Lecture 4 - Cardiac Physiology Flashcards
What is the significance of the plateau during an action potential in a cardiac myocyte?
To ensure another contraction doesn’t occur when one is already happening, this will ensure efficient flow and circulation.
What would be the consequences of no refractory period in a cardiac AP?
Contraction strength will be weak therefore filling and flow will be compromised.
What are the function of the T-Tubules?
Ensure the spread of AP so that electrical current spreads evenly throughout the cell and they are all synchronized.
What are L-Type Channels?
Allow calcium to pass into the cell.
What is Calcium Induced Calcium Release?
Calcium which then causes the SR to release more calcium for contraction
Whys is the SR is close to the sarcomere?
To ensure efficient calcium regulation
Why is it important to get calcium out of the heart?
Because the heart needs to be able to relax and this can happen only when the amount of calcium decreases.
What two pathways take calcium out of the cell?
SERCA and NCX
Which pathway is preferred to take calcium out of the cell?
SERCA - when there is problems with this one the NCX pathway is used. (this one is slower)
Describe the 8 steps of calcium processing for contraction
- AP enters cell through gap junctions
- AP travels along plasma membrane and T-Tubule
- L Type channels allow Calcium to move in
- This calcium then induces the SR to release more calcium (CICR)
- Calcium binds to troponin exposing myosin binding sites
- Crossbridges form and contraction occurs
- Active transportation of Calcium back into SR (via SERCA) or into the ECF (via NCX)
- Tropomyosin blocks myosin binding sites and the muscle relaxes
What are the 7 steps on the top of the Wiggers Diagram?
Cardiac Cycle
- Atrial Contraction
- Isovolumetric Contraction
- Early Ejection Phase
- Late Ejection Phase
- Isovolumetric Relaxation
- Early Filling
- Late Filling
What direction does the heart move in the longitudinal fibre direction?
The base moves towards the apex.
Describe the twist mechanism of the left ventricle
Moves like wringing a towel. Base moves in one direction while the Apex moves another, the base stays and the apex twists and moves upwards toward the base
How does the twisting mechanism of the heart promote recoil?
The twisting mechanism stores alot of kinetic energy in titin, this causes recoil during diastole. (Like pressing a spring down)
What factors affect HR?
Autonomic Innervation
Hormones
What factors affect SV?
Venous Return + Filling time = Preload
Autonomic Innervation + Hormones = Contractility
Vasodilation and Vasoconstriction = Afterload
What does inotropy mean?
The amount of force of contraction
What does lusitropy mean?
The amount of relaxation
What do the x and y co-ordinates represent on the Starling Curve?
Y = Contractile Energy X = Fibre Length
What are some factors of blood flow resistance?
- Pressure differences between the ends of the vessels
- Blood viscosity
- Length of vessel
- Radius of vessel
What is stroke volume?
Amount of blood ejected from the ventricles
How do you calculate stroke volume?
By subtracting the amount of blood that is left in the ventricles after contraction (ESV) from the amount of blood which filled the ventricles at the end of ventricular filling (EDV)
SV = EDV-ESV (ml)
What does the pressure-volume loop represent?
The relationship between ventricular pressure and volume throughout the cardiac cycle
Describe how venous return is increased during exercise
By the skeletal muscle pump and vasoconstriction
What is Cardiac Output?
Amount of blood pumped by each ventricle per minute. (l/min)
What does the cardiac output represent?
BF for the entire CVS
Reflects the ability of the heart to meet the bodys need for BF
What happens to CO during exercise?
Increases to meet the needs of the skeletal muscle for increased blood flow
SV vs CO
SV = amount of blood pumped with each beat CO = amount of blood pumped per minute
What three factors affect SV?
- Preload
- Afterload
- Contractility
What is the Frank Starling law of the heart?
An increased stretch of the heart enhances the contraction of the heart therefore more blood is ejected.
Why is the FS law important?
Provides an intrinsic mechanism to equalise CO between the R and L ventricles
