Cardiovascular System: Heart. I. Anatomy of the heart. A. Location

Transcription

1 Cardiovascular System: Heart I. Anatomy of the heart A. Location 1. Within mediastinun of the medial cavity of the thorax a. Anterior to vertebral column b. Posterior to sternum c. Superior to diaphragm i. At rest d. Superior margin i. 2nd rib e. Inferior margin i. 5th intercostals space f.. 60% of mass to the left of midline g. Base (posterior surface) faces right shoulder h. Apex points inferiorly toward left hip i. Contacts chest wall between 5th and 6th ribs ii. PMI-point of maximum intensity

2 B. Pericardium 1. Fibrous pericardium a. Tense connective tissue i. Protects heart ii. Anchors heart to surrounding tissues iii. Prevents over filling 2. Serous pericardium a. Two layers i. Parietal layer ii. Visceral layer b. Parietal layer i. Internal surface of fibrous pericardium c. Visceral layer-epicardium i. Part of heart wall 3. Pericardial cavity a. Between the serous layers b. Fluid filled i. Reduces friction between serous membranes

3 C. Layers of the heart 1. Three layers a. Epicardium b. Middle myocardium c. Deep endocardium 2. Epicardium (see above) 3. Myocardium a. Primarily cardiac muscle i. Arranged in circular bundles b. Fibrous skeleton i. Holds cardiac muscle together 4. Endocardium a. Inner myocardial surface b. Lines heart and connective tissues of the valves c. Squamous epithelium

4 II. Chambers of the Heart A. Four chambers 1. Two atria 2. Ventricles B. Heart is divided longitudinally 1. Septum a. Interatrial b. Interventricular

5 C. Atria 1. Receive returning blood (i.e., veins) 2. Auricles a. Appendages i. Increase atrial volume 3. Fossa ovalis a. Residual impression of fetal foramen ovale 4. Veins of right atrium a. Superior vena cava i. Return flow from regions superior to diaphragm b. Inferior vena cava i. Return flow from regions inferior to diaphragm c. Coronary sinus i. Drain blood from myocardium 5. Veins of left atrium a. Four pulmonary veins i. Lungs back to heart ii. Most of the posterior surface of the heart D. Ventricles 1. Blood leaving the heart 2. Most of the mass of the heart a. Right i. Anterior surface b. Left i. Inferior surface 3. Muscles a. Trabeculae carneae i. Crossbars

6 b. Papillary muscles i. Valve function ii. Project into heart cavity 4. Pulmonary trunk a. Right ventricle i. Routes blood to lungs 5. Aorta a. Left ventricle i. Systemic circulation III. Blood Flow Through the Heart A. Two circuits 1. Pulmonary: right side of the heart a. Blood to lungs for gas exchange b. Right ventricle to left atrium of the heart (*This is a matter of convention. Technically, oxygen poor blood returning to right atrium is the end of the systemic circuit; not the beginning of the pulmonary circuit.) c. Blood returns from body to right atrium i. Low O2 concentration ii. Relatively high CO2 concentration d. Rt. Atrium to right ventricle e. Rt. Ventricle to lungs i. Pick up O2 and drop off CO2 ii. Pulmonary arteries (away from heart, not CO2 f. Lungs to left atrium i. Pulmonary veins ii. O2 rich 2. Systemic: left side of the heart a. Left atrium to left ventricle b. Left ventricle into aorta c. Aorta to body through systemic arteries i. Gases and nutrients are exchanged d. Systemic veins to right atrium 3. Work loads a. Equal volumes b. Unequal work loads c. Systemic i. Five times as much resistance to blood flow ii. Longer route d. Left ventricle is much larger and thicker to do more work

7 IV. Heart Valves A. Atrioventricular (AV) valves 1. Valves at atrium-ventricular junction 2. Prevent backflow into atria 3. Closed during ventricular contraction (systole) B. Right AV valve: tricuspid 1. Three cusps a. Reinforced endocardium C. Left AV valve: bicuspid (mitral valve) 1. Two cusps D. Chordae tendineae (heart strings) 1. Collagen cords attached to the cusps a. Anchor cusps to papillary muscles 2. During ventricular contraction a. Intraventricular pressure rises b. Forces blood against valve flaps c. Chordae tendinea anchor flaps in closed postion

