Cardiovascular: Cardiac Cycle, Excitation and Contraction Flashcards
What are the five stages of the cardiac cycle
What do the heart sounds correspond to?
What is the purpose of the aorta being elastic?
- It helps smooth out pressure
- It helps maintain pressure (diastolic pressure only about 2/3 of systolic)
What is stroke volume?
The volume of blood ejected from the ventricle per beat
What is ejection fraction?
The % of blood ejected from the ventricle
Quick refresher on preload and afterload
Preload: The force with which the ventricular muscles contract
Afterload: The resistance from the vessels further down the line
Decribe the excitation pathway throughout the heart
- Rythm generated in the SA node
- Action potential activates atria
- Atrial AP activated the AV node
- AV node is slow conducting creating the delay of 0.1s so that the ventricles contract after the atria
- AV node activates bundle of his and then purkinje fibres
- Purkinje fibres activate the ventricles
What does the AV node activate?
Bundle of his and purkinje fibres
Using this graph of the action potential at the SA node. Describe how the different ions are involved in this actions potential and then the effects that adrenaline and acetylcholine have on these ions in order to affect heart rate
Difference between neurogenic and myogenic
Depending on where you listen to the heart, what will the first heart osund be caused by?
The first haert sound is that caused by the mitral (at the apex) and tricuspid (over the left sternal edge) closing.
How does skeletal muscle contract through calcium?
The action potential triggers the DHP receptor which is connected to a ryanodine receptor.
This releases stored calcium in the sarcoplasmic reticulum into the sarcoplasm.
This raised calcium leads to contraction
An ATPase pump then pumps calcium back into the sarcoplasmic reticulum and the muscle relaxes
How does cardiac muscle contract?
It is similar to skeletal in the sense the it needs a critical ammount of calcium in the sarcoplasm to contract.
However as well as the intracellular source from the sarcoplasmic reticulum it also has an external source through voltage gated calcium channels.
The slow influx of calcium from the extracellular space induces the rapid influx from the SR via a ryanodine receptor subtype 2. This is known as calcium induced calcium release.
The constant slow extracullar calcium source allows for a longer action potential and contraction.
Calcium is pumped back into SR through ATPase and in extracellular space through sodium exchangers.
Potassium will want to constantly leave as the charge is very positive inside and also the chemical gradient as potassium is getting pumped in in order to bring sodium out in order to exchange sodium back in for calcium out
