Week 4 - Cardiac cycle Flashcards
What is the function of the cardiovascular system?
to supply and remove materials to tissues around the body
examples of these materials include, glucose, oxygen, carbon dioxide
What is the basal output of the heart?
5 litres a minute
can be 25-30 when exercising
What is the role of the pericardium?
to prevent excessive expansion of the heart
fixes the heart to the mediastinum
protection against infection
What are the two atrioventricular valves and where are they located?
mitral - left side of heart
tricuspid - right side of heart
How many cusps do the semilunar valves have?
both have 3
How many cusps to the atrioventricular valves have?
mitral - bicuspid - 2
tricuspid - 3
What are the chordae tendineae?
chord like tendons (80% collagen, 20% elastin) that attach the papillary muscles to the tricuspid valve and mitral valve in the heart
What is the purpose of the papillary muscles?
to prevent inversion of the valves during systole
ventricles are contracting, blood must not go back into atria but out to body or lungs
What is a chronotrophic change?
a change in rate of contraction
What is an inotropic change?
a change in force of contraction
What nerve supplies the parasympathetic nerve supply to the heart?
vagus CN X
What are the actions of the b1 adrenergic receptor in cardiac muscle?
increase cardiac output by:
increasing heart rate in SA node (chronotropic effect)
increasing strength of atrial and ventricular contraction (inotropic effect)
increases conduction of AV node
What is the receptor of the parasympathetic nervous system in the heart?
M2 muscarinic receptor
slow down heart rate
reduce contractile force of atria
reduce conduction velocity of SA and AV nodes
little effect on ventricular muscle due to sparse innervation of ventricles by parasymathetic nervous sytem
How long does one cardiac cycle last?
0.8 seconds
How long does the heart spend in diastole?
0.4 seconds
How long is atrial systole?
0.1 seconds
How long is ventricular systole?
0.3 seconds
How many heart sounds are produced?
4 - usually only two are audible (S1 and S2)
What causes the aortic valve to open?
when aortic pressure is slighly below left ventricular pressure
What term is typically used to refer to ventricular contraction while no blood is being ejected?
isovolumetric contraction
During what phase does most blood enter the ventricle?
atrial diastole
the movement of blood into the ventricles is passive and caused by a pressure difference
atrial systole ensures the last bit of blood has been ejected
The first heart sound represents which portion of the cardiac cycle?
the closing of the atrioventricular valves
The second heart sound represents which phase of the cardiac cycle?
closure of the semilunar valves
Ventricular relaxation immediately follows:
a) atrial repolarization
b) ventricular depolarization
c) atrial depolarisation
d) ventricular repolarization
d
What is stenosis of a heart valve?
valve does not open completely causing turbulent flow
associated with calcification
What are the characteristics of cardiac muscle?
striated, mononuclear, smaller cells than skeletal muscle, cells connect to each other via desmosomes and gap junctions, no stem cells
What are intercalated discs?
cell junctions that link adjacent cardiac myocytes together to form a synctium
contain desmosomal junctions, adherent-type junctions and communicating gap junctions
What are desmosomes?
cell structure specialised for cell to cell adhesion
What doesthe term ‘calcium induced calcium release’ mean?
refers to the trigger Ca2+ causing the sarcoplasmic reticulum to release more calcium
What triggers the initial Ca2+ influx into the cell?
a cardiac action potential
What are the three patterns of cardiac action potentials?
ventricular, atrial and sino-atrial node
What does phase 0 on this graph refer to?
ventricular depolarisation
What is the resting membrane potential of the ventricular action potential?
-90mV
K+ are open and K+ moves into the cell creating a negative membrane potential
What is a myogenic rhythm?
cardiac muscle can contract rhythmically without nervous input
At what rate do action potentials of the sino-atrial node fire?
100 bpm
What is the route of conduction of electrical impulses through the heart?
What causes phase 2 (prolonged plateau) of the ventricular action potential?
opening of L-type voltage-gated calcium channels causes inward Ca2+ current
this balances out the outward K+ causing a plateau
What does an atrial action potential look like?
similar to ventricular, less obvious plateau, slower repolarisation
What is the ‘pacemaker potential’‘?
the slow positive increase in voltage across the cell membrane after each action potential
represents the non-contracting time between heart beats (diastole)
What are the bipolar (limb) leads?
Lead I
Lead II
Lead III
How is Lead I connected?
negative input connected to right arm
positive input connected to left arm
What does Lead I record?
the wave of excitation moving between the right and left sides of the heart
REMEMBER: wave of excitation always passes from negative to postive
How is Lead II connected?
negative input connected to right arm
positive input connected to left leg
What does Lead II record?
records excitation moving between right upper portion of heart to the apex of the venticle
How is Lead III connected?
positive input connected to left leg
negative input connected to left arm
What does Lead III record?
records excitation moving between left atrium to the apex of the ventricle
What are the two types of unipolar lead used in the recording?
3x augmented limb leads
6x chest leads
What do unipolar leads do?
record voltage between a single lead and an ‘earth’ lead
What is the general direction of depolarisation of the heart known as?
the cardiac axis
electrical activity spreads from 11 o clock to 5 o clock
What causes an upwards deflection on the ECG trace?
an action potential depolarisation moving towards the electrode connected to the positive input of the amplifier
What does the P wave correspond to on an ECG trace?
atrial depolarisation
What does the QRS complex correspond to on an ECG trace?
ventricular depolarisation
What does the T wave correspond to on an ECG trace?
ventricular repolarisation
What are the septal leads?
V1-V2
What are the inferior leads on an ECG?
II, III, aVF
What are the anterior leads?
V3-V4
What are the lateral leads?
V5, V6, I, aVL
What might rarely cause the pathological 4th heart sound?
atrial contraction
How do you calculate mean arterial pressure?
diastolic pressure + 1/3 pulse pressure pulse pressure = systolic - diastolic pressure
What physical factors affect arterial blood pressure?
arterial blood volume arterial compliance
What are the key physiological factors that determine arterial blood pressure?
cardiac output peripheral resistance
Why is the mean arterial pressure not simply an average of systolic and diastolic pressures?
diastole lasts longer than systole so has a greater effect on the mean pressure
How does aortic valve regurgitation affect stroke volume?
stroke volume increases because there is a greater volume of blood in the ventricle failure of the aortic valve to close properly causes a back flow of blood into the left ventricle increasing stroke volume
What is Starling’s law of the heart?
an increase in cardiac stretch increases the strength of contraction (greater stretch, greater force if contraction)
