This chapter is part of a new book:
John N. Maina (editor) (2017)
The Biology of the Avian Respiratory System: Evolution, Development, Structure and Function.
Springer International Publishing
ISBN: 978-3-319-44152-8 (Print) 978-3-319-44153-5 (Online)
DOI: 10.1007/978-3-319-44153-5
https://link.springer.com/book/10.1007/978-3-319-44153-5
http://www.springer.com/us/book/9783319441528?wt_mc=ThirdParty.SpringerLink.3.EPR653.About_eBook
Table of Contents:
Front Matter
Pages i-xviii PDF:
https://link.springer.com/content/pdf/bfm:978-3-319-44153-5/1.pdf
The Evolution of Birds with Implications from New Fossil Evidences
Min Wang, Zhonghe Zhou
Pages 1-26: PDF:
https://link.springer.com/chapter/10...-319-44153-5_1
The Avian Lingual and Laryngeal Apparatus Within the Context of the Head and Jaw Apparatus, with Comparisons to the Mammalian Condition: Functional Morphology and Biomechanics of Evaporative Cooling, Feeding, Drinking, and Vocalization
Dominique G. Homberger
Pages 27-97
Abstract:
The lingual and laryngeal apparatus are the mobile and active organs within the oral cavity, which serves as a gateway to the respiratory and alimentary systems in terrestrial vertebrates. Both organs play multiple roles in alimentation and vocalization besides respiration, but their structures and functions differ fundamentally in birds and mammals, just as the skull and jaws differ fundamentally in these two vertebrate classes. Furthermore, the movements of the lingual and laryngeal apparatus are interdependent with each other and with the movements of the jaw apparatus in complex and little-understood ways. Therefore, rather than updating the existing numerous reviews of the diversity in lingual morphology of birds, this chapter will concentrate on the functional-morphological interdependences and interactions of the lingual and laryngeal apparatus with each other and with the skull and jaw apparatus. It will:
1. Briefly review the salient features of the mammalian head as a baseline against which to understand the uniqueness of the avian head
2. Describe general morphological features of the lingual and laryngeal apparatus within the context of the skull and jaw apparatus
3. Contrast some fundamental functional-morphological differences that exist among the jaw, lingual and laryngeal apparatus of birds
4. Provide models of the movements of the various parts of the lingual and laryngeal apparatus based on biomechanical analyses
5. Integrate these models with behaviors in thermoregulation, feeding, drinking, and vocalization
6. Briefly demonstrate how detailed morphological and functional analyses can be tested and expanded by using 3D visualization and animation
7. Place the provided data in an evolutionary framework
Pulmonary Transformations of Vertebrates
C. G. Farmer
Pages 99-112
Abstract
The structure of the lung subserves its function, which is primarily gas exchange, and selection for expanded capacities for gas exchange is self-evident in the great diversity of pulmonary morphologies observed in different vertebrate lineages. However, expansion of aerobic capacities does not explain all of this diversity, leaving the functional underpinnings of some of the most fascinating transformations of the vertebrate lung unknown. One of these transformations is the evolution of highly branched conducting airways, particularly those of birds and mammals. Birds have an extraordinarily complex circuit of airways through which air flows in the same direction during both inspiration and expiration, unidirectional flow. Mammals also have an elaborate system of conducting airways; however, the tubes arborize rather than form a circuit, and airflow is tidal along the branches of the bronchial tree. The discovery of unidirectional airflow in crocodilians and lizards indicates that several inveterate hypotheses for the selective drivers of this trait cannot be correct. Neither endothermy nor athleticism drove the evolution of unidirectional flow. These discoveries open an uncharted area for research into selective underpinning of unidirectional airflow.
