Is the sheet-flow design a ‘frozen core’ (a Bauplan) of the gas exchangers? (original) (raw)

Abstract

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This review explores the concept of the 'sheet-flow' design as a structural feature in evolved gas exchangers, proposing it as a foundational architectural principle for gas exchange via diffusion. It argues that this design ensures close approximation of internal and external respiratory media across extensive surfaces, while also highlighting the intricate relationship between structure and function in biological adaptations. The paper emphasizes the evolutionary persistence of such designs in various organisms, attributing their success to a combination of morphological efficiency and structural resilience, thereby illustrating the constraints and trade-offs inherent to respiratory system evolution.

Key takeaways

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  1. The sheet-flow design is a fundamental architectural feature of respiratory gas exchangers.
  2. The gas exchange efficiency is influenced by the unique geometric arrangement of pulmonary microvascular systems.
  3. Pulmonary capillary blood pressure in humans averages 1.1 kPa, highlighting low-pressure adaptations.
  4. Birds possess the most efficient respiratory systems with a fractal dimension of 3 in their microvascular units.
  5. Fractal geometry optimizes biological designs, allowing efficient gas exchange with minimal structural material.

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What defines the 'frozen core' concept in respiratory organ evolution?add

The paper describes the 'frozen core' as immutable anatomical features that persist across animal lineages, emphasizing traits essential for survival amidst varying evolutionary pressures.

How does the sheet-flow design facilitate gas exchange efficiency?add

The study reveals that the sheet-flow design allows extensive surface area for gas exchange, with a tissue barrier thickness of just 0.5 mm in human lungs.

What role does fractal geometry play in respiratory microvascular systems?add

The research identifies that fractal properties of vascular networks enable extensive internal surface area for ventilation and low-energy perfusion, with avian lungs achieving a fractal dimension of 3.

How do hemodynamic pressures affect pulmonary capillary structures?add

The review indicates that the variable pulmonary capillary transmural pressures can compress or open blood vessels, influencing perfusion dynamics and maintaining structural integrity during respiratory cycles.

What are the implications of microvascular design in different gas exchangers?add

The findings suggest that common microvascular architectures across species, such as fish gills and mammalian lungs, underline evolutionary advantages in gas exchange functionality.