Review of Cardiovascular Anatomy and Physiology

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Review of Cardiovascular Anatomy & Physiology

by
Louise Diehl, RN, MSN, ND, CCRN, ACNS-BC, NP-C
Nurse Practitioner - Owner
Doctor of Naturopathy
Lehigh Valley Wellness Center

The heart is a cone shaped muscular organ located in the chest behind the sternum in the mediastinal cavity between the lungs and in front of the spine. The heart is approximately the size of a fist.

The heart’s wall (Pericardium) is made up of three layers:

    Epicardium - inner surface
    Myocardium - makes up the largest portion of the heart’s wall. This muscle tissue contracts with each heartbeat.
    Endocardium - innermost layer of the heart’s wall contains endothelial tissue that lines the heart chambers and valves.

A skeleton of connective tissue called the fibrous pericardium surrounds the heart and acts a tough protective sac.

Chambers

The heart has four chambers: two atria and two ventricles.

    Right atrium receives deoxygenated blood from the body
    Left atrium receives oxygenated blood from the lungs

Contraction of the atria forces the blood into the ventricles.

The right and left ventricles are the pumping chambers of the heart.

    The right ventricle receives blood from the right atrium and pumps it through the pulmonary arteries to the lungs where it picks up oxygen and drops off carbon dioxide.
    The left ventricle receives oxygenated blood form the left atrium and pumps it through the aorta and then to the rest of the body.

Valves

The heart has four valves:

    Two atrioventricular (tricuspid and biscupid (mitral) valves and two semilunar (aortic and pulmonic valves). The valves open and close in response to changes in pressure within the chambers they connect and serve as one way doors that keep blood flowing through the heart in a forward direction. When the valves close they prevent backflow or regurgitation from one chamber to another. The closing of the valves creates the heart sounds heard through a stethoscope during a physical examination.
    The biscupid and triscupid vavles have leaflets or cusps which connect to the muscles in the heart wall. Damage to them may cause blood to flow backward into a chamber resulting in a heart murmur.

Coronary Circulation

The heart needs an adequate supply of blood to survive. The coronary arteries which lie on the surface of the heart supply the heart muscle with blood and oxygen.

    Left coronary artery originates off the aorta and supplies blood to the right atrium, the right ventricle, and part of the inferior/posterior surfaces of the left ventricle. The Bundle of His, the AV node and the SA node receive blood from this artery.
    The left coronary artery runs along the surface of the left atrium where it splits into the anterior descending and the left circumflex arteries.
    The left anterior descending artery supplies blood to the anterior wall of the ventricle, the interventricular septum, the right bundle branch and the left anterior fascicle of the left bundle branch.
    The circumflex artery supplies oxygenated blood to the lateral walls of the left ventricle and to the left atrium. The circumflex also supplies blood to the left posterior fascicle of the left bundle branch. This artery circles around the left ventricle and provides blood to the ventricle’s posterior portion.

When two or more arteries supply the same region they usually connect through anastomoses junctions that provide alternative routes of blood flow. These alternate routes of blood are called collateral circulation and provide blood capillaries that directly feed the heart muscle. Collateral circulation becomes so strong that even if major coronary arteries become clogged with plaque collateral circulation can continue to supply blood to the heart.

Transmission of Electrical Impulses

The heart can’t pump unless an electrical stimulus occurs first. Generation and transmission of electrical impulses depend on the automaticity, excitability, conductivity and contractility of cardiac cells.

    Automaticity refers to a cell’s ability to initiate an impulse. Pacemaker cells possess this ability.
    Excitability results from ion shifts across the cell membrane and indicates how well a cell responds to an electrical stimulus.
    Conductivity is the ability of a cell to transmit an electrical impulse to another cardiac cell. Contractility refers to how well the cell contracts after receiving a stimulus.

As impulses are transmitted cardiac cells undergo cycles of depolarization and repolarization.

    Polarized - cardiac cells are at rest meaning - no electrical activity takes place
    Resting potential – cell membranes separate different concentrations of ions such as sodium and potassium and create a more negative charge inside the cell.
    Cell depolarization (action potential) - a stimulus causes the ions to cross the cell membrane.
    Repolarization – electrical charges within the cell reverse and return to normal. The cell attempts to return to its resting state.
    Cycles of depolarization-repolarization This cycle consists of 5 phases 0-4.
        0 – cell receives an impulse from a neighboring cell and is depolarized
        1 - Early rapid repolarization (resting phase)
        2 - Plateau phase period of slow repolarization
        3 - Rapid repolarization phase During the last half of this phase the cell is in the relative refractory period, a very strong stimulus can depolarize it.
    During phases 1,2 and the beginning of phase 3 the cell is in its absolute refractory period. No stimulus can excite the cell.
        4 – Resting phase of the action potential. By the end of phase 4 the cell is ready for another stimulus.
    Once depolarization and repolarization occur the resulting electrical impulse travels through the heart along a pathway called the conduction system Impulses travel
        SA node

            Located in the upper right corner of the right atrium. Pacemaker of the heart. 60-100 times a minute.

        Internodal tracts and Bachmann’s bundle to the
        AV node

            Responsible for (delaying the impulses that reach it.) The nodal tissue itself has no pacemaker ability, but the tissue around it (junctional tissue) has pacemaker ability. 40-60 times a minute.
            This delay allows the ventricles to complete their filling phase as the atria contract.
            Also allows the cardiac muscle to contract to it’s fullest for peak cardiac output.

        Bundle of HIS, the Bundle branches

            Resumes the rapid conduction of the impulse through the ventricles. The bundle divides into the right and left branches.

        Purkenjie Fibers

            Network of nervous tissue that extends through the ventricles. Can serve as a pacemaker at a rate of 20-40 times a minute.