8 E. Semilunar (SL) valves 1. Two a. Aortic i. Between left ventricle and aorta b. Pulmonary i. Between right ventricle and pulmonary trunk 2. Open during ventricular contraction (systole) a. Intraventricular pressure exceeds the blood pressure in aorta and pulmonary trunk 3. Three crescent shaped cusps a. Open out against arterial walls

9 F. Valves between atria and venae cavae and pulmonary veins 1. None 2. Atrial contraction compresses venous entry points V. Blood Flow to the Heart A. Heart requires its own circulatory system 1. Myocardium is too thick to permit diffusion of gases and nutrients B. Coronary circulation 1. Arterial supply 2. Right and left coronary arteries a. Arise at base of aorta 3. Left coronary artery a. Supplies left side of the heart b. Marginal branches i. Anterior interventricular artery ii. Circumflex artery 4. Right coronary artery a. Supplies right side of the heart b. Branches i. Marginal artery ii. Posterior interventricular artery

10 C. Cardiac veins 1. Follow course of coronary arteries 2. Join to form coronary sinus a. Empties into right atrium 3. Coronary sinus a. Tributaries i. Great cardiac vein ii. Middle cardiac vein iii. Small cardiac vein 4. Anterior cardiac veins a. Empty directly into rt. Atrium VI. Cardiac Muscle A. Characteristics 1. Branched, short, and interconnected fibers 2. Striated a. Contract by sliding filament mechanism (see last semesters notes) 3. Cardiac muscle fibers are functionally connected a. Intercalated discs i. Anchoring desmosomes ii. Electrical coupling via gap junctions 4. Functional syncytium a. Entire myocardium acts as a single unit i. Result of gap junctions B. Contraction 1. All cardiac muscle cells contract as a single unit 2. Cardiac muscle is self-excitable (i.e., autorhytmic) a. Initiate action potentials i. Independent of nervous innervation 3. Long refractory period a. Prevents tetanic contractions C. Autorhythmic fibers 1. Pace maker cells (see below) a. 1% of heart muscle b. Depolarize spontaneously D. Contractile muscle fibers 1. Depolarize in response to pacemaker cell activities

11 VII. Heart Physiology A. Intrinsic conduction system 1. Noncontractile cardiac cells that initiate and distribute impulses a. Sequential distribution from atria to ventricles B. Autorhythmic cells 1. Unstable resting membrane potential a. Drift towards threshold 2. Pacemaker potentials a. Membrane potential changes spontaneously 3. Events a. Na+ influx (slow) offset by K+ efflux (slow) b. K+ permeability gradually decreases c. Influx of Na+ depolarizes the cardiac cells d. Depolarization opens fast CA+ channels e. Ca2+ influx from extracellular space causes rising phase of action potential f. Repolarization causes K+ permeability to increase i. Cardiac cells repolarize g. K+ channels inactivate h. Cycle starts again

12 C. Location of autorhythmic cells 1. Sinoatrial (SA) node a. Pacemaker i. Fastest rate of depolarization ii. Characteristic rhythm of the heart: Sinus rhythm b. Located in right atrial wall c. After depolarization is initiated i. Depolarization wave sweeps via gap junctions throughout atria 2. Atrioventricular (AV) node a. Depolarization wave initiated by SA node reaches AV node b. AV node is located in interatrial septum i. Near tricuspid valve c. Diameter of fibers is smaller i. Slows impulse conduction (0.1 s) ii. Permits completion of atrial contraction d. Impulse passes to bundle of His 3. Atrioventricular bundle (bundle of His) a. Functional passage of impulse from atria to ventricles i. No gap junctions between cardiac cells in atria and ventricles b. Located in inferior interatrial septum c. Very short i. Branches to form bundle branches

