Vascular Growth in the Fetal Lung

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    Abstract

    The structure of the lung is truly remarkable. It is primarily composed of three branched tubular networks (the airway, pulmonary artery and vein, bronchial artery and vein) which supply blood and air to the site of gas exchange and which maintain nutrient supply to supporting tissues. This complex interwoven network is packed into a chest cavity with a volume of 6 litres but yet it services a gas-exchange surface area of 130m2, the floor area of a comfortably sized Mediterranean holiday villa! Weibel (1991) tells us that if this surface area were arranged as a balloon it would possess a radius of 3m and a volume of 113,000
    litres, more than 18 thousand times the space available in the chest cavity. The process which drives this exceptional packaging involves repeated cycles of ordered branching to create a fractal network of tubules whose core dimensions decrease at a precise and regular rate with each successive branch. This is a high “gain-of–structure” process. In the airway, 23 generations of branching form a conducting tubular network with 17 million branches and a combined length of more than 7km. This provides convective air flow to 480 million alveoli each of which are located along a path length that is no further than 45cm from the
    external atmosphere. The pulmonary vasculature forms along side the airway but
    undergoes an additional five generations of branching to form the capillary network that surrounds each alveolus. If you simply assumed that each alveolus (diameter ~200?m) was serviced by only one blood vessel you would calculate that the alveolar capillary bed alone runs to nearly 100 km in length. Realistic attempts at modelling this structure in three dimensions suggest that it is, in all probability, between 2 and 6 thousand km long (Muhlfield et al., 2010), illustrating the impressive capacity of fractal branching processes to package colossal structures into ever smaller spaces.

    Original languageEnglish
    Title of host publicationVasculogenesis and Angiogenesis - from Embryonic Development to Regenerative Medcine
    EditorsDan Simionescu
    Place of PublicationCroatia
    PublisherIn Tech - Open Access Publisher
    Pages49-72
    Number of pages23
    ISBN (Print)978-953-307-882-3
    DOIs
    Publication statusPublished - Nov 2011

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  • Cite this

    Land, S. (2011). Vascular Growth in the Fetal Lung. In D. Simionescu (Ed.), Vasculogenesis and Angiogenesis - from Embryonic Development to Regenerative Medcine (pp. 49-72). In Tech - Open Access Publisher. https://doi.org/10.5772/26445