Exs 323: Chap09 Circulatory

Overview of the Circulatory System

  • Respiratory system adds oxygen and removes carbon dioxide from the blood, while the circulatory system is responsible for the delivery of oxygenated blood and nutrients to tissues by their needs

  • Works alongside the pulmonary system (Cardiopulmonary system), emphasizing the role of the heart and lungs in oxygenating blood and supporting systemic circulation.

  • Primary Purposes:

    • Transport oxygen and nutrients to tissues, vital for cellular respiration and energy production.

    • Remove carbon dioxide and wastes from tissues, preventing toxic buildup.

    • Transport signaling molecules, including hormones, vital for body regulation.

    • Regulate body temperature, aiding in homeostasis during varying environmental conditions.

  • Key CV Adjustments during Exercise:

    • Increased cardiac output, essential for meeting elevated metabolic demands during physical activity.

    • Redistribution of blood flow from inactive organs to working muscles, optimizing oxygen delivery and nutrient supply to active tissues.

Structural Components of the Cardiovascular System

  • Heart: Pumps blood to create pressure, consisting of chambers (atria and ventricles) that ensure unidirectional blood flow.

  • Arteries and Arterioles: Carry oxygen-rich blood away from the heart, featuring muscular walls that control blood flow.

  • Capillaries: Sites of gas and nutrient exchange allow diffusion between blood and tissues.

  • Veins and Venules: Carry deoxygenated blood towards the heart, equipped with valves to prevent backflow.

  • Structure of the Heart
Circulatory Response to Exercise

  • The heart consists of two main circuits: -

  • Pulmonary Circuit: The right side pumps deoxygenated blood to the lungs for reoxygenation.

  • Systemic Circuit: The left side pumps oxygenated blood to the body, delivering vital nutrients.

Heart Structure and Cardiac Cycle

  • Layers of Heart Wall:

    • Epicardium: Outer layer providing protection.

    • Myocardium: Thick, muscular middle layer responsible for contraction.

    • Endocardium: Inner layer lining the chambers.

  • Coronary arteries supply oxygen-rich blood to the myocardium to sustain its activity.

  • Myocardial infarction, or heart attack, arises from blockage in coronary blood flow, causing tissue damage.

  • Cardiac Cycle Phases:

    • Systole: Contraction phase; approximately 60-70 mL of blood ejected from ventricles per beat.

    • Diastole: Relaxation phase; heart fills with blood, crucial for effective pumping.

  • Heart sounds correspond to valve operations during systole and diastole, serving as indicators of heart health.

  • why only 1/3 of blood pressure?

    • Note that a rising heart rate results in a greater time reduction in diastole, whereas systole is less affected.

Blood Pressure Regulation

  • Blood pressure can be increased by the following factors:

    a. ↑ in blood volume 

    b. ↑ in heart rate 

    c. ↑ blood viscosity 

    d. ↑ in stroke volume 

    e. ↑ peripheral resistance

  • Mean Arterial Pressure (MAP):

    • Indicates overall blood pressure; influenced by cardiac output and vascular resistance, providing insight into perfusion status.

    • Normal values are approximately 120/80 mmHg, representing healthy cardiovascular function.

  • Short-term regulation:

    • Sympathetic nervous system and baroreceptors regulate blood pressure, allowing rapid response to physical demands or stressors.

  • Long-term Regulation:

    • Governed by kidneys managing blood volume, crucial for sustaining blood pressure over time.

Cardiac Output Regulation

  • Cardiac Output Formula:

    • Q = Heart Rate (HR) x Stroke Volume (SV), illustrating the heart’s efficiency in delivering blood.

  • Key influencers of HR and SV include autonomic nervous system modulations, with sympathetic stimulation increasing both parameters during exercise.

  • Stroke Volume Factors:

    • End-Diastolic Volume (EDV)(pre-load): Volume of blood in ventricles at end of diastole; higher EDV leads to increased stroke volume.

    • Afterload: The pressure the ventricle must overcome to eject blood; significant in determining stroke volume.

    • Contractility: Strength of ventricular contraction, influenced by the sympathetic nervous system, enhancing cardiac output during physical exertion.

End-Diastolic Volume (EDV)(pre-load)

  • Dependent on venous return

  • Venous return increased by:

–Venoconstriction

  • Via SNS

–Skeletal muscle pump

  • Rhythmic skeletal muscle contractions force blood in the extremities toward the heart

  • One-way valves in veins prevent backflow of blood

–Respiratory pump

  • Changes in thoracic pressure pull blood toward heart

  • Result: Frank-Starling mechanism →Greater EDV results in a more forceful contraction

Blood Flow Dynamics

  • Blood flow is governed by pressure differences and resistance; resistance is influenced by vessel diameter, blood viscosity, and vessel length, impacting overall circulation efficiency.

  • So our pressure gradient generated by systole is driving blood from the LV (Left ventricle) towards the RA (Right Atrium).

  • Blood flow dynamics change during exercise due to various physiological adaptations :

Changes in Blood Flow During Exercise

  • During exercise, cardiac output increases significantly, with substantial redistribution towards active muscles: - Up to 80–85% of cardiac output during maximal exercise is redirected to muscle tissues, leading to decreased flow to non-active organs.

    • Regulation of blood flow is facilitated through nitric oxide as a potent vasodilator, enhancing blood supply to working muscles.

Oxygen Delivery and Recovery

  • Oxygen delivery increases due to heightened cardiac output and blood flow redistribution towards active tissues, crucial for sustaining energy production during exercise.

  • Transitioning from rest to exercise causes a rapid increase in heart rate, stroke volume, and cardiac output, with gradual recovery in HR and SV post-exercise as the body returns to homeostasis.

Final Thoughts

Understanding how the cardiovascular system adjusts to exercise helps explain performance in sports and activity-related physiology, providing insights into training adaptations and recovery strategies.

  • Focus on adjustments during different intensities and durations of exercise and their implications for optimal training and performance enhancement strategies.

Rest to exercise / exercise to recovery

  • At the onset of exercise:

–Rapid increase in HR, SV, cardiac output

–Plateau in submaximal (below lactate threshold) exercise

  • During recovery

–Decrease in HR, SV, and cardiac output toward resting levels

–Time to return depends on:

  • Duration and intensity of exercise

  • Training state of subject 

extra -

  • why only 1/3 of blood pressure?

    • Note that a rising heart rate results in a greater time reduction in diastole, whereas systole is less affected.

  • ST segment Depression - & myocardial escimeia

  • what are 2 major alterations of CVS during exercise?

  • frank staling mechanism → adjusts stroke volume

  • Autonomic nervous system is what’s regulating Heart rate and stroke volume

  • Red Blood Cells - deliver oxygen

  • Arteriovenous difference (AV difference) - how much oxygen is extracted from RBC