Physiology Flashcards
What are the different cell types in heart?
- Cardiomyocytes
- Pacemaker cells

What is the function of cardiomyocytes?
Cardiomyocytes make up the atria and the ventricles. These cells must be able to shorten and lengthen their fibers and the fibers must be flexible enough to stretch. These functions are critical to the proper form during the beating of the heart
What is the function of the pacemaker cell?
The cells that create rhythmic impulses, setting the pace for blood pumping. They directly control the heart rate.
In most humans, the concentration of pacemaker cells in the sinoatrial (SA) node is the natural pacemaker, and the resultant rhythm is a sinus rhythm.
What is the resting membrane poterntial of cardiomyocytes?
-90mV - due to high resting potassium permeability

How does cardiac action potential move between cardiomyocytes?
Gap junctions between cells

Describe the process of depolarisation of cardiomyocytes
- As membrane potential becomes more positive, voltage gated Na+ channels open -> Na+ enters the cell and rapidly depolarise it.
- MP reaches about +20mV before the Na+ channels close.
- Cell begins to repolarise as K+ begins to leave the cell .
- Repolarisation plateaus due to two events:
- K+ permeability decreases due to fast channels closing
- Ca2+ permeability increases due to voltage gated calcium channels opening slowly
- Following this, the calcium channels close and potassium channels reopen, and normal depolarisation takes place.

Why is repolarisation prolonged in cardiomyoctyes?
This helps prevent tetanus by allowing the muscle to almost completely relax before the next action potential can be fired
What is the resting membrane potential of pacemaker cells?
-60mV - partly due to specific sodium channels found in pacemaker cells
What is the depolarisation cycle of pacemaker cells?
- Sodium channels (which open during the refractory period of the previous action potential) open, allowing influx of sodium.
- As influx of sodium increases, channels close and large calcium channels open to continue depolarisation towards threshold.
- When threshold is reached, smaller calcium channels open, and calcium rushes into the cell.
- After depolarisation reaches its peak, calcium channels close, and slow potassium channels open, allowing efflux of K+ out of the cell

What are modulators of electrical activity in the heart?
- Autonomic nervous system
- Temperature
- Hyper/hypokalaemia
- Hyper/hypocalcaemia
Where does the electrical activity in the heart start?
Sinoatrial node

What is the speed of conduction of the SA node?
0.5 m/sec
What is the conduction speed of the AV node?
0.05 m/sec
What is the pathway of conduction of the cardiac action potential?
SA node -> AV node-> bundle of His -> right and left bundle branches -> purkinje fibres

Why does the heart conduct from the AV node down to the purkinje fibres?
So that the ventricles contract from the bottom up
Why does that AV node slow down the action potential?
To allow the atria to complete their contraction cycle

What is the 1st heart sound created by?
Mitral and tricuspid valves closing

What is the second heart sound created by?
Aortic and pulmonary valves closing
What is the 3rd heart sound?
Rapid filling phase
What is the fourth heart sound?
Atrial contraction
What is the sequence of changes in chamber contraction throught the cardiac cycle?
- Late diastole
- Atrial systole
- Isovolumic ventricular contraction
- Ventricular ejection
- Isovolumic ventricular relaxation

What is end diastolic volume?
Volume in the ventricles when the end of diastole has been reached, and before the commencement of systolic contraction

What is end systolic volume?
Volume in the ventricles when the end of systole has been reached, when the ventricles have been emptied as much as the force of the contraction causes

What is stroke volume?
End diastolic volume - End systolic volume






















