1. Cardiac Cycle Figure 15.15 Atria relax and fill, the AV valves open
Atrial systole: atria contract and push blood into the ventricles
Figure 15.15

2. Cardiac Cycle
Ventricular systole: ventricles fill and contract as AV valves close and semilunar valves open
Ventricular diastole: ventricles relax and valves open

3. Figure 15.15

4. Figure 15.16

5. Heart Sounds Heard through a stethoscope
Vibrations due to blood flow and opening and closing of the heart valves
Lubb: closing of the A-V valves
Dupp: closing of the semilunar valves
Can indicate the condition of the heart valves
Murmur: abnormal heart sound

6. Cardiac Muscle Fibers
Stimulation to any part of the heart fibers network sends impulses to the heart, which contracts as a unit
Heart cells act as a functional syncytium
atrial syncytium
ventricular syncytium
connected by the cardiac conduction system

7. Cardiac Conduction System
Specialized cardiac muscle cells initiate and send impulses through the myocardium
Sinoatrial node (S-A node)
located in the right atrium near the superior vena cava
rhythmic pacemaker
From the S-A node impulses are conducted along the interatrial muscle

8. Cardiac Conduction System
Atrioventricular Node (A-V nose)
located in the inferior interatrial septum
conducts impulses between the atria and ventricles
Figure 15.18

9. Cardiac Conduction System
A-V bundle (Bundle of His)
located in the interventricular septum
divide into left and right bundle branches
give rise to Purkinje fibers that carry impulses throughout the ventricular myocardium

10. Electrocardiogram ECG
Recording of the myocardial electrical changes during the cardiac cycle
Electrical changes create deflections or waves which can be visualized

11. Electrocardiogram
P wave: corresponds to depolarization of the atria prior to contraction
QRS complex: corresponds to ventricular depolarization prior to contraction
T wave: corresponds to ventricular repolarization
Atrial repolarization is obscured by the QRS complex

12. Figure 15.21

13. Cardiac Cycle Regulation
S-A node normally controls heart rate.
Vagus nerve: cholinergic parasympathetic fibers that decrease heart rate.
Vagal stimulation is constant and works as a brake to keep the heart slowed.
Accelerator nerves: adrenergic sympathetic nerves increase heart rate and strength of contraction.

14. Cardiac Cycle Regulation
Medulla oblongata: cardiac control center
cardioinhibitory reflex center
cardioacceleratory reflex center
Baroreceptors: respond to blood pressure changes
Stretch receptors in the venae cavae control heart rate and force of contraction
Higher centers can play a role, i.e. anxiety

15. Factors That Affect Heart Rate
Temperature
rising body temperature increases heart action
low body temperature decreases heart action
Ions
Potassium affects electrical potential of the heart cell membrane
Calcium affects cardiac muscle fibers because their sarcoplasmic reticulum contains less calcium than skeletal muscle

16. Figure 15.23

17. Blood Vessels
Closed circuit of tubes that carries blood from the heart to the cells and back again
Arteries and arterioles
carry blood away from the ventricles
Capillaries
site of exchange
Venules and veins
return blood from the capillaries to the atria

18. Arteries and Arterioles
Carry blood away from the heart
Three layers or tunics
tunica interna: endothelium
tunica media: smooth muscle and elastin
tunica externa: connective tissue
Figure 15.24

19. Arteries and Arterioles
Vasomotor fibers stimulate smooth muscle controlling vasoconstriction, vasodilation
Metarterioles: join capillaries

20. Figure 15.27