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Heart and Blood Vessels Jugular vein Carotid artery Superior vena cava Inferior vena cava Renal vein Common iliac vein Common iliac artery Subclavian vein Subclavian artery Aorta Renal artery Femoral vein Femoral artery Great saphenous vein Figure 8.9 Three Types of Blood Vessels Transport Blood • Arteries – Carry blood away from heart – Blood under high pressure • Capillaries – Metabolic exchange with tissues • Veins – Return blood to heart – Very low pressure Arteries • Structure – Thick-walled, three layers • Innermost: endothelium • Middle smooth muscle • Outer: connective tissue • Branch into arterioles – Small arteries Arterioles and Precapillary Sphincters – Blood flow • Heart → Arteries → Arterioles → Capillaries – Precapillary sphincters: control flow into capillaries • Vasodilation: increases blood flow to capillaries • Vasoconstriction: decreases blood flow to capillaries Capillaries • Structure – Smallest blood vessels – Thin-walled: one cell-layer thick – Porous • Function: exchange of substances with interstitial fluid Veins • Structure – Three layers, thin-walled – Larger lumen than arteries • Functions – Serve as blood reservoirs – Blood flow • Capillaries → Venules → Veins → Heart Venous Return to the Heart • Mechanisms in blood return – Contraction of skeletal muscles – One-way valves – Pressure changes associated with breathing The Heart - Layers • Surrounded by fibrous sac – pericardium • Layers of the heart – Epicardium: thin covering – Myocardium: cardiac muscle – Endocardium: thin lining Heart Chambers • Four chambers – Right atrium – Left atrium – Right ventricle – Left ventricle Heart Vessels • Superior and inferior vena cava – Carry low-oxygen blood into RA from body • Pulmonary trunk and arteries – Carry low-oxygen blood from RV to lungs • Pulmonary veins – Carry high-oxygen blood from lungs to LA • Aorta – Carries high-oxygen blood from LV to body Aorta L. Pulmonary Artery Superior vena cava Pulmonary trunk R. Pulmonary Artery Inferior vena cava Heart Valves • Prevent backflow – Two atrioventricular valves • Tricuspid valve – Between RA and RV • Mitral (bicuspid) valve – Between LA and LV – Two semilunar valves • Pulmonary valve – Between RV and pulmonary trunk • Aortic valve – Between LV and aorta Two Circuits of Circulation • Pulmonary circuit – RV Pulmonary trunk/arteries lungs (oxygen) pulmonary veins LA • Systemic circuit – LV aorta arteries of body capillaries veins SVC and IVC RA Cardiac Cycle • Atrial systole – Both atria contract – AV valves open, semilunar valves closed – Ventricles fill • Ventricular systole – Both ventricles contract – AV valves close, semilunar valves open – Blood flows into arteries • Diastole – Both atria and ventricles relax – Semilunar valves close Heart Sounds and Heart Valves • Lub-dub heart sound – Lub: closing of AV valves during ventricular systole – Dub: closing of semilunar valves during ventricular diastole • Heart murmurs – Caused when blood flow is disturbed – May be a sign of a defective valve Cardiac Conduction System • SA node – Cardiac pacemaker – Initiates heartbeat – Pace can be modified by nervous system • AV node – Relays impulse • AV bundle and Purkinje fibers – Carry impulse to ventricles Electrocardiogram (EKG/ECG) • Tracks electrical activity of heart • Characteristic pattern – P wave: impulse across atria – QRS complex: spread of impulse thru septum and ventricles – T wave: end of electrical activity in ventricles • EKGs can detect – Arrhythmias – Ventricular fibrillation Blood Pressure • Force blood exerts on walls of blood vessels – Systolic pressure – highest pressure, during ventricular systole – Diastolic pressure – lowest pressure, during ventricular diastole • Measurement – Use sphygmomanometer – “Normal” readings • Systolic pressure <120 mmHg • Diastolic pressure <80 mmHg Blood Pressure • Hypertension: high blood pressure – The silent killer – At risk for stroke, heart attack, bleeding, kidney disease • Hypotension: blood pressure too low – Inadequate blood supply to organs – Clinical signs – dizziness, fainting – Causes – orthostatic, severe burns, blood loss Regulation of Blood Pressure • Baroreceptors: pressure receptors in arteries • Steps in mechanism: 1. Blood pressure rises, vessels stretched 2. Signals sent to cardiovascular center in medulla oblongata 3. Heart signaled to lower rate and force of contraction 4. Arterioles vasodilate, reducing resistance to blood flow 5. Combined effect lowers blood pressure Regulation by Nervous and Endocrine Systems • Medulla oblongata signals – Sympathetic nerves – constrict blood vessels, raise blood pressure – Parasympathetic nerves – dilate blood vessels, lower blood pressure • Hormones: epinephrine (adrenaline) triggers sympathetic response • Local requirements dictate local blood flow • Exercise – increased blood flow and cardiac output Cardiovascular Disorders • Angina pectoris: chest pain – narrowed coronary arteries impair blood flow • Myocardial infarction/heart attack: permanent cardiac damage due to blockage in a coronary artery • Congestive heart failure: decrease in pumping efficiency • Embolism: blockage of blood vessels • Aneurysm: ballooning of artery – due to hypertension, hardening of arteries (atherosclerosis) • Stroke: impaired blood flow to the brain Heart Attack • Also known as myocardial infarction – Permanent damage to myocardium • Symptoms – Intense chest pain, nausea, heaviness in the chest, difficulty breathing, pain radiating to left arm, jaw, back, upper abdomen • Diagnosis – EKG – Blood test for cardiac enzymes • Prevention/Treatment – Clot-busting medications – CABG (bypass) Aorta Vein grafts Plaque blocking blood flow Figure 8.19 Reducing Risk of Cardiovascular Disease • • • • • Smoking – don’t Blood lipids – monitor cholesterol levels Exercise – regular and moderate Blood pressure – treat hypertension Weight – being overweight increases risk of heart attack and stroke • Control of diabetes mellitus – early diagnosis and treatment delays onset of related problems • Stress – avoid chronic stress