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Transcript
Heart & Neck Vessels—A&P Taylor, ch 25 Jensen ch 17 Anatomy of the Heart Coronary Arteries Coronary Circulation • Coronary arteries are first branches of aorta at sinuses of Valsalva. • Provides blood supply to heart during diastole (during resting phase or in between beats). • Has left and right coronary branches Left Coronary Artery • 2 branches: – Left circumflex—goes to left atrium, lateral and posterior ventricles – Left anterior descending (“widow maker”)— goes to anterior and apex of LV, anterior septum, bundle of His, right and left bundle branches Right Coronary Artery & Venous Drainage • Goes to RA, RV, SA and AV nodes, posterior and septum • Venous drainage is done by coronary sinus, cardiac veins, and thesbian veins Physiology of the Heart Blood Flow • Realize that blood flow within the heart is bilateral • Following one deoxygenated RBC: – From body—IVC—RA—tricuspic valve— RV—pulmonic valve—pulmonary artery— lungs—pulmonary vein—LA—mitral valve— LV—aortic valve—aorta—to body Direction of Blood Flow Cardiac Cycle • Systole—ventricular contraction—corresponds to “lub” sound which is closure of AV valves. This is the S1 part of cycle. • Diastole—relaxation phase and atrial contraction-corresponds to “dub” sound which is closure of semilunar valves. This is the S2 part of cycle. • S3 is aortic valve closing just before pulmonic So…to put it together…. • Blood from the vena cava and pulmonary artery flows into both atria when ventricles are relaxed and AV (tricuspid and mitral) valves are open. • Atria have higher pressure than ventricles so blood pours into ventricles (passive filling). • When 75% of blood is in ventricles, other 25% is pushed in by “atrial kick” (active filling). • When ventricles are full, the stretch on the chordae tendinae cause the AV valves to snap shut causing the first heart sound (S1). And then……… • Pressure in ventricles is greater than pressure in great vessels (pulmonary artery and aorta) so… • Milliseconds later, the semilunar valves (pulmonic and aortic) open, and the ventricles contract. • Blood is forced thru the great vessels. • When pressure is low in ventricles, semilunar valves snap shut, causing the second heart sound (S2). Preload & Afterload • Preload—amount of stretch in ventricles at end of diastole • Afterload—resistance in great vessels against which ventricles must pump blood into circulation Cardiac Output • Cardiac output = Stroke Volume x Heart Rate • Stroke volume 70 mL/beat; 4-7 L/min; exercise 20 mL/min. SV is determined by preload, afterload, and contractility • Starling’s Law—greater the stretch, the stronger the contraction • Heart rate is controlled by ANS, CNS, and baroreceptors in heart • Ejection fraction is % of blood ejected by ventricles in one contraction Chemical Conduction • Contraction depends on exchange of ions across the myocardial cell membrane— Na+, K+, Ca++ • Polarization—cell is ready to contract with ions in place • Depolarization—ventricular contraction • Repolarization—resting phase during which ions are moving back to polarization state Cardiac Conduction • Depolarization causes the myocardium to contract • Sodium ions enter cells altering permeability of cell membrane to calcium • Calcium enters cells and is released from intracellular stores • Repolarization occurs as cells return to baseline or resting state resulting in relaxation of muscle Conduction Pathway Conduction and the ECG Conduction & the ECG ECG Interpretation • P wave represents atrial depolarization • QRS complex represents ventricular depolarization • T wave represents ventricular repolarization • U wave may represent repolarization of Purkinje fibers. May also be seen in hypokalemia, hypertension, or heart disease • PR interval normal range is 0.12-0.20 seconds • ST segment is identified as isoelectric, or above or below isoelectric line • QT interval normal range is 0.32-0.40 seconds • TP interval is isoelectric period • PP interval signifies atrial rhythm and rate • RR interval signifies ventricular rate and rhythm Neck Vessels • Carotid artery: – – – – – Transports blood to brain 2nd branch of aorta Pulsations are visible Palpated between thyroid cartilage and SCM Coincides with apical pulse Neck Vessels cont’d • Jugular veins: – Drain head and neck – Return blood to heart via superior vena cava (SVC) – Internal is visible in sternal notch in supine position – External may be visible superior to clavicle, but is difficult to see unless pt is in heart failure Developmental Differences: Fetal Circulation Review • 3 anatomical differences from adult : – Foramen ovale—closes within 1 hr after birth – Ductus arteriosus—closes within 12-15 hrs – Ductus venosus • Blood flow differences: – Returning blood enters RA—60% goes thru foramen ovale to LA to LV, then to aorta – 40% goes to RV into PA, but only 10% goes to lungs. 30% goes to aorta Differences: Infants and Children • • • • • PMI at 4th ICS, MCL until 7 yrs of age Sinus arrhythmia throughout childhood Split S2 Faster pulse: 160 to 90 Lower BP: 70/40 to 110/70 Differences: Older Adults • SBP increases 40 mm d/t arterial wall changes causing slight enlargement of LV. No change in DBP. • More likely to have arrhythmias, murmurs, extra sounds, bruits, activity intolerance, atypical MI sx, and orthostatic BP Cultural Differences • All CV risk factors are higher among Blacks and Hispanics and lower in Asians and Pacific Islanders. • Incidence of HD is higher in both male and female African Americans than in other groups and Latino women have higher incidence than white women.