Development, structure, and function of a novel respiratory organ, the lung-air sac system of birds: to go where no other vertebrate has gone
ABSTRACT Among the air-breathing vertebrates, the avian respiratory apparatus, the lung-air sac system, is the most structurally complex and functionally efficient. After intricate morphogenesis, elaborate pulmonary vascular and airway (bronchial) architectures are formed. The crosscurrent, countercurrent, and multicapillary serial arterialization systems represent outstanding operational designs. The arrangement between the conduits of air and blood allows the respiratory media to be transported optimally in adequate measures and rates and to be exposed to each other over an extensive respiratory surface while separated by an extremely thin blood-gas barrier. As a consequence, the diffusing capacity (conductance) of the avian lung for oxygen is remarkably efficient. The foremost adaptive refinements are: (1) rigidity of the lung which allows intense subdivision of the exchange tissue (parenchyma) leading to formation of very small terminal respiratory units and consequently a vast respiratory surface; (2) a thin blood-gas barrier enabled by confinement of the pneumocytes (especially the type II cells) and the connective tissue elements to the atria and infundibulae, i.e. away from the respiratory surface of the air capillaries; (3) physical separation (uncoupling) of the lung (the gas exchanger) from the air sacs (the mechanical ventilators), permitting continuous and unidirectional ventilation of the lung. Among others, these features have created an incredibly efficient gas exchanger that supports the highly aerobic lifestyles and great metabolic capacities characteristic of birds. Interestingly, despite remarkable morphological heterogeneity in the gas exchangers of extant vertebrates at maturity, the processes involved in their formation and development are very similar. Transformation of one lung type to another is clearly conceivable, especially at lower levels of specialization. The crocodilian (reptilian) multicameral lung type represents a Bauplan from which the respiratory organs of nonavian theropod dinosaurs and the lung-air sac system of birds appear to have evolved. However, many fundamental aspects of the evolution, development, and even the structure and function of the avian respiratory system still remain uncertain.
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ABSTRACT: We employed macroscopic and ultrastructural techniques as well as intratracheal casting methods to investigate the pattern of development, categories, and arrangement of the air conduits in the chicken lung. The secondary bronchi included four medioventral (MVSB), 7-10 laterodorsal (LDSB), 1-3 lateroventral (LVSB), several sacobronchi, and 20-60 posterior secondary bronchi (POSB). The latter category has not been described before and is best discerned from the internal aspect of the mesobronchus. The secondary bronchi emerged directly from the mesobronchus, except for the sacobronchi, which sprouted from the air sacs. Parabronchi from the first MVSB coursed craniodorsally and inosculated their cognates from the first two LDSB. The parabronchi from the rest of the LDSB curved dorsomedially to join those from the rest of the MVSB at the dorsal border. Sprouting, migration, and anastomoses of the paleopulmonic parabronchi resulted in two groups of these air conduits; a cranial group oriented rostrocaudally and a dorsal group oriented dorsoventrally. The neopulmonic parabronchial network formed through profuse branching and anastomoses and occupied the ventrocaudal quarter of the lung. There were no differences in the number of secondary bronchi between the left and right lungs. Notably, a combination of several visualization techniques is requisite to adequately identify and enumerate all the categories of secondary bronchi present. The 3D arrangement of the air conduits ensures a sophisticated system, suitable for efficient gas exchange. Microsc. Res. Tech., 2008. (c) 2008 Wiley-Liss, Inc.Microscopy Research and Technique 09/2008; 71(9):689-702. DOI:10.1002/jemt.20608 · 1.17 Impact Factor
Conference Paper: Dual band operation of the relativistic BWO[Show abstract] [Hide abstract]
ABSTRACT: The possibility of dual-band signal using relativistic backward wave oscillator with a slow-wave system excited by a single beam was described. We demonstrate that a regime of generation at several close frequencies with the same transverse field structure can be rather simply realized in a sectioned system with a stepwise variation of mismatch between the beam and synchronous wave. In this case of high-power relativistic BWO with the microwave system representing sections of a corrugated waveguide, a change of synchronism conditions can provided by variation of the corrugation period.Vacuum Electronics, 2003 4th IEEE International Conference on; 06/2003
Conference Paper: Wideband dual polarized planar antenna arrays[Show abstract] [Hide abstract]
ABSTRACT: The paper presents a novel design of planar multilayered microstrip antenna arrays using aperture-coupled stacked patch radiating elements with dual polarization capability. Frequency bandwidth of up to 26% (VSWR < 2:1), isolation between orthogonally polarized channels better than 30 dB and level of cross-polarization better than -30 dB have been achieved in both E- and H-planes of radiation pattern for the two orthogonal linear polarizations. Numerical results obtained by FDTD computer simulations are compared with measured characteristics of a manufactured antenna samples, operating in frequency bands from 0.9 to 15 GHz.Antenna Theory and Techniques, 2003. 4th International Conference on; 10/2003