Unit Notes: Exchange and Transport System

Course Framework & Unit Assessment Overview

• Unit Title: Exchange & Transport (Respiratory and Cardiovascular Systems)

• Statement of Inquiry: The coordinated functions of organs interact as systems that contribute to the health and well-being of an organism.

• Key Concept: Systems

• Related Concepts: Function, Interaction

• Global Context: Identities and relationships - health and well-being

• Inquiry Questions:

  • Factual: What are the organs and pathways of the cardiovascular and ventilatory systems? How do diffusion and osmosis work?

  • Conceptual: How do organs interact to form integrated systems?

  • Debatable: How do we collect evidence of organ system health?

• Assessment Criteria & Format:

  • Criterion A (Knowing & Understanding): Assessed via Classroom Test ($60\,\text{minutes}$ duration). Strands evaluated: explaining scientific knowledge, applying scientific knowledge and understanding to solve problems set in familiar and unfamiliar situations, and analyzing and evaluating information to make scientifically supported judgments.

  • Criterion B (Inquiring & Designing): Assessed via Lab report on database investigation.

  • Criterion C (Processing & Evaluating): Assessed via Lab report on database investigation.

  • Criterion D (Reflecting on the impacts of science): Not summatively assessed in this unit.

Biological Hierarchy of Organization

• System Definition: An integrated set of components that work together to perform a specific bodily function.

• Levels of Biological Organization:

  • Chemical Level: Consists of atoms, including Carbon ($C$), Hydrogen ($H$), Oxygen ($O$), Nitrogen ($N$), and Phosphorus ($P$), which join to form molecules such as $DNA$.

  • Cellular Level: The cell is the smallest structural and functional unit of an organism.

  • Functions of Life: Performed by all living cells—nutrition, metabolism, growth, response, excretion, homeostasis, and reproduction.

  • Tissue Level: A group of specialized cells with a common structure and/or function working together (e.g., smooth muscle tissue layers, epithelial tissue, serous membrane, connective tissue).

  • Organ Level: A structure consisting of more than one tissue type that performs a particular function (e.g., stomach, heart, lungs).

  • Organ System Level: A group of organs and associated structures that carry out a major bodily function (e.g., respiratory system, cardiovascular system, digestive system).

  • Organismal Level: An individual living thing composed of integrated organ systems.

Anatomy and Pathways of the Respiratory System

• Overview: The respiratory system conducts atmospheric air into the lungs for gas exchange with blood and expels metabolic waste gases.

• Respiratory Tract Pathway:

  • Atmospheric gases move through the nose into the nasal cavity, or through the mouth into the oral (buccal) cavity.

  • Air moves into the pharynx (throat).

  • Air passes through the larynx (voice box).

  • Air enters the trachea (windpipe).

  • The trachea branches into left and right primary bronchi.

  • Bronchi branch into progressively smaller bronchioles within each lung.

  • Bronchioles terminate in alveolar sacs made of individual alveoli.

• Respiratory Organs and Structures:

  • Nasal Cavity & Oral Cavity: Entry points that warm, moisten, and filter incoming atmospheric air.

  • Pharynx: Shared muscular channel for the respiratory and digestive systems.

  • Larynx: Cartilaginous structure that houses the vocal cords and directs air into the lower airway.

  • Trachea: Main air tube supported by cartilage rings to prevent collapse during pressure changes.

  • Ribs & Rib Cage: Bony enclosure protecting the lungs and heart, moving dynamically during ventilation.

  • Lungs: Paired organs containing the bronchial tree, alveolar sacs, and capillary beds.

  • Diaphragm: Dome-shaped muscular sheet separating the thoracic cavity from the abdominal cavity.

  • Bronchi & Bronchioles: Airways that conduct air throughout the internal structure of the lungs.

  • Alveolar Sacs: Clusters of thin-walled microscopic air sacs where pulmonary gas exchange occurs.

