HK 3810 Package 1 notes.docx

Be as permeable as it usually is we will lose a lot

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be as permeable as it usually is, we will lose a lot of K+ in the cell causing membrane potential to change due to the changes in [K+]in and [K+]out; therefore we must decrease our K+ permeability to prevent excess K+ loss from the cell Electrical System of the Heart Trigger for contraction is SA nodal cell Sinoatrial node is a spontaneous depolarizer/pacemaker (spontaneously depolarize at rate of 70-80 times/min) AP goes to atrial myocytes, change in membrane potential is linked to Ca2+, they will contract then atria will contract atrial myocytes are connected to AV node (spontaneously depolarize at rate of 40-60 times/min) AV node are electrically connected to bundle of His and bundle branches Bundle branches are connected to purkinje fibres Purkinje fibres (spontaneously depolarize at rate of 15-40 times/min) are connected to ventricular myocyte contracting ventricular myocytes are connected to other myocytes Why is resting heart rate 70-80 times/min? The SA node dictates heart rate because it’s the first one and it’s the fastest Changing Heart Rate Increasing heart rate is simply increasing rate of Na+ leak SNS NE increase permeability of nodal cells to Na+ increase in Na+ leak rate causing it to depolarize (closer to threshold) and reach threshold faster increase Aps/min and increase heart rate Decreasing heart rate is the effect of the PNS PNS Ach open Ach-dependent K+ channels hyperpolarize (more negative) takes more time to reach threshold fewer AP/min and decrease heart rate Effective refractory period – not absolute Effective refractory period is when voltage gated Na+ channels are in their open or inactive state When HR increases, cycle length and AP duration decreases, as well as refractory period shortens, so there is no absolute period of time that a refractory period is occurring; it shortens as AP duration shortens Molecular structure of proteins plays a role in this; for eg. changing voltage gated channels to different states based on demand or turning down K+ permeability ECG Tells about the electrical conductance of the heart, timing of electrical activity, HR P wave is atrial depolarization (due to SA node depolarization), then AV node, bundle of His, and purkinje fibres received the signal causing QRS wave, which is the ventrical depolarization, to occur, after this, the T wave occurs which is ventricular repolarization Amplitude and direction of the waves are not important; however it is important to examine the appearance and timing of these waves First degree block o Prolonged P-QRS interval o Should be <0.2 secs
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HK 3810 Package 1 Second degree block o Heart skips a beat o SA node started AP but something happened to AV node/bundle of His/purkinje fibres/ventricular myocytes o All QRS preceded by P but not all P are followed by QRS Third degree block o P waves are independent of QRS waves o P waves 70/min driven by SA nodal cells, QRS waves
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  • Fall '16
  • Coral Murrant
  • AP

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