13 4. Bundle branches a. Course interventricular septum toward apex of heart 5. Purkinje fibers a. Reach apex then branch superiorly into ventricular walls b. Impulses in fibers moves faster than cell to cell contact i. Ensures greater pumping efficacy VIII. Cardiac Action Potential 1. Resting membrane potential (Phase 4) a. Associated with diastole b. Cells remain in this phase until electrically stimulated 2. Depolarization phase (Phase 0) a. Due to the opening of the fast Na+ channels b. Rapid influx of Na+ ions c. Gates are voltage gated 3. Inactivation of the fast Na+ channels (Phase 1) a. Transient net outward current i. Due to the movement of K+ and Cl- ions 4. Plateau phase a. Balance between inward movement of Ca2+ and outward movement of K+ i. K+ flows through the slow delayed rectifier potassium channels ii. Ca2+ flows through L-type Ca2+ channels 5. Repolarization (Phase 3) a. L-type Ca2+ channels close b. Slow delayed rectifier K+ channels are still open c. Delayed rectifier K+ channels close when the membrane potential is restored to about -80 to -85 mv

14 IX. Extrinsic Control of the Heart A. Brain-based control 1. Cardioaccelatory center a. Medulla b. Sympathetic NS control i. Innervate SA and AV nodes 2. Cardioinhibitory center a. Vagus nerve b. Parasympathetic system i. Innervate SA and AV nodes ii. Slows heart rate X. Electrocardiography A. Electrical changes during heart activity 1. ECG (EKG)

15 B. Deflection waves 1. P wave a. Depolarization moving from SA node through atria 2. QRS complex a. Ventricular depolarization i. Precedes contraction 3. T wave a. Ventricular repolarization b. Occurs more slowly than depolarization i. More spread out than QRS C. Intervals 1. P-R a. Interval from beginning of atrial excitation and ventricular excitation b. Includes i. Atrial depolarization and contraction ii. Passage of impulse through intrinsic conduction system c. Lasts 0.16 s 2. Q-T a. Ventricular depolarization through repolarization b. Includes i. Time of ventricular contraction

16 XI. Mechanical Events during Heart Contraction A. Cardiac cycle 1. Systole a. Contraction 2. Diastole b. Relaxation 3. Length a. Total i. 0.8 s b. Atrial systole i. 0.1 s c. Ventricular systole i. 0.3 s d. Quiescent period i. 0.4 s

17 B. Events 1. Start point a. Atria and ventricles are relaxed i. Mid-to-late diastole 2. Ventricular filling a. Mid-to-late diastole b. AV valves are open c. Semilunar valves are closed d. Ventricles begin to fill i. 70% occurs prior to atrial contraction e. Atrial systole i. Atria contract (preceded by P wave) ii. Increased atrial pressure propels blood from atria into ventricles f. Atria relax g. Ventricles depolarize (QRS wave) 3. Ventricular systole a. As contraction begins, intraventricular blood pressure increases i. AV valves close ii. Semilunar valves are also closed b. Isovolumetric contraction phase (volume constant) i. Blood pressure in aorta and pulmonary trunk exceeds intraventricular pressure ii. Pressure in ventricles increases without volume changing

18 c. Ventricular ejection phase i. Intraventricular pressure exceeds pressure in large vessels ii. Semilunar valves open iii. Blood is propelled out of ventricles d. Atria begin to fill with blood 4. Isovolumetric relaxation a. Occurs during early diastole b. T wave c. Ventricles relax d. Intraventricular pressure drops e. Blood in vessels outside heart begins to flow back into ventricles i. Semilunar valves close ii. Aortic pressure increases-dicrotic notch f. AV valves still closed i. Isovolumetric relaxation 5. AV valves open when pressure in atria exceeds pressure against AV valves exerted by blood in ventricles a. Start of cycle b. Quiescent period XII. Heart Sounds A. Associated with closing of heart valves B. Lub-dub, pause lub-dub, pause, C. Sound 1 a. AV valves close b. Onset of systole c. Louder and longer than sound 2 D. Sound 2 a. Semilunar valves close b. Beginning of ventricular diastole c. Short, sharp sound E. Pause a. Quiescent period F. Sounds of separate valves can be differentiated a. Timing i. Mitral ii. Tricuspid iii. Aortic semilunar iv. Pulmonary semilunar b. Location i. Four corners

