Lecture 12 & 13 - Biology 2A03 - L12 & L13 (heart...

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(heart relaxed) (heart contracts) Biology 2A03 - 1. Sequence of electrical events that triggers a heartbeat 1) AP Initialed in SA node 1. AV node 2) Transmission slows down at the AV node by ~0.15sec 1. 2. Slows so that Atria have to empty into ventricles 3) AP transmitted through the AV node to the Bundle of His 1. Divides into the left and right bundle branches 4) AP enters a network of branches along the ventricle muscle: Purkinje Fibers 1. Purkinje speed up APs 2. Impulse travels through ventricle from apex towards valves 3. Ventricles have coordinated contractions
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Biology 2A03 - 1. Both atrias contract together and ventricles contract together need heartbeat/APs to contract 2. You want ventricles to contract from the bottom up (squeezing a tube of toothpaste Regulation of Stroke Volume (SV) 1. Volume ejected by ventricles with each heartbeat = Stroke Volume (SV) SV = end diastolic volume (EDV) – end systolic volume (ESV) 1. Ejection fraction = SV / EDV 1. Ejection fraction - amount of blood heart is ejecting with a heartbeat 1. 67% at rest, increases during exercise 2. 33% of blood still left In the heart 3. SV can be regulated by changing amount heart receives when it is at rest 4. Not all blood is ejected in contraction Regulation of SV via EDV 1. All act through the Frank – Starling Law (intrinsic control)
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This note was uploaded on 03/26/2011 for the course BIOLOGY 2a03 taught by Professor Nurse during the Spring '10 term at McMaster University.

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Lecture 12 & 13 - Biology 2A03 - L12 & L13 (heart...

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