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The Cardiovascular System 1 The Cardiovascular System • A closed system of the heart and blood vessels – The heart pumps blood – Blood vessels allow blood to circulate to all parts of the body • The function of the cardiovascular system is to deliver oxygen and nutrients and to remove carbon dioxide and other waste products 2 The Heart • Location – Thorax between the lungs (mediastinum) – Pointed apex directed toward left hip & rests on the diaphragm • About the size of your fist 3 The Heart: Coverings • Pericardium – a double serous membrane – Visceral pericardium (epicardium) • Next to heart – Parietal pericardium • Outside layer • Serous fluid fills the space between the layers of pericardium, decreases friction • Pericarditis – inflammation of pericardium causes a decrease in serous fluid – Pericardial layers touch, stick and form painful adhesions 4 The Heart: Heart Wall • Three layers – Epicardium • Outside layer • This layer is the parietal pericardium • Connective tissue layer – Myocardium • Middle layer • Mostly cardiac muscle – Endocardium • Inner layer • Endothelium 5 External Heart Anatomy 6 The Heart: Chambers • Right and left side act as separate pumps • Four chambers – Atria • Receiving chambers – Right atrium – Left atrium – Ventricles • Discharging chambers – Right ventricle – Left ventricle » Thick walled » Contract 7 Figure 11.2c The Heart: Associated Great Vessels • Aorta – Leaves left ventricle – Largest artery in the body • Pulmonary arteries – Leave right ventricle – Carry deoxygenated blood • Vena cava – Enters right atrium – Largest veins of the body • Pulmonary veins (four) – Enter left atrium – Carry oxygenated blood 8 Blood Circulation – Both sides events occur simultaneously! 1. Blood low in O2 from body returns to the heart via veins flowing into the Superior & Inferior Vena Cava returning blood to RA. 2. Through Tricuspid (AV) valve into RV (atria contracts). 3. RV contracts forcing AV valve shut. Blood flows out pulmonary semilunar valve into pulmonary arteries and to the lungs for gas exchange. 1. Blood high in O2 returns via the pulmonary veins to the LA. 2. LA contracts pushing blood through the bicuspid (mitral or AV) valve into LV. 3. LV contracts forcing AV valves shut. Blood flows out aortic semilunar valve into Aorta and artery network to the body. 9 Figure 11.3 The Heart: Valves • Allow blood to flow in only one direction • Four valves – Atrioventricular valves (AV) – between atria and ventricles • Bicuspid valve (left) (mitral) – 2 flaps • Tricuspid valve (right) – 3 flaps – Chordae tendinae anchor the valve flaps to the ventricle to keep them from being pushed inside the atria during ventricular contraction. » Called your “heart strings” – Semilunar valves between ventricle and artery • Pulmonary semilunar valve • Aortic semilunar valve – Valvular Stenosis – valve flaps become stiff, usually due to infection. • Valves may not close completely, allowing backflow. 10 Operation of Heart Valves Figure11 11.4 Coronary Circulation • Blood in the heart chambers does not nourish the myocardium (NO O2, nothing) • The heart has its own nourishing circulatory system – Coronary arteries branch from the base of the aorta • They are compressed during ventricular contraction and fill during relaxation. – Cardiac veins empty blood into the right atrium via the coronary sinus • Rapid heart beat can lead to a decrease of oxygen to the myocardium. This may cause pain called angina pectoris. – If the heart muscle goes without oxygen long enough, damage occurs or an infarct. – This results in a myocardial infarction or heart attack. 12 The Heart: Conduction System • Intrinsic conduction system (nodal system) – Heart muscle cells contract, without nerve impulses, in a regular, continuous way – Composed of special tissue, a cross of muscle and nervous tissue. – Forces a coordinated depolarization in one direction, about 75 bpm 13 The Heart: Conduction System • Special tissue sets the pace – Sinoatrial (SA) node • Located in the right atrium • Pacemaker – Atrioventricular (AV) node – Atrioventricular bundle (Bundle of His) – Bundle branches (R & L – in septum) – Purkinje fibers (Muscle of Ventricular Walls) 14 Heart Contractions 1. Contraction is initiated by the sinoatrial node – the pacemaker 2. Impulse spreads through atria to AV Node, both atria contract 3. Impulse pauses at AV node. Then goes through the AV bundle, bundle branches and purkinje fibers. 4. This causes the “wringing action” of the ventricles. This starts at the apex and moves up towards the atria. 