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Ch. 11 THE CARDIOVASCULAR SYSTEM Copyright © 2010 Pearson Education, Inc. Heart Anatomy • Approximately the size of a fist • Location • In the mediastinum; superior to diaphragm • Leans to the left • Enclosed in pericardium, a double-walled sac Copyright © 2010 Pearson Education, Inc. Midsternal line 2nd rib Sternum Diaphragm (a) Copyright © 2010 Pearson Education, Inc. Point of maximal intensity (PMI) Figure 18.1a Superior vena cava Aorta Parietal pleura (cut) Pulmonary trunk Left lung Pericardium (cut) Diaphragm Apex of heart (c) Copyright © 2010 Pearson Education, Inc. Figure 18.1c Pericardium • Superficial fibrous pericardium • Protects, anchors, and prevents overfilling • Deep two-layered serous pericardium • Parietal layer lines internal surface of fibrous pericardium • Visceral layer on external surface of heart • Separated by fluid-filled pericardial cavity (decreases friction) Copyright © 2010 Pearson Education, Inc. Pulmonary trunk Pericardium Myocardium Copyright © 2010 Pearson Education, Inc. Fibrous pericardium Parietal layer of serous pericardium Pericardial cavity Epicardium (visceral layer Heart of serous wall pericardium) Myocardium Endocardium Heart chamber Layers of the Heart Wall 1. Epicardium=visceral layer of serous pericardium 2. Myocardium • Cardiac Muscle Tissue 3. Endocardium • Is continuous endothelium of blood vessels Copyright © 2010 Pearson Education, Inc. Chambers • Four chambers • Two atria • Top of heart; receiving chambers • Separated by the interatrial septum • Two ventricles • Bottom of heart; discharging chambers • Separated by the interventricular septum Copyright © 2010 Pearson Education, Inc. Major Blood Vessels of the Heart • Vessels entering right atrium • Superior vena cava • Inferior vena cava • Coronary sinus • Vessels entering left atrium • Right and left pulmonary veins Copyright © 2010 Pearson Education, Inc. Ventricles: The Discharging Chambers • Vessel leaving the right ventricle • Pulmonary trunk • Vessel leaving the left ventricle • Aorta Copyright © 2010 Pearson Education, Inc. Pathway of Blood Through the Heart • The heart is two side-by-side pumps • Right side is the pump for the pulmonary circuit • Vessels that carry blood to and from the lungs • Left side is the pump for the systemic circuit • Vessels that carry the blood to and from all body tissues Copyright © 2010 Pearson Education, Inc. Pulmonary Circuit Pulmonary arteries Venae cavae Capillary beds of lungs where gas exchange occurs Pulmonary veins Aorta and branches Left atrium Left ventricle Right atrium Right ventricle Oxygen-rich, CO2-poor blood Oxygen-poor, CO2-rich blood Copyright © 2010 Pearson Education, Inc. Heart Systemic Circuit Capillary beds of all body tissues where gas exchange occurs Figure 18.5 Pathway of Blood Through the Heart • Right atrium tricuspid valve right ventricle • Right ventricle pulmonary semilunar valve pulmonary trunk pulmonary arteries lungs Copyright © 2010 Pearson Education, Inc. Pathway of Blood Through the Heart • Lungs pulmonary veins left atrium • Left atrium bicuspid valve left ventricle • Left ventricle aortic semilunar valve aorta • Aorta systemic circulation Copyright © 2010 Pearson Education, Inc. Coronary Circulation • Blood supply to the heart muscle itself • Arteries • Right and left coronary arteries • Branch from base of aorta • Veins • Cardiac veins empty into coronary sinus right atrium Copyright © 2010 Pearson Education, Inc. Homeostatic Imbalances • Angina pectoris • Thoracic pain caused by a deficiency in blood delivery to the heart • Myocardial infarction (heart attack) • Prolonged coronary blockage • Areas of cell death are repaired with noncontractile scar tissue Copyright © 2010 Pearson Education, Inc. Heart Valves • Ensure unidirectional blood flow through the heart • Atrioventricular (AV) valves • Prevent backflow into the atria when ventricles contract • Tricuspid valve (right) • Bicuspid valve/Mitral valve (left) • Chordae tendineae anchor AV valve cusps to papillary muscles Copyright © 2010 Pearson Education, Inc. Pulmonary valve Aortic valve Area of cutaway Mitral valve Tricuspid valve Chordae tendineae attached to tricuspid valve flap (c) Copyright © 2010 Pearson Education, Inc. Papillary muscle Figure 18.8c