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IMF-007-01-0001-en	Why do sinoatrial pacemaker cells have no stable resting voltage?	During diastole inward current through hyperpolarisation-activated channels, reduced potassium efflux, and calcium entry depolarise the membrane toward threshold.	Integrated Medical Foundations; chapter 7, TTS module 1; https://theisegoria.github.io/medical-textbook/integrated-medical-foundations-expanded-english.md; module SHA256 at export: 7553fbbb3c6c47c9cf4b25a70b38c39520180dabeac8df9c7ee40a4a384db00e; editorial review pending	imf lang::en chapter::007 module::007-01 review::pending
IMF-007-01-0002-en	Which ionic current generates most of the upstroke in nodal tissue, and what determines heart rate?	Calcium currents generate much of the nodal upstroke; the slope of spontaneous diastolic depolarisation helps set the rate.	Integrated Medical Foundations; chapter 7, TTS module 1; https://theisegoria.github.io/medical-textbook/integrated-medical-foundations-expanded-english.md; module SHA256 at export: 7553fbbb3c6c47c9cf4b25a70b38c39520180dabeac8df9c7ee40a4a384db00e; editorial review pending	imf lang::en chapter::007 module::007-01 review::pending
IMF-007-01-0003-en	What is the mechanical purpose of slow conduction through the atrioventricular node?	It lets atrial contraction contribute to ventricular filling before ventricular systole begins.	Integrated Medical Foundations; chapter 7, TTS module 1; https://theisegoria.github.io/medical-textbook/integrated-medical-foundations-expanded-english.md; module SHA256 at export: 7553fbbb3c6c47c9cf4b25a70b38c39520180dabeac8df9c7ee40a4a384db00e; editorial review pending	imf lang::en chapter::007 module::007-01 review::pending
IMF-007-01-0004-en	Why does the normal activation sequence reach the septum and apex before much of the free wall?	The His bundle, bundle branches and Purkinje fibres distribute activation rapidly in that order, which produces efficient ejection.	Integrated Medical Foundations; chapter 7, TTS module 1; https://theisegoria.github.io/medical-textbook/integrated-medical-foundations-expanded-english.md; module SHA256 at export: 7553fbbb3c6c47c9cf4b25a70b38c39520180dabeac8df9c7ee40a4a384db00e; editorial review pending	imf lang::en chapter::007 module::007-01 review::pending
IMF-007-01-0005-en	What produces the plateau of the ventricular action potential?	Calcium entry through L-type channels balancing potassium efflux; delayed potassium currents then complete repolarisation.	Integrated Medical Foundations; chapter 7, TTS module 1; https://theisegoria.github.io/medical-textbook/integrated-medical-foundations-expanded-english.md; module SHA256 at export: 7553fbbb3c6c47c9cf4b25a70b38c39520180dabeac8df9c7ee40a4a384db00e; editorial review pending	imf lang::en chapter::007 module::007-01 review::pending
IMF-007-01-0006-en	Why does cardiac muscle need a long action potential and refractory period?	They prevent sustained tetanic contraction, so the chambers can fill and eject rhythmically.	Integrated Medical Foundations; chapter 7, TTS module 1; https://theisegoria.github.io/medical-textbook/integrated-medical-foundations-expanded-english.md; module SHA256 at export: 7553fbbb3c6c47c9cf4b25a70b38c39520180dabeac8df9c7ee40a4a384db00e; editorial review pending	imf lang::en chapter::007 module::007-01 review::pending
IMF-007-01-0007-en	Trace the effects of sympathetic beta one receptor activation on the heart.	Cyclic adenosine monophosphate rises, pacemaker depolarisation steepens, atrioventricular conduction speeds, and calcium handling and contractility increase.	Integrated Medical Foundations; chapter 7, TTS module 1; https://theisegoria.github.io/medical-textbook/integrated-medical-foundations-expanded-english.md; module SHA256 at export: 7553fbbb3c6c47c9cf4b25a70b38c39520180dabeac8df9c7ee40a4a384db00e; editorial review pending	imf lang::en chapter::007 module::007-01 review::pending
IMF-007-01-0008-en	How does acetylcholine slow the heart?	Through muscarinic receptors it slows sinoatrial firing and atrioventricular conduction.	Integrated Medical Foundations; chapter 7, TTS module 1; https://theisegoria.github.io/medical-textbook/integrated-medical-foundations-expanded-english.md; module SHA256 at export: 7553fbbb3c6c47c9cf4b25a70b38c39520180dabeac8df9c7ee40a4a384db00e; editorial review pending	imf lang::en chapter::007 module::007-01 review::pending
