Cardio L1 Flashcards
What is the cardiac cell built of ?
Cells ( cardiomyocytes )
Which are divided into 3 types
What is the cardiomyocytes classification?
1- contractile
2- conductive
3- secretory
Explain the contractile cells
- Contractile ( typical , working ) cardiomyocytes they make up 99% of myocardium mass ,
- their contractile structure ( sarcomeres , calcium depots ) have a structure similar to a skeletal muscle ,
- all these cardiomyocytes are interconnected by nexuses A nexuses has a low threshold (high excitability) so excitement of one cardiomyocytes will necessarily cause excitement on neighbouring ones and further to all other cardiomyocytes which will cause contraction of the whole myocardium therefore syncytium
What is the nexuses ?
A nexuses its connect the cardiomyocytes with each other and have low threshold
What is the functional syncytium ؟
Its means that all cardiomyocytes contract simultaneously as one cell
Explain the conductive cells
Conductive (atypical , specilazed ) cardiomyocytes are practically unable to contract and make prat of the conductive system of the heart generating in the heart its own impulsion and transmitting these impulses on contractile cardiomyocytes, that means they perform the function of neurons
Explain the secretory cells
They are located in the atria and perform the function of the glands , producing natrutric hormons
- this hormone increase diuresis by excretion of water and electrolytes with urine
- thereby natriutric hormone lowers the blood pressure so its reducing the volume of circulating blood
Classification of cardiac muscles properties
- specific
- non specific
Explain the non-specific properties of the cardiac muscle
- generation of action potential
- conductivity
- contractility
Explain the specific properties of the cardiac muscle
1-Automatism
2- long refectory period
3- inability to tetanic contraction
4- functioning by the principal- all or nothing
Explain the automatism of cardiac muscle
Its the ability to get self excitement
Without getting outside cell irritation from neurons ,
- automatism if the cardiac muscle is extremely high , a heart removed from the body ( in virto ) continues to contract , this is provided by which so called diastolic depolarisation if atypical cardiomyocytes
What is the long refectory period
Inability to respond to a series of stimuli
What is the inability to tetanic contraction ?
Is the ability to contracts for long term without complete relaxation in respons to a series stimuli
The specific properties provided by ?
Special action potential
In the healthy heart where is the excitation arises from and how it goes ?
In the healthy heart the excitation arises only in the sino-atrial node , then it spreads by the conductive system , covering the whole myocardium
Explain the difference between Skeletal AP and cardiomyocytes AP
1- the absence of slow depolaraztaion phase ( depolarization is only one stage and always complete )
2- depolarization developed not by sodium but by calcium ( sodium poorly effect the heart but calcium preparations can alter significantly its activity.
3- Repolarization develops in 3 stages ( initial stage is quick , then plateau phase , and the final one is quick )
4- long action potential ( the action potential of the cardiac muscle lasts 0,3 sec (300ms) , the action potential of the skeletal muscle only 0,003 sec (3ms)
What is the phases of cardiac action potential?
1- depolarization ( fast)
2- the initial rapid repolaraztion
3 the plateau phase
4 - finite ( fast ) repolaraztion
What is the greatest deference of AP of skeletal muscles and AP of cardiac
Its the plateau phase
— in this phase the charge of a cardiomyocytes dose not change for a long time and its almost equal to total depolarisation , if at this point of time will come another even suprathreshould irritation , then there will be no new depolarisation
What is the refractoriness
Its inability to respond to additional irritation
What is the mechanism of prologend refractoriness ?
Action potential of cardiomyocytes lastes 0,3 sec , plateau phase takes 0,27 sec and therefore almost for the whole time if action potential generation a cardiomyocytes is in a state if absolute refractoriness
- thats mean if there is another irritation even suprathreeshould one there will be no additional contraction , each subsequent contraction starts only after the contraction to previous irritation finish
Explain the mechanism of diastolic depolarazation
Even at rest i. The diastole , part of sodium channel atypical cardiomyocytes remains partially open , a slow entry of sodium and slow depolarisation are observed, as soon as it reach the critical level , generation of completed action potential take place , thus atypical cardiomyocytes differ from contractile ones in that they have slow depolarisation phase called the diastolic depolarisation
Explain the working of the principle ‘ all or nothing “
— As we know that under this law individual cells work , tissue work in accordance with law of force , myocardium is a tissue but it works under principal of all or nothing how thats happen ?
— a cardiac muscle in contrast to a skeletal one reacts to the stimuli according to the principal “ all or nothing “ in response to a subthreshlod irritabt the heart muscle doesn’t respond to a threshold stimulus a cardiac muscle responds by contraction to the maximum strength which it is able ti develop because all the myofibrils are involved inti this reaction
— between muscle cells of the heart there are electrical contacts which is nexuses this disks have very low electrical resistance and that is why excitation spreads freely from fibre to fibre covering whole myocardium
NB ! If the stimulus is subthreshold , it will not be able to excite even one cardiomyocytes and the heart will remain in diastole , if stimulus threshold or supratgreshold fir at least one cardiomyocytes its excitation will pass by nexuses to all cardiomyocytes heart will contract fully
What is the duration cycle of auricles ?
Systole : 0,1 sec
Diastole : 0,7 sec
Cycle of ventricles ?
Systole : 0,33 sec
Diastole : 0,47 sec
How the cardiac cycle happened ?
When the systole of auricles and systole of ventricles matched by time
And thats how is actually happened
Its all the mechanical events where is the blood flowing through different chambers of the heart
On average it take about 0,8 sec
What is the total rest pause ( TRP )
TRP is the time when both auricles and ventricles are in diastole and its 0,37 sec
What is the diastole mean ?
Its relaxation
What is systole mean ?
Its contracting
What is the phases of the heart cycle
1- period of ventricular filling
2- isovolmatric contraction ( systole )
3- ventricular ejection
4- isovolmatric relaxation ( diastole )
Explain the ventricular filling phase
- This phase defined As ventricular diastole
- in this phase the blood returning to the heart from pulmonary veins and systemic veins its start opening the AV valve bcs the atrial pressure is little bit greater then the ventricular pressure
So the tricuspid and and mitral valve opens , so the blood move to the ventricles passively without any contraction it will flow down due to gravity
—In summary
( - )atrial pressure is greater then ventricular pressure and bcs of that the
- AV valve is going to open
- and the pressure in the aorta and pulmonary is greater then the ventricular pressure and thats mean the - semilunar valve will stay closed
Explain the isovolmatric systole
- in this phase the blood its already in the ventricles so the myocardium are going to start slowly squeeze and contract trying to push blood upward slowly, and blood going to start raising
- in this point the pressure of the aorta in average 80mmgh and the pressure of pulmonary trunk is 10mmhg in average
And the pressure of the left ventricle is about 60 mmhg and
right ventricle is 7 mmhg
So the pressure of the ventricles are lower then the arterial pressure so the - semilunar valve will stay closed
- in the same time the ventricular pressure is higher then the atrial pressure so the AV valve will be closed
Explain the phase ventricular ejection
- in this phase the ventricular pressure will start rising the left ventricle is 120mmhg and the right ventricle is about 25mmhg
And the myocardium still contracting
So as we know the substances goes from high pressure to low pressure - semilunar valve will be open
- and while is the blood rising it will keep the AV valves closed and also the pressure of the atrial is 5mmhg so its less then the ventricular
What is the frank starling law
The more cardiomyocytes is stretched in the diastole , the more it will contract on the systole
