Respiratory Systems in Aquatic and Terrestrial Animals

Gas Exchange Structures

• Aquatic arthropods and molluscs use gills, while terrestrial animals utilize lungs for gas exchange.
• Fish respire using gills; reptiles, birds, and mammals utilize lungs.
• Amphibians, such as frogs, can respire through their moist skin.
• Mammals possess a well-developed respiratory system.

Human Respiratory System Structure

• External nostrils lead to the nasal chamber and pharynx, shared passage for food and air.
• Pharynx connects to the larynx, which is involved in sound production and is known as the sound box.
• Larynx covers the glottis with the epiglottis during swallowing to prevent food entry.
• Trachea extends to the mid-thoracic cavity, dividing into right and left primary bronchi.
• Bronchi further divide into secondary and tertiary bronchi, eventually forming bronchioles and terminal bronchioles.
• Terminal bronchioles lead to alveoli, the gas exchange structures, making up the lungs.

Lung Anatomy and Function

• Lungs are covered by a double-layered pleura with pleural fluid to reduce friction.
• Conducting part (nostrils to terminal bronchioles) transports, humidifies, and filters air.
• Respiratory part (alveoli and ducts) facilitates the diffusion of O2 and CO2 between blood and air.
• Lungs are housed in an air-tight thoracic chamber.

Mechanism of Breathing

• Contraction of external intercostal muscles increases thoracic and pulmonary volume, leading to inspiration.
• Relaxation of diaphragm and intercostal muscles decreases thoracic volume, leading to expiration.
• Average human respiration rate is 12-16 breaths per minute.
• Breathing volume can be assessed using a spirometer.

Respiratory Volumes and Capacities

• Tidal Volume (TV): Approx. 500 mL air per breath, totaling 6000-8000 mL per minute for a healthy adult.
• Inspiratory Reserve Volume (IRV): Additional 2500-3000 mL air can be forcibly inhaled.
• Expiratory Reserve Volume (ERV): Additional 1000-1100 mL air can be forcibly exhaled.

Diffusion Characteristics

• Rate of gas diffusion influenced by gas solubility and membrane thickness.
• Partial pressure: Individual gas pressure in a mixture, denoted as pO2 for oxygen and pCO2 for carbon dioxide.
• Concentration gradients exist for O2 and CO2 between alveoli, blood, and tissues facilitating gas exchange.

Partial Pressure Data

• Atmospheric pressure for O2 is 159 mm Hg; for CO2, it is 0.3 mm Hg.
• Alveolar O2 pressure is 104 mm Hg; CO2 pressure is 40 mm Hg.
• Blood oxygenated pressure is 95 mm Hg; deoxygenated CO2 pressure is 45 mm Hg.
• Tissues have pO2 of 40 mm Hg and pCO2 of 45 mm Hg.

Respiratory Physiology

• Understanding vital capacity, the volume of air that can be exhaled after a maximum inhalation, is vital for assessing lung function.
• Residual volume: Air remaining in lungs after normal breathing, crucial for continuous gas exchange.
• Diffusion occurs mainly in the alveolar region due to the thin walls and large surface area.

Additional Insights

• The relationship between partial pressures influences the direction of gas diffusion.
• Exercise, high altitude, and environmental factors impact respiratory function and efficiency.
• Oxygen dissociation curve’s sigmoidal pattern reflects hemoglobin's affinity for oxygen under varying conditions.