Mechanics of Ventilation & Gas Laws

• Definition of Ventilation: The mechanical movement of air into and out of the lungs, occurring either actively (via muscle contraction) or passively (via muscle relaxation).

• Boyle's Law & Pressure Gradients:

  • Air flows naturally along a pressure gradient from regions of higher pressure to regions of lower pressure.

  • Gas volume and pressure are inversely proportional ($P \propto \frac{1}{V}$): expanding thoracic volume lowers intrapulmonary pressure below atmospheric pressure, causing air influx.

• Inhalation (Inspiration) at Rest:

  • Process Type: Active process driven by muscle contraction.

  • Muscular Actions:

  • External intercostal muscles contract, elevating the rib cage and chest upward and outward.

  • Diaphragm contracts, moving downward and flattening.

  • Volume & Pressure Changes: Thoracic cavity and lung volume increase; pressure inside the lungs decreases below atmospheric pressure.

  • Airflow: Air moves along the pressure gradient from the external atmosphere through the respiratory pathway into the alveolar sacs.

• Exhalation (Expiration) at Rest:

  • Process Type: Passive process driven by muscle relaxation and elastic recoil.

  • Muscular Actions:

  • External intercostal muscles relax, causing the rib cage to move downward and inward.

  • Diaphragm relaxes, moving upward into its dome shape.

  • Volume & Pressure Changes: Thoracic cavity and lung volume decrease; pressure inside the lungs increases above atmospheric pressure.

  • Airflow: Air is pushed out of the alveolar sacs through the respiratory pathway into the atmosphere.

• Forced Exhalation During Vigorous Exercise:

  • Process Type: Active process requiring antagonistic muscle contraction.

  • Antagonistic Muscle Actions:

  • Internal intercostal muscles contract actively, pulling the rib cage downward and inward with greater force.

  • Abdominal muscles contract actively, forcing abdominal organs upward against the diaphragm to accelerate volume reduction and increase internal pulmonary pressure.

Measurement of Respiratory Parameters

• Ventilation Rate:

  • Definition: The number of breath cycles (inhalations and exhalations) per minute.

  • Measurement Method: Measured by counting each complete rise and fall of the chest at rest or under specified conditions.

• Lung Volumes and Capacities:

  • Tidal Volume ($VT$): The volume of air inhaled or exhaled per breath during normal, restful breathing.

  • Vital Capacity ($VC$): The total maximum volume of air that can be expelled from the lungs following maximum inhalation.

  • Residual Volume ($RV$): The volume of air remaining in the lungs after complete, maximum exhalation (prevents alveolar collapse).

  • Total Lung Capacity ($TLC$): The total volume of air in the lungs after maximum forced inhalation ($TLC = VC + RV$).

  • Measurement Tools: Measured using a lung volume bag or a spirometer.

• Peak Expiratory Flow (Peak Flow):

  • Definition: The maximum volume and speed of air expelled during forced maximum exhalation.

  • Clinical Use: Assesses airway resistance and assists in diagnosing or monitoring respiratory conditions like asthma.

  • Measurement Method: Recorded by blowing with maximum effort into a peak flow meter.

Passive and Active Transport Mechanisms

• Transport Categories:

  • Passive Transport: Movement of particles down a concentration gradient (from high to low concentration) without expenditure of additional cellular energy ($ATP$). Includes simple diffusion, facilitated diffusion, and osmosis.

  • Active Transport: Movement of particles against a concentration gradient (from low to high concentration), requiring additional energy input in the form of adenosine triphosphate ($ATP$) and protein pumps.

• Principles of Diffusion:

  • Definition: The net movement of solute particles from a region of higher solute concentration to a region of lower solute concentration due to random kinetic movement until equilibrium is reached.

  • Concentration Gradient: The spatial difference in solute particle concentration between two regions.

  • Dynamic Equilibrium: Reached when solute particles are evenly distributed and the movement rate across a boundary becomes equal in both directions.

