Cardiovascular Cardiovascular SystemSystem

PhysiologyPhysiology

Cardiac MuscleCardiac Muscle

Cardiac muscle cells are elongated, Cardiac muscle cells are elongated, branching cells that contain one or branching cells that contain one or occasionally two centrally located nuclei.occasionally two centrally located nuclei.

CM cells contain myosin and actin CM cells contain myosin and actin organized into sarcomeres which join end organized into sarcomeres which join end to end to form myofibrils.to end to form myofibrils.

The arrangement of actin and myosin The arrangement of actin and myosin gives the striations.gives the striations.

Striations of cardiac muscle are less Striations of cardiac muscle are less regularly arranged and less numerous regularly arranged and less numerous than skeletal.than skeletal.

Diagram of muscle contraction and relaxation. The same mechanism exists in skeletal muscle.

Cardiac Muscle ContinuedCardiac Muscle Continued

Another characteristic is the Another characteristic is the intercalated disks; these are intercalated disks; these are specialized cell junctions – they work specialized cell junctions – they work to increase contact between the to increase contact between the cells.cells.

This also serve to allow the cardiac This also serve to allow the cardiac muscle contract in waves to muscle contract in waves to “massage” the blood out of the “massage” the blood out of the heart.heart.

ContractionContraction

Adenosine triphosphate (ATP) provides Adenosine triphosphate (ATP) provides the energy for cardiac muscle the energy for cardiac muscle contraction, and , as in other tissues, ATP contraction, and , as in other tissues, ATP depends on oxygen availability. Cardiac depends on oxygen availability. Cardiac muscle cannot develop a large O2 debt. muscle cannot develop a large O2 debt. A large oxygen debt would result in A large oxygen debt would result in muscular fatigue and the heart would muscular fatigue and the heart would eventually cease beating. What eventually cease beating. What organelle must be present in large organelle must be present in large numbers?numbers?

ContractionContraction Action potentials are conducted through two Action potentials are conducted through two

nodes that are made of modified cardiac muscle nodes that are made of modified cardiac muscle cells. The two nodes are contained in the walls of cells. The two nodes are contained in the walls of the right atrium and are named according to their the right atrium and are named according to their position in the atrium. position in the atrium.

The SA (Sinoatrial) node is medial to the opening The SA (Sinoatrial) node is medial to the opening of the superior vena cava. of the superior vena cava.

The AV (atrioventricular) node is medial to the The AV (atrioventricular) node is medial to the right atrioventricular valve. The AV node gives right atrioventricular valve. The AV node gives rise to a conducting bundle of the heart (the rise to a conducting bundle of the heart (the atrioventricular bundle). Within the septum, this atrioventricular bundle). Within the septum, this bundle divides into the right and left bundle bundle divides into the right and left bundle branches.branches.

ContractionContraction Cardiac muscle cells have the ability to generate Cardiac muscle cells have the ability to generate

spontaneous action potentials, but cells of the SA node do spontaneous action potentials, but cells of the SA node do this at an increased frequency – PACEMAKER.this at an increased frequency – PACEMAKER.

Action potentials that are produced spread from the SA Action potentials that are produced spread from the SA node to adjacent cardiac muscle fibers of the atrium. node to adjacent cardiac muscle fibers of the atrium. Action potentials are conducted from the SA node to the AV Action potentials are conducted from the SA node to the AV node really fast.node really fast.

Action potentials get conducted from the AV node to the Action potentials get conducted from the AV node to the bundle branches and then the velocity of the action really bundle branches and then the velocity of the action really speeds up. It passes through the right and left bundle speeds up. It passes through the right and left bundle branches and penetrates the myocardium of the ventricles. branches and penetrates the myocardium of the ventricles. Ventricular contraction begins at the apex and proceeds Ventricular contraction begins at the apex and proceeds toward the base of the heart. During this process, the toward the base of the heart. During this process, the distance between the base and the apex decreases – distance between the base and the apex decreases – shortening the heart.shortening the heart.

CONTRACTION IS SYSTOLE. VENTRICULAR SYSTOLE CONTRACTION IS SYSTOLE. VENTRICULAR SYSTOLE CAUSES EJECTION OF BLOOD FROM THE HEART.CAUSES EJECTION OF BLOOD FROM THE HEART.

Cardiac CycleCardiac Cycle VD – Pressure decreases in the atria. As the AV VD – Pressure decreases in the atria. As the AV

valves open, blood flows into the ventricles.valves open, blood flows into the ventricles.2/3rds of the way through filling, the SA node 2/3rds of the way through filling, the SA node depolarizes (the action potential is spread over the depolarizes (the action potential is spread over the atria) the atria contracts causing AS.atria) the atria contracts causing AS.

VS – Ventricular contraction causes the ventricular VS – Ventricular contraction causes the ventricular pressure to increase – AV valves close. Pressure pressure to increase – AV valves close. Pressure rises until the ventricular pressure exceeds the rises until the ventricular pressure exceeds the pressure in the blood vessels. Isometric pressure in the blood vessels. Isometric contraction: AV valve is closed and the SL is not yet contraction: AV valve is closed and the SL is not yet open (pressurizes the chambers). When the open (pressurizes the chambers). When the ventricular pressure exceeds the pressure in the ventricular pressure exceeds the pressure in the vessels, the SL’s open and ejection begins. vessels, the SL’s open and ejection begins. Ventricular volume decreases during ejection (VD).Ventricular volume decreases during ejection (VD).

ShockwaveShockwave