Integrative Physiology: Cardiovascular Physiology Study Notes

Cardiovascular System Anatomy Review

  • Outline

    • Cardiovascular system – anatomy review

    • Pressure, volume, flow, and resistance

    • Cardiac muscle and the heart

    • The heart as a pump

    • Cardiac cycle

    • Cardiac output

Transport in the Cardiovascular System

  • Table 14-1: Transport

Cardiovascular Circulation

  • Pulmonary and Systemic Circulation

    • Pulmonary Circulation

      • Pathway:

        1. Right side of heart

        2. Pulmonary arteries

        3. Pulmonary capillaries of alveoli of lungs

        4. Pulmonary veins to left side of heart

    • Systemic Circulation

      • Pathway:

        1. Left side of heart

        2. Systemic arteries

        3. Systemic arterioles

        4. Systemic capillaries of all body organs and tissues

        5. Systemic venules to right side of heart

        6. Venae cavae

  • Heart Anatomy

    • Size of a fist, located in thoracic cavity, mostly left side

    • Composed mostly of myocardium with a membranous sack, pericardium

    • Valves ensure one-way flow:

      • Right Side:

        • Tricuspid AV valve

        • Pulmonary semilunar valve

      • Left Side:

        • Bicuspid AV valve

        • Aortic semilunar valve

    • Heart Valves

      • Have a fibrous skeleton to prevent stretching

      • Open and close to prevent backflow during heart contractions

Pressure Dynamics

  • Pressure Change in CVS

    • Blood pressure created by contracting muscles, mainly by the left ventricle

    • Factors Affecting Blood Pressure:

      • Blood vessel constriction increases blood pressure

      • Blood vessel dilation decreases blood pressure

      • Volume changes greatly affect blood pressure in the cardiovascular system (CVS)

    • Pressure Gradient

      • Blood flows from high pressure to low pressure

      • Flow only occurs with a positive pressure gradient

      • Pressure gradient formula:

        • P1 - P2 = AP

      • Requires a positive pressure difference for flow

  • Resistance to Flow

    • Resistance is affected by radius:

      • R \propto r^{-4}

      • Flow rate is inversely related to resistance:

        • Flow \propto 1/R

    • Example: Tube A and B with differing radii affect flow significantly due to this relationship

Cardiac Muscle vs. Skeletal Muscle

  • Cardiac Muscle Characteristics:

    • Smaller, single nucleus per fiber

    • Contains intercalated disks:

      • Desmosomes transfer force

      • Gap junctions provide electrical connections

    • Larger T-tubules, smaller sarcoplasmic reticulum

    • Higher mitochondria volume, important for ATP production

  • Contraction Mechanism:

    • Action potential initiates calcium influx, inducing contraction through interactions with troponin and actin

    • Relaxation occurs when calcium unbinds from troponin and returns to the sarcoplasmic reticulum

Cardiac Cycle

  • Major Phases:

    • Late Diastole: Both chambers relaxed, ventricles fill passively

    • Atrial Systole: Atria contract, forcing more blood into ventricles

    • Isovolumic Ventricular Contraction: Ventricles contract, pressure builds, AV valves close

    • Ventricular Ejection: Semilunar valves open, blood ejected into circulation

    • Isovolumic Ventricular Relaxation: Semilunar valves close, ventricles relax, and pressure falls

Cardiac Output

  • Definitions:

    • Stroke Volume (SV): Amount of blood pumped by one ventricle per contraction

      • Formula: SV = EDV - ESV

    • Cardiac Output (CO): Volume of blood pumped by one ventricle over time

      • Formula: CO = HR \times SV

      • Average CO = 5 L/min

  • Factors Influencing Stroke Volume:

    • Frank-Starling law: Stroke volume increases with end-diastolic volume (EDV)

    • Affected by venous return, sympathetic innervation, and length-force relationships

Electrical Conduction in the Heart

  • Components:

    • SA node (70 bpm, natural pacemaker)

    • AV node (50 bpm)

    • Purkinje fibers (25-40 bpm under certain conditions)

  • Paths of Electrical Activity:

    • Depolarization spreads from SA node to AV node via internodal pathways

    • Slower conduction through the AV node allows for atrial contraction before ventricular depolarization

  • ECG Waves:

    • P Wave: Represents atrial depolarization

    • QRS Complex: Represents ventricular depolarization

    • T Wave: Represents ventricular repolarization

Modulation of Heart Rate by the Autonomic Nervous System

  • Sympathetic Nervous System: Increases heart rate through norepinephrine, enhancing depolarization rates

  • Parasympathetic Nervous System: Decreases heart rate through acetylcholine, causing hyperpolarization and slower depolarization

Summary of Action Potentials

  • Comparison:

    • Contractile Myocardium vs. Skeletal Muscle

      • Cardiac muscle has a prolonged action potential due to calcium influx, unlike skeletal muscle which has a short refractory period

  • Einthoven’s Triangle: Method for recording the electrical activity of the heart using electrode placement on the body