• Simple Diffusion vs. Facilitated Diffusion:

  • Simple Diffusion: Direct unassisted passage of small or non-polar particles across the plasma membrane.

  • Facilitated Diffusion: Movement of charged particles (ions) or larger polar molecules across the plasma membrane down their concentration gradient through channel or carrier proteins.

• Principles of Osmosis:

  • Definition: The net movement of water (solvent) across a semipermeable membrane down a water concentration gradient.

  • Direction of Flow: Water moves from a region of low solute concentration (high relative water concentration) to a region of high solute concentration (low relative water concentration).

• Solution Concentration Types (Toxicity):

  • Hypertonic Solution: A solution with a relatively higher solute concentration compared to another solution.

  • Isotonic Solution: A solution with an equal solute concentration compared to another solution.

  • Hypotonic Solution: A solution with a relatively lower solute concentration compared to another solution.

• Cellular Responses to Osmotic Solutions:

  • Red Blood Cells (Animal Cells):

  • In a Hypotonic environment: Water enters the cell by osmosis, causing swelling and eventual bursting (hemolysis).

  • In a Hypertonic environment: Water leaves the cell, causing shrinking and crenation.

  • In an Isotonic environment: Equal rate of water movement in and out; cell maintains normal shape.

  • Plant Cells:

  • In a Hypotonic environment: Water enters the cell; the rigid cell wall prevents bursting and builds turgor pressure (turgid).

  • In an Isotonic environment: No net water gain; cell becomes flaccid.

  • In a Hypertonic environment: Water leaves the cell; cytoplasm shrinks away from the cell wall (plasmolysis).

Gas Exchange at the Respiratory Membrane

• Mechanism of Gas Exchange:

  • Gas exchange occurs in the alveolar sacs via simple diffusion driven by partial pressure gradients.

  • Oxygen ($O_2$) moves from high concentration/pressure in the alveolar air space into red blood cells in the pulmonary capillaries.

  • Carbon dioxide ($CO_2$) moves from high concentration/pressure in the capillary blood into the alveolar air space to be exhaled.

• Anatomy of the Respiratory Membrane:

  • Consists of three microscopic layers:

  1. Wall of alveolus (squamous epithelial cells).

  2. Fused basement membranes.

  3. Wall of capillary (endothelial cells).

  • Features pulmonary surfactant lining the internal alveolar surface to reduce surface tension and prevent alveolar collapse.

• Volatile Solute Transfer (Ethanol Breathalyzer Principle):

  • Volatile dissolved substances carried in the blood, such as ethanol, diffuse across the capillary wall and alveolar epithelium into the alveolar space as vapor.

  • This diffusion allows breathalyzer devices to measure breath alcohol levels to deduce blood alcohol concentration.

Cardiovascular Anatomy & Double Circulation Pathways

• Two-Loop One-Directional System:

  • Pulmonary Circuit: Circulates deoxygenated blood from the heart to the lungs for oxygenation and returns oxygenated blood to the heart.

  • Systemic Circuit: Circulates oxygenated blood from the heart to body tissues to deliver oxygen and nutrients, returning deoxygenated blood back to the heart.

• Complete Systemic Blood Flow Pathway:

  • Lungs

  • Pulmonary vein

  • Left atrium

  • Atrioventricular valve (bicuspid / mitral valve)

  • Left ventricle

  • Semilunar valve (aortic valve)

  • Aorta

  • Systemic arteries

  • Arterioles

  • Capillaries (gas, solute, and nutrient exchange with body tissues)

  • Venules

  • Systemic veins (Vena cava)

  • Right atrium

  • Atrioventricular valve (tricuspid valve)

  • Right ventricle

  • Semilunar valve (pulmonary valve)

  • Pulmonary artery

  • Lungs

• Heart Anatomy and Valve Operation:

  • Right Atrium: Receives deoxygenated blood from body tissues via the vena cava.

