Lecture 9: Cardiac APs Flashcards
What is the circle of Willis?
Arteries on the brains inferior surface organised into a circle
What % of CO is used for kidneys?
20-25%
Kidneys are 0.5% of body weight - 50 fold over perfused vol/weight
Where is ACE made?
Kidney
Where is renin made?
Kidney
What % of adult body mass is skeletal muscle?
40%
What is isovolumic contraction?
When the left ventricle is contracting but its pressure is below that of the aorta
What is isovolumic relaxation?
When the LV is relaxing and its pressure falls below aortic pressure
Which valve opens at the end of IVC?
Aortic
Which valve opens at the end of IVR?
Mitral
Which valve closes at the beginning of IVC?
Mitral
Which valve closes at the beginning of IVR?
Aortic
What valve pathology causes decrease in preload and decrease in afterload?
Mitral stenosis
What valve pathology causes increase in afterload?
Aortic stenosis
What valve pathology causes increase in preload and decrease in afterload?
Mitral regurgitation
What valve pathology causes increase in preload?
Aortic regurgitation
When do delayed rectifier K+ channels open?
When the membrane depolarises
When do inward rectifier K+ channels open?
When the Vm goes below -60mV
(more open when the cells are at rest)
Anchors near Ek
What voltage is the threshold for an AP?
-50mV
At what voltage do the Na channels close?
+30mV
What is the difference between the after-hyperpolarisation and the refractory period?
After-hyperpolarisation = description of the membrane voltage
Hyperpolarisation = description of the cells functional state
What happens to permeability during AHP?
Increases K+ permeability and decreases Na+ permeability
What is the duration of a ventricular myocyte AP?
up to 500ms
Vary in duration and size - long refractory period so no tetany
What is the duration of a neural AP?
1ms
What causes the upstroke of the AP in SA node and AV node?
Ca (not Na like in ventricular myocytes)
What causes the instability of the resting potential of SA node?
Lack of inward rectifiers
What determines the rate of AP firing in the SA node or AV node?
Slope of the pacemaker potential
What type of channel is the If channel?
HCN
When does If current increase?
During hyperpolarisation
Leads to net inward current
What effect does a Na channel block have on the heart?
Reduced conduction velocity
No effect on HR
What effect does a Ca channel block have on the heart?
Decreased heart rate and decreased contractile force
