Chapter 20: The Heart Flashcards
The 4 chambers of the heart
-left and right atrium
-left and right ventricles
What do the heart chambers do?
Chambers contract in unison to deliver equal volumes of blood through the pulmonary and systemic circuits
What are the differences in ventricles?
-RV is pouch shaped, LV is round
-RV has thin walls, LV is very thick
-RV produces less pressure (lungs are close)
-LV requires 4-6X the pressure to push systemic circulation
Pericardium
sac-like network of collagen fibers
-visceral pericardium (epicardium)
-parietal pericardium
Flow of blood through the heart
- superior/inferior vena cava
- right atrium
- tricuspid valve
- right ventricle
- pulmonary arteries
- lungs
- pulmonary veins
- left atrium
- biscupid (mitral) valve
- left ventricle
- aortic valve
- aorta
- body
Coronary circulation
-heart pumps continuously
-needs a reliable supply of O2 and nutrients
What vessels have the highest blood pressure?
left and right coronary arteries
Conducting system
generates and distributes electrical impulses necessary to push blood through the systemic and pulmonary systems
Components of conducting system
-sinoatrial node (SA node)
-atrioventricular node (AV node)
-conducting cells of internodal pathways
-AV bundle and bundle branches
-Purkinje fibers
Sinoatrial (SA) node
-embedded in posterior wall of RA near entrance of superior vena cava
-depolarizes first
-established heart rate
-80-100 action potentials/ min
-connected to AV node
Atrioventricular (AV) node
conducts normal electrical impulse from the atria to the ventricles.
Purkinje fibers
distribute impulse to ventricular myocardium
Pacemaker action potential
-resting embrane potential = 60 mV
-threshold potential = 40 mV
Cardiac muscle potential
- Rapid depolarization
- Plateau
- Repolarization
- Refractory period
Rapid depolarization
sodium channels open and close quickly allowing a lot of Na+ into the cell
Plateau
sodium channels close and slow calcium channels open
Repolarization
slow calcium channels close, slow potassium channels open and K+ efflux returns cell to resting potential
Refractory period
when muscle cannot respond to AP
Cardiac cycle
beginning of one heartbeat to the beginning of the next
-800 msec; 75 bpm,
-includes both contraction and relaxation
Systole
contraction; blood pressure rises
Diastole
relaxation; blood pressure falls
Atrial systole
atrial contraction begins
-AV valves open
-semilunar valves close
-atria eject blood into ventricles
-ends with closed AV valves
Atrial diastole
atrial relaxation begins
-av valves are closed
-semilunar valves closed
-ventricles contain maximum blood volume (End-Diastolic Volume EDV)
Ventricular systole
ventricles contract (isovolumetric contraction) and pressure builds with AV valves
-ventricular pressure exceeds atrial pressure
-isotonic contraction opens semilunar valves and ventricular ejection
Stroke Volume (SV)
amount of blood pumped out of the ventricles in a single beat
End systolic volume (ESV)
blood remaining in ventricles
ventricular diastole
`ventricular pressure drops
-all heart valves closed
-ventricles relax via isovolumetric relaxation
-blood flows into relaxed atria
Cardiac cycle steps
- atrial contraction begins
- atria eject blood into ventricles
- atrial systole ends; AV valves close
- isovolumetric ventricular contraction
- ventricular ejection occurs
- semilunar valves open
- isovolumetric relaxation occurs
- AV valves open; passive ventricular filling occurs
SV =
EDV-ESV
Ejection fraction =
EDV/SV
Cardiac output (CO)
amount of blood pumped out of the left ventricle in one minute
-represents blood flow through systemic circuit
-measure of ventricular efficiency over time
CO =
HR x SV
If HR increases,
SV must decrease
What affects HR?
autonomic nervous system or hormones
What affects SV?
changes in EDV, ESV, or both
Cardiac centers of the medulla oblongata that regulate autonomic inputs
cardioaccelatory center and cardioinhibitory center
Cardioaccelatory center
controls sympathetic neurons
-increases heart rate
Cardioinhibitory center
controls parasympathetic neurons
-slows heart rate