IMF-007-01-0009-en	Describe calcium-induced calcium release in a cardiac myocyte.	Depolarisation opens L-type calcium channels in transverse tubules, and the incoming calcium triggers a larger release from the sarcoplasmic reticulum through ryanodine receptors.	Integrated Medical Foundations; chapter 7, TTS module 1; https://theisegoria.github.io/medical-textbook/integrated-medical-foundations-expanded-english.md; module SHA256 at export: 7553fbbb3c6c47c9cf4b25a70b38c39520180dabeac8df9c7ee40a4a384db00e; editorial review pending	imf lang::en chapter::007 module::007-01 review::pending
IMF-007-01-0010-en	What does cytosolic calcium bind in the myofilament, and what follows?	Troponin C; tropomyosin then moves and actin-myosin cross-bridge cycling proceeds.	Integrated Medical Foundations; chapter 7, TTS module 1; https://theisegoria.github.io/medical-textbook/integrated-medical-foundations-expanded-english.md; module SHA256 at export: 7553fbbb3c6c47c9cf4b25a70b38c39520180dabeac8df9c7ee40a4a384db00e; editorial review pending	imf lang::en chapter::007 module::007-01 review::pending
IMF-007-01-0011-en	Which three mechanisms remove calcium to permit relaxation?	Sarcoplasmic-reticulum pumps, sodium-calcium exchange, and membrane calcium pumps.	Integrated Medical Foundations; chapter 7, TTS module 1; https://theisegoria.github.io/medical-textbook/integrated-medical-foundations-expanded-english.md; module SHA256 at export: 7553fbbb3c6c47c9cf4b25a70b38c39520180dabeac8df9c7ee40a4a384db00e; editorial review pending	imf lang::en chapter::007 module::007-01 review::pending
IMF-007-01-0012-en	What does the P R interval include?	Atrial conduction together with delay through the atrioventricular node.	Integrated Medical Foundations; chapter 7, TTS module 1; https://theisegoria.github.io/medical-textbook/integrated-medical-foundations-expanded-english.md; module SHA256 at export: 7553fbbb3c6c47c9cf4b25a70b38c39520180dabeac8df9c7ee40a4a384db00e; editorial review pending	imf lang::en chapter::007 module::007-01 review::pending
IMF-007-01-0013-en	What do the S T segment and the T wave correspond to?	The S T segment corresponds broadly to the ventricular plateau and the T wave to ventricular repolarisation.	Integrated Medical Foundations; chapter 7, TTS module 1; https://theisegoria.github.io/medical-textbook/integrated-medical-foundations-expanded-english.md; module SHA256 at export: 7553fbbb3c6c47c9cf4b25a70b38c39520180dabeac8df9c7ee40a4a384db00e; editorial review pending	imf lang::en chapter::007 module::007-01 review::pending
IMF-007-01-0014-en	Name three things an electrocardiogram does not directly show.	Contraction, cardiac output, and coronary anatomy.	Integrated Medical Foundations; chapter 7, TTS module 1; https://theisegoria.github.io/medical-textbook/integrated-medical-foundations-expanded-english.md; module SHA256 at export: 7553fbbb3c6c47c9cf4b25a70b38c39520180dabeac8df9c7ee40a4a384db00e; editorial review pending	imf lang::en chapter::007 module::007-01 review::pending
IMF-007-01-0015-en	What arrhythmia can excessive corrected Q T prolongation permit, and through what mechanism?	Torsades de pointes, by allowing early afterdepolarisations; bradycardia, low potassium, low magnesium, interacting drugs and channel variants predispose.	Integrated Medical Foundations; chapter 7, TTS module 1; https://theisegoria.github.io/medical-textbook/integrated-medical-foundations-expanded-english.md; module SHA256 at export: 7553fbbb3c6c47c9cf4b25a70b38c39520180dabeac8df9c7ee40a4a384db00e; editorial review pending	imf lang::en chapter::007 module::007-01 review::pending
IMF-007-01-0016-en	Define stroke volume and ejection fraction in terms of ventricular volumes.	Stroke volume is end-diastolic volume minus end-systolic volume; ejection fraction is stroke volume divided by end-diastolic volume.	Integrated Medical Foundations; chapter 7, TTS module 1; https://theisegoria.github.io/medical-textbook/integrated-medical-foundations-expanded-english.md; module SHA256 at export: 7553fbbb3c6c47c9cf4b25a70b38c39520180dabeac8df9c7ee40a4a384db00e; editorial review pending	imf lang::en chapter::007 module::007-01 review::pending
