Gas Exchange and the Cardiovascular System

B3.1 Gas Exchange

  • Theme: Form and Function

  • Level of Organisation: Organisms

  • IB Guiding Question: How are multicellular organisms adapted to carry out gas exchange?

  • Learning Objective: Outline how gas exchange happens in animals and plants.

Overview of Diffusion

  • Extracellular Space

  • Lipid Bilayer (cell membrane)

  • TIME

  • Intracellular Space

Sugar Cube Competition

  • Goal: Dissolve your sugar cube as quickly as possible.

  • Supplies for each participant:

    • A cup

    • A sugar cube

    • A spoon

    • Water from the sink

B3.1.1: Gas Exchange as a Vital Function in Organisms

  • Cells require gas exchange for the processes of respiration and photosynthesis.

  • Cells performing aerobic respiration require:

    • Oxygen to enter the cell

    • Carbon Dioxide (CO₂) to exit the cell

  • Cells performing photosynthesis require:

    • Carbon Dioxide (CO₂) to enter the cell

    • Oxygen (O₂) to exit the cell

  • Gas Exchange Definition: The exchange of carbon dioxide and oxygen gases at cells and tissues through the process of diffusion.

Specialized Gas Exchange Surfaces

  • Unicellular organisms can exchange gases directly through their plasma membrane due to a large surface area to volume ratio.

  • Larger animals have a smaller surface area to volume ratio, making it challenging to supply sufficient oxygen to all cells.

  • Diffusion: A slow process; thus, larger animals require specialized gas exchange and transport systems for efficient oxygen acquisition.

B3.1.2-3.1.3: Properties of Gas-Exchange Surfaces and Concentration Gradients

  • Adaptations of gas exchange systems include:

    • Large Surface Area: Increases the quantity of gas exchanged.

    • Very Thin Tissue Layers: Reduces gas travel distance (often one cell thick).

    • Permeable Membranes: Allow gases to diffuse through them.

    • Concentration Gradient: Facilitates diffusion from high to low concentration.

    • Moist Surface: Exchange surfaces must be covered with moisture for rapid gas dissolution and diffusion.

Maintaining Concentration Gradients

  • Gas exchange via diffusion depends on maintaining concentration gradients.

  • Animals adapt to ensure a high concentration gradient:

    • Dense networks of capillaries surround gas exchange tissues.

    • Continuous blood flow through surrounding capillaries.

    • Mechanisms in animals with lungs include:

    • Ventilating lungs with air to bring high oxygen concentration to alveoli while removing CO₂.

    • Moving water through gills to maintain high oxygen concentration.

Gas Exchange Through Gills

  • Gills in fish are adapted to facilitate rapid gas exchange through:

    • Large Surface Area: Increases interaction with water.

    • Continuous Blood Flow: Maintains gradient for gases.

    • Water Movement: Regularly passing through gills facilitates efficient oxygen absorption and carbon dioxide removal.

B3.1.4: Adaptations of Mammalian Lungs for Gas Exchange

  • Gas Exchange, Ventilation, and Respiration:

    • Gas Exchange: Involves the diffusion of gases at alveoli and respiring tissues.

    • Ventilation: The mechanical movement of air in and out of the lungs to support gas exchange (breathing).

    • Respiration: The biochemical release of ATP energy from organic compounds in cells.

Lungs

  • Lungs facilitate:

    • Exchange of Oxygen from air into bloodstream.

    • Exchange of Carbon Dioxide from bloodstream to air.

Diagram of the Lungs

  • Key Components:

    • Trachea

    • Right Lung

    • Bronchus

    • Bronchioles

    • Left Lung

    • Alveoli (located at the end of bronchioles)

Adaptations of the Lungs

  • Facilitates rapid gas exchange between alveoli and bloodstream:

    • Branching Bronchioles: Connect to numerous alveoli.

    • Extensive Alveoli Surface Area: Maximizes gas exchange.

    • Surfactant Secretion: Prevents alveoli walls from adhering and maintains moisture.

Ventilation of the Lungs

  • Two Stages of Ventilation:

    • Inspiration (Breathing In):

    • Diaphragm contracts and moves down.

    • External intercostal muscles contract, lifting ribcage.

    • Thoracic volume increases, lowering lung pressure, drawing air in.

    • Expiration (Breathing Out):

    • Abdominal muscles contract, pushing diaphragm up.

    • External intercostal muscles relax; internal intercostal muscles contract, lowering ribcage.

    • Thoracic volume decreases, increasing lung pressure, forcing air out.

Lung Volumes

  • Key Lung Volumes:

    • Tidal Volume: Volume of air in a normal breath.

    • Inspiratory Reserve: Extra volume that can be inhaled.

    • Expiratory Reserve: Extra volume that can be exhaled.

    • Vital Capacity: Maximum volume expelled after deepest breath, calculated as:
      extVitalCapacity=extTidalVolume+extInspiratoryReserve+extExpiratoryReserveext{Vital Capacity} = ext{Tidal Volume} + ext{Inspiratory Reserve} + ext{Expiratory Reserve}

Measuring Lung Volumes

  • Spirometers: Instruments used for measuring lung air capacity, used in lab exercises.

