L43: CVS 1 Flashcards
Where does deoxygenated blood enter the heart?
Right atrium, via superior vena cava
What are the atrioventricular valves and what are their function?
- Tricuspid (right);
- Bicuspid (left);
- Separate blood in the atria and ventricles.
What are the semilunar valves and what are their function?
- Aortic;
- Pulmonary;
- Control blood movement into the exit arteries.
What determines the opening and closing of valves?
Pressure gradients (movement from high to low)
What is the clinical risk of calcified valves?
Reduced efficiency due to effected chamber pressures which may lead to backflow, can also lead to LV hypertrophy
What does a cardiac cycle consist of?
- Contraction (SYSTOLE) of the atria;
- Relaxation (DIASTOLE) of the atria;
- Contraction (SYSTOLE) of the ventricles;
- Relaxation (DIASTOLE) of the ventricles.
After leaving the heart chambers, how does pressure change through the cardiac cycle of the body?
Decreases
What is end-diastolic volume (EDV)?
The amount of blood at the end of diastole, i.e. 100mL
What is end-systolic volume (ESV)?
The amount of blood left after contraction (systole) i.e. 40mL
How is stroke volume (SV) calculated from EDV and ESV?
SV = EDV - ESV, SV = 60mL
What is stroke volume (SV)?
The amount of blood ejected per beat
What is cardiac output (C.O.)?
C.O. = SV x HR, ~5L/min at rest
Where are impulses generated in the heart?
Sinoatrial node (SA), heart’s natural pacemaker
How do impulses, generated in the SA node, spread across the heart?
From atria to ventricles:
SA > AV > His-Purkinje Network
How can the atrioventricular node effect conduction?
It can act as a secondary pacemaker and slow conduction, this gives time for the atria to contract before the ventricles do
What is excitation-contraction (EC) coupling?
The physiological process of converting an electrical stimulus to a mechanical response, i.e. AP generated in sarcolemma and the start of muscle contraction.
Describe the SA node action potential.
- (Threshold is stimulated by Ca2+ IN);
- K+ out;
- Ca2+ in and reduced K+ out.
How does the permeability of Ca2+ and K+ effect heart rate?
- If permeability of K+ increases, longer will be taken to reach next threshold;
- Fewer bpm;
- HR down.
- If permeability of Ca2+ increases, shorter time will be taken to reach next threshold;
- More bpm;
- HR up.
How does the PNS regulate HR?
- Increase in HR detected by CNX;
- ACh released;
- Activates M2 receptors;
- Increases permeability of K+ on SA node;
- Longer time taken to reach threshold;
- HR down.
How does the SNS regulate HR?
- Decrease in HR detected by SNS;
- NA released;
- Increases permeability of Ca2+ on SA node;
- Shorter time taken to reach threshold;
- HR up.
What happens in the cardiac muscle to stimulate a contraction?
- Ca2+ into muscle tissue cell, triggers contraction (from exterior of myocyte);
- This induces further calcium release from the sarcoplasmic reticulum, inside the cell (‘calcium-induced calcium release’);
- Allows for a greater contraction, like an amplifier.
What is Starling’s Law?
Force of contraction is increased, as the muscle is stretched in response to filling of the heart chambers, this is essential to modulate the circulation of blood.
(HR x SV = C.O.)
What are adrenoreceptors?
Receptor binding sites for adrenaline
What is the predominant type of adrenoreceptors in the heart?
β1, on nodal tissue (conducting system and myocardium)
What binds to β1 receptors?
Adrenaline, from SNS and circulation
What are the effects of β1-adrenaline binding?
- ^ force;
- ^ HR;
- ^ rate of relaxation/ conduction;
- ^ speed of relaxation/ conduction.
Where does CN X terminate?
- Right vagus, SA node;
- Left vagus, AV node.