19 XII. Cardiac Output (CO) A. Amount of blood pumped by each ventricle per minute 1. Stroke volume X Heart rate a. Stroke volume i. Volume of blood pumped out of each ventricle per beat 2. Increases or decreases with increases or decreases in either stroke volume or heart rate B. Regulation of stroke volume (SV) 1. SV a. Difference between EDV and ESV i. EDV-end diastolic volume ii. ESV-end systolic volume 2. EDV a. Determined by: i. Length of ventricular diastole ii. Venous pressure b. Increase either i. or ii., EDV increases c. 120 ml is normal 3. ESV a. Determined by: i. Arterial pressure ii. Force of ventricular contraction b. 50 ml is normal C. Factors that affect stroke volume 1. Preload-degree of stretch prior to contraction a. Most important factor affecting EDV b. Greater the stretch of cardiac fibers, the greater the force of contraction c. Factors increasing stretch i. Volume and speed of venous return ii. Heart rate-time for filling 2. Contractility a. Increase in contractile strength i. Independent of muscle stretch b. Increase Ca2+ into cardiac cells i. Increases contractility and volume ejected from heart c. Decreases ESV d. Molecular regulation of contractile events 3. Afterload-arterial blood pressure a. Pressure ventricular contraction must overcome i. Back pressure in aorta and pulmonary valves b. Normal: 80 mm Hg (aorta) and 10 mm Hg (pulmonary trunk) c. Not normally a factor in healthy individuals i. May have an adverse effect in individuals with hypertension

20 XIII. Heart Rate regulation A. Cardiac output is homeostatically regulated 1. Extrinsic factors induce change to cardiac function through a. Neural mechanisms b. Chemical mechanisms c. Physical mechanisms

21 B. Autonomic nervous system 1. Sympathetic nervous system a. Responds to real or perceived threats b. 4 F's: flight, fright, fight and sex 2. Sympathetic postganglionic neurons release NE at cardiac targets a. Mediated by ß1 adrenergic receptors i. Pacemaker cell resting membrane potential is brought closer to threshold (depolarized) ii. Increases heart rate b. Increases Ca2+ influx into contractile cells i. Increases ESV 3. Parasympathetic division a. Opposes the effects of sympathetic nervous system i. Decreases heart rate b. Mediated by acetycholine i. Hyperpolarizes (inhibits) SA node 4. Vagal tone a. Sympathetic and parasympathetic divisions are continuously active i. Effect of parasympathetic division predominates b. Dominant effect is reduce activity of AV node i. 25 beats/min reduction in HR

22 C. Chemical regulation 1. Hormones a. Adrenal medulla i. Epinephrine ii. Sympathetic nervous system iii. Increases HR and contractility (like NE) 2. Ions a. Ca2+ concentrations i. Decreases cause depressed heart function ii. Increases cause heart irratability D. Physical factors 1. Age a. Inverse relation 2. Gender a. Female faster 3. Exercise a. Increased HR during exercise b. Resting rate is lower i. Bradycardia ii. SV and muscle mass increased in athlete 4. Body temperature a. HR lowered when cold

23 Blood Vessels I. Arterial System A. Classification based on size and function 1. Elastic (conducting) arteries a. Characteristics i. Thick-walled ii. Near heart iii. Largest diameter iv. More elastic v. Large lumen b. Properties i. Dampen BP changes associated with heart contraction ii. Passive accommodation results in smooth flow of blood c cm 2. Muscular arteries-distributing arteries a. Distal to elastic arteries b. Deliver blood to specific organs c. Thick media layer i. More smooth muscle d cm 3. Arterioles a. Determine flow into capillary beds b. Mostly smooth muscle c. 10 µm cm 4. Capillaries a. Smallest blood vessels i µm b. Tunica interna only c. Exchange of materials B. Capillary beds