  • Right Ventricle: Pumps deoxygenated blood into the pulmonary artery toward the lungs.

  • Left Atrium: Receives oxygenated blood from lungs via pulmonary veins.

  • Left Ventricle: Has thick muscular walls to pump oxygenated blood through the aorta under high pressure to systemic organs.

  • Atrioventricular (AV) Valves: Located between atria and ventricles; prevent backflow into atria during ventricular contraction.

  • Semilunar Valves: Located at the bases of the aorta and pulmonary artery; prevent backflow into ventricles during ventricular relaxation.

Cardiac Cycle & Conduction System

• Phases of the Cardiac Cycle:

  • Phase 1: Atrial and Ventricular Diastole ($0.4\,\text{sec}$):

  • Atria and ventricles are relaxed.

  • Atrioventricular (AV) valves are open; semilunar valves are closed.

  • Blood passively fills the atria and flows directly into the ventricles.

  • Phase 2: Atrial Systole & Ventricular Diastole ($0.1\,\text{sec}$):

  • Atria contract, actively squeezing remaining blood past open AV valves into ventricles.

  • Phase 3: Ventricular Systole & Atrial Diastole ($0.3\,\text{sec}$):

  • Ventricles contract forcefully, increasing ventricular pressure.

  • AV valves close abruptly, creating the first heart sound ("lub").

  • Semilunar valves are forced open, ejecting blood into the aorta and pulmonary artery.

  • As ventricles begin relaxing, semilunar valves snap shut, creating the second heart sound ("dub").

• Electrical Conduction Sequence of the Heart:

  • Sinoatrial (SA) Node: Functions as the primary pacemaker located in the right atrial wall; spontaneously generates electrical impulses.

  • Atrial Propagation: The impulse spreads through atrial muscle walls, inducing synchronous atrial contraction.

  • Atrioventricular (AV) Node Delay: Signal arrives at the AV node, where the impulse is briefly delayed to ensure complete ventricular filling.

  • Ventricular Bundle & Purkinje Propagation: Signal passes through the bundle branches down to the heart apex and spreads upward through ventricular walls via Purkinje fibers.

  • Ventricular Contraction: Ventricles contract upward from apex to base, pushing blood up toward outflow arteries.

Structural Comparison & Hemodynamics of Blood Vessels

• Blood Vessel Pathway Sequence: Heart $\rightarrow$ Arteries $\rightarrow$ Arterioles $\rightarrow$ Capillaries $\rightarrow$ Tissues $\rightarrow$ Capillaries $\rightarrow$ Venules $\rightarrow$ Veins $\rightarrow$ Heart.

• Structural Comparison of Vessels:

  • Arteries:

  • Walls: Thick walls composed of smooth muscle, elastic fibers, and connective tissue.

  • Lumen: Narrow lumen to maintain high blood pressure generated by heart contractions.

  • Valves & Pores: No valves (blood pressure is high); no pores.

  • Capillaries:

  • Walls: Single-cell layer of endothelium resting on a basement membrane.

  • Lumen: Extremely narrow lumen (allows red blood cells to pass single file).

  • Valves & Pores: No valves; contains microscopic pores to facilitate rapid solute exchange with body tissues.

  • Veins:

  • Walls: Thin walls with minimal muscular and elastic layers.

  • Lumen: Wide lumen to store blood and minimize flow resistance at low pressure.

  • Valves & Pores: Contains internal valves to prevent blood backflow; no pores.

• Venous Blood Movement & Skeletal Muscle Pump:

  • Blood in veins flows under very low pressure.

  • Contraction of surrounding skeletal muscles compresses thin vein walls, propelling blood upward.

  • Proximal valves open to allow forward flow toward the heart, while distal valves close to prevent backflow.

• Hemodynamic Changes Along the Vascular Tree:

  • Total Area: Total cross-sectional area spikes sharply in capillary beds ($\sim 4,000-5,000\,\text{cm}^2$).

