The Cardiac Cycle

The simultaneous contraction of both atria followed by both ventricles. The simultaneous contraction of both atria followed by both ventricles. The cardiac cycle is all of the physiological process that are used to carry out the functions of the cardiovascular system. The cardiac cycle is all of the physiological process that are used to carry out the functions of the cardiovascular system. Heart Sounds of the Cardiac Cycle Heart Sounds of the Cardiac Cycle –The rhythm of the heart (lub-dup, pause, lub-dup, pause, lub-dup…)  Lub: sound of the Av valves closing during ventricle contraction.  Dup: The sound of the semi-lunar valves during ventricle relaxation.

Heart Conduction System The heart contains specialized cells that send electrical impulse to cardiac muscle cells. The heart contains specialized cells that send electrical impulse to cardiac muscle cells. The rhythm of the heart (heartbeat) is controlled by pace-setting (pace maker) cells that control those electrical impulses. The rhythm of the heart (heartbeat) is controlled by pace-setting (pace maker) cells that control those electrical impulses. Those electrical impulses are what stimulate the series of muscle contractions within the atria and ventricles to push blood throughout the system. Those electrical impulses are what stimulate the series of muscle contractions within the atria and ventricles to push blood throughout the system.

The Cardiac Cycle The impulses follow a specific pathway in order for the cycle to occur properly The impulses follow a specific pathway in order for the cycle to occur properly Sinoatrial (SA) node (pacemaker): Begin each cardiac cycle, initiates atrial contraction, then stimulates AV node. Sinoatrial (SA) node (pacemaker): Begin each cardiac cycle, initiates atrial contraction, then stimulates AV node. Atrio-ventricular (AV) node: Sends the impulse down the AV bundle (bundle of His): conducting fibers that run to the apex of the heart, the impulse then reaches the Purkinje Fibers (in ventricle wall), which results in rhythmic ventricle contraction. Atrio-ventricular (AV) node: Sends the impulse down the AV bundle (bundle of His): conducting fibers that run to the apex of the heart, the impulse then reaches the Purkinje Fibers (in ventricle wall), which results in rhythmic ventricle contraction.

The Cardiac Cycle Stroke Volume: The volume of blood pumped out of the heart by one ventricle (can be either one) per heartbeat. Stroke Volume: The volume of blood pumped out of the heart by one ventricle (can be either one) per heartbeat. Cardiac Output: The volume of blood pumper out of the heart by the ventricles in a given period of time. (usually expressed as liters per minute) Cardiac Output: The volume of blood pumper out of the heart by the ventricles in a given period of time. (usually expressed as liters per minute)

Blood Pressure (Bp) Is the force exerted by blood against the inner walls of vessels. Is the force exerted by blood against the inner walls of vessels. Given as two numbers in (mm Hg). Given as two numbers in (mm Hg). First number represents systolic pressure (heart muscle contraction). First number represents systolic pressure (heart muscle contraction). Second number represents diastolic pressure (resting period between contractions). Second number represents diastolic pressure (resting period between contractions). Systolic/diastolic ( Example: 120/80). Systolic/diastolic ( Example: 120/80).

Factors that Influence Blood Pressure Blood Volume: Amount of blood occupying the space with the blood vessels (Hemorrhage). Blood Volume: Amount of blood occupying the space with the blood vessels (Hemorrhage). Peripheral Resistance: Diameter of vessels, vasoconstriction, vasodilatation. Peripheral Resistance: Diameter of vessels, vasoconstriction, vasodilatation.