Gas Exchange

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  The Respiratory System

  • Britannica Educational Publishing, Kara Rogers(Authors)
  • 2010(Publication Date)
  • Britannica Educational Publishing

    (Publisher)

  AS EXCHANGE AND RESPIRATORY ADAPTATION

  I nhaled air is rich in oxygen, which is needed to support the functions of the body’s various tissues. For inhaled oxygen to reach these tissues, however, it must first undergo a process of Gas Exchange that occurs at the level of the alveoli in the lungs. Blood vessels that pass alongside the alveoli membranes absorb the oxygen and, in exchange, transfer carbon dioxide to the alveoli. The oxygen is then distributed by the blood to the tissues, whereas the carbon dioxide is expelled from the alveoli during exhalation. At high altitudes or during activities such as deep-sea diving, the respiratory system, as well as other organ systems, adapt to variations in atmospheric pressure. This process of adaptation is necessary to maintain normal physiological function.

  Gas Exchange

  Respiratory gases—oxygen and carbon dioxide—move between the air and the blood across the respiratory exchange surfaces in the lungs. The structure of the human lung provides an immense internal surface that facilitates Gas Exchange between the alveoli and the blood in the pulmonary capillaries. The area of the alveolar surface in the adult human is about 160 square metres (1,722 square feet). Gas Exchange across the membranous barrier between the alveoli and capillaries is enhanced by the thin nature of the membrane, about 0.5 micrometre, or 1/100 of the diameter of a human hair.

  Changes in the atmosphere’s pressure occur when deep-sea diving and require the respiratory system to adapt . Shutterstock.com

  Respiratory gases move between the environment and the respiring tissues by two principal mechanisms, convection and diffusion. Convection, or mass flow, is responsible for movement of air from the environment into the lungs and for movement of blood between the lungs and the tissues. Respiratory gases also move by diffusion across tissue barriers such as membranes. Diffusion is the primary mode of transport of gases between air and blood in the lungs and between blood and respiring tissues in the body. The process of diffusion is driven by the difference in partial pressures of a gas between two locales. In a mixture of gases, the partial pressure of each gas is directly proportional to its concentration. The partial pressure of a gas in fluid is a measure of its tendency to leave the fluid when exposed to a gas or fluid that does not contain that gas. A gas will diffuse from an area of greater partial pressure to an area of lower partial pressure regardless of the distribution of the partial pressures of other gases. There are large changes in the partial pressures of oxygen and carbon dioxide as these gases move between air and the respiring tissues. The partial pressure of carbon dioxide in this pathway is lower than the partial pressure of oxygen, caused by differing modes of transport in the blood, but almost equal quantities of the two gases are involved in metabolism and Gas Exchange.

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  Biology 2e

  • Mary Ann Clark, Jung Choi, Matthew Douglas(Authors)
  • 2018(Publication Date)
  • Openstax

    (Publisher)

  At the same time, these reactions release carbon dioxide (CO 2 ) as a by-product. CO 2 is toxic and must be eliminated. Carbon dioxide exits the cells, enters the bloodstream, travels back to the lungs, and is expired out of the body during exhalation. Chapter 39 | The Respiratory System 1223 39.1 | Systems of Gas Exchange By the end of this section, you will be able to do the following: • Describe the passage of air from the outside environment to the lungs • Explain how the lungs are protected from particulate matter The primary function of the respiratory system is to deliver oxygen to the cells of the body’s tissues and remove carbon dioxide, a cell waste product. The main structures of the human respiratory system are the nasal cavity, the trachea, and lungs. All aerobic organisms require oxygen to carry out their metabolic functions. Along the evolutionary tree, different organisms have devised different means of obtaining oxygen from the surrounding atmosphere. The environment in which the animal lives greatly determines how an animal respires. The complexity of the respiratory system is correlated with the size of the organism. As animal size increases, diffusion distances increase and the ratio of surface area to volume drops. In unicellular organisms, diffusion across the cell membrane is sufficient for supplying oxygen to the cell (Figure 39.2). Diffusion is a slow, passive transport process. In order for diffusion to be a feasible means of providing oxygen to the cell, the rate of oxygen uptake must match the rate of diffusion across the membrane. In other words, if the cell were very large or thick, diffusion would not be able to provide oxygen quickly enough to the inside of the cell. Therefore, dependence on diffusion as a means of obtaining oxygen and removing carbon dioxide remains feasible only for small organisms or those with highly-flattened bodies, such as many flatworms (Platyhelminthes).