  • Velocity: Blood velocity is highest in the aorta ($\sim 45-50\,\text{cm/sec}$), drops near zero in capillaries (maximizing exchange time), and increases moderately in venules and veins ($\sim 20-25\,\text{cm/sec}$).

  • Pressure: Blood pressure fluctuates between systolic ($\sim 120\,\text{mmHg}$) and diastolic ($\sim 80\,\text{mmHg}$) in arteries, steadily decreases through arterioles, drops significantly in capillaries, and approaches near $0\,\text{mmHg}$ in the venae cavae.

Blood Composition and Hematopoiesis

• Overview of Blood: A circulating fluid tissue responsible for transporting dissolved solutes, respiratory gases, metabolic wastes, and heat.

• Blood Composition Fractions:

  • Plasma ($55\%$ of total volume): Fluid component carrying solutes.

  • Cellular Elements ($45\%$ of total volume): Formed cellular components.

• Plasma Constituents & Functions:

  • Water: Primary solvent for carrying solutes throughout the body.

  • Electrolytes / Ions: Includes Sodium ($Na^+$), Potassium ($K^+$), Calcium ($Ca^{2+}$), Magnesium ($Mg^{2+}$), Chloride ($Cl^-$), and Bicarbonate ($HCO_3^-$). Maintain osmotic balance, buffer pH, and regulate membrane permeability.

  • Plasma Proteins:

  • Albumin: Maintains osmotic balance and pH buffering.

  • Fibrinogen: Essential factor for blood clotting.

  • Immunoglobulins (Antibodies): Provide immune defense.

  • Transported Solutes: Nutrients (glucose, fatty acids, amino acids, vitamins), metabolic waste products (urea), respiratory gases ($O_2$ and $CO_2$), and endocrine hormones.

• Cellular Elements:

  • Erythrocytes (Red Blood Cells):

  • Count: $5-6\,\text{million per }\mu\text{L (mm}^3\text{)}$ of blood.

  • Function: Transport oxygen and assist in carbon dioxide transport.

  • Leukocytes (White Blood Cells):

  • Count: $5,000-10,000\,\text{per }\mu\text{L (mm}^3\text{)}$ of blood.

  • Function: Defense and immunity.

  • Subtypes: Basophils, Eosinophils, Neutrophils, Monocytes, and Lymphocytes (B cells and T cells).

  • Platelets (Thrombocytes):

  • Count: $250,000-400,000\,\text{per }\mu\text{L (mm}^3\text{)}$ of blood.

  • Function: Cell fragments involved in blood clotting.

• Hematopoiesis (Blood Cell Differentiation):

  • Blood cell development occurs in bone marrow starting from pluripotent stem cells.

  • Differentiates into two major cell lines:

  1. Lymphoid Stem Cells: Form B cells and T cells (Lymphocytes).

  2. Myeloid Stem Cells: Form Erythrocytes, Platelets, Monocytes, Neutrophils, Eosinophils, and Basophils.

Factors Affecting Heart Rate, Ventilation Rate, and Lung Capacity

• Internal Factors:

  • Physical Activity & Cellular Respiration: Exercise increases cellular metabolic demands, elevating carbon dioxide production and lowering tissue pH. Central and peripheral chemoreceptors trigger physiological responses that increase heart rate, ventilation rate, and tidal volume.

  • Hormonal Regulation: Release of epinephrine (adrenaline) increases sinoatrial node firing rate, elevating heart rate and cardiac output while causing bronchodilation.

• External Factors:

  • Environmental Altitude: Reduced atmospheric pressure at high altitudes lowers ambient oxygen partial pressure, causing compensatory increases in ventilation rate and resting heart rate.

  • Respiratory Pathologies (e.g., Asthma): Airway inflammation and smooth muscle contraction narrow bronchioles, reducing forced expiratory volume and peak expiratory flow.