12 1 COMPONENTS OF THE CIRCULATORY SYSTEM A major components of cardiovascular system 1 blood circulating elements 2 heart pump a formed elements cells and cell fragments b erythrocytes red blood cells 99 of blood cells c leukocytes white blood cells fight infection and cancer d platelets function in clotting e plasma liquid portion of blood that contains dissolved nutrients ions wastes gases and other substances f average volume 5 5 L a two chambers upper atrium and lower ventricle b atria chambers through which blood flows from veins to ventricles atrial contraction adds to ventricular filling but is not essential for it c ventricles chambers whose contractions produce the pressures that drive blood through the pulmonary and systematic vascular systems and back to the heart d pulmonary circulation right ventricle lungs left atrium blood leaves via pulmonary trunk divides into 2 pulmonary arteries one for each lung leaves lungs via pulmonary veins e systematic circulation left ventricle aorta all organs and tissues in body right atrium closed system inferior vena cava superior vena cava veins converge in IVC and SVC 3 vascular system blood vessels conduits a bulk flow rapid flow of blood throughout the body produced by pressures created by the pumping action of the heart b arteries vessels carrying blood away from heart low resistance tubes c veins carrying blood from organs tissues back to heart d arterioles smallest arteries responsible fro the pattern of blood flow distribution to the various organs participate in the regulation of arterial blood pressure e capillaries very small vessels major sites of nutrient metabolic end product and fluid exchange between blood and tissues f venules made up of capillaries g veins made up of venules in systematic circulation h inferior vena cava collects blood from below the heart i superior vena cava collects blood from above the heart both return blood to right atrium B components of a closed circulatory system characteristics of vessel types 1 hearts pump through left ventricle a 120 0 mm Hg pressure varies 2 aorta and large arteries a high elasticity pressure reservoir b 120 80 mm Hg pressure never goes to 0 would be dead 3 arterioles a thick smooth muscle layer high sympathetic NS innervations regulation of blood flow pressure 4 capillaries single cells layer a exchange vessels waste products CO2 picked up b will go next to either interstitial fluid cells lymphatic vessels veins veins 5 veins high compliance volume reservoir 12 2 PRESSURE FLOW RESISTANCE A hemodynamics B blood flow 1 includes blood pressure P blood flow F and the resistance to blood flow R 1 always from a region of higher pressure to lower pressure 2 blood flow difference in pressure resistance 3 proportional to the PRESSURE gradient between 2 points a F P R p1 100 mmHg and p2 10mmHg then pressure is 90 mmHg 4 inversely proportional to the resistance C blood pressure D resistance 1 hydrostatic pressure pressure exerted by any fluid 2 force exerted by blood generated in the blood by the contraction of the heart 3 not the absolute pressure at any point in the cardiovascular system that determines the flow rate rather the difference in pressure between the relevant points 1 how difficult it is for blood to flow between 2 points at any given pressure difference measure of friction the impedes flow 2 cannot be measured directly 3 viscosity function of the friction between molecules of a flowing fluid a greater friction greater viscosity b increases as hematocrit increases 4 also effected by length and radius of tube most important 5 more resistance more viscosity more vessel length less vessel radius 12 3 ANATOMY A overview 1 layers around the heart a pericardium protective fibrous sac around heart space filled with watery fluid lubricant b epicardium fibrous layer on the heart 2 myocardium wall of the heart composed primarily of cardiac muscle cells 3 endothelial cells endothelium lines the inner surface of cardiac chambers and blood vessels 4 interventricular septum separates 2 ventricles 5 atrioventricular valves AV located between atrium and ventricle a tricuspid valve right AV b bicuspid valve left AV aka mitral valve c heart valves open and close passively by chamber pressure gradient function is to prevent backflow securing unidirectional flow results in pressure differences across the valves when pressure in ventricle is greater than that in atrium valve closes 6 pulmonary semilunar valve between right ventricle and pulmonary trunk 7 aortic semilunar valve between left ventricle and aorta heart valves offer little resistance to flow so very small pressure differences across them suffice to produce large flows B summary of circulatory plan Left atrium left AV valve left ventricle aortic valve aorta arteries arterioles capillaries venules veins venae cavae right atrium right AV valve right ventricle pulmonary valve pulmonary trunk pulmonary arteries capillaries of lungs pulmonary veins left atrium C cardiac muscle 1 conducting system a 1 do not function in contraction specialized features that are essential for normal heart excitation b cells are in electrical contact with the cardiac muscles via gap junctions c initiates heartbeat and helps spread an action potential rapidly throughout the heart 2 Innervation a effects of ANS on heart function parasympathetic rest or digest vagus nerve acetylcholine atria muscanaric type ACh receptors Reduces heart rate blood pressure respiration Activates intestinal activity contractility conduction rate sympathetic fight or flight thoracic spinal nerves norepinephrine atria and ventricles receptors mainly B adrenergic epinephrine adrenal medulla Increases heart rate blood pressure respiration blood glucose blood flow to muscles contractility conduction rate 3 blood supply a coronary arteries supply the myocardium blood flowing through them is coronary blood flow exit behind the aortic valve b most of the cardiac veins drain into single larger vein coronary sinus which empties into right atrium 12 4 HEARTBEAT COORDINATION A overview 1 initial excitation of one cardiac cell leads to the excitation of all the cardiac cells 2 sinoatrial SA node a where the initial depolarization arises b small group of conduction system cells c near in right atrium near the entrance of the superior vena cava B sequence of excitation 1 SA node is normally the pacemaker for the entire heart a sympathetic and parasympathetic inputs b determines heart