Flashcards in Heart Deck (65)
What is the name of the groove between the sinus venarum and pectinate muscles in the right atrium?
The sulcus terminalis on the outside, and crista terminalis on the inside.
What is the formula for blood pressure?
Blood pressure = cardiac output * peripheral resistance
Does the septum secundum develop of the left or right side of the septum primum?
Right side, it develops from the top and grows down and also from the endocardial cushions and grows up.
What causes the pacemaker potential in nodal cells?
Funny channels opening and allowing a slow influx of sodium ions (a funny current). Also, transient Ca2+ ions briefly open.
L-type calcium channels open as phase 0 is initiated.
What are SERCA channels in the myocardium?
Sarco-Endoplasmic Reticulum Ca2+-ATPase, which pump Ca2+ back into the sarcoplasmic reticulum to relax the cardiac muscle.
What happens in phase 0 of a ventricular action potential?
There is rapid depolarisation as voltage-gated fast Na+ channels open.
What happens in phase 1 of a ventricular action potential?
K+ channels open so there is a transient outward current of K+, and the Na+ channels are inactivated.
What happens in phase 2 of a ventricular action potential?
L-type Ca2+ channels open so that Ca2+ diffuses into the cell and the depolarisation is maintained. (Calcium induced - calcium release occurs in the cell.)
What happens in phase 3 of a ventricular action potential?
The Ca2+ conductance is decreased, the K+ delayed rectifier channels open, and the SERCA channels open so Ca2+ is removed from the cytosol.
At a normal heart rate of 70bpm, what is the duration of systole?
At a normal heart rate of 70bpm, what is the duration of diastole?
What is the Frank-Starling law of the heart?
The strength of the heart's systolic contraction is directly proportional to its diastolic expansion (preload) with the result that under normal physiological conditions the heart pumps out of the right atrium all the blood returned to it without letting any back up in the veins.
What factors affect cardiac output?
1) Preload. (The degree of stretch experienced by the ventricular muscles during diastole - directly proportional to end diastolic volume.)
2) Afterload. (Tension required by ventricular muscles to force open the semilunar valves and eject blood.)
3) Contractility. (Force produced by contraction of the ventricles at a given preload.)
What is the equation that links pressure gradient to blood flow?
Flow = Change in pressure/Resistance.
What is the action of vasodilators and local vasodilators?
To promote the relaxation of pre-capillary sphincters.
What is the name of the sounds you hear when measuring blood pressure?
What is pulse pressure?
The difference between systolic and diastolic pressure.
What is mean arterial pressure (MAP)?
MAP = diastolic pressure + (pulse pressure)/3.
What factors affect blood pressure?
Blood volume, blood viscosity, peripheral resistance, total length of blood vessels, cardiac output, age, gender.
What is the mechanism of action of digoxin and other cardiac glycosides?
Digoxin inhibits the K+/Na+ ATPase in the myocardium. This causes a build up of Na+ inside the cells so that the Na+/Ca2+ exchanger can no longer work, so Ca2+ accumulates inside the cells so the force of contraction is increased (positive inotropy), but the rate of contraction is decreased because the ionic balance is not restored (negative chronotropy and negative lusitropy).
What is the mechanism of action of acetylcholine released by parasympathetic stimulation of the vagus nerve in the myocardium?
The acetylcholine binds to muscarinic receptors (GPCR) which activate GIRK receptors (G protein inwardly rectifying channel) which pumps K+ out of the cell to depolarise it and decrease contractility.
ACh also inhibits the T-type calcium channel to stop Ca2+ entry from extracellular fluid.
What is the Haldane effect?
The lower the amount of oxyhaemoglobin in the blood, the higher the carbon dioxide carrying capacity of the blood.
What is the mechanism of action of adrenaline and noradrenaline released by sympathetic nerves in the myocardium?
Adrenaline and noradrenaline bind to B1 adrenergic receptors (GPCR) in the myocardium. This activates adenylate cyclase to produce cAMP from ATP, which then activates protein kinase A. Protein kinase A phosphorylates the L-type Ca2+ channels (dihydropyridine channels) so they stay open longer. This means there is a bigger Ca2+ influx into the myocardium so more troponin-C is bound and tropomyosin moved to expose myosin binding site, and the contractility is increased.
Also, lusitropy requires two channels to remove Ca2+ from the cytosol (Na+/Ca2+ exchanger in the sarcolemma, and SERCA in the sarcoplasmic reticulum). Protein kinase A phosphorylates phospholamban to stop it inhibiting SERCA, so faster relaxation, and more Ca2+ stored in sarcoplasmic reticulum, and more released for the next contraction.
What does the R wave on the ECG represent?
The depolarisation of the inter ventricular septum down to the apex.
What is the P-R interval on an ECG?
The time taken for the signal to pass from the AV node to the ventricle.
Why does atropine increase heart rate?
Atropine generally decreases the activity of the parasympathetic system, so the firing of the SA node is increased.
Does the autorrhythmic firing of the nerve fibres in the myocardium increase or decrease in rate as you proceed from the SA node to the Purkinje fibres and the cardiac myocytes?
Decrease in rate, so that sinus rhythm (caused by spontaneous depolarisation of the SA node) has the fastest rate, and each subsequent nerve fibre has a slower rate if it is stimulating itself and not being stilted from outside nervous impulses.
What might cause a murmur?
1) Blood flow through a leaking valve.
2) Blood flow through a narrowed (stenotic) valve.
3) Blood flow through an abnormal shunt.
4) Excessive blood flow through a normal valve.
What happens when the atria release atrial natriuretic peptide?
When the stretch receptors in the atria detect high blood pressure, atrial natriuretic peptide is secreted which is a vasodilator and stimulated the excretion of sodium and therefore water.