Heart physiology A. General 1. William Harvey -1628 a. discovered the circulatory system b. stated that blood circulates by leaving the heart in arteries and returns in veins. B. The heart 1. General a. is the major organ of the circ. system b. is a 4 chambered double pump c. in 24 hours, it contracts 100,000 times and pumps 7200 liters of blood d. its primary purpose is to transport O2 and CO2 2. Description a. a cone shaped hollow muscular organ b. lies obliquely between the lungs in the mediastinum c. 2/3 of the mass lies left of the mid-line d. varies in size, length, and width (1) approx. the size of a fist (2) 12 cm long * 9 cm wide * 6 cm thick (3) wt = approx 9 oz. (a) males = 300, females = 270 grams (4) vol. = 800 ml (untrained subjects) e. THE APEX test (1) rounded interiorly and projects downward, forward, and to the left, reaching the fifth intercostal space 8 cm left of the mid-sternal line. test f. THE BASE (1) projects up, back, and to the right, lying behind the sternum at the second intercostal space 3. Gross structure a. consists of a fiber skeleton made up of dense CT which separates the muscles of the atria from the ventricles (1) the only connection is the Bundle of His b. the CT forms the annuli fibrosis, a fibrous ring (1) it surrounds the orifices of the aorta, the pul art., and the A-V valves (2) it provides for attachment sites of valves and muscles 4. Atrium (atria pl.) a. blood collecting chambers (or) primer pumps b. helps to make the vents more efficient c. the myocardia here has two layers (1) the superficial oblique that covers both atria (2) the deeper layer that covers each separately a)the deep layer is at right angles to the superficial d. has three functions (1) elastic reservoir and conduit of blood to the ventricles (2) booster pump to enhance vent. filling (a) not as important at low HR's (b) vents fill during diastole (c) at high HR's, this can increase CO by as much as 20%. i) will therefore notice an atrial malfunction more with exercise than at rest (3) by the A-V valve, it helps to close before vent. systole 5. Ventricles a. Consists of four major bands of muscle (1) runs at right angles, both superficial and deep b. the walls are thicker than the atria's (1) left = 3 * the right (2) this forms most of the posterior surface and left margin ? of the heart c. weight (1) Left = 85 g. (2) right = 50 g (3) interventricular septum = 64 g (a) quite a bit in comparison to each other and to the atria (b) Left atrium = 17 g (c) right = 13 g (d) inter atrial septum = 10 g 6. The Valves a. Primary function is to ensure the one way flow of blood b. Two sets (1) AV - atrio-ventricular (a) tricuspid valve i) located at the 4th intercostal cartilage ii) separates the right atrium from the right ventricle (b) mitral i) located at the 5th intercostal cartilage ii) separates the left atrium from the left vent. (c) the chordae tendon (parachute shrouds) and papillary muscles join these valves to the fibrous rings (2) Semi-lunar Valves i) 1/2 moon or crescent shaped (a) aortic valve test i) aortic stenosis is a contraindication to exercise testing ii) it is located at the 3rd intercostal space iii) it separates the L vent. from the rest of the body (b) pulmonic valve i) separates the right ventricle from the lungs c. Heart Sounds (1) are made by the opening and closing of the valves, and movement of blood thur the valves (a) Lub - Dub (2) Lub = first sound (a) softer, longer, and lower in pitch (b) is due to the closure of the AV valves i) contraction of the vents (3) Dub = 2nd sound (a) short and sharp (b) closure of pulmonary and aortic valves i) occurs at the end of vent. contraction / systole (4) Pause (a) is twice as long as the Dub d. Heart Murmurs (1) is an abnormal sound in the valves (2) has nothing to do with the ECG or +/- (a) has been described as a blowing or a vibrating sound as blood goes thur the valves (3) causes (a) faulty closure i) Rheumatic fever can cause this a) the edges of the valves get fibrosis or eaten away b) cusps don't seal tightly c) leads to regurgitation or retrograde flow ii) turbulent flow is produced by a) a decrease in blood viscosity (ex. anemia) b) an increase in blood flow (ex. hyperthyroidism) iii) the absence of any organic disease a) 1/2 of all youths have one at some time in life b) is associated with the mitral valve c) non-pathological d) can be caused by heavy exercise (b) Stenosis i) heart valves lose flexibility a) become stiff and rough ii) don't open and close as well iii) increase the