The heart Flashcards
Inotropic =
affects contractility
Chronotropic =
affects heart rate
Dromotropic =
affects conduction speed at AVN - so rate of electrical impulses
Afterload =
the load against which the heart must contract to eject the stroke volume
Preload =
the initial stretching of the cardiac myocytes prior to contraction (we use EDV as sarcomere length can’t be measured in intact heart)
CVP =
the pressure in the thoracic vena cava near the right atrium (therefore CVP and right atrial pressure are essentially the same)
ABP =
TPR x CO
Cardiac output is
the volume of blood ejected from the heart in 1 minute
Stroke volume is
the volume of blood ejected from the heart in 1 beat
CO =
SV X HR
SV =
EDV - ESV
Parasympathetic activity to the CVS is modulated via which area of the brain
Nucleus ambiguus and dorsal vagal nucleus (both in the medulla)
Sympathetic activity to the CVS is modulated via which area of the brain
Rostral ventrolateral medulla (RVLM)
What happens to large elastic arteries in ageing and how does this effect SP and DP?
Elastin and smooth muscle circularly arranged in tunica media; collagen in tunica adventitia.
- Elastic will stretch but shows elastic recoil,
- Collagen is flexible but tough and unstretchable.
In systole, SV ejected, elastin stretches, collagen limits stretch.
In diastole, elastic recoil helps to propel blood and keep pressure up.
In normal ageing loss of elastic function and artery properties determined more by collagen. Therefore, less distension in systole and loss of elastic recoil in diastole: SP increases, DP decreases.
What is systolic pressure related to?
CV and arterial compliance
What is diastolic pressure related to?
TPR
Why is there a delay at the AV node?
To ensure the atria has depolarised contracted and ejected blood into the ventricles before ventricular depolarisation
What is the absolute refractory period?
the neuron cannot be excited to generate a second action potential (no matter how intense the stimulus)
What is the relative refractory period?
a stronger than normal stimulus is needed to initiate a new action potential
The spread of electrical activity through the heart from SAN goes…
SAN (right atrium) Spreads across right atrium, to left atrium via Bachmans bundle and to the AVN (delay) Bundle of His Left and right bundle branches purkinje fibres ventricular muscle
Depolarisation spreads from endocardium to epicardium
EDV is normally
~120ml
SV is normally
~70ml
The amount of blood usually left in the heart after contraction (ESV) is
~50ml
