PHYS: Heart as Pump & Electrical Activity Flashcards
Blood flow goes from an area of ___ pressure to ___ pressure.
High pressure to low pressure.
Right heart dealing with blood at low pressure.
Right part less muscular.
RHS pumps blood into arterial system.
Blood drived all over body and through capillary beds (pre-capillary sphincters).
Pressure to drive blood to all places at once is VERY high.
LHS has two valves. what are they?
Diastole = state of relaxation.
–> pressure in L ventricle drops below pulmonary system, atrioventricular valve passively opens and blood flows in.
Systole
–> huge amount of pressure generated. Eject blood into the aorta. Increased pressure in the aorta.
When blood exits ventricle, it HAS to go the other way.
Heart sounds characteristic of different pathologies.
Pathology: Valves have hardened eg stenosis (whistling)
Insufficient valves = gurgling
Describe the cardiac cycle
Heart is a cyclic organ.
Ventricular diastole = nice and relaxed. Heart ready to receive new blood.
Ejection fraction = 70%?
Ventricle at lower pressure than atrium. P difference causes atrioventricular valves forced to be open.
(Speed up heart rate –> not as much time to passively fill the ventricles)
Ventricular filling is passive.
Need atrial systole (contraction).
VENTRICULAR SYSTOLE
Both contract (ventricles) at the same time
Cardiac muscle contracts all in unison. Kicks off at the apex and spreads. That increases the pressure inside ventricles. Pressure in ventricle > Pressure in atrium. Closed system now. Pressure skyrockets. Keeps happening until p_ventricle > p_aorta. Pulmonary and aortic valve snap open. This causes ventricular ejection.
Mononuclear
Intercalated discs
Small branching cells
Cells need to be held together by desmosomes, important for contractile cells
Gap junctions in intercalated discs; holes that ions can go through. Direct electrical connection in all muscle cells in that aprt of the heart.
Weird looking AP.
Depolarisation: rapid (causes by Na channels)
Repolarisation: caused by K channels. Plateau in the middle. Cardiac APs also use calcium channels. Bridge in between de and repolarisation. The function is extending the action potential.
These are called L-type voltage-dependent Ca2+ channels. Open and close slowly.
Cardiac AP is about 100 ms (don’t need to know)
Ca channel in cardiac muscles are different to the ones in skeletal muscle. AP opens calcium channel. A little bit of calcium goes in. This opens up the SR Ca2+ channel. Ca/Na exchanger pump that keeps Ca out. Also, ATPase channel to keep Ca out.
REFRACTORY PERIOD
Need to prevent cardiac muscle cells from undergoing tetanus. Ridiculously long refractory period where cells deactivated longer than usual (skeletal muscle and nerve cells). About 250 ms. This means we MUST have a maximum HR (only so many beats we can get out of that)
Some cells are depolarising during the heartbeat. Rhythmic action potentials. Cells do it to themselves.
Sinoatrial node (SA node)
- Highest rate of depolarisation. This spreads between left and right atria. Spreads to AV node.
Atrioventricular node (AV node)
- Conducting system that goes down to ventricles.
- Squeeze blood UP, when you get contraction.
Self-excitation
Leaky Na/K channels - slowly allow sodium to flux in, rise in membrane potential –> AP generated. L type channels and T [FAST] channels.
RMP very close to threshold *important* not much needed to “kick it all of”
SA AP
- Pre potential phase. Na slowly leaks into the cell.
Important to slow down gap between atrial and ventricular contraction
–> trying to slow down conduction pathways
–> 1 m/s
Contract from the top and goes down.
Bundle of His(?)
Initiates at apex
Spreads up through each ventricle
Synchronous and simultaneous contraction between L and R ventricle
low calcium involvement at sinoatrial node
huge amount of involvement at the ventricles
Most cells in the heart have autorhythmicity
SA node depolarises first
If SA fails, you don’t lose heart contraction.
–> AV node takes over - relatively respectable HR. Can function with an ablated SA node.
ANS innervates the pacemakers.
ACh from the PSNS innervates the pacemakers. ACh dumped on the SA nodes. Good at slowing down HR.
NA from the SNS dumped everywhere.
Sitting around with a HR of 60 = parasympathetic dominant.
- What do ECGs record?
- What is significant about the amplitude?
- P wave?
ECG records change in electrical potential
Amplitude of the change = how much surface area of change
P wave = atrial depolarisation.
QRS wave = ventricle depolarisation. Because ventricles are massive.
T wave = repolarisation of our ventricles. Area under the curves QRS and T SHOULD be the same.
Atrial repolarisation during the same time as the QRS wave. Gaps between waves tell us how fast impulses are transmitted.
PR interval = how long does it take for the electrical impulse to get from AV node to ventricles.
QT interval = tells us something about ion handling.
Look at rate, rhythm, cardiac myopathies.