24 1. Capillaries act as networks-capillary beds 2. Microcirculation a. Arteriole to venule 3. Parts of a capillary bed a. Vascular shunt i. Connects arteriole with venule b. True capillaries D. Sequence of blood movement through capillary bed 1. Terminal arteriole 2. Metateriole a. True capillaries branch off i. Pre-capillary sphincter controls blood flow into capillary 3. Thoroughfare channel a. Capillaries rejoin 4. Post-capillary venule II. Venous System A. Types of vessels 1. Venules a µm b. Characteristics vary with size i. Little muscle ii. Thin externa 2. Veins a. Formed from venules b. Thinner walls and less muscle than arteries c. Little muscle in media i. Mostly elastin d. Externa is thickest wall layer B. Capacitance vessels 1. Veins act as reservoirs a. Large lumens b. Low blood pressure allows walls to thin 2. Venous valves a. Prevent backflow b. Folds of interna III. Systemic Blood Pressure A. Background 1. Heart pumping generates blood flow 2. Pressure results when flow opposed by resistance 3. Blood flows along a pressure gradient a. From higher to lower pressure i. Highest in aorta

25 B. Arterial blood pressure ii. Lowest in right atrium C. Capillary blood pressure mm Hg entering mm Hg exiting D. Venous blood pressure 1. Characteristics a. Relatively steady throughout cardiac cycle b. Gradient from venules to vena cava i. 20 mm HG (60 from aorta to arterioles) 2. Venous return a. Venous pressure is too low to promote adequate return b. Need additional functional modifications 3. Functional modification a. Respiratory pump i. Abdominal (ventral body cavity) pressure increases squeeze local veins ii. Backflow is prevented by valves iii. Blood is forced toward the heart iv. Chest cavity pressure decreases v. Thoracic veins expand vi. Blood enters right atrium b. Muscular pump (more important) i. Contraction of skeletal muscle surrounding veins compress vein ii. Backflow is prevented by valves iii. Blood moves in direction of heart

26 IV. Regulation of Blood Pressure A. Factors influences blood pressure 1. Cardiac output 2. Peripheral resistance 3. Blood volume B. Blood pressure = Cardiac output X Peripheral resistance 1. Cardiac output is directly related to blood volume 2. Blood pressure is directly related to CO, BV and PR C. CO = Stroke volume X HR D. Factors that enhance CO 1. Reduce parasympathetic control a. Reduce effect of vagus nerve i. HR increases 2. Increase sympathetic activity a. Increases contractility of heart i. Reduces ESV ii. Increases stroke volume b. Releases Epi into blood stream from adrenal medulla i. Increases heart rate 3. Increase activity of respiratory and muscular pumps a. Increases venous return i. Increases EDV ii. Increases stroke volume

27 E. Neural control of blood pressure 1. Short-term mechanisms 2. Nervous control of peripheral resistance a. Alter blood distribution b. Alter blood vessel diameter 3. Vasomotor center a. Regulation of blood vessel diameter b. Vasomotor fibers i. Sympathetic efferents ii. Innervate smooth muscle of blood vessels iii. Primarily arterioles iv. Release NE v. Vasoconstrictor c. Vasomotor tone i. Tonic vasoconstriction

28 4. Baroreceptors a. Detect changes in arterial blood pressure i. Pressure sensitive mechanoreceptors ii. When BP rises, receptors are stretched b. Located in carotid sinuses, aortic arch and walls of all large vessels c. Stretching increases signaling to vasomotor center i. Inhibits vasomotor center ii. Causes dilation of arteries and veins d. Arteriole dilation reduces peripheral resistance e. Venodilation shifts blood to venous reservoirs i. Venous return decreases ii. Cardiac output declines f. Baroreceptors also send efferent signals to cardiac centers in the medulla i. Inhibit sympathetic NS ii. Stimulate parasympathetic NS iii. HR and contractile force decrease g. Respond to acute changes in blood pressure i. Carotid sinus reflex protects blood supply to brain ii. Aortic reflex maintains supply to systemic circuit

