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

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

Figure 15.15

Figure 15.16

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

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

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

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

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

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

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

Figure 15.21

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.

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

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

Figure 15.23

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

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

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

Figure 15.27