Integrative Physiology: Cardiovascular Physiology

Cardiovascular Physiology Study Guide

Overview of the Cardiovascular System

  • Anatomy Review: Understanding the components including the heart, blood vessels, and major functions.

  • Key Concepts:

    • Pressure, Volume, Flow, and Resistance: Fundamental principles that govern the circulation of blood.

    • Cardiac Muscle and the Heart: Structure and function of the heart and its musculature.

    • The Heart as a Pump: Mechanisms by which the heart generates blood flow.

    • Cardiac Cycle: Phases of the heart's activity in one complete heartbeat.

    • Cardiac Output: Volume of blood pumped by the heart per minute.

Transport in the Cardiovascular System

  • Table 14-1: Transport of Various Substances:

    • Oxygen: Moves from lungs to all cells.

    • Nutrients and Water: Transferred from the intestinal tract to all cells.

    • Wastes: Eliminated from some cells to kidneys.

    • Immune Cells and Antibodies: Present in blood continuously for defense.

    • Hormones: Secreted by endocrine cells and delivered to target cells.

    • Metabolic Wastes: Transported from all cells to kidneys for removal.

    • Heat: Exchanged through skin.

    • Carbon Dioxide: Exhaled from lungs, produced by all cells.

Pulmonary and Systemic Circulation

  • Comparison: Diagram depicting blood flow from the large vessels to systemic circulation to pulmonary circulation.

    • Pulmonary Circulation: Moves blood between heart and lungs.

    • Systemic Circulation: Moves blood between heart and the rest of the body.

Pressure Differences in Fluids

  • Basic Concept: Blood exerts pressure on vessel walls which constitutes blood pressure.

  • Pressure Gradient in Systemic Circulation: Blood flows down pressure gradients.

  • Friction Losses: Pressure decreases over distances due to energy loss from friction, contributing to pressure drop from the aorta to venae cavae.

  • Key Formulas:

    • Pressure Gradient: P1 - P2 = AP

    • Flow Dependence: Flow only occurs with a positive pressure gradient (i.e., when AP > 0).

Resistance to Flow

  • Fundamental Formula: Flow inversely related to resistance. Resistance is determined by tube radius:

    • R ext{ is proportional to } rac{1}{radius^4}

  • Effects of radius on flow: E.g., if radius doubles, resistance decreases sixteenfold, drastically increasing flow.

Cardiac Structure and Function

Heart Anatomy

  • Size and Location: Hollow organ about the size of a fist located in the thoracic cavity, predominantly positioned left.

  • Composition: Mainly myocardium, encased in the pericardium (a protective sac).

  • Layers of the Heart Wall: Epicardium, myocardium, endocardium.

Heart Valves

  • Function: Ensure unidirectional blood flow through the heart's chambers.

  • Types of Valves:

    • Right Side: Tricuspid (AV) valve, pulmonary semilunar valve.

    • Left Side: Bicuspid (mitral) valve, aortic semilunar valve.

  • Mechanism: Valves close when blood attempts to flow backward, utilizing valve cusps and chordae tendineae.

Cardiac Muscle Characteristics

  • Differences from Skeletal Muscle: Smaller in cell diameter, single nucleus per fiber, intercalated disks allowing force transfer and electrical connection.

  • Key Components: Larger T-tubules, smaller sarcoplasmic reticulum, and abundant mitochondria.

Cardiac Electrical Activity

Autorhythmic Cells

  • Pacemaker Potential: Ion movements involving Na+ and K+, resulting in gradual depolarization that triggers action potentials for heart contractions.

  • Role of SA Node: Sets heart rate at approximately 70 beats per minute, with AV node and Purkinje fibers acting as secondary pacemakers.

Action Potential Comparison

  • Table 14-3: Compare cardiac and skeletal muscle action potentials, noting differences in duration and ionic mechanisms leading to heart contraction.

Mechanical Events of the Cardiac Cycle

Phases of the Cardiac Cycle

  1. Late Diastole: Chambers are relaxed; ventricles fill passively.

  2. Atrial Systole: Atrial contraction forces additional blood into ventricles.

  3. Isovolumetric Ventricular Contraction: Ventricles contract, AV valves close but pressure is insufficient to open semilunar valves.

  4. Ventricular Ejection: Ventricular pressure exceeds arterial pressure; semilunar valves open and blood is ejected.

  5. Isovolumetric Ventricular Relaxation: Ventricles relax, pressure falls, blood backflows closes semilunar valves.

Cardiac Output Calculations

  • Formulas for Cardiac Output:

    • Stroke Volume: SV = EDV - ESV (EDV = End-diastolic volume, ESV = End-systolic volume)

    • Cardiac Output: CO = HR imes SV. Average output is approximately 5 L/min.

Factors Influencing Stroke Volume

  • Frank-Starling Law: Increased EDV results in increased stroke volume.

  • Contractility: Influenced by catecholamines, changing force and speed of heart contractions.

  • Venous Return: Affected by the skeletal muscle and respiratory pumps and sympathetic innervation.

Detailed Mechanism of Contraction

  • Calcium Influx Mechanisms: Norepinephrine increases contractility via B1-receptors activating the cAMP pathway, enhancing calcium release and influence of phospholamban on Ca2+ handling in the sarcoplasmic reticulum.

Conclusion

  • Understanding the intricacies of the cardiovascular system, structure and function of the heart, the dynamics of blood circulation, and the role of electrical activities provide a holistic view of cardiovascular physiology essential for further study or clinical applications.