Breathing: Note About Respiration

Breathing / Respiration Atmospheric Oxygen Exchange Co₂ produced by cells. (Catabolic Process) Respiratory Organs Based on: Habitat Level of organization Organism - Function: Invertebrate: Sponges, Coelenterate, Flat Echinoderm: Simple Diff. Earthworm: Moist Cuticle Insects: Tracheal Tubes Aquatic Arthropod, Mollusc, Fish (Vertebrates): Branchial / Gills Amphibian, Reptile, Aves, Mammal: Pulmonary / Lungs Note: Amphibian (frog) show cutaneous respiration also. Human Respiratory System Diagram of the human respiratory system: Nasal cavity, epiglottis, larynx (voice box), trachea, bronchus, bronchioles, alveoli Pleural membrane: Outer and Inner Pleural fluid: Reduces friction on lung surface Breathing and Exchange of Gases Conducting Zone: Humidification of air Transport of air Trap dust in inhaled air Bring air to body temperature Pathway: External nostril → Terminal bronchiole Respiratory Zone: Exchange of gases Mechanism of Breathing Lungs are enclosed in an anatomically air-tight thoracic chamber essential for breathing as we cannot alter the pulmonary volume directly. Movement of air follows the pressure gradient. Change in volume of the thoracic cavity will be reflected in lung cavity. Specialized set of structures involved in breathing: Inspiration Contraction of diaphragm → ↑ Volume (Antero-Posterior axis) Contraction of external intercostal muscles (EICM) → ↑ Volume (Dorso Ventral axis) → ↓ Pulmonary Pressure (less than atmospheric pressure) Expiration Relaxation of diaphragm and EICM → ↓ Volume → ↑ Pressure Ability to increase the strength of inspiration and expiration by additional muscles in abdomen. Normal rate of breathing: 12-16 times/min in adult humans. Inspiration vs. Expiration: Intrapulmonary Pressure: Low vs. High Pressure in Lungs w.r.t atmosphere: Negative vs. Positive Shape of diaphragm: Flat vs. Dome Exchange of Gases Partial pressure gradient drives respiration. Site of exchange: Alveoli (Primary) Between blood and tissue Partial Pressure: Pressure of individual gas in the mixture. Gas exchange diagram: Inspired Air vs. Expired Air at Alveolus Pulmonary artery (deoxygenated) and Pulmonary vein (oxygenated) Systemic artery (oxygenated) and Systemic vein (deoxygenated) Body tissue Transport of Gases Oxygen (O₂): 5 ml O₂ delivered/100 ml of oxygenated blood. 3% dissolve in Plasma. 97% as Oxyhaemoglobin (HbO₂). Binding of O₂ with Hb is primarily related with pO₂ (partial pressure of oxygen). ​ ↔Oxyhaemoglobin Carbon Dioxide (CO₂): 4 ml of CO₂ delivered by alveoli/100 ml of deoxygenated blood. 7% dissolve in Plasma. 20-25% as Carbaminohaemoglobin (HbCO₂). Binding of CO₂ with Hb is related to pCO₂ (partial pressure of carbon dioxide). ​ ↔Carbaminohaemoglobin Important Points: Each Hb can bind with 4 O₂ molecules in a reversible manner. Maximum 70% CO₂ transport as Bicarbonate (HCO₃⁻) facilitated by Carbonic Anhydrase (C. Anhy.) enzyme in RBC and Plasma (more in RBC). Oxygen Dissociation Curve: Sigmoid curve for O₂ dissociation with Hb. P₅₀ (partial pressure of oxygen when Hb is 50% saturated) is inversely proportional to affinity. Parameters affecting O₂-Hb affinity: High pO₂, High pCO₂, High H⁺ (acidity), High Temperature increase O₂ dissociation from Hb. Association and Dissociation of Gases: Association (Alveoli): High pO₂, High pCO₂, High H⁺, High Temperature favor association. Dissociation (Tissue): High pCO₂, High H⁺ (acidity) favor dissociation. Carbaminohaemoglobin: Dissociation at Alveoli, Association at Tissue.