physiology notes:cardiac physiology
NOTES: Cardiac Physiology
- Atria: superior chambers; contraction of atria fill the ventricles, left to left,
right to right
- Ventricles: the two inferior chambers; the left is larger due to blood
- Atria: the uppermost chambers for blood collection from the vena cava
Auricles: external appendages; allow atria to hold more blood
- Interatrial septum: wall separating left and right atria
- Interventricular septum: internal separating the left and right ventricles
- Contraction as one unit: accomplished by gap junctions allow communication between atria and ventricles (intercalated disks)
- A.V. valves: between atria and ventricles; bicuspid on left, tricuspid on right
Valves prevent backflow during contraction phases
Pulmonary valves: between right ventricle and pulmonary trunk (semilunar valve)
Aortic valve: between left ventricle and aorta (semilunar valve)
- Blood is forced from ventricles to lungs/ systemic circulation
a. Blood fills atria from vena cava (superior and inferior)
8. Systole: contraction; diastole: relaxation
Cardiac Cycle events:
9. Isovolumetric contraction: rise in intraventricular pressure; AV valves shut; no blood entering the chamber; pressure building.
10. Ejection: pressure in left ventricle now grater than pressure in aorta; semilunarvalves open.
11. Isovolumetric relaxation: lower pressure in left ventricle falls below that in Aorta; back pressure causes semilunar valves to close
12. Rapid filling: pressure in the ventricles falls below pressure in the atria
13 Atrial contraction: emptying of final amount of blood into ventricles just prior to next phase of isovolumetric contraction of ventricles.
14. Heart sounds: “lub-dub”: first sound (lub) made by closing of AV valves
Dub: made by closing of semilunar valves
15. Heart murmur: extra sound produced by blood leaking through one of thevalves causing vibration of the valves.
16. Automatcity: contraction of cardiac muscle cells without input from the nervous system
17. Sinal atrial node (S.A. Node): tissue in wall of right atrium near superior venacava opening; acts as a pacemaker for the heart
18. Pacemaker potential: SA node has spontaneous depolariazations due to an influx of calcium ions.
19. Repolarization in cardiac muscle: takes longer than skeletal muscle due to influx of calcium while the K+ are flowing out; prevents heart from having tetanic contractions.
20. Ectopic foci: other areas of the heart can act as pacemakers; they depolarize more slowly than SA node; if SA node stops functioning, ectopic foci will begin acting as pacemakers
21. Atrioventricular node (AV node): tissue near interatrial septum above tricuspid valve: conducts impulses from SA node to Bundle of His.
22. Atrioventricular bundle: splits into left and right bundle branches that travel along interventricular septum to heart apex.
23. Conduction myofibers (Purkinje fibers) : penetrate into ventricular walls
a. P wave: depolarization of the atria
b. QRS complex: depolarization of the ventricles
c. T wave: ventricular repolarization
25. Cardiac output: total volume of blood pumped per minute
Cardiac output (ml/min)= stroke volume (ml/beat) x cardiac rate (beats/min)
Average cardiac rate is 70 beats/min; average stroke volume is 80 ml/beat
giving a cardiac output of 5.5L/min; total blood volume is 5.5L; therefore, heart
pumps the entire blood volume in one minute
26. Cardiac rate: set by autonomic innervation of SA node; resting heart rate set by parasympathetic system slowing SA node’s rate of depolarization; during exercise, heart rate ↑ first by removal or parasympathetic inhibition, then by stimulation of sympathetic system.
27. Stroke volume: amount of blood ejected by heart in each beat; controlled by:
a. end diastolic volume
b. total peripheral resistance
c. contractility of ventricles
A. End diastolic volume: amount of blood I n ventricles just before systole;
Strength of contraction directly proportional to the EDV; lower EDV gives lower stroke volume; EDV controlled by venous return to atria;
B. Total peripheral resistance: amount of resistance in arterial system that ventricles must overcome; when pressure in arteries is higher than pressure exerted by ventricle, blood ejection stops; proportion of EDV ejected from heart is the ejection fraction (60%).
C. Contractility of ventricles: stronger ventricular contraction= more forceful pumping of blood
29. Intrinsic control of contraction: ↑ in EDV causes ventricles to stretch= more forceful contraction; during diastole, actin and myosin overlap in middle of sarcomere; cells contract weakly; as ventricles fill, walls are stretched causing actin and myosin overlap at edges of A band= more forceful contraction.
extrinsic control of contraction: sympathetic system can ↑ strength of contraction
At any given degree of stretch by causing release of more calcium ions into