Heart Valves • Semilunar (SL) valves • Prevent backflow into the ventricles when ventricles relax • Aortic semilunar valve • Pulmonary semilunar valve Copyright © 2010 Pearson Education, Inc. Opening of inferior vena cava Tricuspid valve Mitral valve Chordae tendineae Myocardium of right ventricle Myocardium of left ventricle Papillary muscles (d) Copyright © 2010 Pearson Education, Inc. Interventricular septum Pulmonary valve Aortic valve Area of cutaway Mitral valve Tricuspid valve Figure 18.8d Microscopic Anatomy of Cardiac Muscle • Cardiac muscle cells are striated, short, branched • Endomysium connects to the fibrous skeleton • T tubules are wide but less numerous; SR is simpler than in skeletal muscle • Numerous large mitochondria Copyright © 2010 Pearson Education, Inc. Nucleus Intercalated discs Gap junctions Cardiac muscle cell Desmosomes (a) Copyright © 2010 Pearson Education, Inc. Figure 18.11a Microscopic Anatomy of Cardiac Muscle • Intercalated discs: junctions between cells anchor cardiac cells • Desmosomes prevent cells from separating during contraction • Gap junctions allow ions to pass; electrically couple adjacent cells • Heart muscle behaves as a functional syncytium Copyright © 2010 Pearson Education, Inc. Cardiac muscle cell Mitochondrion Intercalated disc Nucleus T tubule Mitochondrion Sarcoplasmic reticulum Z disc Nucleus Sarcolemma (b) Copyright © 2010 Pearson Education, Inc. I band A band I band Figure 18.11b Heart Physiology: Electrical Events • Intrinsic cardiac conduction system • Defined: A network of noncontractile (autorhythmic) cells that initiate and distribute impulses to coordinate the depolarization and contraction of the heart Copyright © 2010 Pearson Education, Inc. Autorhythmic Cells • Spontaneously depolarize • Do not require neural stimulation Copyright © 2010 Pearson Education, Inc. Heart Physiology: Sequence of Excitation 1. Sinoatrial (SA) node (pacemaker) • Generates impulses about 75 times/minute (sinus rhythm) • Depolarizes faster than any other part of the myocardium Copyright © 2010 Pearson Education, Inc. Heart Physiology: Sequence of Excitation 2. Atrioventricular (AV) node • Delays impulses ~ 0.1 second • Depolarizes 50 times/min. in absence of SA node input Copyright © 2010 Pearson Education, Inc. Heart Physiology: Sequence of Excitation 3. Atrioventricular (AV) bundle (bundle of His) • Only electrical connection between the atria and ventricles Copyright © 2010 Pearson Education, Inc. Heart Physiology: Sequence of Excitation 4. Right and left bundle branches • Two pathways in the interventricular septum that carry the impulses toward the apex of the heart Copyright © 2010 Pearson Education, Inc. Heart Physiology: Sequence of Excitation 5. Purkinje fibers • Complete the pathway into the apex and ventricular walls • AV bundle and Purkinje fibers depolarize only 30 times per minute in absence of AV node input Copyright © 2010 Pearson Education, Inc. Superior vena cava Right atrium 1 The sinoatrial (SA) node (pacemaker) generates impulses. Internodal pathway 2 The impulses pause (0.1 s) at the atrioventricular (AV) node. 3 The atrioventricular (AV) bundle connects the atria to the ventricles. 4 The bundle branches conduct the impulses through the interventricular septum. 5 The Purkinje fibers Left atrium Purkinje fibers Interventricular septum depolarize the contractile cells of both ventricles. (a) Anatomy of the intrinsic conduction system showing the sequence of electrical excitation Copyright © 2010 Pearson Education, Inc. Homeostatic Imbalances • Defects in the intrinsic conduction system may result in 1. Arrhythmias: irregular heart rhythms 2. Fibrillation: rapid, irregular contractions; useless for pumping blood Copyright © 2010 Pearson Education, Inc. Homeostatic Imbalances • Defective AV node may result in • Partial or total heart block • Few or no impulses from SA node reach the ventricles Copyright © 2010 Pearson Education, Inc. Extrinsic Innervation of the Heart • Heartbeat is modified by the ANS • Cardiac centers are located in the medulla oblongata • Cardioacceleratory center innervates: SA and AV nodes, heart muscle, and coronary arteries • Cardioinhibitory center inhibits: SA and AV nodes Copyright © 2010 Pearson Education, Inc. The vagus nerve (parasympathetic) decreases