29 F. Chemical control of blood pressure 1. Short-term 2. Levels of O2 and CO2 (see Respiration Lecture) 3. Blood-borne chemicals a. Adrenal medulla hormones i. NE and EPI (nicotine is a monoamine agonist) ii. NE is a vasoconstrictor iii. EPI increase cardiac output by increasing cardiac muscle contractility b. Atrial natriuretic peptide (ANP) i. Atrial peptide hormone ii. Reduces blood pressure by antagonizing aldosterone iii. Increases water excretion from kidney c. Antidiuretic hormone (ADH) i. Posterior pituitary hormone ii. Increases blood pressure by increasing water absorption by distal tubule iii. At high concentrations, causes vasoconstriction d. Angiotensin II i. Mediated by release of renin by JGA of kidney tubule ii. When amount of blood entering kidney tubule is too low, renin is released iii. Renin catalyzes the conversion of angiotensinogen into angiotensin II iv. Angiotensin II causes vasoconstriction of systemic arterioles v. Increases BP vi. Angiotensin II also causes release of aldosterone from adrenal cortex

30 vii. Aldosterone increases absorption of water by kidney tubules e. Endothelium-derived factors i. Endothelin-vasoconstrictor ii. Prostaglandin-derived growth factor (PDGF)-vasoconstrictor iii. Nitrous oxide (NO)-fast acting, local vasodilator f. Inflammatory chemicals-vasodilators i. Histamine, etc. (see Immune Lecture) ii. Increase capillary permeability g. Alcohol i. Reduces blood pressure ii. Inhibits ADH release-increases loss of water in urine iii. Increases vasodilation (skin) by depressing vasomotor center G. Renal regulation of blood pressure 1. Long-term mechanisms for blood pressure regulation 2. Kidney controls blood volume by regulating water loss in urine 3. Blood volume affects cardiac output via: a. Venous pressure b. Venous return c. EDV d. Stroke volume 4. Blood pressure change parallels change in blood volume a. Increase in volume increases BP i. Kidney responds by eliminating water to reduce volume b. Decrease in volume decreases BP i. Kidney responds by absorbing water to increase volume V. Capillary Dynamics

31 A. Gases and nutrients diffuse from capillary to interstitial fluid 1. Water-soluble solutes pass through clefts and fenestrations 2. Lipid-soluble diffuse through the plasma membranes of capillary epithelial cells B. Forces responsible for the direction and amount of fluid crossing capillary walls 1. Hydrostatic and osmotic pressure a. Forces oppose Circulatory System I. Pulmonary Circulation A. Function 1. Gas exchange only B. Sequence 1. Pulmonary trunk a. Bifurcates into rt. and lt. pulmonary arteries 2. Pulmonary arteries a. In the lungs, arteries subdivide into lobar arteries i. Three in right ii. Two in left 3. Lobar arteries branch to form arterioles 4. Further branching to form pulmonary capillaries 5. Capillaries drain into venules 6. Venules join to form two pulmonary veins per lung 7. Four pulmonary veins drain into left atrium II. Systemic Circulation A. Aorta and Major Arteries of the Systemic Circulation

32 B. Aortic arch (branches in sequence relative to lt. ventricle) 1. Coronary arteries 2. Brachiocephalic a. R. common carotid i. R. internal carotid ii. R. external carotid b. R. subclavian i. R. vertebral ii. R. axillary 3. L. common carotid a. L. internal carotid b. L. external carotid 4. L. subclavian a. L. vertebral b. L. axillary C. Thoracic aorta (above the diaphragm) 1. Parietal branches 2. Visceral branches D. Abdominal aorta (below diaphragm) 1. Parietal branches 2. Visceral branches 3. R. common iliac 4. L. common iliac III. Major Veins of the Systemic Circulation

33 A. Superior vena cava runs from union of brachiocephalic veins (L. and R.) to R. atrium B. Veins that drain into R. brachiocephalic vein 1. R. internal jugular vein 2. R. vertebral vein 3. R. subclavian vein a. R. external jugular vein empties into R. subclavian vein *Left side corresponds to right side C. Inferior vena cava runs from junction of common iliac veins to R. atrium D. Veins that drain into inferior vena cava 1. Hepatic veins (R. and L.) 2. R. suprarenal vein 3. Renal veins (R. and L.) 4. R. gonadal vein 5. Lumbar veins