Haemoglobin, a protein in red blood cells, plays a vital role in the transport of oxygen and carbon dioxide in the blood. For oxygen transport, haemoglobin binds oxygen molecules in the lungs, where the concentration of oxygen is high. This binding is facilitated by the high affinity of haemoglobin for oxygen in the oxygen-rich environment of the alveoli. Once the oxygen-laden blood reaches tissues with lower oxygen levels, the affinity of haemoglobin for oxygen decreases, leading to the release of oxygen into the tissues. Conversely, haemoglobin also assists in the transport of carbon dioxide, though in a different manner. A small amount of carbon dioxide binds directly to haemoglobin, forming carbaminohaemoglobin. However, the majority of carbon dioxide is transported in the form of bicarbonate ions, which are formed from carbon dioxide and water through a reaction catalysed by the enzyme carbonic anhydrase in red blood cells. This reaction is reversible, allowing carbon dioxide to be released from bicarbonate in the lungs and then exhaled. The ability of haemoglobin to transport both oxygen and carbon dioxide is crucial for maintaining the efficiency of gas exchange and the body's acid-base balance.

Changes in breathing rate significantly impact the efficiency of gas exchange. The breathing rate is typically regulated by the body's need to maintain optimal levels of oxygen and carbon dioxide in the blood. During physical activity or in response to high levels of carbon dioxide in the blood (hypercapnia), the breathing rate increases. This enhanced ventilation results in more air being moved in and out of the lungs per unit time, which in turn increases the amount of oxygen that can be absorbed and the amount of carbon dioxide that can be expelled. Conversely, a slower breathing rate, which might occur during rest or sleep, is sufficient to meet the body's reduced demand for oxygen and carbon dioxide removal at these times. The body's ability to adjust breathing rate ensures that the gas exchange remains efficient under varying physiological conditions. If the breathing rate is too slow (hypoventilation), carbon dioxide can accumulate in the blood, leading to respiratory acidosis. If it is too fast (hyperventilation), it can lead to a decrease in blood carbon dioxide levels, causing respiratory alkalosis. Therefore, maintaining an appropriate breathing rate is key to efficient gas exchange.

Environmental factors can significantly affect the composition of inspired air, impacting respiratory health in various ways. Pollutants such as particulate matter, nitrogen oxides, sulfur dioxide, and ozone can reduce air quality, leading to a higher concentration of harmful substances in inspired air. Inhaling such polluted air can cause respiratory issues like asthma, bronchitis, and other lung diseases. Additionally, high levels of carbon monoxide, a colourless, odourless gas found in car exhaust and industrial emissions, can bind to haemoglobin more effectively than oxygen, reducing the amount of oxygen that reaches the body's tissues. Climate change also affects respiratory health indirectly. Rising temperatures can exacerbate air pollution and increase the prevalence of allergens like pollen, affecting those with respiratory allergies and asthma. Furthermore, changes in humidity and air pressure can impact lung function, particularly in individuals with pre-existing respiratory conditions. Therefore, maintaining a clean and healthy environment is crucial for ensuring that the air we breathe supports, rather than hinders, respiratory health.

The temperature difference between inspired and expired air is primarily due to the heat exchange that occurs within the respiratory system. When we inhale, the inspired air is typically cooler than our body temperature. As this air travels through the nasal passages, trachea, and bronchi, it absorbs heat from the surrounding tissues. This process helps to warm the air to a temperature closer to that of the body's internal environment before it reaches the delicate lung tissues. This warming is beneficial as it prevents cold air from causing a shock or irritation to the lungs, which can lead to respiratory complications. Conversely, when we exhale, the air has been warmed by the body and is typically warmer than the ambient temperature. This is why expired air often feels warm when it is exhaled, especially in cooler environments. The heat exchange process is an important aspect of the respiratory system's role in maintaining homeostasis, ensuring that the air reaching the lungs is at an optimal temperature for gas exchange.

The increased moisture content in expired air plays a crucial role in maintaining the health of the respiratory system. As air travels through the respiratory tract, it is conditioned – warmed, humidified, and filtered. The humidification process, in particular, is important for several reasons. Firstly, it helps to keep the mucosal lining of the respiratory tract moist. This moisture is essential for the mucosal lining to function properly, as it traps and removes particulate matter and pathogens, preventing them from reaching the delicate lung tissue. Secondly, moist air reduces the risk of irritation and damage to the respiratory tract, which can be caused by dry air. Finally, the presence of water vapour in the air assists in the efficient exchange of gases in the lungs. Water vapour helps in maintaining the elasticity of lung tissues and alveoli, facilitating their expansion and contraction during breathing. Thus, the moisture in expired air is a by-product of the respiratory system's efforts to protect itself and to optimise the conditions for gas exchange.