Review Concept Map for Heart

Introduction to the Heart and Cardiovascular System

  • Dr. Wong introduces the topic of Chapter 18, focusing on the heart.

  • Concept maps are used to organize information, visualize connections, and understand the heart's structure, function, and circulatory paths.

Heart Structure

  • Location:

    • The heart is located in the mediastinal cavity, specifically in the pericardial cavity within the thoracic cavity.

    • Positioned between the second and fifth intercostal spaces.

    • Size is approximately that of a fist; about two-thirds is oriented towards the left of the sternum.

  • Protection:

    • The heart is protected by the ribcage and sternum, as well as the pericardial cavity that surrounds it.

    • The lining consists of serous membranes (named after the cavity they line).

  • Pericardium:

    • A two-fold membrane consisting of:

      • Parietal Layer: lines the wall of the cavity.

      • Visceral Layer: covers the heart’s surface.

      • Fibrous Layer: a dense fibrous outer layer anchoring the heart and preventing overflow.

  • Myocardium:

    • The heart wall is mainly made of cardiac muscle.

    • Fibrous tissues direct the path of electrical currents, acting as non-conductive and non-contractile pathways.

Functions of the Heart

  • The heart includes:

    • Pumping mechanism: Different parts of the heart are responsible for pumping and receiving blood.

    • Unidirectional flow control: AV valves position is crucial for preventing backflow of blood.

Valves and Their Functions

  • Atrioventricular (AV) Valves:

    • Include the tricuspid and bicuspid valves, they control blood flow from atria to ventricles.

    • The papillary muscles contract to keep these valves secured, preventing backflow when the ventricles contract.

  • Semilunar Valves:

    • Ensure unidirectional flow from the ventricles into the arteries (aorta and pulmonary artery).

    • Prevent backflow from the arteries into the ventricles.

Cardiac Cycle

  • The cardiac cycle consists of:

    • Ventricular Filling: AV valves must be open for this to occur, as pressure in the ventricles falls below that of the atria.

    • Atrial Contraction: Atria depolarize, contract, and push blood into the ventricles.

    • Ventricular Contraction: Increased pressure causes AV valves to close; blood is pumped into the systemic and pulmonary circuits.

Electrical Activity

  • Depolarization and Repolarization:

    • Depolarization leads to contraction while repolarization leads to relaxation, essential for rhythmic heart activity.

  • Septa: The heart has partitions between chambers, consisting of two atria and two ventricles.

  • The right side handles deoxygenated blood; the left side handles oxygenated blood.

Circulatory Pathways

  • Right Atrium: Receives deoxygenated blood from the systemic circulation via the vena cava.

  • Right Ventricle: Pumps deoxygenated blood to lungs for oxygenation.

  • Left Atrium: Receives oxygenated blood from lungs via pulmonary veins.

  • Left Ventricle: Pumps oxygenated blood into systemic circulation through the aorta.

Cardiovascular Function

  • Cardiac Output: Volume of blood pumped per minute, calculated by stroke volume and heart rate.

  • Key factors affecting stroke volume:

    • Preload: initial stretching of cardiac muscle cells.

    • Contractility: inherent strength and vigor of the heart's contraction.

    • Afterload: force against which the heart must work to eject blood.

Conclusion

  • Understanding heart structure, function, the cardiac cycle, and the intrinsic conduction system is essential for grasping cardiovascular physiology.

  • Dr. Wong encourages exposure to various presentations of these concepts for better understanding.