breathing

UNIT 5: The Reductionist Approach to Study of Life Forms

  • Overview: The reductionist approach led to the use of physico-chemical concepts in studying life forms. This, in turn, increased the knowledge in molecular biology.

  • Key Concepts and Techniques:

    • Surviving Tissue Model: A common model used in the studies.

    • Cell-Free Systems: Another approach adopted in molecular biology.

  • Molecular Biology: Molecular physiology has become almost synonymous with biochemistry and biophysics.

  • Systems Biology:

    • Emergent Properties: Biological processes are emergent properties resulting from the interactions of various components within a system.

    • Components of the System:

    • Regulatory networks of molecules

    • Supramolecular assemblies

    • Cells, tissues, organisms, populations, and communities

  • Focus of Unit: The following chapters describe major physiological processes:

    • Exchange of Gases

    • Blood Circulation

    • Locomotion and Movement

    • Coordination and regulation of body events at the organismic level.

HUMAN PHYSIOLOGY

  1. Chapter 14: Breathing and Exchange of Gases

  2. Chapter 15: Body Fluids and Circulation

  3. Chapter 16: Excretory Products and their Elimination

  4. Chapter 17: Locomotion and Movement

  5. Chapter 18: Neural Control and Coordination

  6. Chapter 19: Chemical Coordination and Integration

ALFONSO CORTI

  • Birth: 1822, Italian anatomist.

  • Scientific Work:

    • Initially studied the cardiovascular systems of reptiles.

    • Shifted focus to the mammalian auditory system.

    • Key Publication: In 1851, published about the organ of Corti located on the basilar membrane of the cochlea which contains hair cells converting sound vibrations into nerve impulses.

  • Death: 1888.

BREATHING AND EXCHANGE OF GASES

Introduction

  • Participants in Respiration: Oxygen (O2) is essential for organisms to metabolize substrates like glucose, leading to energy production and carbon dioxide (CO2) release.

  • Definition: The exchange process of O2 and CO2 is termed as breathing or respiration, ensuring continuous supply of O2 and removal of CO2 from cells.

14.1 RESPIRATORY ORGANS

  • Variation in Mechanisms: Breathing mechanisms differ among animals based on habitat and organization level.

    • Lower Invertebrates: Use simple diffusion for gas exchange.

    • Earthworms: Utilize moist cuticle for respiration.

    • Insects: Have tracheal tubes for air transport.

    • Aquatic Organisms: Use gills for gas exchange (branchial respiration).

    • Terrestrial Organisms: Use lungs for gas exchange (pulmonary respiration).

    • Amphibians: Can respire through moist skin (cutaneous respiration).

14.1.1 Human Respiratory System

  • Components:

    • Nostrils: Lead to the nasal chamber.

    • Nasal Chamber: Opens into the pharynx.

    • Pharynx: Common passage for food and air, opening to the larynx.

    • Larynx: Cartilaginous box for sound production.

    • Trachea: Tubular structure dividing into primary bronchi.

    • Bronchi & Bronchioles: Hollow tubes supporting gas movement.

    • Alveoli: Gas exchange sites with vascularized structures.

  • Pleura: Double-layered covering of lungs reducing friction with the thoracic cavity.

  • Thoracic Chamber: Anatomical setup crucial for breathing.

14.2 MECHANISM OF BREATHING

  • Phases:

    • Inspiration: Air drawn into lungs.

    • Expiration: Air expelled from lungs.

  • Pressure Gradient: Movement is based on differential pressures between the lungs and atmosphere.

  • Muscles Involved: Diaphragm and intercostal muscles facilitate changes in lung volume and intra-pulmonary pressure.

14.2.1 Respiratory Volumes and Capacities

  • Tidal Volume (TV): Average volume of air for a normal breath, approx. 500 mL.

  • Inspiratory Reserve Volume (IRV): Additional air breathed in forcefully, averaging 2500-3000 mL.

  • Expiratory Reserve Volume (ERV): Additional air expelled forcefully, averaging 1000-1100 mL.

  • Residual Volume (RV): Air remaining after forceful expiration, averaging 1100-1200 mL.

  • Pulmonary Capacities: Derived by adding respiratory volumes.

    • Inspiratory Capacity (IC): Total air inspired after normal expiration (TV + IRV).

    • Expiratory Capacity (EC): Total air expired after normal inspiration (TV + ERV).

    • Functional Residual Capacity (FRC): Air remaining after a normal expiration (ERV + RV).

    • Vital Capacity (VC): Maximum volume inspired or expired after forced effort (ERV + TV + IRV).

    • Total Lung Capacity (TLC): Maximum lung volume after forced inspiration (RV + ERV + TV + IRV).