Flying High: The Unique Physiology of Birds that Fly at High Altitudes
Graham R. Scott, Neal J. Dawson
Pages 113-128
Abstract
Birds that fly at high altitudes must support vigorous exercise in oxygen-thin environments. Here we discuss the characteristics that help high-fliers sustain the high rates of metabolism needed for flight at elevation. Many traits in the O2 transport pathway distinguish birds in general from other vertebrates. These include enhanced gas-exchange effectiveness in the lungs, maintenance of O2 delivery and oxygenation in the brain during hypoxia, augmented O2 diffusion capacity in peripheral tissues, and a high aerobic capacity. These traits are not high-altitude adaptations, because they are also characteristic of lowland birds, but are nonetheless important for hypoxia tolerance and exercise capacity. However, unique specializations also appear to have arisen, presumably by high-altitude adaptation, at every step in the O2 pathway of some highland species. The distinctive features of high-fliers include an enhanced hypoxic ventilatory response and/or an effective breathing pattern, large lungs, haemoglobin with a high O2 affinity, further augmentation of O2 diffusion capacity in the periphery, and multiple alterations in the metabolic properties of cardiac and skeletal muscle. These unique specializations improve the uptake, circulation, and efficient utilization of O2 during high-altitude hypoxia. High-altitude birds also have larger wings than their lowland relatives, presumably to reduce the metabolic costs of staying aloft in low-density air. High-fliers are therefore unique in many ways, but the relative roles of adaptation and plasticity (acclimatization) in high-altitude flight are still unclear. Disentangling these roles will be instrumental if we are to understand the physiological basis of altitudinal range limits and how they might shift in response to climate change.
Molecular Aspects of Avian Lung Development
Rute S. Moura, Jorge Correia-Pinto
Pages 129-146
Abstract
The pulmonary system develops from a series of complex events that involve coordinated growth and differentiation of distinct cellular compartments. After lung specification of the anterior foregut endoderm, branching morphogenesis occurs generating an intricate arrangement of airways. This process depends on epithelial-mesenchymal interactions tightly controlled by a network of conserved signaling pathways. These signaling events regulate cellular processes and control the temporal-spatial expression of multiple molecular players that are essential for lung formation. Additionally, remodeling of the extracellular matrix establishes the appropriate environment for the delivery of diffusible regulatory factors that modulate these cellular processes. In this chapter, the molecular mechanisms underlying avian lung development are thoroughly revised. Fibroblast growth factor, WNT, sonic hedgehog, transforming growth factor-β, bone morphogenetic protein, vascular endothelial growth factor, and regulatory mechanisms such as microRNAs control cell proliferation, differentiation, and patterning of the embryonic chick lung. With this section, we aim to provide a snapshot of the current knowledge of the molecular aspects of avian lung development.
Development of the Airways and the Vasculature in the Lungs of Birds
Andrew N. Makanya
Pages 147-178
Abstract
Generally, the vertebrate lung has its origin from the endoderm in the region of the primitive foregut, where the epithelium gives rise to the airway system and the gas-exchanging units and the mesenchyme forms the connective tissue, muscles, and vessels. The lung starts as a primordium, which splits into a left and right bud each of which forms the respective lung. In birds, the lung buds form the primary bronchi from which the secondary bronchi (SB) arise. The parabronchi (PB) sprout from the SB and occupy specific locations within the lung. Atria start as excavations with attenuating cells and give rise to infundibula and finally to air capillaries. The mechanisms underlying the formation of the remarkably thin blood–gas barrier (BGB) closely resemble those of exocrine secretion, but occur in a programmed, time-limited manner. In general, they result in cutting or decapitation of the cell until the required thickness is attained. In the first step, the high columnar epithelium undergoes dramatic size reduction and loses morphological polarization by two main processes: secarecytosis (cell decapitation by cutting) and peremerecytosis (cell decapitation by squeezing, spontaneous constriction, or pinching off). Secarecytosis has at least two facets: transcellular double-membrane formation followed by separation between such membranes or cell cutting by vesiculation. Both processes lead to formation of a thin BGB. Blood vessel formation in the avian lung occurs concomitantly with formation of the airway system. There is close interaction between the budding endoderm and the surrounding mesenchyme, where their crosstalk leads to development and differentiation of the components of the functional lung. Blood vessel formation starts with vasculogenesis where blood islands are formed. The islands then form blood vessels that expand further through sprouting, and once a network is established, it is augmented and remodeled through intussusceptive angiogenesis.