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  The Physiology of Fishes

  • Suzanne Currie, David H. Evans, Suzanne Currie, David H. Evans(Authors)
  • 2020(Publication Date)
  • CRC Press

    (Publisher)

  3  Gas Exchange Jodie L. Rummer and Colin J. Brauner CONTENTS 3.1 Introduction 3.2 From Environment to Gill Branchial Gas Transfer 3.2.1 Ventilation 3.2.2 Morphology 3.2.3 Diffusion across Membranes 3.2.4 The Osmorespiratory Compromise 3.3 Circulatory Transport of Respiratory Gases 3.3.1 Blood 3.3.1.1 Oxygen 3.3.1.2 Carbon Dioxide 3.3.2 Blood Flow and Perfusion 3.4 Diffusion at the Tissue Level 3.5 Conclusion Acknowledgements References

  3.1 Introduction

  Oxygen is a prerequisite for life for all fish species with no known exceptions. Oxygen (O2 ) uptake from the environment, transport across respiratory surfaces and through the circulatory system, and ultimately, delivery to metabolizing tissue, with the reverse for carbon dioxide (CO2 ), which is produced in approximately equal amounts, have been topics of interest for fish physiologists for centuries. Yet, Gas Exchange is not just restricted to O2 and CO2 . Ammonia (NH3 ) excretion, also collectively part of Gas Exchange, is the key pathway for nitrogenous waste elimination for both marine and freshwater fishes. Therefore, Gas Exchange includes O2 , CO2 , and NH3 and, at least in most adult fishes, primarily occurs at the gills. The skin and air-breathing organs can also be used for Gas Exchange, depending on life stage and species, and will be discussed briefly here but elaborated upon in other chapters. As Gas Exchange in fishes has been reviewed relatively recently in detail (Evans et al., 2005; Randall et al., 2014; Harter and Brauner, 2017), only the fundamentals are reviewed here (focusing on O2 and CO2 ) along with more recent advances in the field. In this chapter, we focus on the role of the gill in Gas Exchange, reviewing aspects related to ventilation, morphology, contact with the external environment, diffusion across membranes, blood flow and perfusion, and diffusion at the tissue level (Figure 3.1 ). Cellular metabolism, the next logical step in this cascade, is discussed at both the cellular and the whole-organism level in Chapter 10

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  Fish Larval Physiology

  • Roderick Nigel Finn(Author)
  • 2020(Publication Date)
  • CRC Press

    (Publisher)

  Part 2

  Respiration & Homeostasis

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  CHAPTER

  4

  Gas Exchange

  Bernd Pelster1 , 2 , *

  Introduction

  The form and function of animal respiratory and circulatory systems have attracted considerable attention for several hundred years. While the main organs of Gas Exchange (J O2 , J CO2 , J NH3 ) in adult fishes are the gills, they are also responsible for hydromineral and acid-base balance (Evans et al. 1999, 2005), nitrogenous waste excretion (Randall et al. 1999; Terjesen, this volume), hormone production (Zaccone et al. 1996, 2006), and activation or inactivation of circulating metabolites (Olson, 1998). Although the circulatory system is typically the first functioning organ during early embryonic development (Rombough, 1997; Pelster, 1999, 2002, Hall, this volume, Burggren & Bagatto, this volume), gills develop much later (Rombough, 2002, 2004). Gas Exchange, however, is required right from the start of development of the fertilised egg. This implies that Gas Exchange initially must occur through the cellular integument of the developing embryo, having traversed the boundary layer, chorion and perivitelline fluids (PVF ) of the embryo, or the surface epithelium of the hatched larva. The gills only supersede this function once they have developed. In addition, the autonomic nervous system, which controls cardiac activity and other organs, only becomes fully functional during later stages of development (Protas & Leontieva, 1992; Jacobsson & Fritsche, 1999; Schwerte et al ., 2006; Holmberg et al.,

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  Human Biology

  • Cecie Starr, Beverly McMillan(Authors)
  • 2015(Publication Date)
  • Cengage Learning EMEA

