physiology notes:cardiac physiology

NOTES: Cardiac Physiology

1. Collecting chambers:
   1. Atria: superior chambers; contraction of atria fill the ventricles, left to left,

right to right

1. 2. Ventricles: the two inferior chambers; the left is larger due to blood

distribution.

2. Atria: the uppermost chambers for blood collection from the vena cava

Auricles: external appendages; allow atria to hold more blood

3. Interatrial septum: wall separating left and right atria
4. Interventricular septum: internal separating the left and right ventricles
5. Contraction as one unit: accomplished by gap junctions allow communication between atria and ventricles (intercalated disks)
6. 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)

7. Contraction:
   1. Blood is forced from ventricles to lungs/ systemic circulation

Relaxation:

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

24. Electrocardiogram:

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

28.

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

sarcomere.