Thin and strong! The bioengineering dilemma in the structural and functional design of the blood-gas barrier.

  title={Thin and strong! The bioengineering dilemma in the structural and functional design of the blood-gas barrier.},
  author={John Ndegwa Maina and John B West},
  journal={Physiological reviews},
  volume={85 3},
In gas exchangers, the tissue barrier, the partition that separates the respiratory media (water/air and hemolymph/blood), is exceptional for its remarkable thinness, striking strength, and vast surface area. These properties formed to meet conflicting roles: thinness was essential for efficient flux of oxygen by passive diffusion, and strength was crucial for maintaining structural integrity. What we have designated as "three-ply" or "laminated tripartite" architecture of the barrier appeared… 

Morphological and Morphometric Properties of the Blood-Gas Barrier: Comparative Perspectives

The thin, essentially three-ply laminated architecture of the BGB has been widely and greatly conserved in the lungs of animals that remarkably differ morphologically, phylogenetically, behaviourally, and ecologically.

Comparative physiology of the pulmonary blood-gas barrier: the unique avian solution.

  • J. West
  • Biology
    American journal of physiology. Regulatory, integrative and comparative physiology
  • 2009
Two opposing selective pressures have shaped the evolution of the structure of the blood-gas barrier in air breathing vertebrates, and the avian barrier is about 2.5 times thinner than that in mammals and also is much more uniform in thickness.

Comparative physiology of the pulmonary circulation.

  • J. West
  • Biology
    Comprehensive Physiology
  • 2011
A remarkable feature throughout the evolution of air-breathing vertebrates has been the tight conservation of the tripartite structure of the blood-gas barrier with its three layers: capillary endothelium, extracellular matrix, and alveolar epithelium.

The anatomy, physics, and physiology of gas exchange surfaces: is there a universal function for pulmonary surfactant in animal respiratory structures?

The theoretical analysis suggests that a surfactant system may be required, in order to cope with surface tension during processes, such as molting, when the tracheae collapse and fill with water, and the current status of the field is summarized.

Role of the fragility of the pulmonary blood-gas barrier in the evolution of the pulmonary circulation.

  • J. West
  • Biology, Medicine
    American journal of physiology. Regulatory, integrative and comparative physiology
  • 2013
The vulnerability of the blood-gas barrier is a key factor in the evolution of the pulmonary circulation and was implicated in the pathogenesis of High Altitude Pulmonary Edema, but it was soon clear that stress failure of pulmonary capillaries is common.

Structural and Biomechanical Properties of the Exchange Tissue of the Avian Lung

In light of the new morphological findings of the ACs and the BCs, the functional model which is currently in use to assess the gas exchange efficiency of the avian lung should be revised and the inappropriateness of the terms ‘blood capillary’ and ‘air capillary' for theGas exchange units of theAvian lung is pointed out.

Critical appraisal of some factors pertinent to the functional designs of the gas exchangers

  • J. Maina
  • Environmental Science
    Cell and Tissue Research
  • 2016
Gas exchangers evolved under certain immutable physicochemical laws upon which their elemental functional design is hardwired to satisfy metabolic needs for O2, environmental conditions, respiratory medium utilized, lifestyle pursued and phylogenetic level of development: correlation between structure and function exists.

Spatial and functional relationships between air conduits and blood capillaries in the pulmonary gas exchange tissue of adult and developing chickens

The mode of gas exchange in the parabronchial mantle is clarified and the basis for the functional efficiency of the avian lung is illuminated.

Perspectives on the Structure and Function of the Avian Respiratory System: Functional Efficiency Built on Structural Complexity

  • J. Maina
  • Biology
    Frontiers in Animal Science
  • 2022
The exceptional respiratory efficiency of the avian respiratory system stems from synergy of morphological properties and physiological processes, means by which O2 uptake is optimized and high metabolic states and capacities supported.



Thoughts on the pulmonary blood-gas barrier.

  • J. West
  • Biology
    American journal of physiology. Lung cellular and molecular physiology
  • 2003
The structure of the blood-gas barrier is apparently continually regulated in response to wall stress, and this regulation is essential to maintain the extreme thinness but adequate strength.

Strength of the pulmonary blood-gas barrier.

Structure, strength, failure, and remodeling of the pulmonary blood-gas barrier.

Recent experimental work suggests that rapid changes in gene expression for extracellular matrix proteins and growth factors occur in response to increases in capillary wall stress, which is a central issue in lung biology.

Fundamental Structural Aspects and Features in the Bioengineering of the Gas Exchangers: Comparative Perspectives

  • J. Maina
  • Biology
    Advances in Anatomy Embryology and Cell Biology
  • 2002
Since animals occupy inconstant environmental milieus and their metabolic states vary, gas exchangers are designed to operate optimally across a spectrum of conditions that range from resting to exercise and even under hypoxia.

Invited review: pulmonary capillary stress failure.

  • J. West
  • Engineering
    Journal of applied physiology
  • 2000
The pulmonary blood-gas barrier is an extraordinary bioengineering structure because of its vast area but extreme thinness and is able to maintain its extreme thickness with sufficient strength as a result of continual regulation of its wall structure.


This analysis suggested that the gas conductance of the barrier is nearly optimal if one considers the mass of tissue and the minimal barrier thickness as fixed properties which are determined by other functional requirements on the alveolo-capillary membrane.

Some recent advances on the study and understanding of the functional design of the avian lung: morphological and morphometric perspectives

  • J. N. Maina
  • Medicine
    Biological reviews of the Cambridge Philosophical Society
  • 2002
The small highly aerobic avian species have morphometrically superior lungs while the large flightless ones have less well‐refined lungs, and two parabronchial systems occur in the lungs of relatively advanced birds, which may explain the paucity of SMs in the avian lung.

Structure, function and evolution of the gas exchangers: comparative perspectives

Over the evolutionary continuum, animals have faced similar fundamental challenges of acquiring molecular oxygen for aerobic metabolism. Under limitations and constraints imposed by factors such as

Thickness of the air-blood barriers in vertebrate lungs.

The data indicate that the process of optimization of lung architecture for gas exchange is most marked in mammals, and the ratio of the arithmetic mean thickness to the harmonic mean thickness of the barriers was highest in mammals.