L18 Cardiovascular system
10 important questions on L18 Cardiovascular system
Inititation and conduction of impulse during heartbeat:
- AP initiated in SA node, travels to AV by internodal pathways
- conducted to cells in AV node (less rapid 0,1 delay -> AV nodal delay)
- impulse travels from AV through bundle of His (atrioventricular bundle) (this is the only electrical connection between atria and ventricles)
- signal splits into bundle branches. They conduct to left and right ventricles.
- impulse travels through purkinje fibers. Spreads through ventricular myocardium (form apex to valves)
What is ventricular filling?
pressure of ventricles greater than in atria. Semilunar valves are closed, ventricular pressure is lower.
What is isovolumetric contraction?
ventricles contract, pressure gets higher than in atria and AV valves close.
semilunar valves remain closed till ventricular pressure is high enough
no blood flows in or out of the ventricles because all the valves are closed.
it ends when pressure is great enough to open semilunar valves
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What is ventricular ejection?
blood ejected into aorta and pulmonary arteries.
ventricular pressure is highest. When pressure falls below aortic pressure, semilunar valves close.
end ejection and systole -> beginning diastole
What is isovolumetric relaxation?
ventricular myocardium relaxes
the ventricular pressure is too high to allow AV vales to open, but too low to keep semilunar valves open. All valves are closed.
once pressure decreases below atrial pressure, AV open
Neural control of cardiac output:
Hormonal control of cardiac output:
it increases AP frequency at SA node and thus heart rate
Thryoid hormone, insulin (heart rate up) and glucagon increase the force of myocardial contraction
Heart rate is controlled by 3 factors:
- sympathetic neurons affect SA node (raise HR)
- parasympathetic neurons affect SA node (lower HR)
- epineprine raises HR
Causes of increased contraction force:
- Cardiac muscle is streched closer to optimal lenght for contraction -> greater force.
- increased affinity of troponin for calcium. Binding increases and the number of cross bridges increases with each contraction
How do organs and tissues sense whether their blood flow is adequate?
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