heart rate. Cardioinhibitory center Medulla oblongata Cardioacceleratory center Sympathetic trunk ganglion Sympathetic cardiac nerves increase heart rate and force of contraction. AV node SA node Parasympathetic fibers Sympathetic fibers Interneurons Copyright © 2010 Pearson Education, Inc. Electrocardiography • Electrocardiogram (ECG or EKG): a composite of all the action potentials generated by nodal and contractile cells at a given time • Three waves 1. P wave: depolarization of SA node 2. QRS complex: ventricular depolarization 3. T wave: ventricular repolarization Copyright © 2010 Pearson Education, Inc. QRS complex Sinoatrial node Atrial depolarization Ventricular depolarization Ventricular repolarization Atrioventricular node P-Q Interval S-T Segment Q-T Interval Copyright © 2010 Pearson Education, Inc. Figure 18.16 SA node Depolarization R Repolarization R T P S 1 Atrial depolarization, initiated by the SA node, causes the P wave. R AV node T P Q Q S 4 Ventricular depolarization is complete. R T P T P Q S 2 With atrial depolarization complete, the impulse is delayed at the AV node. R Q S 5 Ventricular repolarization begins at apex, causing the T wave. R T P T P Q S 3 Ventricular depolarization begins at apex, causing the QRS complex. Atrial repolarization occurs. Copyright © 2010 Pearson Education, Inc. Q S 6 Ventricular repolarization is complete. (a) Normal sinus rhythm. (b) Junctional rhythm. The SA node is nonfunctional, P waves are absent, and heart is paced by the AV node at 40 - 60 beats/min. (c) Second-degree heart block. (d) Ventricular fibrillation. These chaotic, grossly irregular ECG Some P waves are not conducted deflections are seen in acute through the AV node; hence more heart attack and electrical shock. P than QRS waves are seen. In this tracing, the ratio of P waves to QRS waves is mostly 2:1. Copyright © 2010 Pearson Education, Inc. Figure 18.18 Mechanical Events: The Cardiac Cycle • Cardiac cycle: all events associated with blood flow through the heart during one complete heartbeat • Systole—contraction • Diastole—relaxation Copyright © 2010 Pearson Education, Inc. Cardiac Output (CO) • Volume of blood pumped by each ventricle in one minute • CO = heart rate (HR) x stroke volume (SV) • HR = number of beats per minute • SV = volume of blood pumped out by a ventricle with each beat Copyright © 2010 Pearson Education, Inc. Cardiac Output (CO) • At rest • CO (ml/min) = HR (75 beats/min) SV (70 ml/beat) = 5.25 L/min • Maximal CO is 4–5 times resting CO in nonathletic people • Maximal CO may reach 35 L/min in trained athletes Copyright © 2010 Pearson Education, Inc. Regulation of Stroke Volume • SV = EDV – ESV • Three main factors affect SV • Preload • Contractility • Afterload Copyright © 2010 Pearson Education, Inc. Homeostatic Imbalances • Tachycardia: abnormally fast heart rate (>100 bpm) • If persistent, may lead to fibrillation • Bradycardia: heart rate slower than 60 bpm • May result in grossly inadequate blood circulation Copyright © 2010 Pearson Education, Inc. Congestive Heart Failure (CHF) • Progressive condition where the CO is so low that blood circulation is inadequate to meet tissue needs • Caused by • Coronary atherosclerosis • Persistent high blood pressure • Multiple myocardial infarcts • Dilated cardiomyopathy (DCM) Copyright © 2010 Pearson Education, Inc. Developmental Aspects of the Heart • Fetal heart structures that bypass pulmonary circulation • Foramen ovale connects the two atria • Ductus arteriosus connects the pulmonary trunk and the aorta Copyright © 2010 Pearson Education, Inc. BLOOD VESSEL PHYSIOLOGY Copyright © 2010 Pearson Education, Inc. Blood Vessels • Arteries: carry blood away from the heart; oxygenated except for pulmonary arteries • Capillaries: contact tissue cells and directly serve cellular needs • Veins: carry blood toward the heart Copyright © 2010 Pearson Education, Inc. Venous system Large veins (capacitance vessels) Small veins (capacitance vessels) Postcapillary venule Thoroughfare channel Copyright © 2010 Pearson Education, Inc. Arterial system Heart Large lymphatic vessels Lymph node Lymphatic system Arteriovenous anastomosis Elastic arteries (conducting vessels) Muscular arteries (distributing vessels) Lymphatic Sinusoid capillary Arterioles (resistance