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Transcript
Cardiovascular Physiology Dr. Khalid Alregaiey Gross Anatomy of Heart: Frontal Section Pathway of Blood Through the Heart and Lungs • Right atrium tricuspid valve right ventricle • Right ventricle pulmonary semilunar valve pulmonary arteries lungs • Lungs pulmonary veins left atrium • Left atrium bicuspid valve left ventricle • Left ventricle aortic semilunar valve aorta • Aorta systemic circulation Pathway of Blood Through the Heart and Lungs The Sectional Anatomy of the Heart The Sectional Anatomy of the Heart Heart chambers and valves • Structural Differences in heart chambers • The left side of the heart is more muscular than the right side • Functions of valves • AV valves prevent backflow of blood from the ventricles to the atria • Semilunar valves prevent backflow into the ventricles from the pulmonary trunk and aorta Atrioventricular Valve Function Semilunar Valve Function Cardiac Physiology • Two classes of cardiac muscle cells • Specialized muscle cells of the conducting system • Contractile cells The Conducting System of The Heart • The conducting system includes: • Sinoatrial (SA) node (pacemaker) • Atrioventricular (AV) node • atrioventricular bundle (bundle of His) • Purkinje fibers The Conducting System of The Heart Impulse Conduction through the heart • SA node generates impulses about 75 times/minute (pacemaker) • Stimulus spreads to the AV node • Impulse is delayed at AV node • Impulse passes from atria to ventricles via the atrioventricular bundle (bundle of His) • Then distributed by Purkinje fibers Sequence of Excitation The electrocardiogram (ECG) • A recording of the electrical events occurring during the cardiac cycle • The P wave corresponds to the depolarization of SA node • The QRS complex corresponds to ventricular depolarization • The T wave corresponds to ventricular repolarization An Electrocardiogram Electrocardiogram (ECG): • Einthoven's triangle • P-Wave – atria • QRS- wave – ventricles • T-wave – repolarization An Electrocardiogram ECG Information Gained • (Non-invasive) • Heart Rate • Signal conduction • Heart tissue • Conditions Figure 14-24: Normal and abnormal electrocardiograms Autonomic Innervation of the Heart Extrinsic Innervation of the Heart • Heart is stimulated by the sympathetic center • Heart is inhibited by the parasympathetic center Sympathetic and Parasympathetic • Sympathetic – speeds heart rate by Ca++ & I-f channel flow • Parasympathetic – slows rate by K+ efflux & Ca++ influx Heart Excitation Related to ECG Heart Sounds • Auscultation – listening to heart sound via stethoscope • Four heart sounds • S1 – “lubb” caused by the closing of the AV valves • S2 – “dupp” caused by the closing of the semilunar valves • S3 – a faint sound associated with blood flowing into the ventricles • S4 – another faint sound associated with atrial contraction Cardiac Cycle • Cardiac cycle refers to all events associated with blood flow through the heart • Systole – contraction of heart muscle • Diastole – relaxation of heart muscle Heart Cycle: 1. Late diastole: all chambers relax, filling with blood 2. Atrial systole: atria contract, add 20% more blood to ventricles 3. Isovolumic ventricular contraction: closes AV valves ("lub"), builds pressure Heart Cycle: Finish and Around To the Start 4. Ventricular ejection: pushes open semi lunar valves, blood forced out 5. Ventricular relaxation: Backflow of blood in aorta and pulmonary trunk closes semilunar valves ("dup") AV valves open refilling starts – back to start of cycle Heart Cycle Phases of the Cardiac Cycle Cardiac Output (CO) and Reserve • CO is the amount of blood pumped by each ventricle in one minute • CO = heart rate (HR) X stroke volume (SV) • HR is the number of heart beats per minute • SV is the amount of blood pumped out by a ventricle with each beat • Cardiac reserve is the difference between resting and maximal CO Cardiac Output: Example • CO (ml/min) = HR (75 beats/min) x SV (70 ml/beat) • CO = 5250 ml/min (5.25 L/min) Regulation of Stroke Volume • SV = end diastolic volume (EDV) minus end systolic volume (ESV) • EDV = amount of blood collected in a ventricle during diastole • ESV = amount of blood remaining in a ventricle after contraction Factors Influencing Stroke Volume • Force of contraction • Venous return: • Skeletal pumping • Respiratory pumping Regulation of Heart Rate: Autonomic Nervous System • Heart rate range: about 50 – near 200 • Typical resting: near 70 (60-100). • Hormones like epinephrine, norepinephrine, thyroid hormone (T3) increase heart rate. • Sympathetic stimulation • Releases norepinephrine (NE) • Increases heart rate • Parasympathetic stimulation • Releases acetylcholine (Ach) • Decreases heart rate Regulators of the Heart Rate Figure 14-28: Reflex control of heart rate Factors Influencing CO Blood Flow, Blood Pressure, and Resistance • Blood flow (F) is directly proportional to the difference in blood pressure (P) between two points in the circulation • If P increases, blood flow speeds up; if P decreases, blood flow declines • Blood flow is inversely proportional to resistance (R) • If R increases, blood flow decreases • R is more important than P in influencing local blood pressure Systemic Blood Pressure • The pumping action of the heart generates blood flow through the vessels along a pressure gradient, always moving from higher- to lowerpressure areas • Pressure results when flow is opposed by resistance • Systemic pressure: • Is highest in the aorta • Declines throughout the length of the pathway • Is 0 mm Hg in the right atrium • The steepest change in blood pressure occurs in the arterioles Systemic Blood Pressure Maintaining Blood Pressure • The main factors influencing blood pressure are: • Cardiac output (CO) • Peripheral resistance (PR) • Blood volume • Blood pressure = CO x PR • Blood pressure varies directly with CO, PR, and blood volume Chemicals that Increase Blood Pressure • Adrenal medulla hormones: norepinephrine and epinephrine increase blood pressure • Antidiuretic hormone (ADH) – causes intense vasoconstriction in cases of extremely low BP • Angiotensin II – kidney release of renin generates angiotensin II, which causes intense vasoconstriction • Endothelium-derived factors – endothelin and prostaglandin-derived growth factor (PDGF) are both vasoconstrictors Chemicals that Decrease Blood Pressure • Atrial natriuretic peptide (ANP): causes blood volume and pressure to decline • Nitric oxide (NO): has brief but potent vasodilator effects • Inflammatory chemicals: histamine, prostacyclin, and kinins are potent vasodilators • Alcohol: causes BP to drop by inhibiting ADH Alterations in Blood Pressure • Hypotension: low BP in which systolic pressure is below 100 mm Hg • Hypertension: condition of sustained elevated arterial pressure of 140/90 or higher • Transient elevations are normal and can be caused by fever, physical exertion, and emotional upset • Chronic elevation is a major cause of heart failure, vascular disease, renal failure, and stroke Factors Aiding Venous Return • Venous BP alone is too low to promote adequate blood return and is aided by the: • Respiratory “pump” – pressure changes created during breathing suck blood toward the heart by squeezing local veins • Muscular “pump” – contraction of skeletal muscles “milk” blood toward the heart • Valves prevent backflow during venous return The Function of Valves in the Venous System Capillaries • Narrowest of vessels; wide enough to allow only for single file passage of RBCs • Causes slowest flow rate of any vessels in system • Thinnest of vessels; walls composed of a single cell layer • No smooth muscle • No elastic • More capillaries than all other types of vessels • Greatest cross-sectional area of all vessels in system Capillary Structure Capillaries (continued) • • • • Slowest flow rate Thinnest walls Narrowest Diameters Greatest total cross-sectional area Optimal conditions for maximum diffusion of gases, nutrients and wastes in capillary beds Processes that move fluids across capillary walls • Diffusion • Filtration • Hydrostatic pressure (CHP) • Reabsorption Forces Acting across Capillary Walls