d as ventricles relax the pressure in the ventricular space drops this causes

D as ventricles relax the pressure in the ventricular

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d) as ventricles relax, the pressure in the ventricular space drops, this causes the AV valves to swing open since pressure in atria is now greater --blood rushes into the ventricles, initiating the 1st 1/3rd of ventricle filling (rapid filling) 2) P wave a) SA node fires, impulse travels throughout the 2 atria as myofibers depolarize b) as the P wave is halfway complete, the atria begin to contract/undergo systole (why not at the beginning of the P wave: it has taken a split second for the action potential to travel over the sarcolemma, through T-tubules to sarcomeres, and for the calcium to move troponin & tropomyosin out of the way) c) the AV valves are open; semilunar valves are closed d) after the initial flow, blood continues to flow into the ventricles at a slower rate (diastasis, the 2nd 1/3rd) --an enlarged P wave may indicate an enlarged atrium (which may result from a narrow AV valve as in mitral stenosis) 3) P-Q Interval ; measured from the beginning of the P wave to the beginning of Q a) after a delay at the AV node, the impulse travels through the AV bundle, right & left bundle branches, and conduction myofibers b) atria are in systole c) AV valves are open d) the last 1/3rd of ventricular filling as 30 ml is pumped to them; ventricles can pump 70% their capacity without atrial contraction, this is sufficient for survival
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11 4) QRS COMPLEX a) ventricular depolarization as impulse spreads over myofibers; has this odd shape because the 2 ventricles are different in size and they don't depolarize precisely together; the electrical event of atrial repolarization is hidden by this complex b) atria relax after repolarization; ventricles begin systole halfway into the QRS complex c) AV valves shut d) ventricular contraction, as contract, blood is pushed against the AV valves, forcing them shut --resulting blood turbulence results in "lubb" sound --this is isometric contraction (no shortening of the muscle, just an increase of force), increases ventricular pressure --an enlarged Q wave may indicate a myocardial infarction; enlarged R may indicate enlarged ventricles 5) S-T Segment , measured from the end of S to the beginning of T a) as ventricular myofibers plateau, the contraction is maintained b) atria are in diastole; ventricles in systole c) AV valves shut; semilunar valves open d) when ventricular pressure surpasses the pressure of the arteries running from them (80 mm Hg for the left ventricle, 15-20 mmHg for the right), the semilunar valves open --the amount of blood ejected (usually around 70 ml) is known as the stroke volume --ventricular ejection, requires .25 seconds -- as blood is ejected into aorta, its pressure rises from its minimum of 80 mm Hg to its maximum of about 120 mm Hg
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