IMF-007-01-0017-en	What produces the first heart sound, and what happens during isovolumetric contraction?	Closure of the mitral and tricuspid valves when ventricular pressure exceeds atrial pressure; with all valves shut, volume is constant while pressure rises rapidly.	Integrated Medical Foundations; chapter 7, TTS module 1; https://theisegoria.github.io/medical-textbook/integrated-medical-foundations-expanded-english.md; module SHA256 at export: 7553fbbb3c6c47c9cf4b25a70b38c39520180dabeac8df9c7ee40a4a384db00e; editorial review pending	imf lang::en chapter::007 module::007-01 review::pending
IMF-007-01-0018-en	Why does extreme tachycardia impair both filling and coronary supply?	The cycle shortens with disproportionate loss of diastolic time, and left-ventricular coronary flow occurs predominantly during diastole.	Integrated Medical Foundations; chapter 7, TTS module 1; https://theisegoria.github.io/medical-textbook/integrated-medical-foundations-expanded-english.md; module SHA256 at export: 7553fbbb3c6c47c9cf4b25a70b38c39520180dabeac8df9c7ee40a4a384db00e; editorial review pending	imf lang::en chapter::007 module::007-01 review::pending
IMF-007-01-0019-en	Why can ejection fraction look reassuring in significant mitral regurgitation?	Volume ejected during systole includes backward flow into the atrium as well as forward flow into the aorta, so effective forward output is lower than the fraction suggests.	Integrated Medical Foundations; chapter 7, TTS module 1; https://theisegoria.github.io/medical-textbook/integrated-medical-foundations-expanded-english.md; module SHA256 at export: 7553fbbb3c6c47c9cf4b25a70b38c39520180dabeac8df9c7ee40a4a384db00e; editorial review pending	imf lang::en chapter::007 module::007-01 review::pending
IMF-007-01-0020-en	Why does acute severe mitral regurgitation cause breathlessness when chronic regurgitation may not?	An unadapted atrium develops a large pressure rise transmitted toward the pulmonary circulation, whereas chronic atrial enlargement and increased compliance absorb the volume first.	Integrated Medical Foundations; chapter 7, TTS module 1; https://theisegoria.github.io/medical-textbook/integrated-medical-foundations-expanded-english.md; module SHA256 at export: 7553fbbb3c6c47c9cf4b25a70b38c39520180dabeac8df9c7ee40a4a384db00e; editorial review pending	imf lang::en chapter::007 module::007-01 review::pending
IMF-007-01-0021-en	What is preload, and what does the Frank-Starling mechanism do with it?	Myocardial fibre stretch before contraction, related to end-diastolic volume; within a physiological range increased filling increases contraction force, matching stroke volume to venous return.	Integrated Medical Foundations; chapter 7, TTS module 1; https://theisegoria.github.io/medical-textbook/integrated-medical-foundations-expanded-english.md; module SHA256 at export: 7553fbbb3c6c47c9cf4b25a70b38c39520180dabeac8df9c7ee40a4a384db00e; editorial review pending	imf lang::en chapter::007 module::007-01 review::pending
IMF-007-01-0022-en	Contrast the remodelling produced by chronic pressure load and chronic volume load.	Pressure load promotes concentric hypertrophy; volume load tends to promote chamber dilation and eccentric remodelling.	Integrated Medical Foundations; chapter 7, TTS module 1; https://theisegoria.github.io/medical-textbook/integrated-medical-foundations-expanded-english.md; module SHA256 at export: 7553fbbb3c6c47c9cf4b25a70b38c39520180dabeac8df9c7ee40a4a384db00e; editorial review pending	imf lang::en chapter::007 module::007-01 review::pending
IMF-007-01-0023-en	Why must increased myocardial oxygen demand be met almost entirely by increased coronary flow?	The myocardium already extracts a high fraction of delivered oxygen at rest, so extraction cannot rise much further.	Integrated Medical Foundations; chapter 7, TTS module 1; https://theisegoria.github.io/medical-textbook/integrated-medical-foundations-expanded-english.md; module SHA256 at export: 7553fbbb3c6c47c9cf4b25a70b38c39520180dabeac8df9c7ee40a4a384db00e; editorial review pending	imf lang::en chapter::007 module::007-01 review::pending
IMF-007-01-0024-en	What three conditions does re-entry require?	A circuit, unidirectional block, and conduction timing slow enough for previously refractory tissue to recover and be re-excited.	Integrated Medical Foundations; chapter 7, TTS module 1; https://theisegoria.github.io/medical-textbook/integrated-medical-foundations-expanded-english.md; module SHA256 at export: 7553fbbb3c6c47c9cf4b25a70b38c39520180dabeac8df9c7ee40a4a384db00e; editorial review pending	imf lang::en chapter::007 module::007-01 review::pending