B3.1.7-B3.1.10: Adaptations for Gas Exchange in Leaves

  • Leaves facilitate gas exchange for respiration and photosynthesis while minimizing water loss.

Adaptations of Leaf Structure

  • Waxy Cuticle:

    • Covers epidermis to reduce water evaporation.

  • Epidermis:

    • Provides protection; transparent for light penetration.

  • Spongy Mesophyll:

    • Irregular shape maximizes surface area for gas exchange, containing air spaces.

Stomata and Veins

  • Air Spaces: Facilitate gas diffusion between mesophyll and atmosphere.

  • Stomata: Openings allowing gas entry/exit, controlled by guard cells.

  • Veins: Structural support containing xylem (water/mineral transport) and phloem (nutrient transport).

Transpiration

  • Definition: Movement of water through a plant and evaporation from aerial parts, a natural consequence of gas exchange.

Factors Affecting Transpiration

  • Light Intensity: Increased light leads to more open stomata, enhancing water diffusion.

  • Temperature: Higher temperatures increase kinetic energy of water particles leading to faster diffusion and evaporation.

  • Humidity: Increased humidity slows water diffusion by reducing concentration gradients.

  • Air Flow (Wind): Moving air removes water vapor, enhancing concentration gradients favoring increased transpiration.

Calculating Stomal Density

  1. Determine the area of the field of view:

    • Calculate using: extArea=extπr2ext{Area} = ext{πr}^2 where 'r' is radius (radius = diameter/2).

  2. Count stomata:

    • Use a microscope to count within the field of view, being consistent.

  3. Calculate stomatal density:

    • extStomatalDensity=racextTotalNumberofStomataextAreaofFieldofViewext{Stomatal Density} = rac{ ext{Total Number of Stomata}}{ ext{Area of Field of View}}

    • Example: For 20 stomata in 0.25 mm², density = rac200.25extmm2=80extstomata/mm2rac{20}{0.25 ext{ mm}^2} = 80 ext{ stomata/mm}^2

B3.2.1-3.2.6: The Cardiovascular System

  • Theme: Form and Function

  • Level of Organisation: Organisms

  • IB Guiding Question: What adaptations facilitate transport of fluids in animals?

  • Learning Objective: Outline how the human cardiovascular system transports fluids.

Capillaries

  • Function: Small blood vessels connecting arteries to veins, facilitating exchange between blood and cells.

Adaptations of Capillaries

  • Large Surface Area: Highly branched structure increases contact.

  • Narrow Lumen: Only allows one red blood cell through at a time.

  • Thin Walls: Typically one cell thick for rapid material exchange by diffusion.

Micrograph of Arteries and Veins

  • Artery Structure:

    • Thicker wall, narrower lumen.

  • Vein Structure:

    • Thinner wall, wider lumen.

Structure of Arteries

  • Function: Transport blood away from the heart.

  • Adaptations for High Blood Pressure:

    • Thick Walls: To withstand high pressure.

    • Collagen: Provides strength to the artery wall.

    • Smooth Muscle: Contraction helps maintain blood pressure.

    • Elastic Fibres: Allow stretching and recoiling to propel blood.

    • Narrow Lumen: Maintains high blood pressure.

    • Endothelial Lining: Reduces friction during blood flow.

Measuring Pulse Rate

  • Pulse: Caused by heart beats, felt at radial artery in wrist or carotid artery in neck.

  • Determining Pulse Rate:

    • Count beats per unit time.

    • Tools like smart watches can be utilized.

Veins Structure

  • Function: Return blood to the heart.

  • Adaptations:

    • Thin Walls: Allows compression by skeletal muscles to assist blood flow.

    • Wide Lumen: Facilitates large blood volume transport.

    • Valves: Prevent backflow of blood.

Arteries and Veins Comparison

  • Arteries:

    • Thick outer wall, narrow lumen.

  • Veins:

    • Thin wall with large lumen, valves present to prevent backflow.

  • Capillaries:

    • Very small lumen, thin wall (single cell).

B3.2.6: Causes and Consequences of Occlusion of the Coronary Arteries

  • Atherosclerosis: Hardening and narrowing due to plaque (cholesterol and other substances) buildup.

Occlusion of Coronary Arteries

  • Coronary arteries supply the heart; blockage can lead to tissue death and heart attacks.

Causes of Atherosclerosis

  • Damaged Inner Lining: Leads to macrophage response, fibrous tissue growth, and plaque formation, eventually occluding arteries and causing clots.

Risk Factors for Atherosclerosis

  • Non-Controlled Risk Factors:

    • Genetics, Age, Gender (males more at risk).

  • Controlled Risk Factors:

    • Obesity, Physical inactivity, Smoking, High fat/cholesterol diet.

Correlation vs Causation

  • Correlation Coefficients: Pearson correlation coefficient (r) quantifies relationships; close to zero implies no correlation, differing from causation which necessitates direct influence.

Saturated Fat and Coronary Heart Disease

  • Correlation Identified: Saturated fat intake is associated with increased death rates from coronary heart disease.

  • Key Takeaway: Correlation does not imply causation, but evidence suggests saturated fat contributes to heart disease.