pressure in the heart a) may increase muscle mass b) may cause pul. edema c) the cardiac muscles may compensate d) fibers will get longer an thicker, and then have less reserve 7. Myocardial Cell Morphology a. Tissues (1) tissues are composed of discreet separate cells bounded by intact plasma membranes (2) connect with each other , and form a functional syncytium (a) in this, an action potential (in either the atria or the vent) can travel easily (b) is a syncytium for both the vents and the atria (3) separated lengthwise by a intercalated disk (a) a mechanical junction of low electrical resistance (b) allows the AP to travel cell to cell b. Cells (2 types) (1) impulse formation and conduction cells (a) General i) capable of spontaneously generating and AP ii) the heart is therefore referred to as a myogenic organism iii) this ability is referred to as rhythmicity (esp. in the SA node, as it is the primary pacemaker as it can generate an AP faster than anywhere else in the heart (in most cases)). iv) the cause of rhythmicity is the permeability of the membrane to Na++ v) rhy. varies in the heart a) SA = 72 b/min b) atria = 60 c) vents = 20 d) PVC's cause the QRS to widen out because of slower depolarization (b) Pacemaker cells (3 types) i) P - cells a) located in the SA and AV nodes b) pale, primitive, and pacemaking c) oval, or rounded smooth surface ii) transitional a) slender and elongated b) found in the SA node region only! c) connect the P cells of the SA node with the cells of the rest of the heart d) is intermediate in complexity between the P and the purkinje cells iii) purkinje cells a) shorter and broader b) joined end to end c) found on the bundle of his, the bundle branches, and the purkinje network (c) Contractile Cells i) make up the bulk of the heart ii) differences a) contractile cells frequently branch and interdigitate to adjacent cells b) connect laterally, end to end, to form a chain c) creates a syncytium d) if end to end, the intercalated disks join e) numerous mitochondria f) referred to as sarcosome g) 30 % is mitochondria h) can also be equal to the amount of myofibrils 8. Coronary Blood Flow a. General (1) approx 225 ml/min in the heart (5% of CO) (2) does not rely on blood from the chambers (3) is the greatest during diastole (a) 2 1/2 * greater than systole b. Composed of the (1) right coronary artery (a) is the size of a pencil (b) serves the L and R vents., the R. atrium, the SA and the AV nodes, and the Bundle of His (2) the left coronary artery (2 parts) (a) anterior descending = LAD i) goes to the walls of the vent's and the bundle branches (b) circumflex i) left vent. and left atrium c. Venous system (1) arteries and veins (2) primary vein is the coronary sinus i) sinus = cavity (a) is posterior at the atrial level, and it empties into the right atrium 9. Ischemia a. lack of blood flow and consequently low O2 b. weakens, but does not kill the cardiac tissue c. develops into angina pectoralis (1) pain in heart muscle, referenced to the surface of the body (2) repeated attacks weaken the heart, may lead to more trouble 10. Coronary Occlusion = "anastomoses" a. is the development of other vessels to deliver blood b. is dependant on size of vessel occluded (1) occurs where the vessel is greater than a small arteriole c. sudden occlusion = death of the tissue d. gradual occlusion promotes collateral circ. I. The Cardiac conduction system (learn sequence) A. SA node (sino atrial) 1. Normal sinus rhythm (NSR), the SA node is the primary pacemaker 2. it is located near the opening of the superior Vena Cava, within the right atrium's wall B. Internodal Pathways 1. located in the atrium 2. conduct +/- through the atrium, and eventually to the AV Junction 3. consists of three distinct pathways a. anterior tract (Bachman's Bundle) b. Middle tract (Wenkeback's) c. Posterior tract (Thorel's) C. AV Junction 1. consists of: a. AV Node (1) right posterior portion of the interatrial septum near the coronary sinus b. Bundle of His (1) slows down the conduction of the AV node so that the vent's can fill completely before contraction 2. connects the atria and the Vents a. is a +/- bridge D. Bundle Branches 1. either side of the septum a. the left => left ventricle (1) the left => 2 bundle branches (fascicles) because the left vent needs more blood flow (a) anterior and posterior b. the right => right ventricle E. Purkingie Fibers 1. continuous tracts of atypical muscle fibers than lie just below the endocardium a. contraction takes place inside out