Glossary: Breathing & Exchange of Gases | Biology for Grade 11 PDF Download

Breathing

• Breathing (respiration): The process of exchange of O₂ from the atmosphere with CO₂ produced by the cells is called breathing, commonly known as respiration.

Respiratory Organs

• Gills: Special vascularised structures called gills (branchial respiration) are used by most of the aquatic arthropods and molluscs.
• Lungs: Vascularised bags called lungs (pulmonary respiration) are used by the terrestrial forms for the exchange of gases.
• Sound Box: Larynx is a cartilaginous box which helps in sound production and hence called the sound box.

Mechanism of Breathing

• Inspiration: Oxygen from fresh air taken by lungs and diffused into the blood.
• Expiration: CO₂ given up by venous blood in the lungs is sent out to exterior.
• Diaphragm: A muscular, membranous partition separating the thoracic cavity from the abdominal cavity.
• Spirometer: The volume of air involved in breathing movements can be estimated by using a spirometer which helps in clinical assessment of pulmonary functions.
• Tidal volume (TV): Volume of air taken in/given out during normal respiration (500 mL.)
• Inspiratory Reserve Volume (IRV): Additional volume of air inspired by a forcible inspiration. 2500mL to 3000mL.
• Expiratory Reserve Volume (ERV): Additional volume of air, a person can expire by a forcible expiration.
• Residual volume (RV): Volume of air remaining in the lungs even after a forcible expiration (1100 mL to 1200 mL)
• Inspiratory capacity (IC) = (TV + IRV) Total volume of air a person can inspire after a normal expiration.
• Expiratory Capacity:  Total Volume of air a parson can expire after a normal inspiration E.C. = TV + ERV
• Functional Residual Capacity: Volume of air that will remain in lungs after a normal expiration (FRC) = (ERV + RV)
• Vital Capacity (VC) = (ERV + TV + IRV) or the maximum volume of air a person can breathe out after a forced inspiration.
• Total Lung Capacity: It includes RV, ERV, TV and IRV or vital capacity + residual volume.

Exchange of Gases

• Partial Pressure: Pressure contributed by an individual gas in a mixture of gases is called partial pressure and is represented as pO₂ for oxygen and pCO₂ for carbon dioxide.

Transport of Gases

• Haemoglobin: Haemoglobin is a red coloured iron containing pigment present in the RBCs. 
• Oxyhaemoglobin: O₂ can bind with haemoglobin in a reversible manner to form oxyhaemoglobin.
• Oxygen dissociation curve: A sigmoid curve is obtained when percentage saturation of haemoglobin with O₂ is plotted against the pO₂ . This curve is called the Oxygen dissociation curve.
• Carbamino haemoglobin: Compound formed in RBCs when CO₂ combine with haemoglobin.

Regulation of Respiration

• Respiratory rhythm centre: A specialised centre present in the medulla region of the brain called respiratory rhythm centre is primarily responsible for this regulation.
• Pneumotaxic centre: Another centre present in the pons region of the brain called pneumotaxic centre can moderate the functions of the respiratory rhythm centre.

Disorders of Respiratory System

• Asthma: Asthma is a difficulty in breathing causing wheezing due to inflammation of bronchi and bronchioles.
• Emphysema: Emphysema is a chronic disorder in which alveolar walls are damaged due to which respiratory surface is decreased.