vessels) Terminal arteriole Metarteriole Precapillary sphincter Capillaries (exchange vessels) Structure of Blood Vessel Walls • Arteries and veins • Tunica intima – Endothelium that lines the lumen of all vessels • Tunica media - Smooth muscle and sheets of elastin • Sympathetic vasomotor nerve fibers control vasoconstriction and vasodilation of vessels • Tunica externa - Collagen fibers protect and reinforce • Lumen • Central blood-containing space • Capillaries • Endothelium with sparse basal lamina; Size allows only a single RBC to pass at a time • Functions: exchange of gases, nutrients, wastes, hormones, etc. Copyright © 2010 Pearson Education, Inc. Tunica intima • Endothelium Valve Internal elastic lamina Tunica media (smooth muscle and elastic fibers) External elastic lamina Tunica externa (collagen fibers) Lumen Artery (b) Copyright © 2010 Pearson Education, Inc. Capillary network Capillary Lumen Vein Basement membrane Endothelial cells Pinocytotic vesicles Red blood cell in lumen Endothelial cell Endothelial cell nucleus Basement membrane Tight junction Copyright © 2010 Pearson Education, Inc. Fenestration (pore) Intercellular cleft Figure 19.16 (1 of 2) Capillary Exchange of Respiratory Gases and Nutrients • Diffusion of • O2 and nutrients from the blood to tissues • CO2 and metabolic wastes from tissues to the blood • Lipid-soluble molecules diffuse directly through endothelial membranes • Water-soluble solutes pass through clefts and fenestrations • Larger molecules are actively transported in pinocytotic vesicles etc. Copyright © 2010 Pearson Education, Inc. Lumen Intercellular cleft Caveolae Pinocytotic vesicles Endothelial fenestration (pore) 4 Transport via vesicles or caveolae (large substances) 3 Movement Basement through membrane fenestrations 1 Diffusion through membrane (lipid-soluble substances) Copyright © 2010 Pearson Education, Inc. 2 Movement through intercellular clefts (water-soluble substances) (water-soluble substances) Hydrostatic Pressures • Capillary hydrostatic pressure (HPc) (capillary blood pressure) • Tends to force fluids through (out of) capillary walls • Is greater at arterial end (35 mm Hg) than venous end (17 mm Hg) Copyright © 2010 Pearson Education, Inc. Colloid Osmotic Pressures • Capillary oncotic pressure (OPc) • Created by nondiffusible plasma proteins, which draw water toward themselves • ~26 mm Hg Copyright © 2010 Pearson Education, Inc. Net Filtration Pressure (NFP) • NFP = (HPc—Opc) • At arterial end = hydrostatic forces dominate • At venous end =osmotic forces dominate • Excess fluid is returned to blood (lymphatic system) Copyright © 2010 Pearson Education, Inc. Arteriole Venule Interstitial fluid Capillary Net HP—Net OP (35 – 25 = 10 Net HP 35 mm Net OP 25 mm NFP (net filtration pressure) is 10 mm Hg; fluid moves out Copyright © 2010 Pearson Education, Inc. HP = hydrostatic pressure • Due to fluid pressing against a wall • “Pushes” • In capillary (HPc) • Pushes fluid out of capillary • 35 mm Hg at arterial end and 17 mm Hg at venous end of capillary in this example Net HP—Net OP (17 -25 = -8) Net HP 17 mm Net OP 25 mm NFP is ~8 mm Hg; fluid moves in OP = osmotic pressure • Due to presence of nondiffusible solutes (e.g., plasma proteins) • “Sucks” • In capillary (OPc) • Pulls fluid into capillary • 26 mm Hg in this example BLOOD VESSEL PHYSIOLOGY Copyright © 2010 Pearson Education, Inc. Arteries of the head and trunk Common carotid arteries Subclavian artery Brachiocephalic trunk Aortic arch Ascending aorta Thoracic aorta (above diaphragm) Celiac trunk Abdominal aorta Superior mesenteric artery Renal artery Gonadal artery Common iliac artery Inferior mesenteric artery Internal iliac artery (b) Illustration, anterior view Copyright © 2010 Pearson Education, Inc. Arteries that supply the upper limb Subclavian artery Axillary artery Brachial artery Radial artery Ulnar artery Deep palmar arch Superficial palmar arch Digital arteries Arteries that supply the lower limb External iliac artery Femoral artery Popliteal artery Anterior tibial artery Posterior tibial artery Figure 19.21b Anterior Cerebral arterial circle (circle of Willis) • Anterior communicating artery • Anterior cerebral artery • Posterior communicating artery • Posterior cerebral artery Basilar artery Middle cerebral artery