Human Gas Exchange

8 Key excerpts on "Human Gas Exchange"

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  eBook - ePub

  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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  Human Biology

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

    (Publisher)

  In this chapter your knowledge of concentration gradients and diffusion (3.10) will help you understand the mechanisms that move oxygen into and carbon dioxide out of the body. You will see how the respiratory system works together with the cardiovascular system (7.1) to supply oxygen and remove carbon dioxide. You will also learn how hemoglobin and red blood cells function in gas exchange (8.2). LINKS TO EARLIER CONCEPTS Top three: © Cengage Learning; Bottom: © Brian Chase/Shutterstock.com Tobacco smoke is a major risk factor for lung cancer and also is linked with cancers of the tongue, throat, and other tissues and organs. For example, females who start smoking in their teens are about 70 percent more likely to develop breast cancer than those who don’t smoke. Tobacco smoke doubles the risk of heart disease because it elevates blood pressure and blood levels of LDL (“bad”) cholesterol and lowers levels of “good” cholesterol (HDL). Anything we inhale that enters the bloodstream gets there by way of the respiratory system, our focus in this chapter. Its parts collectively have one basic job—to bring in oxygen, which cells need for their metabolism, and to dispose of carbon dioxide, which is the cells’ waste product. 10 THE RESPIRATORY SYSTEM © Tim Large/Shutterstock.com 177 Homeostasis Preview Cells require oxygen for making ATP in mitochondria and also must get rid of potentially toxic carbon dioxide produced by the reactions. The respiratory system exchanges these gases with the bloodstream. KEY CONCEPTS The Respiratory System Respiration provides the body with the oxygen for aerobic respiration in cells. It also removes waste carbon dioxide. These gases enter and leave the body by way of the respiratory system. Sections 10.1–10.4 Gas Exchange Oxygen and carbon dioxide are exchanged across the thin walls of microscopic sacs in the lungs called alveoli. Circulating blood car-ries gases to and from the lungs.

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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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  A Thinking Approach to Physiology

  • Ian N Sabir, Juliet A Usher-Smith(Authors)
  • 2008(Publication Date)
  • WSPC

    (Publisher)

  CHAPTER 4 The Respiratory System      

  All living cells have an absolute requirement for a regular supply of energy. Energy is usually handled in the form of the molecule adenine triphosphate (ATP), a product of a series of metabolic reactions within the mitochondria of each cell together referred to as respiration. A fuel such as glucose is the only essential substrate for respiration. However, the efficiency of the process is increased by up to eight times in the presence of O2 , which ultimately takes the role of an oxidising agent. The provision of O2 to the mitochondria, and the removal of the waste product of respiration, CO2 , are therefore essential for life. This chapter considers how these two goals are achieved at the level of the whole organism.

  The process of delivering O2 to and removing CO2 from the body may be split into three: transporting the gases into and out of the organism, getting the substance to or from the active cells within the organism and finally getting the substance to or from the mitochondria within each cell. In organisms such as bacteria where surface area to volume ratio is large and distances within the organism are small, simple diffusion is sufficient to solve these problems. This same strategy is used to supply O2 to the human cornea. However, in larger multicellular organisms such as humans, distances are ordinarily limiting. We therefore require a dedicated organ, the lungs, to provide a large surface area over which gas exchange can occur. Furthermore, we also require a specialised circulatory system, the bloodsteam, to carry these gases around the body. We will begin by discussing the transport of gases into and out of the lungs, then focus on the exchange of gases between the lungs and the blood before finally considering how these gases are carried in the blood. The transport of this blood to the tissues is dealt with in Chapter 5

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  Biomedical Engineering

  Bridging Medicine and Technology

  • W. Mark Saltzman(Author)
  • 2015(Publication Date)
  • Cambridge University Press

    (Publisher)

  The remainder of this chapter uses the principles of mass balance to examine the physiology of respiration and digestion. 7.3 Respiratory physiology In many senses, respiration is the basis of human life. The concept of respiration involves two related concepts ( Figure 7.9 ). The fi rst, which is called internal respiration , is the metabolic process by which energy is derived from organic materials in the diet. The process of internal respiration occurs in cells within the body. As internal respiration occurs, cells consume oxygen and produce carbon dioxide as a by-product. Thus, internal respiration — or the normal operation of all the cells in the body — creates a need for the intake of large quantities of oxygen and the expulsion of large quantities of carbon dioxide from the body. The lung accomplishes this intake and expulsion of oxygen and carbon dioxide, in a process called external respiration . External and internal respiration are physically linked by the circulatory system, the chief function of which is the distribution of oxygen-rich blood from the lungs to all of the cells in the body and the collection of carbon dioxide – rich blood from cells for gas exchange in the lungs. The mechanics of external respiration are reviewed in this section; internal respiration is described brie fl y in Chapter 2 and is expanded further later in this chapter. External respiration is accomplished by an elegant engineering system, the human lung. The exchange of oxygen and carbon dioxide occur by the diffusion (recall Box 2.3 ) across a complex membrane that separates fl owing blood from the Engineering Balances: Respiration and Digestion 295 A B C Left Lung Right Lung Trachea Alveoli Deoxygenated blood entering lung Oxygenated blood leaving lung Capillary network Bronchiole bringing air to alveoli Figure 7.9 Internal and external respiration are linked by the circulatory system.

