VPB 121: Veterinary Physiology - II (2+1)

REGULATION OF RESPIRATION

• Respiratory centres as are as in mammals, Chemoreceptors are also important for regulation of respiration in birds Most of these receptors are present in lungs and they detect CO₂ levels in lungs and not of blood.
• They are stimulated by low CO₂ level and once stimulated they reduce respiration. The central chemoreceptors of brain respond to PCO₂ or H⁺ ion concentration.
• Carotid and aortic chemoreceptors are also present in birds. Stretch receptors are present in lungs and their activity is modified by CO₂ level.
• Mechanoceptors are chemoceptors in muscle or joints activated by movements or build up of metabolites increases ventilation. Thermoceptors of skin, muscle and hypothalamus on stimulation lead to rapid shallow, panting type of respiration.
• During heat stress in birds, respiratory frequency markedly increases, while tidal volume decreases and panting occur (dead space ventilation increase for evaporative water loss).
• There is no marked change in arterial blood gases and pH. However, in chicken, there is severe hypocaprina and alkalosis during panting.
• Birds hyperventilate during running or flying, and arterial PCO₂ decreases.
• In high altitude due to low PO₂ of air, hyperventilation occurs.
• The birds become highly alkalotic but they tolerate this condition much better than mammals.