Physiology 3 - Cardiac Contractility Flashcards
In cardiac muscle, what does troponin bind to?
Tropomyosin
With regard to calcium, how does muscle relaxation occur?
Calcium is repackaged away, either in the sarcoplasmic reticulum or exchanged for sodium, which is in turn pumped out via the sodium potassium pump
By implementing sympathetic innervation as opposed to parasympathetic innervation, what is the effect on the ventricles?
Tension (not volume) increases and quicker
During what period is it possible to depolarise the membrane again?
Relative Refractory Period
Look at slide 5
Look at slide 5!
Why does the volume of the ventricles never go down to 0?
Allows for room to move - by having a 50ml reserve of blood in the ventricle, it means relaxation and contraction is a lot smoother - not having to contest with suction
What occurs during (normal) systole?
Ventricular contraction
What occurs during (normal) diastole?
Ventricular relaxation
11:49
Isovolumetric
When will the aortic valve open?
When the pressure in the ventricle exceeds the pressure in the aorta
Why is there a small jump in the aortic pressure just as it starts to decrease?
As the aortic valve closes, there is a slight rebound of blood against the valve, briefly pushing the pressure up
How is the stroke volume (SV) measured/calculated?
End diastolic volume - End systolic volume
How is the cardiac output (CO) calculated (L/min)
Stroke Volume x Heart Rate
During cardiac contraction, what type of ion channels does an action potential cause to open?
L type DHP channels
What is the result of L type DHP channels opening?
Large Ca2+ influx
Which type of T-tubule (cardiac or skeletal muscle) is larger and by how much?
Cardiac is larger - 5x greater in diameter and 25x greater in volume
What does DHPR activation cause?
Release of Ca2+ from SR via RyR channels
What is the preload?
How much blood is in the heart before it contracts
What increase the preload?
Increased venous return
What is responsible for the cardiac muscle refractory period?
Inactivation of Na+ channels
How does cardiac muscle’s period of contraction differ to skeletal muscle’s period of contraction?
250ms long, as opposed to 200ms long
Name the three ‘periods’ of cardiac contraction.
Absolute refractory period
Relative refractory period
Period of supranormal excitability
What is the average duration of the ARP?
245ms
At each of these contraction periods, can the cardiac muscle cells be stimulated to depolarise again and if so, how easily is this depolarisation achieved?
ARP - cannot be stimulated
RRP - may be stimulated, but stimulus would have to be larger than the original
SNP - smaller than normal stimulus will result in depolarisation
What is the period of isovolumetric contraction?
Brief period when aortic and mitral valves are both closed, but ventricle is contracting, allowing pressure to build up to that of the aortic pressure
What is the period of isovolumetric relaxation?
Period when the aortic and mitral valves are both closed and the ventricular pressure is falling, but not below that of the pressure in the atria
What are the 4 stages of ventricular contraction/pumping?
- Isovolumetric contraction
- Period of rapid ejection (1/3rd of the time) - 70% of ejection fraction
- Period of slow ejection (2/3rds of the time) - 30% of ejection fraction
- Isovolumetric relaxation
What is the average/normal aortic pressure?
120/80mmHg
What is the average/normal pulmonary pressure?
30/12mmHg
What is the End Systolic Volume?
Volume in ventricle at the end of systole (80% + 20%)
What is the End Diastolic Volume?
Volume in ventricle at the end of diastole
What is the Stroke Volume?
The quantity of blood expelled per beat. EDV – ESV.
What is the Cardiac Output?
The volume of blood pumped by the heart over a given time period (L/min). HR x SV.
What is normal, resting CO?
5L/min