    (Publisher)

  respiratory surface The thin, moist surface across which oxygen and carbon dioxide diffuse during res-piration; the thin walls of alveoli in the lungs provide this surface. Respiration 5 Gas Exchange only diffuse rapidly over short distances. The respiratory surface must be moist because gases can’t diffuse across it unless they are dissolved in fluid. The thin walls of the millions of alveoli in the lungs meet these requirements. Oxygen and carbon dioxide also move between body cells and tissue fluid. Blood circulated by the cardiovascu-lar system carries these gases to and from the tissue fluid that bathes cells (Figure 10.6B). Two factors affect how many gas molecules can move into and out of lung alveoli in a given period of time. The first is surface area, and the second is the partial pressure gradient across it. Diffusion occurs faster when the surface area is large and the gradient is steep. The millions of alveoli in your lungs provide a huge surface area for Gas Exchange. As we see next, the interaction between hemo-globin and oxygen helps maintain a steep gradient that in turn helps bring oxygen into the lungs. n All living cells in the body rely on respiration to supply them with oxygen and dispose of carbon dioxide wastes. n Links to Mitochondria 3.8, Cellular respiration 3.15 Chapter 3 described aerobic cellular respiration—the process inside cell mitochondria that uses oxygen and pro-duces carbon dioxide wastes that enter the bloodstream. Respiration , in contrast, refers to overall Gas Exchange: the processes that deliver oxygen in inhaled air to body cells and remove waste carbon dioxide from the body (Figure 10.4). In Gas Exchange, oxygen and carbon dioxide diffuse down a pressure gradient Gas Exchange in the body relies on the tendency of oxy-gen and carbon dioxide to diffuse down their respective concentration gradients—or, as we say for gases, their pressure gradients .

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  Dynamic Aquaria

  Building Living Ecosystems

  • Walter H. Adey, Karen Loveland(Authors)
  • 1991(Publication Date)
  • Academic Press

    (Publisher)

  Curtis, N. 1985. Longman Ulustrated Dictionary of Biology. Longman York Press, Burnt Mill, Essex, England. Keeton, W. T., and Gould, J. L. 1986. BioJogicaJ Science. 4th Ed. Norton and Co., New York. Lawlor, D. W. 1987. Photosynthesis: Metabolism, Control and Physiology. Longman Scien-tific/John Wiley, New York. Lovelock, J. 1979. Gaia: A New Look at Life on Earth. Oxford University Press, Oxford. Lovelock, J. 1988. The Ages of Gaia: A Biography of Our Living Earth. Norton and Co., New York. Mayr, E. 1988. Toward a New Philosophy of Biology. Harvard University Press, Cambridge, Massachusetts. CHAPTER 10 Pressure t L I F E 1 ANIMAL CYCLE PLANTS Respiration Photosynthesis ORGANISMS AND Gas Exchange Oxygen, Carbon Dioxide, and pH The metabolism of living organisms affects water chemistry in two basic ways: (1) Gas Exchange (mostly oxygen and carbon dioxide) and (2) ex-change of dissolved nutrients (nitrogen, phosphorus, and a variety of micronutrients). Animals also release undigested food in the form of feces and plants lose or detach parts, which relative to the environment are dead organic materials undergoing further breakdown primarily by mi-crobes. They also excrete organic compounds such as ammonia and urea that will undergo further microbe degradation. All of these are steps that will ultimately use oxygen, release carbon dioxide, and produce nu-trients. In this chapter and the next, we will discuss gas and nutrient exchange, respectively. For perspective, we will briefly discuss selected wild aquatic and marine environments followed by examples from a vari-ety of captured ecosystems. Finally, in Chapter 12, we will examine meth-ods of controlling gas and nutrient exchange in microcosms, mesocosms, and aquaria. In these model ecosystems, control or compensation is needed either because of the small size of the system in a day-night cycle, the presence of unnaturally large biomass, or the lack of a compensating larger adjacent body of water.

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  Organism and Environment

  • John B. West(Author)
  • 2013(Publication Date)
  • Academic Press

    (Publisher)

  5 Gas Exchange during Liquid Breathing Johannes A. Kylstra I. Ventilation of Liquid-Filled Lungs 188 II. Distribution of Ventilation and Blood Flow in Liquid-Filled Lungs 190 III. Diffusion of Dissolved 0 2 and C 0 2 in Liquid-Filled Air Spaces . 191 IV. Diffusion of Xenon in Liquid-Filled Air Spaces 197 V. Stratified Inhomogeneity of Oxygen 199 VI. Composite Breathing Liquids 200 References 202 The exchange of oxygen and carbon dioxide between multicellular organisms and their environment occurs by diffusion along partial pres-sure gradients maintained by ventilation and perfusion of the organs of respiration. The structure of these organs reflects evolutionary adapta-tions that meet the functional demands of the organisms in their natural surroundings. The gills of fish are adapted to the exchange of gases with an aquatic environment, but when an air-breathing animal is suddenly sub-merged serious problems arise that ordinarily cannot be met. At the sur-face of the earth, a volume of air normally contains about 40 times more oxygen than an equal volume of water. Hence, to supply the same amount of oxygen per minute to the circulating blood, the tidal flow of water in the lungs should be at least 40 times greater than of air. As we shall see, how-ever, the lungs of terrestrial mammals are not designed for tidal flows, at such a high rate, of a fluid that is much denser and more viscous than air. Second, natural waters (fresh water or seawater) usually have a composi-tion very different from that of blood; hence, when the water is inhaled it can damage the lung tissues and can cause fatal alterations in the volume and composition of body fluids. Under laboratory conditions, however, it is possible to adjust the salt content of the water so that its composition resembles that of blood plasma. Alternatively, an animal can be made to P U L M O N A R Y G A S E X C H A N G E , V O L .

