resulting from pressure differernces sacross the valves ,The opening and closeing of the av valve is a possive process resulting from pressure differences across the valves.when the blood pressure in an atrium is greater than that in the ventricle separted from it by a valve,the valve is pushed open and flow proceeds from atrium to ventricle.in cintrast,when a contracting ventricle achieves an internal pressure greater than that in its connected atrium to ventrice.in cuntrast,when a contracting ventricle achieves an internal pressure greater open and flow proceeds from atrium to ventricle.in contrast,when a contracting ventricle achieves an internal pressure greater than that in its connected atrium ,the av valve between them is forced into the pulmonary trunk from the right ventricle and into the aorta from the left ventricle.To prevent the av valves from being pushed up into the strium.the valves are fastened to muscular projections of the ventricular walls by fibrous strands.the papillary muslces do not open or close the valves,they act only to limit the valves movements and prevent them from being everted.The opening of the right ventricle into the pulmonary trunk and of the left ventricle into the aorta also contain valves.the pulmonary and aortic valves.these valve permit blood to flow into the arterries during ventricular contraction but prevent blood from moving in the opposite direction during ventricular contraction relaxation.like the av valves,they act in a purely during ventricular relaxation.like the av valves, they act in a purely passive manner,their being open or closed depends upon the pressure differences across them.Another important point concerning the heart valves is that ,when open.they offer very little resistances to flow,in such a state,the contracting cardiac chamber must produce an unusually high pressure to cause flow across the valve.ArteriesArteries are vessels essential to both the systemic and pulminary circulation.because of their function and size,arteries are divided into three groups.elastic arties,muscular arteries and arterioles.elastic arteries are the largest in diameter and the most elastic in order to carry out their function tasks.their largh diameter serves as low-resistance conduits to transport blood to the medium-sized arteries,their elasticty enables them to withatand great pressure flunctation when the heart contracts,forcing blood into them,and recoiling when blood flows forward into the circulation during heart relaxation.thay are more active in vasodilation .because of the alternating expansion and recoil of elastic arteries during each cardic cycle.a pressure wave is created.that is ,a pulse which is transmitted throught the arteries with each heart beat,the pulse provides an easy way to count the heart beat,.you can feel the pules in any artery lying close to the body surface by applying firm pressure .there are nine pressure points in the body including the radial artery ,brachial artery ,popliteal artery, common cartid aryery .facial artery.,temporal artery,femoral artery ,popliteal artery.facial artery,temporal artery ,femoral artery.because the arterial pulse represents the heart rate ,is influenced by emotions ,postural changes and activity. CapillariesCapillaries are microscopic dense networks that branch throughout nearly all body tissues and join the arterial system with the venous system.the tissues that are poorly vascularized include tendous and ligaments while cartilage,the cornea and lens of the eye have no capillary supply at all.capillary walls are thin and are just large enough to let red blood cells slip through in single file ,they provide for gaseous diffusion and exchange of nutrients and waste products .capillary beds drain into venules ,which reprsent the initial part of the benous return to the heart. VeinsVeins are formed when the benules join toghter ,they have thin walls and large lumens to accommodate the large blood volume .veins carry the same volume of blood as the arteries bur at a lower pressure .65 of the body blood supply is found in the veins at any time .since the blood pressure in the veins is very low.they rely on other methods of propulsion in order to return is very low,they rely on other methods of propulsion in order to return the blood to the heart ,veins have valve that prevent the blood from flowing backward,therefore maintaining its forward progress.skeletal muscle contraction ,gravity and respiratrory activity are the other methods taht help pump the blood towad the heart.Blood flow through the heart and major blood vesselsBlood enters the right atrium by the superior vena cara which collects blood from the body regions superior to the heart .the inferior vena cava which collects the blood from the body regions inferior to the heart and the coronary sinus which collects the blood from the myocardium itself .four pulmonary veins enter the left atrium.they transport oxygenated blood from the lungs back to the heart.The deoxygenated blood from the right atrium passes throught the tricuspid valve to the right ventricle ,the right ventricle pumps oxygen-poor blood into the pulmonary trunk which routes the blood via the pulmonary arteries to the back flow of blood into the right ventricle. The pulmonary veins then carry the oxygenated blood back to the heart and enters at the left atrium.from the left strium,the blood passes through the mitral vlave ,also called the bicuspid valve ,to the left ventricle ,from the left ventricle the oxygenated blood passes into the aorta,the largst artery in the body which branches into smaller srteries for distribution to the rest of the body.the aortic valve or semilunar valve within the aorta permits the blood to flow in only one direction ,from the left ventricle to the aorta.the myocardium has its own blood supply provided by the coronary arteries which are branches of the aorta,if the blood flow in the coronary arteries is diminished ,myocardial damage may occur and if severe,necrosis of the muscle results.Conducting system of the heartHeart activity is due to the ability of the cardiac muscle to depolarize and contract .the heart contracts as a unit or it does not contract at all.this action is accmplished by the transmission of the depolarized wave from cell to within the haert through gap junctions which unite all cardiac muscles together into a single contractile unit.this dependent ,coordinated heart activity is due to the gap junctions and the conducting system initiate and distribute impulses throughout the heart so that the myocardium depolarizes and contracts in an orderly sequential fashion ,from atria to ventricles ,therefore the heart beasts nearly as one cell.The conducting system includes the sinoatrial node,the atrioventricular node.the atrioventricular bundle ,the right and left bundle branches and the purkinje fibers ,the sinoatrial node,also known as the pacemaker ,is located in the right atrial wall just inferior to the entrance of the inferior vena cava.as the pacemaker ,the sinoatrial node initiates each depolarized wave that travels across the heart and sets the pace for the heart as a whole.the sinoatrial nodes depolarize spontaneously about 70 to 80 times per minute.,its rhythm is called the sinus rhythm.The depolarized wave leaves the sinoatial node and spreads to the atrioventricular node located in the right atrial floor,near the interatrial septum.it has a slow conduction velocity ,therefore ,allowing the atria to complete their contractions before quickly passing along to the bundle of his and its branches and onto the purkinje fibers that penetrate the ventricular myocardium ,while the bundle of his and branches ensure excitation of the septal cells .the bulk of its larger size.ventricular contraction almost immediately follows the ventr