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Cardiovascular System: Structure, Function, and Response to Exercise

Cardiovascular System: Structure & Functions

Overview

  • The cardiovascular system's structure includes the heart, blood vessels (arteries, veins, capillaries), and blood (platelets, plasma, red and white blood cells).

  • Functions include transporting oxygen, water, and nutrients to cells, removing wastes, fighting diseases, circulating blood, and thermoregulation.

  • Responses to exercise vary with intensity, influencing stroke volume, heart rate, and cardiac output.

Key Knowledge Areas

  • Structure and function of the cardiovascular system, including the heart, blood vessels, and blood flow at rest and during exercise.

  • Role in thermoregulation: vasodilation and vasoconstriction effects on blood distribution during rest and physical activity.

  • Relationship between stroke volume, heart rate, and cardiac output at rest, submaximal, and maximal exercise.

Functions

  • Circulates blood throughout the body.

  • Delivers oxygen, water, and nutrients to cells.

  • Removes carbon dioxide and other wastes from cells.

  • Maintains body temperature and hydration levels.

  • Fights diseases.

Anatomy of the Heart

  • The heart has two pumps:

    • Left Pump: Left atrium and left ventricle; handles oxygenated blood for the body.

    • Right Pump: Right atrium and right ventricle; handles carbon dioxide-rich blood, which is sent to the lungs.

  • Key Structures:

    • Aorta

    • Pulmonary artery

    • Right atrium

    • Tricuspid valve

    • Right ventricle

    • Inferior vena cava

    • Left atrium

    • Pulmonary vein

    • Bicuspid valve

    • Left ventricle

    • Superior vena cava

    • Septum

Cardiac Cycle

  • Systole: Heart contracts, forcing blood out.

  • Diastole: Heart relaxes and fills with blood.

  • Cardiac cycle: One complete heartbeat, including systole and diastole.

  • Blood Flow:

    • Diastole (Atria Filling): All valves closed; blood returns to atria.

    • Diastole (Atria Contracting): Tricuspid and mitral valves open; atria contract, pushing blood into ventricles.

    • Systole (Ventricles Contracting - Initial): All valves closed.

    • Systole (Ventricles Emptying): Pulmonary and aortic valves open; ventricles contract, pushing blood into pulmonary and systemic circulation.

Blood Composition

  • Blood cells make up 45% of blood volume, while plasma makes up 55%.

  • Types of blood cells:

    1. Red blood cells

    2. White blood cells

    3. Platelets

Red Blood Cells

  • Make up 99% of blood cells.

  • Carry oxygen to cells and carbon dioxide from cells.

  • Contain hemoglobin.

  • Produced in bone marrow.

  • Lifespan of about four months.

White Blood Cells

  • Ratio of 1:700 with red blood cells.

  • Larger than red blood cells.

  • Fight diseases by digesting them.

  • Lifespan of a few days.

Platelets

  • Cause blood to clot.

  • Smaller than red blood cells.

  • Produced in bone marrow.

Plasma

  • 90% water.

  • Carries nutrients.

  • Assists platelets in blood clotting.

  • Reduced plasma levels (dehydration) reduce blood volume and oxygen supply to muscles.

Blood Vessels

  • Control the direction and volume of blood flow.

  • Three types: arteries, veins, capillaries.

Arteries

  • Carry oxygenated blood away from the heart.

  • Elastic walls expand with each heartbeat.

  • Common pulse measurement areas: carotid (neck) and radial (wrist).

Veins

  • Carry deoxygenated blood back to the heart.

  • More rigid walls than arteries.

  • Muscle contractions and one-way valves aid blood flow.

  • Proper warm-down prevents blood pooling.

Capillaries

  • Smallest blood vessels.

  • Exchange nutrients and waste between blood and body cells.

  • Dilate during exercise to increase blood flow.

  • Long-term exercise can increase capillary number.

Blood Circulation

  • Systemic Circulation: Oxygenated blood from the left ventricle and aorta circulates to the body (excluding lungs), and deoxygenated blood returns to the right atrium via the vena cava.

  • Pulmonary Circulation: Deoxygenated blood goes from the right ventricle to the lungs via the pulmonary artery, and oxygenated blood returns to the left atrium via the pulmonary vein.

Heart Response to Exercise

  • Changes in heart rate during exercise and recovery periods.

  • Differences between trained and untrained individuals.

Blood Pressure

  • Blood pressure drives blood circulation.

  • Measured using a sphygmomanometer and stethoscope.

