The Cardiac Cycle Flashcards
What is the length of one cardiac cycle?
0.8s
What length of time of one cardiac cycle is spent in systole (ejecting the blood by contracting)
0.25s
What length of time of one cardiac cycle is spent in diastole (heart filling with blood by relaxing)
0.55s
What is the stroke volume of each beat?
70ml
What is the circulation time?
1minute because blood volume is 5L and CO = 5L/min
What kind of blood flow do the tissues require and why is this a problem when it comes to the contractility of the heart?
The require a smooth continue flow of blood and blood is pumped from the heart is 72 rapid squirts of 70ml blood
What ensures the tissues get a smooth constant supply of blood?
Keeping the vascular system under pressure
What is the pressure in the major arteries?
80mmHg
Qhat is the pressure at the start of the capillary bed?
35mmHg
What is the pressure at the end of the capillary bed?
15mmHg
What is the pressure in the veins?
5mmHg
what maintains the pressure gradient that allows a constant flow of blood?
A system of valves
What kind of valves are involved in maintaining the pressure in the vascular system?
Semilunar valves at the entrance to the aorta, the pulmonary artery and the large veins
What do the semilunar valves do?
Prevent back flow of blood
What is the blood pressure in the aorta at rest and what is this called?
Diastolic blood pressure at 80mmHg
What is the blood pressure in the aorta during contraction of the left ventricle and what is this called?
Systolic blood pressure at 120mmHg
What is pulse pressure?
The force that the heart generates each time it contracts (going from systolic to diastolic) so can be worked out by minusing diastolic from systolic so is 40mmHg
How do you work out the mean blood pressure?
Diastolic pressure (80) + 1/3rd pulse pressure (40/3=13) = 93mmHg
What are the atrio-ventricular valves and where are they found?
The tricuspid valve found between the right ventricle and right atrium and the bicuspid valve between the left ventricle and left atrium
Why are the atrioventricular valves held by chordae tendinae attached to pappilary muscles?
To stop them being blown out during ventricular contraction
How much more pressure does the left ventricle work at compared to the right?
5 x the pressure
What is the dicrotic notch?
When the pulmonary artery and the aorta show a secondary rise in pressure when the semilunar valves shut
What is the reason for the dicrotic notch?
Because closing of the valves leads to elastic recoil in the PA and A which causes further pressure change
Does the heart empty upon ventricular contraction
No 70ml of blood of risidual volume is left when 70ml of blood is pumped out (stroke volume) from the 140ml of blood in the heart
Would a sudden change in heart beat upon ventricular filling affect this process?
No because most of the filling occurs within the first 1/3rd of diastole
What are the three requirements for contraction of the heart?
- Left and right atrium must contract synchoniously
- Left and right ventricles must contract synchronisouly
- Ventricles must contract after atria
Where is the origin of the heartbeat?
In the sino atrial node
Where is the sino atrial node located?
In the right atrium
What ensures synchoronised contraction of the left and right atriums?
Rudimentary conducting bundles connecting the two atria ensure rapid conduction and synchronised contraction
Why cant the conduction go straight to the ventricles?
Because of the insulating connective tissue
How long after the origin in the SA node does it travel to the AV node?
0.04s
How long is the conduction delay at the AV node and why is there a delay?
0.125s and because of the small diameter of the conducting cells
Where does excitation then go after the AV node?
Through to the ventricles
What is the reason for the excitation spreading from the AV node to the ventricles?
Large diameter purkinje cells leave from the AV node and split at the bundle of His into the left and right bundle branches to spread excitation to the ventricles
Where does the excitation spread through the ventricles end up and what is the reason for the whole ventricle contracting?
In the cardiac cells (myocytes) which have membrane between them for cell to cell communication
What does the vagus nerve of the parasympathetic nervous system act on in order to slow the heart beat?
The SA and AV nodes
What kind of effect does the vagus nerve have on the SA node?
A negative chronotropic effect
What is a chronotropic effect?
A change in heart rate (chronos = time)
What effect does the vagus nerve have on the AV node?
A negative dromotropic effect
What is a dromotropic effect?
Changes in condction
What parts of the heart does the sympathetic nervous system act on?
- The SA node
- The AV node
- Ventricles
How does the sympathetic nervous system affect the SA node?
Positive chronotropic effect (increase in heart rate)
How does the sympathetic nverous system affect the AV nodes?
Postivie dromotropic effect (increase conduction)
What two effects does the sympathetic nervous system have on the ventricles?
Positive ionotropic effect (increased contractility) and positive leucitropic effect (increased relaxation rate)
What is the consequence of the excitation of numerous cardiac cells during the electrical conduction of the heart?
An electrical field is generated
What are the three areas on the electrocardiogram?
The P wave
The QRS complex
The T wave
What happens during the P wave
The atria contraction (depolarisation)
What happens during the QRS complex
The ventricles contract (depolarisae) andwhich blocks out the artia relaxing (repolarising)
What happens during the T wave
The ventricles relax (repolarise)
