Sesion 2.2 Flashcards
(15 cards)
What happens to pressure of fluid in a tube when it encounters resistance?
- pressure as blood exerts drops as it flows through resistance
- arterioles offer greatest resistance
- constriction of arterioles increases the resistance = pressure in capillaries and on venous side to fall but will cause pressure on arterial side to rise
What happens if total peripheral resistance falls and cardiac output stays the same?
- arterial pressure will fall
- venous pressure will increase
What happens if TPR increases and CO is unchanged?
- arterial pressure will increase
- venous pressure will fall
What happens if CO increases and TPR is unchanged?
- arterial pressure will increase
- venous pressure will fall
What happens when CO decreases and TPR is unchanged?
- arterial pressure will fall
- venous pressure will rise
How can you calculate stroke volume and what is it in a typical 70kg man?
Stroke volume = end diastolic volume - end systolic volume
Typically 70ml
What affect does venous pressure have on filling on the ventricles?
Higher venous pressure = greater filling in the heart
What if the frank - starling law of the heart?
If you stretch the fibres of the heart before contracting, it will contract harder
So, the more the heart fills, the harder it contracts (up to a limit) = bigger stroke volume
What is contractility and what can increase or decrease it?
Contractility = the force of contraction for a given fibre length.
Increased by sympathetic nervous system/ action of adrenaline = bigger stroke volume and so will have a steeper curve on the frank starling curve
Decreased by heart failure = curve will be flatter and tail off as contractility decreases,
How does aortic pressure vary with TPR?
It increases with it
What factors determine cardiac output?
end systolic volume depends on
1) contraction strength = determines end diastolic volume and contractility
2) how hard it is to eject blood
- determined by rough arterial pressure
How does metabolism vary with TPR?
- if the metabolism of the body increases, then TPR will fall to supply more blood
- this will result in a fall in arterial pressure and increase in venous pressure
- the heart will respond by pumping more = increased HR and stroke Volume resulting in an increased cardiac output
- results in a rise in arterial pressure and a fall in venous pressure
What effect does standing up have on blood pressure and why? What happens to fix this?
- decrease venous pressure
- decreased cardiac output
- decreased arterial pressure
This is due to pooling of blood in legs
To fix it, get baroreceptor reflex and autonomic nervous system increases HR and TPR.
NB: If reflexes don’t work you get postural hypertension
What effect does exercise have on TPR and cardiac output?
- decreased TPR
- increased HR
- increased venous pressure
- increased contractility (increased sympathetic drive)
Overall increased cardiac output!:)
What conditions increase jugular venous pressure?
- Right sided heart failure
- stab wound to the heart
- impaired filling
