Cardiovascular system function and blood Flashcards
What is the proportion of contractile cells and pacemaker cells in the heart?
Contractile - 99% Pacemaker activity (auto rhythmic cells) - 1%
Where are the SA nodes located and what is special about them? (2)
They are located in the right atrial wall near the vena cava opening
Cells in the SA node fire the fastest - generate heart beat
Do not have a resting potential
Describe the action potential of a SA node cell graph: (3)
Never a flat line - always moving
Constant movement of ions
Refractory period
What is different about the ventricular cells? (2)
No pacemaker potential
Cells remain at rest until excited from the pacemaker
What are the 3 phases of ventricular cells:
Rapid depolarisation - Na+ influx
Plateau phase - Ca2+ influx (refractory period)
Depolarisation - K+ efflux
Graph looks like a n shape
Describe cardiac excitation: (4)
- APs generated at SA node
- Rapid excitation through both atria
- Excitation reaches AV node where conduction is SLOW (atria can contract and empty blood in Ventricles)
- Excitation spreads rapidly down the bundle of His and Purkinje fibres to allow simultaneous activation of ventricular cells
What parts of the heart rate can we see from a trace? (3)
P wave - atrial depolarisation
QRS - ventricular depolarisation
T wave - ventricular repolarisation
What factors effect stroke volume? (3)
- End diastolic volume
- Aortic pressure (stiffness, peripheral resistance, blood volume)
- Contractility
What is the cardiac output equation?
Cardiac output = stroke volume x heart rate
What are the heart rate factors that effect cardiac output? (3)
Pacemaker cells
Noradrenaline - increase HR
ACh - decrease HR
What factors effect heart rate? (3)
Pacemaker (SA node)
Conduction (AV node)
Noradrenaline, adrenaline and ACh all effect them too
What its the standard cardiac output, stroke volume, and heart rate in a person at rest?
Cardiac output = 5L/min (x4 at exercise)
Stroke volume = 70ml/beat (x2 at exercise)
Heart rate = 70beats/min (x3 at exercise)
What is the equation for Flow (cardiac output)?
Mean BP/Peripheral resistance
What are the stroke volume factors that effect cardiac output? (3)
Preload
Afterload
Contractility (noradrenaline) - increase
Factors effecting peripheral resistance:
Changes in vessel radius have the greatest influence on resistance - vasoconstriction and vasodilation