Structure and Function of Avian Pulmonary Capillaries: Comparison with Mammals
John B. West
Pages 179-190
Abstract
The avian pulmonary circulation has many interesting features and much information can be gained by comparing the avian and mammalian systems. Two features are primarily responsible for the unique features of avian capillaries. First, the avian lung has separated the ventilation and gas exchange functions. Second, the avian lung uses a flow-through process for ventilation rather than the reciprocal pattern adopted by mammals. As a consequence, the environment of the pulmonary capillaries is very different in the avian compared with the mammalian lung. The avian capillaries are nested in a syncytium of air capillaries, whereas the capillaries of the mammalian lung are strung out along the alveolar walls. This means that the mechanical support of the categories is very different in birds compared with mammals. A consequence of this is that the walls of the capillaries are very different. In the avian lung, the blood–gas barrier is extremely thin and uniform throughout the capillaries. Contrast this with the mammalian lung where a type I collagen cable is required for the support of the capillaries, and as a result the blood–gas barrier is much thicker in places and the diffusion characteristics are therefore inferior. Another striking difference is that avian pulmonary capillaries are remarkably rigid unlike those in mammals, which undergo recruitment and distention when the cardiac output rises. The implications of this for pulmonary vascular resistance during intense exercise such as flying are still unclear.
Functional Design of the Mature Avian Respiratory System
John N. Maina
Pages 191-218
Abstract
The avian respiratory system is structurally exceptionally complex and functionally remarkably efficient. It comprises a lung that serves as the gas exchanger and air sacs that function as the ventilators. Topographically, the lung is located between two sets of air sacs, namely, a cranial and a caudal group. They continuously ventilate the lung in a craniocaudal direction by synchronized activities. The air sacs are delicate, transparent and compliant structures. Since they are avascular, they play no part in gas exchange. The lung is attached to the ribs and the vertebrae on the dorsolateral aspects and to the horizontal septum on the ventral one. It renders the lung practically rigid. This allows the exchange tissue (parenchyma) to be very intensely subdivided, resulting in minuscular terminal respiratory units, the air capillaries. That way, the respiratory surface area is increased. The bronchial system of the avian lung forms a continuous loop that consists of a three-tier system of airways. These are a primary bronchus, secondary bronchi and tertiary bronchi (parabronchi). The arrangement of the airways and the blood vessels in the lung determines where and how air and blood are distributed and the respiratory media exposed to each other for gas exchange. A cross-current system is formed by the essentially perpendicular disposition between the flow of air in the parabronchial lumen and that of venous blood in the exchange tissue; an auxiliary counter-current arrangement is formed by the relationship between the direction of the flow of air in the air capillaries and that of the blood in the blood capillaries, and a multicapillary serial arterialization system consists of the sequential interaction between the blood in the blood capillaries and the air in the capillaries in the parabronchus. In addition to these features, the bird lung has large capillary blood volume, extensive surface respiratory surface area and particularly thin blood-gas (tissue) barrier. The morphological specializations and the adaptive physiological features such as large tidal volume and cardiac output all together explain the exceptional gas exchange efficiency of the avian respiratory system, supporting the high metabolic capacity and energetic lifestyles of birds.
Structure and Function of the Shell and the Chorioallantoic Membrane of the Avian Egg: Embryonic Respiration
John N. Maina
Pages 219-247
Abstract
The evolution of a cleidoic (self-supporting) egg in the amniotes was pivotal to the transition of animal life from water to land: embryonic development could occur without the direct presence of water. For birds, remarkable adaptive radiation occurred after the achievement of volancy. It has culminated in ~10,000 species. Among the air-breathing vertebrates, the taxon Aves is the most speciose. In the developing avian egg, exchange of respiratory gases (O2 and CO2) and water vapour occurs entirely by passive diffusion across the shell and the chorioallantoic membrane (CAM) along existing concentration gradients. A multifunctional structure, the shell displays compromise design. On one hand it has to be thin enough to allow optimal flux of O2 and CO2 and loss of water which is generated by metabolism of the developing embryo. On the other hand, the shell must not be too thin to admit pathogens and injurious substances and susceptible to failure (breaking). Also, the shell must not be too strong for the chick to be unable to break out of at hatching. The thickness of the shell and the numbers, shapes and sizes of the pores determine the hatchability of the egg and probably the incubation period of the egg. The CAM of the developing chick embryo is analogous to the placenta of the viviparous animals. While the number of pores may be fixed at the formation of the eggshell, during incubation, the surface area and vascularization of the CAM increase considerably. Here, the structure and function of the avian eggshell and that of the CAM are succinctly outlined. Particular consideration is given to the recent observations made using X-ray microcomputer tomography, a highly instructive technique for studying biological structures. The impact of the evolution of the amniotic egg on the diversification of the animal life especially that of birds, is highlighted.
Back Matter
Pages 249-250
PDF:
https://link.springer.com/content/pdf/bbm:978-3-319-44153-5/1.pdf
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The Biology of the Avian Respiratory System
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