Unit 6 - Cardiac Physiology Flashcards
Heart is composed of what three components?
Arteries, Veins, Septum
Arteries
carry blood away from the ventricles to tissues
Veins
Vessels that return blood from tissues to the atria
Septum
continuous muscular partition that prevents mixture of blood from the two sides of heart
Blood flow though heart
Inferior/superior vena cava, right atrium, right AV valve (tricuspid), right ventricle, pulmonary valve, pulmonary artery, lungs, pulmonary veins, left atrium, left AV valve (micuspid), left centricle, aortic valve, aorta.
Three things pulmonary circulation does (R heart)
- Circuit of vessels carrying blood between heart and lungs
- lungs add O2 and remove CO2
- flows through pulmonary veins to LA
Two things Systemic circulation does (L heart)
- circuit of vessels carrying blood between heart and body systems
- oxygen rich blood pumped from LA to LV to body through aorta
What side of the heart has oxygen rich blood?
left side
What side of the heart has de-oxygenated blood?
right side
Coronary Circulation
Coronary arteries on outside of heart and come from aorta. Per fused from aorta during diastole.
Right coronary artery supplies blood to
right side of heart
Left coronary artery supplies blood to
left side of heart
AV valves
R & L valves are positioned b/w atria and ventricles to prevent back-flow of blood from ventricles into atria during ventricular emptying
Right AV valve
tricuspid valve
Left AV valve
bicuspid valve
Chordae tendinae
fibrous cords prevent valves from being everted and papillary muscles
Heart valves pressure
atrial pressures not much higher than venous pressures
What is partially compressed during atrial contraction
superior, inferior venae cavae and pulmonary vein
Three things semi-lunar valves do
- aortic and pulmonary valves
- lie at juncture where major arteries leave ventricles
- prevented from everting by anatomic structure and positioning of cusps
Electrical Activity of Heart
heart beats rhythmically as result of action potentials it generates by itself
two specialized types of cardiac muscle cells
- contractile cells
2. auto rhythmic cells (pacemaker cells)
Contractile cells
99% of cardiac muscle cells. Contract-do mechanical work pumping. RMP is -80 mV with threshold of -40 mV
Autorhythmic cells
1% of cardiac muscle cells. Initiate & conduct action potentials that result in contraction of working cells. Do not contract no RMP
4 locations of pacemaker cells
- SA node
- AV node
- Bundle of His
- Purkinje fibers
Sinoatrial Node
- Specialized region in R atrial wall near opening of superior vena cava
- PACE MAKER OF THE HEART 60-100 time/min
- AP spreads throughout right and left atria
- impulse passes from atria into centricles though AV node (only point of electrical contact between chambers)
Atrioventricular Node
- Small bundle of specialized cardiac cells located at base of RA near septum
- slows impulse conduction between atria and ventricles, allowing atria to fill with blood before ventricles contract
- impulse then travels to bundle of his
Bundle of His
Divides to for R and L bundle branches
AP travels down septum, curve around tip of ventricular chambers, travel back toward atria along outer walls
Purkinje fibers
- small terminal located at distal portions of both bundles
- impulse travels through myocardium
- ventricular cells activated by cell to cell spread of impulse
- ventricles then contract
Back-up System
- SA node (60-100 beats/min)
- AV node (40-60 beats/min)
- Bundle of His & Purkinje Fibres (20-40 beats/min)
- Ectopic focus
ECG waveforms
PQRSTP
P wave
atrial depolarization
PR segment
AV nodal delay
QRS complex
ventricular depolarization (atria repolarizing simultaneously)
ST segment
time during which ventricles are contracting and emptying
T wave
Ventricular repolarization
TP interval
time during which ventricles are relaxing and fillin
Cardiac cycle
beginning of one heart beat to beginning of next
Two phases of cardiac cycle
systole and diastole
systole
contraction and emptying
diastole
relaxation and filling
Ventricular diastole (relaxation)
- mid ventricular diastole
2. late ventricular diastole
Mid ventricular diastole
atria in diastole (TP) and atrial filling
Late ventricular diastole
SA node reaches threshold (P)
atrial pressure >ventricular pressure -> AV valves open and 50-90% of blood fills ventricles
Late ventricular diastole (atrial systole)
atrial contraction and last 10-25% of blood emptied into ventricle (atrial kick)
End of ventricular diastole
ventricular filling complete. end diastole volume 135ml. max volume of blood that ventricle contains just before systole
Ventricular systole (contraction)
heart contracting
onset of ventricular systole
impulse at AV node (starts QRS) and ventricular pressure begins to rise
Isovolumetric ventricular contraction
brief period before semilunar valves are open.
ventricular pressure > atrial pressure -> AV valves shut.
ventricle is closed chamber
Ventricular pressure rises
semilunar valves opened and ejection of blood begins
Stroke volume
amount of blood pumped out of each ventricle with each contraction (70ml)
End of ventricular systole
only pumps out 50% of blood. blood left in ventricle is end systolic volume (ESV 65ml)
Ventricular Diastole (Relaxation)
repolarization of ventricles (T wave)
Repolarization of ventricles (T wave)
ventricular pressure drops below aortic/pulmonic pressure -> semilunar valves close
isovolumetric ventricular relaxation
briefly, ventricular pressure exceeds atrial pressure
AV closed and no blood from atrium.
All valves closed
atrial pressure > ventricular pressure
AV valve opens, ventricles filled and cardiac cycle begins again
Heart sounds
Two major sounds
1st low pitched and soft lub (closure of AV valves during systole)
2nd has a higher pitch dup (closure of the semilunar valves during diastole)
S1 -> S2
Diastole
S2 -> S1
Systole
Cardiac output
blood volume ejected each minute from LV into aorta and from RV to pulmonary artery
HR x SV
Heart Rate
varied by altering balance of parasympathetic and sympathetic influence on SA node
Parasympathetic stimulation
CN X (Vagus)
SLows down SA node to reduce heart rate
Decreases the AV nodes excitability
Weakens atrial contraction but little effect on ventricular contraction
Sympathetic stimulation
increases heart rate speeding up SA node depolarization
Reduces AV nodal delay and speeds up spread of action potential
increases force of contraction
Stroke Volume
amount of blood pumped out of each ventricle with each contraction
SV calculation
EDN - ESV
70ml apx
Stroke volume is influenced by
intrinsic control and extrinsic control
intrinsic control
EDV
venous return
strength of cardiac contraction
Extrinsic control
sympathetic activity
increased strength of contraction
Frank-Starling Law of the Heart
Relationshop b/w EDV and stroke volume
Heart normally pumps out during systole the volume of blood returned to it during diastole
the high EDN the higher SV
The more the fibres stretch, the more forcefully the ventricles contract during systole
Preload
the greater the volume of blood into ventricles, the greater the heart muscle is stretched during diastole and the greater the force of contraction.
“Filling”
Contractility
ability of myocardium to contract
influenced by preload (greater the stretch -> the more forceful the contraction)
Afterload
pressure required for ventricular muscles to overcome resistance in P & A valves to pump blood out of heart
Factors affecting HR
autonomic innervation
hormones
fitness levels
age
factors affecting SV
heart size fitness levels gender contractility duration of contraction Preload (EDV) Afterload (Resistance)
