w2 The heart as a pump

Question 1

Draw an ECG and label the different segments/intervals.
Can is happening in each interval?*

Answer 1

Question 2

How long does each section of an ECG last in terms of seconds and squares on the ECG graph?

Answer 2

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.

Question 3

What is the difference between isometric v isotonic contraction?

Answer 3

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)

Question 4

How does isometric and isotonic muscle contraction work together?

Answer 4

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.

Question 5

What are the five different stages of cardiac contraction?

Answer 5

1) Passive ventricular filling
2) Atrial Ejection
3) Isovolumic ventricular contraction
4) Ventricular ejection
5) Isovolumetric ventricular relaxation.

Question 6

What happens during passive ventricular filling?

Answer 6

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

Question 7

What happens during atrial ejection?

Answer 7

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.

Question 8

What happens during isovolumic ventricular contraction?

Answer 8

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.

Question 9

What happens during ventricular ejection?

Answer 9

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.

Question 10

What happens during isovolumetric ventricular relaxation?

Answer 10

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.

Question 11

What creates the characteristic heart sounds?

Answer 11

Slamming shut of the AV valves during isovolumetric ventricular contraction (lub)
Slamming shut of the pulmonary and aortic valves during isovolumetric ventricular relation (dub)

Question 12

Explain the length tension relationship in the sacromere.

Answer 12

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.

Question 13

How does the length-tension relationship differ between the cardiac and the skeletal muscle?

Answer 13

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.

Question 14

What is Lmax for myocardial cells?

Answer 14

The length at which maximum tension is developed, normally around 2.2 micrometers.

Question 15

What is the velocity of shortening in cardiac muscle?
How is it affected by afterload?

Answer 15

The speed at which the sarcomere shortens.
Decreases as the afterload increases, (think greater afterload means less blood is ejected so less contraction)

Question 16

What is afterload and preload?

Answer 16

Afterload = the volume of blood left in the ventricles after it has contracted, this is equal to the aortic pressure
Preload = the volume of blood that sits in the ventricles before it contracts, this is the left ventricular end diastolic volume, this sets the length at which the muscle stretches hence the tension generated.

Question 17

Explain the following image.

Answer 17

Increasing the end diastolic volume will also increase the ventricular pressure for diastole and systole.
For diastole the end diastolic volume change has greatest effect at higher volumes, because the muscle is already stretched out (the empty ventricles must be filled before a change can be made)
The systole their is a greater effect at lower volumes, the muscle is already shortend, small changes will have a greater effect, becomes more difficult to short and already short thing).

Question 18

What is the basic principle of the Frank-Starling relationship?

Answer 18

The volume of blood ejected by the ventricle depends on the volume present in the ventricle at the end of diastole.
And vice versa.
This governs normal ventricular functioning and ensures the volume of the blood the heart ejects during systole is able to be replaced in diastole.

Question 19

What are the three parameters used t describe the function of the ventricles?

Answer 19

Stroke volume
Ejection Fraction
Cardiac output

Question 20

What is stroke volume?
How do you calculate it?

Answer 20

The volume of blood ejected by the ventricle on each beat.
= EDV - ESV
Normally 70ml

Question 21

What is ejection fraction?

Answer 21

The fraction of the end diastolic volume that is ejected as the stroke volume.
Normally 55%

Question 22

What is cardiac output?

Answer 22

The total volume of blood ejected by the ventricles in a unit of time (often per minute).

Question 23

What factors affect stroke volume?
How?

Answer 23

Preload - changes the length and tension within the cardiac muscle, intrinsic to the heart
Contractility - extrinsic to the heart, changes the force with which the heart beats.
Afterload - intrinsic to the heart, changes in afterload is indicative of changes in aortic pressure, hence how long the aortic valve remains open for.

Question 24

What is an inotropic effect?

Answer 24

changes the intrinsic ability of a myocardiocyte to develop tension at a GIVEN length.
Increasing contractility will increase the amount of pressure the ventricle is able to produce.
Positive inotropic effect - more contractility
Negative inotropic effect - less contractility.

Question 25

What can cause different inotropic effects?

Answer 25

Inotropic -changes in contractility +ve = sympathetic nervous system, catecholamines, increased Calcium availability -ve = beta blockers, calcium ion channel blockers, parasympathetic nervous system.

Question 26

What happens to stroke volume during a haemorrhage?

Answer 26

Originally a large blood loss causes a decrease in venous return so a smaller preload, this decreases the stroke volume by Frank Starling mechanisms. The sympathetic nervous system aims to counteract this by causing a positive inotropic effect (increasing contractility of the heart), this leads to a greater storke volume at the same EDV. However, can also stimulate tachycardia so less ventricular filling time so eventually decreases the EDV again leading to lower SV.

Question 27

Explain the sympathetic effects on force of contraction MOA.

Answer 27

Nor/adrenaline binds to beta adrenergic receptors. This causes the phosphorylation of calcium ion channels. This causes increased influx of calcium ions, hence stronger force of contraction and more actin/myosin cross-bridges are able to form. Relaxation is also quickened by increase Ca2+ active transport back into the SR reducing cytosolic calcium ion conc. This means more Ca2+ is stored for release so the next heart can beat sooner and stronger.

Question 28

How is ejection fraction related to contractability?

Answer 28

Increased ejection fraction indicates and increase in contractability. decrease = decrease.

Question 29

What are the different stages of the cardiac cycle on a ventricular volume pressure loop?

Answer 29

1. Atrial systole 2. Isovolumetric ventricular contraction 3. Rapid Ventricular ejection 4. Decreased ventricular ejection 5. Isovolumetric ventricular relaxation 6. Ventricular relaxation, followed by rapid the reduced ventriculae filling.

Question 30

When do the different valves open/close on a ventricular volume pressure loop?

Answer 30

A. mitral valve closes B. Aortic valve opens C. Aortic valve shuts D. Mitral valve opens

Question 31

How does increasing preload change the ventricular pressure loop?

Answer 31

Increasing preload means larger SV (Frank Starling mechanism) The pressure generated increases.

Question 32

How does increasing the afterload cause changes in the ventricular pressure volume loop?

Answer 32

Increased afterload leads to larger increase in pressure during contraction (length tension relationship) However, the stroke volume must decrease in order to maintain the higher afterload, so smaller decrease in volume during ventricular ejection.

Question 33

How does increased contractility affect the ventricular pressure volume loop?

Answer 33

Increased contractility means more blood is ejected from the ventricles and increased pressure in the ventricles during contraction. This increases the SV.

Question 34

How do different stages of the cardiac cycle relate to an ECG?

Answer 34

Atrial systole - P wave and PR segment Isovolumetric ventricular contraction - QRS complex Ventricular ejection (rapid) - ST segment Slow v, ejection and v relaxation - T wave Passive ventricular filling = the time between T wave and P wave in the next cycle.

Question 35

What are the four different heart sounds?

Answer 35

s1 - AV valves close (lub) s2 - pulmonary and aortic valves close (dub) S1 to s2 = systole. s2 to s1 = diastole s3 = occurs during early diastole, just after s2, caused by rapid filling of ventricles during diastole (called ventricular gallop) s4 = late diastole, just before s1, caused by atrial contraction forcing blood into the non compliant ventricles (Atrial gallop rhythm)