Respiration Biology 1107 Lecture 19 Lecture 19 Overview 2 44 cid 25 Overview gas exchange 3 5 cid 25 Respiratory vs circulatory systems 6 cid 25 Breathing air vs water 7 13 cid 25 Understanding partial pressure 8 12 cid 25 Breathing water 13 cid 25 Respiratory surfaces 14 22 cid 25 Skin gas exchange 15 cid 25 Gill gas exchange 16 19 cid 25 Insect tracheal system 20 21 cid 25 Lungs 22 cid 25 Mammalian lung structures 23 25 cid 25 Lung ventilation 26 33 cid 25 Positive pressure breathing 26 cid 25 Negative pressure breathing 27 30 cid 25 Homeostatic control of ventilation 31 33 cid 25 Transportation of O2 and CO2 in blood 34 cid 25 Red blood cells 35 cid 25 Hemoglobin and O2 cooperative binding mechanisms 36 39 cid 25 CO2 transport and blood pH buffering 40 41 Introduction 3 44 In aerobes oxygen required for and carbon dioxide produced by cellular respiration must be continuously exchanged with the environment Cells must obtain oxygen and expel carbon dioxide continuously to support ATP production by mitochondria In addition these gases along with wastes nutrients and other types of molecules must be transported throughout the body 4 44 The Respiratory and Circulatory Systems Gas exchange also known as respiration not to be confused with cellular respiration is the uptake of molecular O2 from the environment and the discharge of CO2 to the environment Gas exchange involves four steps ventilation gas exchange circulation and cellular respiration 5 44 1 2 3 4 The Four Steps of Gas Exchange Ventilation occurs when air or water moves through a specialized gas exchange organ such as lungs or gills Gas exchange takes place as CO2 and O2 diffuse between air or water and the circulatory fluid at the respiratory surface Through circulation the dissolved O2 and CO2 are transported throughout the body Gas exchange between circulatory fluid and cells occurs in tissues where cellular respiration has led to low O2 levels and high CO2 levels O2 and CO2 diffuse between circulatory fluid and cells 6 44 The Respiratory and Circulatory Systems The respiratory system is responsible for ventilation and gas exchange that brings O2 into the body and removes CO2 The respiratory system is comprised of the structures responsible for gas exchange between the individual and its environment In some animals the gas exchange surface is the skin but in most species it is located in a specialized organ like the lungs of tetrapods the tracheae of insects or the gills found in mollusks arthropods and fish The circulatory system is responsible for moving O2 CO2 and other materials around the body In most species a specialized liquid transport tissue is propelled throughout the body by a muscular heart via a system of vessels Air and Water as Respiratory Media Gas exchange between the environment water or air and cells is based on diffusion 7 44 Oxygen is high in the environment and low in tissues while carbon dioxide is high in tissues and low in the environment Oxygen thus tends to move from the environment into tissues and carbon dioxide tends to move from tissues to the environment How Do O2 and CO2 Behave in Air 8 44 To understand how gases move by diffusion it is important to express their presence in terms of partial pressures instead of percentages Partial pressure is the pressure of a particular gas in a mixture of gases To calculate the partial pressure of a particular gas multiply the fractional composition of that gas by the total pressure exerted by the entire mixture Atmospheric pressure at sea level is 760 mm Hg and O2 makes up 21 of the atmospheric gases Thus PO2 0 21 760 160 mm Hg How Do O2 and CO2 Behave 9 44 Oxygen and carbon dioxide diffuse between the environment and cells along their respective partial pressure gradients In both air and water oxygen and carbon dioxide move from regions of high partial pressure to regions of low partial pressure 10 44 Coordination of Circulation and Gas Exchange The partial pressures of O2 and CO2 in the blood vary at different points in the circulatory system Blood flowing into the lung alveolar capillaries 2 from the body has a lower Po2 and higher Pco2 than the air in the lungs thus O2 diffuses into the blood and CO2 diffuses out of the blood 11 44 Coordination of Circulation and Gas Exchange The partial pressures of O2 and CO2 in the blood vary at different points in the circulatory system Blood flowing into the body tissue systemic capillaries 5 has a higher Po2 and lower Pco2 than the surrounding interstitial fluid thus O2 diffuses into the cells and CO2 diffuses into the blood 12 44 Coordination of Circulation and Gas Exchange Oxygen and carbon dioxide move from regions of high partial pressure to regions of low partial pressure 13 44 How Do O2 and CO2 Behave in Water In both air and water oxygen and carbon dioxide move from regions of high partial pressure to regions of low partial pressure To obtain oxygen water breathers face a much more challenging environment than air breathers do Water contains much less oxygen than air does thus to extract a given amount of oxygen an aquatic animal has to process 30 40 times more water than the amount of air a terrestrial animal breathes Water is about a thousand times denser than air and flows less easily so water breathers e g fish and lobsters have to expend more energy to ventilate their respiratory surfaces than do air breathers Aquatic organisms have evolved adaptations that enable efficient gas exchange many of which involve the organization of respiratory surfaces to allow sufficient ventilation 14 44 Characteristics of Respiratory Surfaces Like all living cells the cells that carry out gas exchange have a plasma membrane that must be in contact with an aqueous solution thus respiratory surfaces must always be moist The movement of O2 and CO2 across moist respiratory surfaces takes place entirely by diffusion the rate of diffusion is proportional to the surface area across which it occurs and inversely proportional to the square of the distance through which molecules must move In other words gas exchange is fast when the area for diffusion is large and the path for diffusion is short Many respiratory surfaces reflect adaptations that increase the rate of gas exchange e g long thin filaments folded and branching structures 15 44 Gas Exchange in Animals Relatively simple animals such as sponges cnidarians and flatworms have every cell in close contact with the external environment allowing for efficient gas