w2 The heart as a pump Flashcards
Draw an ECG and label the different segments/intervals.
Can is happening in each interval?*
How long does each section of an ECG last in terms of seconds and squares on the ECG graph?
P wave - 4 mini squares
QRS Complex - 2 mini sqaures
T wave - 7 mini sqaures
PR interval - 8 mini squares
ST segment - 2 mini squares
Each mini square is 0.04 seconds.
What is the difference between isometric v isotonic contraction?
Isometric - the length of the muscle stays the same but the tension increases (straining to pick up a heavy bag)
Isotonic - the tension in the muscle stays the same but the length of the muscle changes.(moving the heavy bag)
How does isometric and isotonic muscle contraction work together?
Initially when the tension in the muscle in below the load isometric contraction occurs.
Eventually the tension is equal to the load on the muscle so isotonic muscle contraction can occur.
Allowing the load to be moved.
What are the five different stages of cardiac contraction?
1) Passive ventricular filling
2) Atrial Ejection
3) Isovolumic ventricular contraction
4) Ventricular ejection
5) Isovolumetric ventricular relaxation.
What happens during passive ventricular filling?
Pressure in the ventricles falls lower than the atria so the AV valves open.
Ventricles begin to passively fill with blood.
70% of blood enters the ventricles
What happens during atrial ejection?
Following the P wave atria contract.
Aortic and Pulmonary vaves are shut as pressure is higher in the arteries than the ventricles.
30% of blood enters the ventricles.
What happens during isovolumic ventricular contraction?
Following the QRS complex, ventricles start to contract.
Isometric contraction so volume in the ventricles does not change.
Pressure becomes higher in the ventricles than the atria so the AV valves slam shut. (lub)
Pressure is not yet high enough to open the atrial valves.
What happens during ventricular ejection?
Isotonic contraction occurs, and decreases the volume available in the ventricles so the pressure increases.
Pressure in the ventricles is now higher than the arteries so the aortic and pulmonary valves open.
Blood is ejected from the ventricles.
What happens during isovolumetric ventricular relaxation?
Following the T wave ventricles start to relax.
Pressure decrease and falls below that of the arteries, this causes the pulmonary and aortic valves to slam shut. (dub)
But ventricular pressure is still higher than the atria so the AV valves remain shut.
What creates the characteristic heart sounds?
Slamming shut of the AV valves during isovolumetric ventricular contraction (lub)
Slamming shut of the pulmonary and aortic valves during isovolumetric ventricular relation (dub)
Explain the length tension relationship in the sacromere.
Is a bell-shaped curve.
When the sarcomere is too short the actin and myosin overlap too much and are distorted poor crossbridge formation so poor tension.
Increasing length increases tension as less distortion and more cross bridge formation, this reaches a maximal value when all myosin is able to form a crossbridge.
Increasing the length further will decrease the tension as actin and mysoin will no longer overlap so cross bridges will be unable to form so no tension is generated.
NOTE: potential crossbridge formation, Ca2+ determines the actual amount formed.
How does the length-tension relationship differ between the cardiac and the skeletal muscle?
Cardiac muscle - only follows the ascending limb as is more stiff muscle so is a lot more difficult for the length to increase too much.
Cardiac muscle has a high resting tension meaning a small increase in length causing a large increase in resting tension.
What is Lmax for myocardial cells?
The length at which maximum tension is developed, normally around 2.2 micrometers.
What is the velocity of shortening in cardiac muscle?
How is it affected by afterload?
The speed at which the sarcomere shortens.
Decreases as the afterload increases, (think greater afterload means less blood is ejected so less contraction)