  • Systolic pressure: Highest pressure when the left ventricle pumps.

  • Diastolic pressure: Lowest pressure when the left ventricle relaxes.

Thermoregulation

  • Maintenance of body temperature.

  • Core temperature range: 36.5-37.5^{\circ}C.

  • Mechanisms controlled by the hypothalamus:

    • Sweating

    • Shivering

    • Controlling blood flow to the skin.

  • Vasodilation: Blood vessels expand to increase blood flow to the skin for heat loss.

  • Vasoconstriction: Blood vessels contract to reduce blood flow to the skin for heat retention.

Blood Distribution

  • At rest, blood is directed away from muscles (vasoconstriction) and towards vital organs (vasodilation).

  • During exercise, blood is directed away from inactive organs and muscles (vasoconstriction) and towards working muscles (vasodilation).

Hyperthermia & Hypothermia

  • Hyperthermia: Core temperature above 36.5-37.5^{\circ}C.

    • The body redirects blood flow to the skin and increases sweating.

    • Can impair performance due to reduced blood flow to muscles. Maintain hydration.

  • Hypothermia: Core temperature below 35^{\circ}C.

    • The body responds with shivering and redirects blood flow to major organs.

    • Vasoconstriction reduces heat loss.

    • Impairs performance due to reduced blood flow to working muscles.

Heart Features & Calculations

  • Heart size: Approximately the size of a large fist.

  • Resting heart rate: Average is 72 bpm.

  • Stroke Volume (SV): Blood pumped by the left ventricle per beat.

  • Cardiac Output (Q): Blood pumped by the heart per minute.

  • Males: ~5L/min, Females: ~4L/min.

  • Formula: Q = SV \times HR Example: 72 bpm \times 70 \frac{mL}{beat} = 5.04 \frac{L}{min}

Heart Rate Factors

  • Gender (males tend to have lower resting HR)

  • Eating, laughing, and smoking increase HR

  • Body position

Pulse Measurement

  • Locations: Radial pulse (wrist) and carotid artery (neck).

  • Count pulses for 30 seconds and multiply by two to get beats per minute (heart rate).

Calculating Max Heart Rate

  • Maximum heart rate = 220 - age.

  • Max HR decreases with age.

Cardiovascular Responses to Physical Activity

  • Acute responses meet the increased demands for oxygen and fuel delivery to working muscles.

Cardiovascular Variable Responses to Exercise

  • Heart Rate: Increases

  • Stroke Volume: Increases

  • Cardiac Output: Increases

  • Systolic blood pressure: Increases

  • Blood Flow: Increases to working muscles, decreases to non-vital organs/muscles

  • Blood volume: Decreases

  • A-vo2 difference: Increases

Increased Heart Rate (HR)

  • Increases quickly during exercise.

  • Increases linearly with exercise intensity.

  • Average resting HR is approximately 72 bpm, reaching over 200 bpm during maximal exercise.

  • Returns to resting levels after exercise.

Increased Stroke Volume (SV)

  • Increases with exercise intensity to a certain point.

  • Resting values: Females ≈ 60mL/beat, Males ≈ 80mL/beat.

  • Increases to 110–130mL/beat during maximal exercise; higher in trained athletes.

Increased Cardiac Output (Q)

  • Increases proportionally with exercise intensity.

  • Resting cardiac output for the average adult male is approximately 5–6 litres.

Submaximal Exercise

  • Heart rate increases until it meets the body's demands, reaching a steady state.

High-Intensity Exercise

  • Heart rate increases linearly until it reaches maximum heart rate (near 200 bpm).

  • Stroke volume plateaus when exercise intensity reaches around 40–60% of maximal capacity.

Increased Systolic Blood Pressure

  • Average BP at rest: 120/80 mm Hg

  • Systolic reading rises during exercise due to increased heart rate, stroke volume, and cardiac output (can reach around 200 mm Hg at maximal intensity)

  • Diastolic reading remains largely unchanged.

Blood Flow Redistribution During Exercise

  • Blood is directed away from organs and inactive muscles via vasoconstriction.

  • Blood vessels surrounding working muscles vasodilate, increasing blood flow.

Decreased Blood Volume

  • Blood volume decreases due to fluid loss through sweat.

  • The size of the decrease depends on the exercise duration, intensity, hydration level, and environmental conditions.

Increased Arteriovenous Oxygen Difference (a-VO2 diff.)

  • Difference in oxygen concentration in arterioles compared to venuoles.

  • Increases due to increased O2 extraction by muscles.