lecture15 - Lecture 15 The cardiac cycle 1.Ventricular...

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1 .Ventricular Filling. • venous blood passively fills atrium at beginning •pressure higher in atrium than ventricle (AV valve open), and blood flows into ventricle. semilunar valve closed •then the atrium contracts, forcing more blood into ventricle (small jump in pressure). 2 . Ventricles start to contract (start systolic phase). Both AV and semilunar valves now are closed. Closing of AV valve gives the first heart sound. Because the AV valve is closed no more blood is entering the ventricle. This is ventricular End Diastolic Volume . Because both valves are closed this is Isovolumetric Ventricular Contraction . 3. Pressure in ventricle now higher than in aorta. Semilunar valve opens, and Ejection Phase starts. Notice how ventricular volume decreases. 4 . Ventricles relax, start of ventricular diastolic phase. When ventricular pressure drops below aortic the semilunar valves close (second heart sound). Both valves are closed, thus: isovolumetric Ventricular Relaxation . Not all of the blood in the ventricle (End Diastolic Volume) is emptied during Ejection Phase. The blood remaining in ventricles is the End Systolic Volume. The amount of blood pumped by the ventricle in one heart contraction ( Stroke Volume ) is End Diastolic Volume minus End Systolic Volume. Lecture 15 The cardiac cycle
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response to exercise increased venous return increased arterial pressure increased cardiac output (up to seven fold) Control of Heart Rate Cardiac output : the amount of blood pumped by each ventricle per minute = heart rate (beats/minute) X stroke volume (end diastolic volume - end systolic volume). Both rate and stroke volume can be changed 0 -60 mV parasympathetic stimulation Parasympathetic stimulation decreases heart rate through innervation of heart. Parasympathetic Action: Vagus nerve innervates the SA and AV nodes and releases acetylcholine (ACh). The myocardial cells have the muscarinic receptor. Binding of ACh results in fewer If (also called F-type) channels opening. Also increases K+ permeability (hyperpolarizing). The pacemaker cells thus take longer to get to threshold.
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This note was uploaded on 02/14/2011 for the course MCDB 111 taught by Professor Smith during the Spring '11 term at UCSB.

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lecture15 - Lecture 15 The cardiac cycle 1.Ventricular...

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