Chapter 9: Circulatory System - SPE 325

Introduction to Blood Flow and Cardiac Function

  • The body redistributes blood flow to prioritize skeletal muscles during physical activity, while reducing flow to less crucial organs like the digestive organs.

    • Importance of this redistribution can be observed during exercise or emergencies, highlighting the body's adaptive physiology.

Understanding the Cardiovascular System

Basic Terminology and Structure

  • Heart: The central organ that creates pressure to circulate blood.

  • Arteries and Arterioles:

    • Arteries carry blood away from the heart, often oxygenated, to various tissues throughout the body.

    • Arterioles are smaller branches of arteries responsible for regulating blood flow to specific areas.

  • Capillaries:

    • Function as the sites for gas exchange, allowing oxygen to enter tissues while carbon dioxide is transported back into the blood.

    • Crucial for maintaining oxygen levels during physical activity.

  • Veins:

    • Collect deoxygenated blood from tissues and return it to the heart.

Circulatory Pathways

  • Pulmonary Circuit:

    • Transports deoxygenated blood from the right side of the heart to the lungs for oxygenation.

    • Major steps include:

    1. Blood enters the right atrium.

    2. Blood moves into the right ventricle.

    3. Blood is pumped to the lungs.

    4. Blood returns to the left atrium, now oxygenated.

  • Systemic Circuit:

    • Supplies oxygenated blood from the left side of the heart to the rest of the body.

    • Involves:

    1. Blood pumped from the left ventricle into the aorta.

    2. Distribution through systemic arteries to all parts of the body.

    3. Return of deoxygenated blood through veins back to the heart.

Myocardium and Heart Structure

Layers of the Heart Wall

  • Epicardium:

    • The outer layer, consisting of a membrane with blood capillaries and nerve fibers.

  • Myocardium:

    • The middle muscular layer, composed of cardiac muscle tissue, critical for heart contractions and thus blood circulation.

    • Contains blood capillaries and nerve fibers to support muscle function with adequate oxygen and nutrient supply.

  • Endocardium:

    • The inner layer, consisting of connective tissue layers that line the heart chambers and cover heart valves.

Blood Supply to Myocardium

  • Coronary Arteries:

    • Supply the heart muscle itself with oxygenated blood.

    • Development of coronary artery disease can result in blocked arteries, necessitating bypass surgery or interventions to restore blood flow.

  • Myocardial Infarction:

    • Known as a heart attack, represents blockage in coronary blood flow resulting in damage or death of heart cells.

Muscle Types: Cardiac vs. Skeletal Muscle

Points of Comparison

  • Skeletal Muscle vs. Cardiac Muscle:

    • Cardiac muscle cells contain one nucleus per cell, while skeletal muscles have multiple nuclei.

    • Cardiac muscle features intercalated discs that allow for synchronized contractions by enabling ion exchange between fibers.

    • The synchronous contraction of cardiac muscle is vital for effective heart function; irregular contractions can lead to serious health issues.

Benefits of Exercise on Heart Health

Positive Impact of Regular Exercise

  • Regular exercise reduces the incidence of heart attacks and improves survival rates from heart attacks.

  • Exercise has the following impacts on myocardial damage:

    • Trained individuals experience reduced myocardial damage during a heart attack compared to untrained individuals.

    • A graph reveals that approximately 60% damage might occur in untrained individuals compared to only about 20% in trained individuals during myocardial infarctions.

Electrical Activity of the Heart

Overview of Cardiac Electrical Conduction

  • SA Node (Sinoatrial Node):

    • The natural pacemaker of the heart, initiating depolarization and causing atrial contraction.

  • AV Node (Atrioventricular Node):

    • Receives impulses from the SA node and conveys them to the ventricles, allowing for coordinated contraction.

  • Bundle Branches:

    • Conduct depolarization impulses from the AV node to the ventricles while allowing brief delays for the ventricles to fill with blood.

  • Purkinje Fibers:

    • Deliver electrical impulses throughout the ventricles, ensuring that ventricular contraction occurs synchronously.

Components of an ECG (Electrocardiogram)

  • P Wave:

    • Represents atrial depolarization.

  • QRS Complex:

    • Represents ventricular depolarization, as the ventricles contract.

  • T Wave:

    • Represents ventricular repolarization, indicating recovery after contraction.

  • ECG abnormalities such as ST segment depression can signal underlying myocardial ischemia, highlighting the importance of ECG in assessing heart health.

Conclusion

  • Understanding the cardiovascular system, its functioning, and the role of exercise in promoting heart health is essential.

  • Continued study of related topics such as ECG readings and the physiological adaptations to exercise is crucial for anyone pursuing a career in health, fitness, or rehabilitation.