Review of Physiology from Foundations Flashcards
Where does excitation of the heart originates from?
Pacemaker cells in the Sino-Atrial Node
Where is the SA Node located
Upper right Atrium close to where the superior vena cava enters
What is a heart called that is controlled by the SA node
Sinus Rhythm
Phase 0 of cardiac action potential
fast Na+ influx causing reversal of resting membrane potential from -90mV to +30 mV
Phase 1 of cardiac action potential
Pacemaker potential, closure of Na+ channels and transition of K+ efflux causes some depolarisation
Plateau phase (phase 2) of cardiac potential
rising phase, Ca++ influx
Falling phase (phase 3) of cardiac potential
K+ efflux, closure of Ca++ channels, depolarisation of membrane potential back to -90mV
Which drugs slows the heart rate in the sinus rhythm
Drugs which Block HCN (funny current (If)
How does the signal travel from the SA node to the AV node
mainly cell-to-cell conduction via gap junctions but also internal pathways
Why is the conduction to the AV node delayed
Allows atrial systole to proceed ventricular systole
What allows rapid spread of action potential to the ventricles
Bundle of His and network of Purkinje fibres
The effect of Sympathetic nervous system on the heart rate
Noradrenaline increases slope of pace maker potential -> increases pacemaker cell Na+ and Ca++ influx -> decreases AV node delay -> increases heart rate
The effect of Parasympathetic (vagel) nervous system on the heart rate
Acetyl-choline decreases the slope of the pacemaker potential -> decreases the pacemaker cell Na+ and Ca++ influx -> increases AV node delay -> decreases heart rate
What do Beta Blockers do
Block sympathetic action, decrease slope of pacemaker potential in SA and increases AV delay , slow heart rate, reduces force of contraction, reduces myocardial oxygen consumption
What nerve supplies the Heart with parasympathetic supply
Vagus nerve
What does Atropine do
Competitive binding to acetylcholine receptors, increases slope of pacemaker potential in SA and decreases AV delay -> increases heart rate
What does Atropine do
Competitive binding to acetylcholine receptors, increases slope of pacemaker potential in SA and decreases AV delay -> increases heart rate
What happens during Systole - ventricular muscle contraction
When action potential has passed, Ca++ influx ceases, Ca++ re-sequestered in SR by Ca++-ATPase, heart muscle relaxes
What are calcium channel blockers
Interact with L-type calcium channels, can reduce heart and conduction via AV node, reduce force of conduction
What do Dihydropyride Ca+2 blockers act on
Smooth muscles - decrease blood pressure
What does intrinsic mean
within the heart muscle
What does extrinsic mean
nervous and hormonal control
Stroke volume
the volume of blood ejected by each ventricle per heart beat, regulated by intrinsic and extrinsic mechanisms
SV calculation
SV=End diastolic volume (EDV) - End systolic volume (ESV)
Cardiac output
Volume of blood pumped by each ventricle per minute, Healthy adult = 5 litres per minute
CO calculation
CO=SV x HR
Systemic Vascular Resistance
Sum of Resistance of all vasculature in the systemic circulation
Mean arterial pressure calculation
Mean arterial Pressure = Stroke volume x Heart Rate x Systemic Vascular Resistance
Resistance to blood flow:
directly proportional to blood viscosity and length of blood vessels; inversely proportional to radius of blood vessel
What does the Baroreceptor do
Short-term regulation of mean arterial blood pressure
what nerve fibres are the smooth muscles supplied by? What is the neurotransmitter? What receptor do they act on?
Sympathetic, Noradrenaline, Alpha
What is the partial constriction of the vascular smooth muscles at rest called
Vaosmotor tone
Where does adrenaline come from
adrenal medulla
Adrenaline acting on Alpha receptors causes … and are predominant in …
Vasoconstriction
Skin, gut, kidney arterioles
Adrenaline acting on Beta 2 receptors cause … and are predominant present in …
Vasodilation
Cardiac and skeletal muscle arterioles
What factors cause relaxation of arteriolar smooth muscles resulting in vasodilation
Decreased local PO2
Increased local PCO2
Increased local H+ (decreased pH)
Increased extra-cellular K+
Adenosine
the use of Organic Nitrates
Relaxes smooth muscles via their metabolism if nitric oxide
Decreases preload (dilation of veins) and after load (dilation of arterioles)
Increases coronary blood flow
Treats angina
Examples: GTN, ISMN
SV consists of
Venous return->Preload, Myocardial contractility, Afterload
What is Postural Hypotension
Results from failure of Baroreceptor response to gravitational shifts in blood
Postural Hypotension is indicated by a drop within 3 minutes of standing from lying position
In systolic blood pressure of at least 20 mmHg
A drop in diastolic blood pressure of at least 10mmHg (with symptomes)
What are symptoms of Postural Hypotension
Lightheadedness, dizziness, blurred vision, faintness and fall
Hormones regulating extracellular fluid volume include
RAAS, NPs, ADH
What are ACEIs and ARBs
Treatment of hypertension and heart failure
ACEIs inhibits conversion of Angiotensin 1 to 2
ARBs blocks action of Angiotensin 2
What are NPs
Cause excretion of salt and water in the kidneys thereby reduce blood volume and blood pressure
The first heart sound is caused by … it sounds like … and heralds the beginning of …
closure of mitral and tricuspid valves
lub
systole
The second heart sound is caused by … it sounds like a … heralds the end of … and beginning of …
closure of aortic and pulmonary valves
dub
systole
diastole
what causes the 3rd heart sound
early-diastolic rapid distension of the left ventricle that accompanies rapid ventricular filling and abrupt deceleration of the atrioventricular blood flow
what causes the 4th heart sound
ontraction of the atria pushing blood into a stiff or hypertrophic ventricle, indicating failure of the left ventricle.
