cardiac cycle and control Flashcards
what do gap junctions allow for
cell to cell conduction and propagation of an action potential through the whole myocardium
process of excitation contraction coupling
1- calcium ion moves into cardio myocytes via t tubules and binds to troponin
2- causing conformational change in tertiary structure of troponin and exposes actin binding site
3- ca binds to Ryanodine receptor to release more ca from SR.
4- actin myosin cross bridges formed using atp , part of the power stroke , pulls actin and myosin together
how is the actin myosin bridge formed
calcium binds to troponin
conformational change in the tertiary structure and exposes binding site of myosin
myosin heads link with actin through action of atpase
myosin head pivots causing muscle contraction
why does cardiac muscle contraction last longer than skeletal
due to faster calcium channels
increased permeability to membrane for k after action potential
symapthetic stimulation of the heart
incease HR
increase force of contraction
increase CO
Physiological parasympathetic stimulation of the heart
decrease HR
decreases force of contraction
increases cardiac output
what is sympathetic stimulation of the heart caused by
adrenaline and noradrenaline
by increasing adenlyl cyclase
what is absolute refractory period
period where the cell is completely unexcitable
What is the electrode for ecg
what you place on the body to pick up signals
what is a lead for ecg
a plane in which you are looking in the heart
p wave?
atrial depolarisation
qrs complex?
ventricular depolarisation
t wave
ventricular repolarisation
where do leads 1-6 go
on the chest
how many leads on the right chest
2
how many leads on the left chest
4
stroke volume DEFINE AND EQUATION
amount of blood ejected in one heartbeat
end diastolic - end systolic
what happens during isovolumetric contraction
ventricular contraction, increases ventricular pressure, , AV valves close
factors affecting stroke volume
preload, afterload, contractility
PAC
what is cardiac preload
Initial stretching of cardiac myocytes prior to contraction
factors that affect preload
atrial contractility, heart rate, valvular resistance , ventricular compliance
Function of avn
Delays impulse and allows atria to empty into ventricle
Purpose of refractory period
Prevents excessive contraction
Allows time for the heart to fill
What is long QT syndrome
Abnormality of k channels
Slower k release delays depolarisation
Delayed depolarisation increases risk of early afterdepolarisations
Where is the san located
Near the opening of svc on the superior lateral wall of RA
What is ohms law
Voltage = current x resistance
Normal timing for p wave
80-100ms
Normal timing of QT interval
Men 350-440
Women 350-460
How many bipolar , unipolar chest and limb leads
Three bipolar
Three unipolar limb six unipolar chest leads
Where do all the six chest electrodes go
V1- 4th intercostal space at right sternal angle
V2- 4th intercostal space at the left sternal angle
V3- midway between v2+v4
V4- 5th intercostal space in midclavicular line
V5- left anterior auxiliary at same level as v4
V6- left mid auxiliary lane at the same horizontal level as 4+5
Names of the 4 steps of cardiac cycle
Diastole
Isovolumetric contraction
Systole
Isovolumetric relaxation
Describe the 4 steps of cardiac cycle with valves
Diastole - blood enters the atrium through pv veins and svc
Av valves open blood can enter ventricle with gravity
Ap>vp
Iso- vp> ap
Av valve shuts
Sml valve also closed
Ventricle contracts but not enough pressure to Open sl valve
Systole - enough pressure
Slv opens
Blood leaves through aorta and pulmonary artery
Define contractile the in terms of myocardial work
The state of the heart which enables it to increase its contraction to achieve higher pressures
Components of the myocardium
Contractile tissue
Connective tissue
Fibrous frame
Specialised conduction system
Function of plasma membrane in cardiac myocyte
Regulates excitation contraction coupling
Spreads the cytosol from extra cellular space and sarcoplasmic reticulum
Structure of myosin
2 heavy chains
4 light chains
Heads are perpendicular on the thick filament at rest
Structure of actin
Globular protein
Double stranded macromolecule helix
Three parts of troponin protein and function
I- inhibit actin and myosin interaction
T- binds troponin complex to tropomyosin
C- high affinity to ca2+ so it binds
Describe actin
Globular protein
Single polypeptide
Polymerises with actin to make double helix
what does preload mean
the stretch of myocardium or end-diastolic volume of the ventricles
what is your pulse pressure
upper and lower numbers of your blood pressure
Define cardiac output
Blood ejected by each ventricle per minute
Define stroke volume
Volume of blood ejected per beat
Physiological factors that can affect cardiac output
Exercise Emotion Pregnancy Posture Sweating Age Gender
Another term for end diastolic volume
Preload
Starlings law of the heart basics
More heart chambers filled with blood
Increased ventricular pressure
Stronger force of contraction
Increased sv
Why does frank starling law work
Increased stretch of muscle fibres
Increase formation of actin myosin cross bridge
Increased force of contraction
Blood pressure differences between systemic and pulmonary circulation
Systemic 120/80
Pulmonary 20/8
What is the ejection fraction
Sv/ edv
Factors that affect preload
Atrial contractility Venous return Ventricular compliance Valvular resistance Heart rate
What is afterload
Resistance left ventricle must overcome to circulate blood
Indirectly proportional to SV
Define blood flow
The volume of blood that flows through the systemic circulation
Location of baroreceptors
Present in carotid sinus and aortic arch
Mechanism of Parasympathetic control of heart rate
Via vagus nerve which synapses with post ganglionic cells in san and avn
When stimulated ach binds to m2 receptors which act to decrease hr
Mechanism of Sympathetic control of heart rate
Via postganglionic fibres from sympathetic trunk which innervate the SAN and AVN
fibres release noradrenaline which acts on b1 adrenoreceptors to increase HR
Baroreceptor reflex for increase in bp
Increase bp Increase receptor activity Increase afferent impulses to cardiovascular centre Increase psns and decrease sns . Decrease in CO and vasodilation
Examples of vasoconstrictors and vasodilators
Con- endothelin 1 and internal pressure
Dilate - adenosine , prostacyclin , hypoxia
Role and location of chemoreceptors
Detect changes in o2 and co2
In aortic arch and carotid sinus same as baroreceptors
Action potential in cardiac myocytes 5 steps
Phase 4 resting potential -90
Phase 0- action potential arrives at myocytes , if threshold is reached na channels open
Phase 1- partial depolarisation , k channels open the outflix decreases membrane potential
Phase 2- ca channels open allow influx of ca to balance k outflux
Phase. 3 depolarisation ca shut k remain open
What is a relative refractory period
When a greater than normal stimulus can depolarise the cell
How long is the pr and qrs interval
Pr 120-200 ms
Qrs - 0.06-0.1 ms
What does the st segment represent
Starts at the end of S wave and ends at the start of t wave
An isoelectric line that represents the time between depolarisation and depolarisation of the ventricles
Where do the three unipolar leads go
Avr right wrist
Avf left wrist
Avf left foot
How to work out heart rate from an ecg
Differences between two qrs complexes
Difference between cardiac and skeletal muscle
Cardiac muscle is involuntary
Skeletal is voluntary
How to conduct a heartbeat
San Bachmann bundles Avn delayed Bundle of his Purkyne fibres Contraction from the base upwards
how long does cardiac cycle last
0.8 secs
what causes a dicrotic notch
caused by an increase in aortic pressure upon closure of the
aortic valve- this happens due to the blood rebounding against the valve
In which layer do action potentials occur in the heart
Myocardium
What does a q wave show
Interventricular septum depolarisation
Where is av node located
Bottom of right atrium
