[The oxygen pathway: how well-built is the respiratory system?].

The research is about exploring the structural systems that deliver oxygen from the air, through the lungs, into the blood circulation and finally to the mitochondria in muscle cells. The study considers whether these structures are designed optimally for their function according to the symmorphosis hypothesis.

Testing Symmorphosis Hypothesis in Oxygen Pathways

• The symmorphosis hypothesis suggests that the structural design of an organism’s system (in this case the respiratory system) is closely matched to its overall functional demand. In this research, the hypothesis is tested with regards to the oxygen pathway in the human body, including the lungs, the circulatory system, and the mitochondria in muscle cells.

Physiological and Morphometric Studies

• The research combines physiological and morphometric studies to examine the diffusing capacity of the human lung. This determines the rate at which oxygen travels from the air through the lung tissues into the bloodstream.
• Results showed that the human lung’s diffusing capacity is slightly larger than what is needed for maximal oxygen uptake. This indicates that our respiratory system might have more capacity than what is typically required, suggesting a safety factor.

Comparative Studies Across Species

• The study also includes comparative research across species of different sizes (from mice to cows) and lifestyles (athletic vs. sedentary, e.g., horses vs. cows). This was done to examine if the design parameters of the oxygen pathway components – muscle cells and their mitochondria, blood capillaries, and circulation – adjust to the varying levels of oxygen demand during physical activity.
• The finding suggests that these elements are indeed capable of co-adjusting to meet increased oxygen requirements. However, the lung only partially adjusts to increased demand levels, which may relate to its slightly larger-than-required diffusing capacity.

Assessing Lung’s Excess Capacity

• While the partial adjustment of the lung to the increased oxygen demand might seem inefficient, the authors suggest that this might be a beneficial feature. Since the lung interfaces directly with the environment, having an excess capacity could provide a safety margin, allowing for adaptation to external variables such as pollution or changes in air pressure and composition.