14.3 EXCHANGE OF GASES

  • Location: Alveoli are the primary sites of gas exchange.

  • Mechanism: Gases exchanged via diffusion based on pressure gradients.

  • Partial Pressure:

    • pO2: Oxygen partial pressure (higher in alveoli).

    • pCO2: Carbon dioxide partial pressure (higher in tissues).

  • Diffusion Factors: Solubility and membrane thickness impact diffusion rates significantly.

  • Diffusion Membrane Layers:

    • Thin squamous epithelium of alveoli.

    • Endothelium of alveolar capillaries.

    • Basement membrane.

Table 14.1: Partial Pressures of Oxygen and Carbon Dioxide

Location

O2 (mm Hg)

CO2 (mm Hg)

Atmospheric Air

159

0.3

Alveoli

104

40

Blood (Deoxygenated)

40

45

Blood (Oxygenated)

95

40

Tissues

40

45

14.4 TRANSPORT OF GASES

  • Transport Medium: Blood carries O2 and CO2.

    • Oxygen Transport:

    • 97% carried by red blood cells (RBC) as oxyhaemoglobin.

    • 3% dissolved in plasma.

    • Carbon Dioxide Transport:

    • 20-25% carried by RBCs as carbamino-haemoglobin.

    • 70% in bicarbonate form (HCO3–).

    • 7% dissolved in plasma.

  • Hemoglobin Binding Dynamics:

    • Each molecule can carry up to four O2 molecules.

    • Binding influenced by factors such as pO2, pCO2, H+ concentration, and temperature.

    • Oxygen Dissociation Curve: Sigmoid curve showing hemoglobin saturation concerning pO2.

14.4.1 Transport of Oxygen

  • Binding and Release of O2:

    • High pO2 in the alveoli favors oxyhaemoglobin formation.

    • Low pO2 in tissues favors O2 release.

  • Oxygen Delivery: Approx. 5 mL O2 is delivered to tissues per 100 mL oxygenated blood.

14.4.2 Transport of Carbon Dioxide

  • CO2 Binding Dynamics:

    • CO2 primarily exists in the form of bicarbonate.

    • Reactions facilitated by carbonic anhydrase.

    • High pCO2 in tissues favors CO2 binding, while low pCO2 in alveoli favors CO2 release.

  • CO2 Delivery: Approx. 4 mL CO2 delivered to alveoli per 100 mL deoxygenated blood.

14.5 REGULATION OF RESPIRATION

  • Control Centers:

    • Respiratory Rhythm Centre: Located in the medulla responsible for rhythm regulation.

    • Pneumotaxic Centre: In the pons, moderates respiratory rhythm.

  • Chemosensitive Area: Sensitive to changes in CO2 and H+ concentrations, influencing rhythm adjustments.

14.6 DISORDERS OF RESPIRATORY SYSTEM

  • Asthma: Difficulty breathing due to bronchial inflammation.

  • Emphysema: Chronic respiratory disorder decreasing respiratory surface area due to alveolar damage, often due to smoking.

SUMMARY

  • Utilization of Oxygen: Cells metabolize O2 to produce energy; CO2 is a byproduct.

  • Respiratory Mechanisms: Variations exist across species, with humans having a specialized respiratory system.

  • Breathing Process: Involves inspiration and expiration facilitated by pressure differences.

  • Gas Exchange and Transport: Occurs through diffusion at the alveoli and tissues, with specific roles for hemoglobin.

  • Regulatory Mechanisms: Control respiration through brain centers and signal responses to changing body demands.

  • Occupational Disorders: Long exposure to dust in industrial environments can provoke lung damage and diseases, necessitating protective measures.

EXERCISES

  1. Define vital capacity and its significance.

  2. State the volume of air remaining in the lungs after normal breathing.

  3. Explain why gas diffusion solely occurs in the alveolar region.

  4. Describe the major mechanisms for CO2 transport.

  5. Compare partial pressure variations of pO2 and pCO2 in atmospheric air vs. alveolar air.

  6. Discuss the process of inspiration under normal conditions.

  7. Outline how respiration is regulated.

  8. Examine the effect of pCO2 on oxygen transport.

  9. Describe changes in the respiratory process during ascents.

  10. Identify gas exchange sites in insects.

  11. Define the oxygen dissociation curve and reasons for its sigmoidal nature.

  12. Research hypoxia and discuss findings.

  13. Distinguish between IRV and ERV, inspiratory capacity and expiratory capacity, and vital capacity and total lung capacity.

  14. Define tidal volume and calculate its approximate value for a healthy human over one hour.