Revision Flashcards
What is the normal range of plasma K+?
3.5- 5.5 mmol/L
What is the RMP of a cardiac myocyte?
-80 mV
Why are cardiac myocytes so sensitive to changes in plasma potassium?
K+ permeability dominates the rmp
What effect does hyperkalaemia have on the cardiomyocye action potential?
SLOW UPSTROKE
Ek becomes less negative, so the membrane depolarises.This inactivates some voltage gated Na+ channels .
What can you do to treat hyperkalaemia?
Calcium gluconate - decrease excitability
Insulin - facilitates glucose uptake into cells, K+ follows
What effect does hypokalaemia have on the cardiomyocyte AP?
Lengthens AP, delaying repolarisation
What is a danger associated with a lengthened AP?
Lead to arrhythmia - early after depolarisations and ventricular fibrillation.
How does a ventricular septal defect affect pulmonary circulation?
Damage to pulmonary vasculacuture leading to vascular re-modelling and increased pulmonary resistance.
May lead to Eisenmenger syndrome where shunt is reversed.
What proportion of a thoracic cage should be occupied by the heart shadow?
50%
What 3 congenital defects lead to acyanotic L to R shunts?
- Patent ductus arteriosus
- Atrial septal defect
- Ventricular septal defect
What action must be taken immediately in infants born with transposition of the great arteries
Drugs given to maintain ductus arterioles and foramen ovale until surgical correction.
What are the segments of the primitive heart tube?
Aortic roots Truncus arteriosus Bulbus cordis Ventricle Atrium Sinus Venosus
What does the RA develop from?
Most of primitive atrium
Part of sinus venosus
What does the LA develop from?
Small part of primitive atrium
Absorbs proximal parts of pulmonary veins
What is the sequence of atrial pressure changes?
A wave C wave X descent V wave Y descent
What catecholamine receptor is present in the eye to cause pupil dilation?
Alpa 1
What cholindergi receptor is present in the eye to cause pupil constriction?
M3
Which cranial nerve is the vagus nerve?
10th
Where does the vagal nerve synapse with post-ganglionic fibres?
Epicardial surface or SA and AV node.
NOT myocardium
Where do post-ganglionic fibres from the sympathetic trunk innervate the heart?
SA node, AV node and myocardium
How does the parasympathetic input to the heart result in negative chronotropy?
M2 receptors are alpha i coupled. Decrease cAMP and beta,gamma subunit increases K+ conductance, cell moves further away from threshold.
Which vasculature have B2 receptors as well as a1?
Coronary, skeletal muscle and liver
At physiological concentration, which vascular receptors will adrenaline bind to?
B2, but at higher levels will activate alpa 1.
How does activation of B2 receptors cause vasodilation?
Gs coupled, cAMP and PKA. PKA opens K+ channels and inhibits MLCK causing relaxation.
What local metabolites have a strong vasodilator effect?
Adenosine, H+, K+, increase pCO2
What is most important for ensuring skeletal and coronary muscle is perfused?
Release of active metabolites! More important then B2 activation.
Where are baroreceptors?
Carotid sinus
Aortic arch
What is dobutamine and when might it be given?
B1 agonist
Cardiogenic shock
Give an example of a muscarinic agonist and what it might be used to treat.
Pilocarpine - glaucoma