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  Human Physiology

  • Bryan H. Derrickson(Author)
  • 2019(Publication Date)
  • Wiley

    (Publisher)

  Chapter Review 684 CHAPTER 18 The Respiratory System 18.4 Exchange of Oxygen and Carbon Dioxide 1. The partial pressure of a gas is the pressure exerted by that gas in a mixture of gases. It is symbolized by P x , where the subscript is the chemical formula of the gas. 2. According to Dalton’s law, each gas in a mixture of gases exerts its own pressure as if all the other gases were not present. 3. Henry’s law states that the quantity of a gas that will dissolve in a liquid is proportional to the partial pressure of the gas and its solubility (given that the temperature remains constant). 4. In pulmonary and systemic gas exchange, O 2 and CO 2 diffuse from areas of higher partial pressures to areas of lower partial pressures. 5. Pulmonary gas exchange is the exchange of gases between alveoli and pulmonary blood capillaries. It depends on partial pressure differ- ences, a large surface area for gas exchange, a small diffusion distance across the respiratory membrane, and the rate of airflow into and out of the lungs. 6. Systemic gas exchange is the exchange of gases between systemic blood capillaries and tissue cells. 18.5 Transport of Oxygen and Carbon Dioxide 1. In each 100 mL of oxygenated blood, 1.5% of the O 2 is dissolved in blood plasma and 98.5% is bound to hemoglobin as oxyhemoglobin (Hb–O 2 ). 2. The binding of O 2 to hemoglobin is affected by P O 2 , acidity (pH), P CO 2 , temperature, and 2,3-bisphosphoglycerate (BPG). 3. Fetal hemoglobin differs from adult hemoglobin in structure and has a higher affinity for O 2 . 4. In each 100 mL of deoxygenated blood, 7% of CO 2 is dissolved in blood plasma, 23% combines with hemoglobin as carbaminohemo- globin (Hb–CO 2 ), and 70% is converted to bicarbonate ions (HCO 3 − ). 5. In an acidic environment, hemoglobin’s affinity for O 2 is lower, and O 2 dissociates more readily from it (Bohr effect). 6. In the presence of O 2 , less CO 2 binds to hemoglobin (Haldane effect).

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  Biology for AP® Courses

  • Julianne Zedalis, John Eggebrecht(Authors)
  • 2018(Publication Date)
  • Openstax

    (Publisher)

  The lungs recoil and airways close. The air passively exits the lung. There is high surface tension at the air-airway interface in the lung. Surfactant, a mixture of phospholipids and lipoproteins, acts like a detergent in the airways to reduce surface tension and allow for opening of the alveoli. Breathing and gas exchange are both altered by changes in the compliance and resistance of the lung. If the compliance of the lung decreases, as occurs in restrictive diseases like fibrosis, the airways stiffen and collapse upon exhalation. Air becomes trapped in the lungs, making breathing more difficult. If resistance increases, as happens with asthma or emphysema, the airways become obstructed, trapping air in the lungs and causing breathing to become difficult. Alterations in the ventilation of the airways or perfusion of the arteries can affect gas exchange. These changes in ventilation and perfusion, called V/Q mismatch, can arise from anatomical or physiological changes. 1340 Chapter 30 | The Respiratory System This OpenStax book is available for free at http://cnx.org/content/col12078/1.6 30.4 Transport of Gases in Human Bodily Fluids Hemoglobin is a protein found in red blood cells that is comprised of two alpha and two beta subunits that surround an iron-containing heme group. Oxygen readily binds this heme group. The ability of oxygen to bind increases as more oxygen molecules are bound to heme. Disease states and altered conditions in the body can affect the binding ability of oxygen, and increase or decrease its ability to dissociate from hemoglobin. Carbon dioxide can be transported through the blood via three methods. It is dissolved directly in the blood, bound to plasma proteins or hemoglobin, or converted into bicarbonate. The majority of carbon dioxide is transported as part of the bicarbonate system.

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  Medical Management of Pulmonary Diseases

  • Theodore Marcy(Author)
  • 1999(Publication Date)
  • CRC Press

    (Publisher)

  1 Anatomi; of the Respiratory System Theodore W. Marcy and Gerald S. Davis University of Vermont College of Medicine Fletcher Allen Health Care Burlington , Vermont OVERVIEW To understand respiratory system disorders, one first must have an appreciation of the normal respiratory system, its functions, and how its anatomy serves those functions. To those who specialize in pulmonary medicine, one of its attractions is how these principles illuminate what we observe daily in patients. This chapter is an introduction to the function and anatomy of the respiratory system. Space constraints dictate that this chapter be a very brief overview. However, concepts mentioned here are further expanded in the chap­ ters that immediately follow on respiratory muscles and control of ventilation, airflow, gas exchange, and host defense. They are then echoed in the chapters on diagnostic evaluation, specific disorders, and common therapies. Excellent chapters or monographs on anatomy and physiology are listed at the end of the chapter. FUNCTION OF THE RESPIRATORY SYSTEM Gas Exchange The principal function of the respiratory system is to accomplish exchange of oxygen (0 2) and carbon dioxide (C 0 2) between the atmosphere and the blood. The mitochodria that generate adenosine triphosphate by oxidative phosphorylation for metabolism consume a total of 250 mL/min of oxygen at rest in the normal adult. With exertion, oxygen consump­ tion can rise to as high as 4000 mL/min in trained athletes. Unlike the digestive system, which consumes large quantities of calories intermittently and converts the excess to stores for times of fasting, the respiratory system cannot store significant amounts of oxygen in tissues. Instead, the respiratory system must tirelessly replenish the venous blood with oxygen. At the same time, the lung must excrete from the blood into the atmosphere carbon dioxide (C 0 2) as a metabolic waste product.

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