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  The Comparative Physiology of Respiratory Mechanisms

  • Auqust Krogh(Author)
  • 2015(Publication Date)
  • University of Pennsylvania Press Anniversary Collection

    (Publisher)

  The functional difference between the two organs comes out very clearly. By large variations in total exchange (70-170 ml/kg/hour) the oxygen intake through the skin, which is limited mainly by the conditions for diffusion, remains practically constant at about 50, while the variations are brought about by the ventilation of the lungs and the blood-flow through them. CO2, which diffuses so much more rapidly, is eliminated at all metabolic levels mainly through the skin where the blood is exposed to an atmosphere practically CO2 free. The elimination through the lungs is limited by the alveolar CO2 tension and is there-fore closely correlated with the ventilation. In a small number of vertebrates (tortoise, pigeon, man) Krogh (1904.2) determined the cutaneous uptake of 0 2 . It is too small to be of any respiratory significance. In blowfly larvae having a very thin cuticle, Fraenkel and Herford (1938) find that in a normal atmosphere about 10% of the total oxygen is absorbed through the integument. Air-breathing gills, formed by the internal branches of some of the abdominal feet and protected by the external, are found in some terrestrial isopods {Ligia, Oniscus ) living in moist sur- RESPIRATION IN AIR 55 roundings, but others belonging to the same group have developed functional lungs and have a greater power to withstand desiccation ( Porcellio). Lungs as physiologically defined are respiratory surfaces folded into the body. T h e Gas Exchange takes place through these surfaces between the alveolar air and the blood, and the gases are transported between the tissues and the lungs by the circulation of the blood. T h e distinction between lungs and tracheae carrying air directly to the tissue cells is not quite sharp. In certain small insects and in several arachnoids the tracheal system is poorly developed and does not reach all parts of the body, so that some circulation is essential for respiration.

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  Air-Breathing Fishes

  Evolution, Diversity, and Adaptation

  • Jeffrey B. Graham(Author)
  • 1997(Publication Date)
  • Academic Press

    (Publisher)

  Ar and Zacks (1989) reviewed respiratory par- titioning in air-breathing fishes and provided an espe- cially detailed analyses of this in Clarias lazera. Works by Bridges (1993a,b) and Martin (1993, 1995) explore the relationships between the rates of oxygen con- sumption (VO2) and carbon dioxide release (VCO2) during amphibious air breathing. The explosion of air-breathing fish respiratory data over the past thirty-five years invites a resynthesis to determine if the underlying principles guiding this field remain intact and to discover areas needing addi- tional study. This chapter begins with a historical overview which is followed by a comparison of air- breathing cycles (i.e., breath frequency and duration) and a review of whole-organism respiratory Gas Exchange. The final section examines specialized aspects of respiratory organ function. Unlike the pri- marily phylogenetic approach adopted in previous chapters, this review emphasizes the comparative physiological aspects of air breathing. A similar approach is followed in subsequent chapters on respi- ratory control and integration (Chapter 6), on blood-respiratory properties (Chapter 7) and bio- chemical adaptations (Chapter 8). HISTORICAL The need for studies of Gas Exchange was recog- nized by the early naturalists who wondered if air breathing was sufficient to completely replace or only supplement the normal aquatic mode. Taylor (1831), 153 154 5. Aerial and Aquatic Gas Exchange in noting atrophied gills of Monopterus, drew attention to the necessity for bimodal respiration, a process described by Day (1868) as compound breathing. Physiological investigation of air breathing began with the pond loach (Misgurnus fossilis) for which Erman (1808) and Bischof (1818) made the earliest measurements of ABO gas levels.

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