Cardiovascular System, Lecture 3

Question 1

Phases, pressure and valves - systole and diastole

Answer 1

phases named for ventricular events:
systole - ventricular contraction and ejection
- isovolumetric ventricular contraction (same volume) - valves are all closed because volume is staying the same; no ejection (no blood coming in or out)
- ventricular ejection (semiulnar is open but atrioventricular remains closed) - blood flows out of the ventricle
diastole - ventricular relaxation and filling
- isovolumetric ventricular relaxation: the conditions are exactly the same, the valves are both going to be closed when relaxing
- ventricular filling: majority of the filling prior to the atrial systole and remaining filling during atrial systole (blood flows into ventricles)
* AV valve for bringing blood flowing in and Aortic and pulmonary valves for blood flowing out

Question 2

Atrioventricular valve & Semiulnar valve

Answer 2

Atrioventricular valve:
* Valve open – forward flow – atrial pressure > ventricular pressure.
* Valve closed – preventing backward flow –
papillary muscles contract pulling chordae
tendineae attached to cusp (draws cusp edges
closed).
Semilunar valve:
* Valve open – forward flow – ventricle pressure >
blood vessel pressure (either ascending aorta or
pulmonary trunk depending on side of heart).
* Valve closed – preventing backward flow – blood
filling cusps (draws cusp edges closed).

Question 3

Conduction system

Answer 3

99% cardiac muscle cells - contractile
1% cardiac muscle cells (what the muscular part of the heart is composed of) - specialized to initiate and transmit electrical impulses
- form a conduction system (yellow)
- initiation in right atrium to termination with right and left ventricular contraction

Question 4

Nerve Conduction

Answer 4

• resting potential: membrane potential prior to stimulation (-70 is common seen number)
• there are failed initiations as well before it reaches threshold
• if a stimulus reaches threshold (-55) generates an action potential (AP):
  - depolarization: membrane potential becomes less negative relative to resting level (going in a positive direction)
  - repolarization: membrane potential returns to resting level after depolarization (going back down)
• action potential (APs) can propagate (signal spreads) from initial generation (get signal to move along)

Question 5

Conduction System - pacemaker

Answer 5

SA or sinoatrial node:
* “Pacemaker”; generates APs resulting in a heart beat
* No steady resting potential; a slow depolarization (pacemaker potential; cardiac muscle cells are autorhythmic)
* Pacemaker potential brings to threshold where APs are generated
Signal not starting in SA node – ectopic focus.
* Common triggers: anxiety, lack of sleep, excess caffeine, nicotine, alcohol