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.