15 Heart block – damage to AV node causes ventricles to contract on their own at a slower rate Artificial Pacemaker – needed when there is damage to SA node causing the heart to slow Ischemia – lack of blood flow to heart which leads to fibrillation – shuddering of heart, no pumping, can lead to death Tachycardia - >100 bpm, can become fibrillation Bradycardia - < 60 bpm 16 Cardiac Cycle • Atria contract simultaneously • Atria relax, then ventricles contract • Systole = contraction, Diastole = relaxation (of the ventricles) • Cardiac cycle – events of one complete heart beat • Lub is AV valves closing • Dub is semilunar valves closing • Murmur – unusual heart sound caused by faulty 17 valves and a back flow of blood Cardiac Output Regulation Figure18 11.7 The Heart: Regulation of Heart Rate • Increased heart rate – Sympathetic nervous system • Crisis • Low blood pressure – Hormones • Epinephrine • Thyroxine – Exercise – Decreased blood volume – Increased Temperature 19 Regulation of Heart Rate • Cause Decreased heart rate – Parasympathetic nervous system – High blood pressure or blood volume – Decreased venous return – Decreased temperature • CHF (Congestive Heart Failure) – Left Side Dec. Function causes pulmonary congestion, blood backs up in lungs, causing fluid to leak into lungs – Right Side Dec. Function causes peripheral congestion, blood backs up in systemic circulation, causing edema in extremities. 20 Blood Vessels: The Vascular System • Taking blood to the tissues and back – Arteries – Arterioles – Capillaries – Venules – Veins Figure21 11.8a The Vascular System Figure22 11.8b Differences Between Blood Vessel Types • Walls of arteries are the thickest • Lumens of veins are larger & have valves • Skeletal muscle “milks” blood in veins toward the heart • Walls of capillaries are only one cell layer thick (tunica intima) to allow for exchanges between blood and tissue (capillary beds) 23 Movement of Blood Through Vessels • Most arterial blood is pumped by the heart • Veins use the milking action of muscles to help move blood Figure24 11.9 Capillary beds consist of two types of vessels Capillary Beds 1. Vascular shunt – directly connects an arteriole to a venule 2. True capillaries – exchange vessels • Oxygen and nutrients cross to cells • Carbon dioxide and metabolic waste products cross into blood http://www.youtube.com/watch?v=Q530H1 WxtOw&safe=active Figure25 11.10 • Blood may move through shunt or true capillaries. • Precapillary sphincters close off the true capillaries when blood flow is needed elsewhere. • Varicose veins- valves are faulty, blood pools & vein twists • Thromobphlebitis – clot forms in a vein Capillary Beds Figure26 11.10 Major Arteries of Systemic Circulation Figure27 11.11 Major Veins of Systemic Circulation Figure28 11.12 Hepatic Portal Circulation • Veins from digestive organs, spleen and pancreas take blood to the liver • After a meal, this blood is nutrient rich. • Liver stores glucose and further processes nutrients. • This is why blood goes here from the digestive system BEFORE going out to “feed” the body. Figure29 11.14 Pulse • Pulse – pressure wave of blood • Monitored at “pressure points” where pulse is easily palpated Figure30 11.16 Blood Pressure • Measurements made on the pressure in large arteries – Systolic – pressure at the peak of ventricular contraction – Diastolic – pressure when ventricles relax • Pressure exerted on inner walls of blood vessels 31 Blood Pressure: Effects of Factors • Neural factors – Autonomic nervous system adjustments (sympathetic division) – causes vasocostriction - BP • Renal factors – Regulation by altering blood volume – retain water BP & Blood Volume – Renin – hormonal control, vasoconstriction 32 Blood Pressure: Effects of Factors • Temperature – Heat has a vasodilation effect – Cold has a vasoconstricting effect • Chemicals – Alcohol – vasodilator – Nicotine - constrictor • Diet – low in salt, saturated fats & cholesterol help prevent hypertension 33 Factors Determining Blood Pressure Figure34 11.19 Variations in Blood Pressure • Human normal range is variable – Normal • 140–110 mm Hg systolic • 80–75 mm Hg diastolic – Hypotension • Low systolic (below 110 mm HG) • Often associated with illness • Orthostatic hypotension – positional drop in BP 35 – Hypertension • High systolic (above 140 mm HG) • Can be dangerous if it is chronic – Strains the heart & damages arteries – Eventually myocardium enlarges, heart weakens & walls become flabby – Causes small tears in arteries where clots can form, leading blockage – Atherosclerosis • Damage to tunica interna & clot response • Continual injuries to area & plaque begins to form • Fats & cholesterol enter & collect, eventually protrude into the lumen 36 Capillary Exchange • Substances exchanged due to concentration gradients – Oxygen and nutrients leave the blood – Carbon dioxide and other wastes leave the cells 37 Capillary Exchange: Mechanisms • Direct diffusion across plasma membranes • Endocytosis or exocytosis • Some capillaries have gaps (intercellular clefts)- not in brain – Plasma membrane not joined by tight junctions • Fenestrations of some capillaries – Fenestrations = pores w/ a thin membrane covering – Found where absorption is a priority or filtration occurs (kidney, intestine, endocrine) 38