Internal carotid artery Vertebral artery Posterior (d) Major arteries serving the brain (inferior view, right side of cerebellum and part of right temporal lobe removed) Copyright © 2010 Pearson Education, Inc. Vertebral artery Common carotid arteries Left subclavian artery Right subclavian artery Brachiocephalic trunk Axillary artery Descending aorta Brachial artery Radial artery Ulnar artery Deep palmar arch Superficial palmar arch Digital arteries Anterior view Copyright © 2010 Pearson Education, Inc. Liver (cut) Inferior vena cava Diaphragm Esophagus Celiac trunk Common hepatic artery Hepatic artery proper Gastroduodenal artery Right gastric artery Gallbladder Left gastric artery Stomach Splenic artery Pancreas (major portion lies posterior to stomach) Right gastroepiploic artery Superior mesenteric mesenteric Duodenum Abdominal aorta Left gastroepiploic artery Spleen (b) The celiac trunk and its major branches. The left half of the liver has been removed. Copyright © 2010 Pearson Education, Inc. Figure 19.24b Diaphragm Inferior phrenic artery Adrenal (suprarenal) gland Renal artery Kidney Superior mesenteric artery Celiac trunk Abdominal aorta Lumbar arteries Gonadal (testicular or ovarian) artery Inferior mesenteric artery Common iliac artery (c) Major branches of the abdominal aorta. Copyright © 2010 Pearson Education, Inc. Figure 19.24c Common iliac artery Internal iliac artery External iliac artery Femoral artery Popliteal artery Anterior tibial artery Posterior tibial artery Fibular artery (b) Anterior view Copyright © 2010 Pearson Education, Inc. Figure 19.25b Popliteal artery Anterior tibial artery Posterior tibial artery Lateral plantar artery Medial plantar artery (c) Posterior view Copyright © 2010 Pearson Education, Inc. Fibular artery Plantar arch Veins of the head and trunk Veins that drain the upper limb External jugular vein Subclavian vein Axillary vein Internal jugular vein Right and left brachiocephalic veins Superior vena cava Brachial vein Ulnar vein Radial vein Digital veins Veins that drain the lower limb External iliac vein Inferior vena cava Femoral vein Common iliac vein Popliteal vein Internal iliac vein Posterior tibial vein Anterior tibial vein (b) Illustration, anterior view. The vessels of the pulmonary circulation are not shown. Copyright © 2010 Pearson Education, Inc. Inferior vena cava (not part of hepatic portal system) Hepatic veins Liver Hepatic portal vein Small intestine Gastric veins Spleen Inferior vena cava Splenic vein Inferior mesenteric vein Superior mesenteric vein Large intestine Rectum (c) The hepatic portal circulation. Copyright © 2010 Pearson Education, Inc. Cystic vein Hepatic portal system Inferior vena cava Inferior phrenic veins Hepatic veins Hepatic portal vein Superior mesenteric vein Splenic vein Suprarenal veins Renal veins Inferior mesenteric vein Gonadal veins Lumbar veins R. ascending lumbar vein L. ascending lumbar vein Common iliac veins External iliac vein (a) Schematic flowchart. Copyright © 2010 Pearson Education, Inc. Internal iliac veins Figure 19.29a Common iliac vein Internal iliac vein External iliac vein Inguinal ligament Femoral vein Great saphenous vein (superficial) Popliteal vein Small saphenous vein Fibular vein Anterior tibial vein Dorsalis pedis vein Dorsal venous arch Dorsal metatarsal veins Copyright © 2010 Pearson Education, Inc. (b) Anterior view Figure 19.30b Great saphenous vein Popliteal vein Anterior tibial vein Fibular vein Small saphenous vein (superficial) Posterior tibial vein Plantar veins Deep plantar arch (c) Posterior view Copyright © 2010 Pearson Education, Inc. Digital veins Figure 19.30c Brachiocephalic trunk Superior vena cava Right pulmonary artery Ascending aorta Pulmonary trunk Right pulmonary veins Right atrium Right coronary artery (in coronary sulcus) Anterior cardiac vein Right ventricle Right marginal artery Small cardiac vein Inferior vena cava (b) Anterior view Copyright © 2010 Pearson Education, Inc. Left common carotid artery Left subclavian artery Aortic arch Ligamentum arteriosum Left pulmonary artery Left pulmonary veins Auricle of left atrium Circumflex artery Left coronary artery (in coronary sulcus) Left ventricle Great cardiac vein Anterior interventricular artery (in anterior interventricular sulcus) Apex Figure 18.4b