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A4658 - On the Three Dimensional Growth, Form and Function of the Distal Air Exchange Surfaces Within the Lung
Author Block: D. Warburton1, C. M. Wigfall2, H. A. Pollack3, D. S. Koos4, D. Al Alam5, G. Turcatel6, W. Shi7, S. E. Fraser8, R. Moats4; 1Surgery, Childrens Hosp Los Angles Rsch Inst, Los Angeles, CA, United States, 2Radiology/Imaging Services, Childrens Hospital, Los Angeles, Los Angeles, CA, United States, 3Radiology, Childrens Hosp Los Angles Rsch Inst, Los Angeles, CA, United States, 4Radiology, Children's Hospital Los Angeles, Los Angeles, CA, United States, 5Developmental Biology and Regenerative Medecine, Childrens Hospital Los Angeles, Los Angeles, CA, United States, 6Pediatrics, Childrens Hospital Los Angeles, Los Angeles, CA, United States, 7Surgery, Childrens Hospital Los Angeles, Los Angeles, CA, United States, 8University of Southern California, Los Angeles, CA, United States.
The air exchange surface of the lungs is customarily drawn simplified as a ball on a stick. Herein we will show how, using several novel imaging and computational approaches, that the air exchange surface of the lung develop from the tips and sides of tortuous ducts, that themselves ramify as distinct families distal to the bronchoalveolar duct junction (BADJ), prenatally in humans but postnatally in mice. The mature air exchange surfaces thus consist of highly indentedspheroids, tightly packed between quite regularly spaced distal ducts. Since the diameter of the BADJ and the distal ducts increases rather than decreasing during lung growth, we further deduce that the air sacs may form by precisely controlled epithelial precursor buckling, with resulting extrusion of the airway lumens into the surrounding mesenchyme, in addition to or perhaps instead of being effected entirely by “erection” of septae subdividing existing spaces. The mouth of each air exchange sac is stabilized firstly by interlocking rings of elastin and secondly later on by rings of mixed elastin and collagen fibers that surround the mouth of each prospective air exchange sac, thus determining precisely where the epithelial buckling and extrusion occurs. Furthermore, we show that the surface of each of the air exchange sacs is highly rugose, being indented by the capillary network that lies close beneath the air exchange surface membrane. We propose that a version of the kissing theorem of Newton that expresses the number of times billiard balls may touch within their frame as a parsimonious solution to achieving optimum packing of the distal air sacs, while leaving sufficient space between them to accommodate conducting airways, arteries, veins, closely applied pulsatile capillary blood vessels, lymphatics, nerves and other key components within the complex environment of the interstitial mesenchyme. This arrangement would optimize gas diffusion and functional efficiency of the lung over the more prevalent stick and ball concept.