Cardiac physiology and ECG Flashcards
Describe the process of the cardiac cycle?
Diastole
- During diastole, the atrioventricular valves are closed.
- Blood flows into the left and right atria from the veins
- As the atria fill, the Atrioventricular valves open allowing the passage of blood from the atria to the ventricles
- The atrioventricular valves then close to prevent the backflow of blood from the ventricles back into the atria
- The ventricles contract and the pressure increases above that of the major arteries and so the semi-lunar valves open. This causes the push of blood from the ventricles into the aorta and the pulmonary artery.
What are they types of valves in the heart and where are they?
- Atrioventricular valves:
Are found between the atria and the ventricles
Bicuspid (Left)
Tricuspid (Right)
Prevent backflip from the ventricles back into the atria - Semi-lunar valves:
Are found between the ventricles and the major arteries
Between the right ventricle and the pulmonary artery
Between the left ventricle and the aorta
What is the end systolic volume?
The volume of blood in the ventricles at the end of systole
What is the end diastolic volume?
The volume of blood at the end of diastole
What is the stroke volume?
Stroke volume = End diastolic volume - end systolic volume
- it is the amount of blood ejected from the heart in a single heart beat
What are the types of intercalated discs incorporated into cardiac muscle and what is their function?
The intercalated discs are found in the sarcolemma- the plasma membrane of the cardiac muscle cells
- Desmosomes- are structures found at the end of the cardiac muscle fibres to anchor them together. They provide mechanical support and prevent the cells from pulling apart during the individual fibres contracting
- Gap junctions- is a channel between adjacent cardiac muscle fibres that allow the transmission of action potentials from one cardiac muscle cell to the next.
What is the pericardium and what are its functions?
- The pericardium is a fibrous, double-walled sac that encloses and protects the heart and its vessels.
It has 2 main functions;
- It anchors the heart and keeps the heart and its vessels protected
- Also provides lubrication via pericardial fluid that prevents the heart from rubbing against the ribcage and Wreduces the friction generated by the heart as it moves within the thoracic cavity
What is pericarditis?
When the pericardial sac becomes infected and inflamed- can have a viral or bacterial cause or can be a result of other inflammatory conditions e.g. rheumatoid arthritis
- it presents itself as chest pain on the left side behind the breast bone.
- When the fluid becomes inflamed, it leads to the person being able to feel the rubbing of the heart against other structures and can be painful
What in the heart is known as the ‘Pacemaker region’?
The sino-atrial node
What is the process of transmission of the action potential around the heart?
- The action potential is fired from the pacemaker cells in the SA node
- It then travels across the atria node to the AV node
- Once in the ventricles, the action potential followed the Bundle of His down the septum and into the walls of each ventricle
- These then branch into the purkinje fibres
What are the two cell types that initiate an action potential in the heart?
- Pacemaker cells in the Sino-atrial node
- Cardiomyoctye cells (don’t actually generate the AP, but can pass it along)
The pacemaker cells in the SA node are ____?
Autorhythmic- they generate the action potential themselves without any outside stimulation
What is the process of generating cardiac action potentials in the pacemaker cells and the effect on the membrane? (write like an exam q)
Pacemaker cells are found in the Sino-atrial node of the heart. They have autorhythmicity and so generate the action potentials without any nervous stimulation and control the heart rate.
- The ion channels known as ‘Funny channels’ open which allow the entry of Na+ into the cell.
- This causes the inside of the cell to become more positive and an increase in the membrane potential (slow depolarisation- slow influx of Na+ ions). this is known as a slow drift to threshold potential.
- As this membrane potential nears threshold potential, the long-lasting transient calcium channels open. This causes Ca2+ ions to move into the cell, leading to a more rapid depolarisation of the membrane.
- At this point, rectifier K+ channels are opened, this causes K+ ions to move out of the cell and leads to rapid repolarisation of the membrane.
- In the pacemaker cells, there is no resting potential, so as soon as repolarisation has occurred, the process restarts immediately and the funny channels are reopened.
DRAW A PICTURE OF THE MEMBRANE POTENTIAL V TIME GRAPH AND LABEL IT WITH THE IONS.
How are action potentials transmitted in cardiomyocytes (Write like an exam question)?
Cardiomyocytes are muscle cells that are found in the heart. They cannot generate action potentials like the pacemaker cells can, but can pass them along purkinje fibres to the next cardiomyocyte cells via gap junctions.
- The Na+ channels open, leading to rapid influx of sodium ions and rapid depolarisation of the membrane.
- This leads to the opening of K+ channels, causing K+ ions to be pumped out- causing a slight repolarisation of the membrane.
- This leads to a plateau phase. As K+ is slowly being pumped out and Ca2+ channels are opened, causing calcium to be pumped in slowly. These two actions balance the charges out and so leads to a plateau in the membrane potential.
- The K+ ions then begin to rapidly efflux from the cell (via rectifier K+ channels) causing rapid repolarisation of the membrane.
- The cell then remains at resting potential until the next action potential is fired.
DRAW A PICTURE OF THE MEMBRANE POTENTIAL V TIME GRAPH AND LABEL IT WITH THE IONS.
Explain the differences between generating an action potential in the cardiomyocytes and the pacemaker cells? (Answer like an exam Q)
Pacemaker cells are found in the Sino-atrial node of the heart. They have autorhythmicity and so generate the action potentials without any nervous stimulation and control the heart rate.
- The ion channels known as ‘Funny channels’ open which allow the entry of Na+ into the cell.
- This causes the inside of the cell to become more positive and an increase in the membrane potential (slow depolarisation- slow influx of Na+ ions). this is known as a slow drift to threshold potential.
- As this membrane potential nears threshold potential, the long-lasting transient calcium channels open. This causes Ca2+ ions to move into the cell, leading to a more rapid depolarisation of the membrane.
- At this point, rectifier K+ channels are opened, this causes K+ ions to move out of the cell and leads to rapid repolarisation of the membrane.
- In the pacemaker cells, there is no resting potential, so as soon as depolarisation has occurred, the process restarts immediately and the funny channels are reopened.
DRAW A PICTURE OF THE MEMBRANE POTENTIAL V TIME GRAPH AND LABEL IT WITH THE IONS.
Cardiomyocytes are muscle cells that are found in the heart. They cannot generate action potentials like the pacemaker cells can, but can pass the potentials along to the next cells via gap junctions.
- The Na+ channels open, leading to rapid influx of sodium ions and rapid depolarisation of the membrane.
- This leads to the opening of K+ channels, causing K+ ions to be pumped out- causing a slight repolarisation of the membrane.
- This leads to a plateau phase. As K+ is slowly being pumped out and Ca2+ channels are opened, causing calcium to be pumped in slowly. These two actions balance the charges out and so leads to a plateau in the membrane potential.
- The K+ ions then begin to rapidly efflux from the cell (via rectifier K+ channels) causing rapid depolarisation of the membrane.
- The cell then remains at resting potential until the next action potential is fired.
DRAW A PICTURE OF THE MEMBRANE POTENTIAL V TIME GRAPH AND LABEL IT WITH THE IONS.
