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Gas Exchange

VIEWS: 3 PAGES: 39

									Gas Exchange

By Zoe Kopp-Weber
  Coevolution of circulatory
  and respiratory systems
 Allowed for vertebrates to develop
 larger bodies and locomotion.
   As these abilities grew, the need for
   efficient delivery of nutrients and O2
   and removal of wastes and CO2 from
   the growing mass of tissues grew too.
   Coevolution of circulatory
   and respiratory systems
            (cont.)
 Gills developed in fish and with it the 4-
  chamber heart, one of the major
  evolutionary innovations in vertebrates.
 Mammals, birds and crocodiles also
  have a 4-chamber heart, with 2
  separate atria and 2 separate
  ventricles.
   Right atrium receives deoxygenated blood
    and sends it to right ventricle which pumps
    blood to lungs. Left atrium receives
    oxygenated blood and delivers it to the left
    ventricle to pump the blood to the rest of
    the body.
         QuickTime™ an d a
TIFF (Uncompressed) decompressor
   are need ed to see this picture .
 For most multicellular animals, gas
 exchange requires special
 respiratory organs which provide
 intimate contact between gases in
 the external environment and the
 circulatory system.
 Respiration describes the uptake of O2
  from the environment and disposal of
  CO2 into the environment at a body
  system level.
 Cellular respiration = internal
  respiration
 Gas exchange = external respiration
   Communication between internal and
    external respiration is provided by the
    circulatory system.
 Respiration involves processes ranging
  from the mechanics of breathing to the
  exchange of O2 and CO2 in respiratory
  organs.
 Respiratory organs
   Invertebrates: epithelium, trachae and gills
   Fish and larval amphibians: gills
   Other amphibians: skin or epithelia used as
    supplemental/primary external respiratory
    organ.
   Mammals, birds, reptiles, adult amphibians:
    lungs
 Respiration involves the diffusion
 of gases across the plasma
 membrane
   Which must be surrounded by water
    to be stable.
   Thus the external environment is
    always aqueous, even in terrestrial
    animals.
 Rate of diffusion between 2 sides of the
  membrane has a relationship called
  Frick’s Law of Diffusion
 R=D x A delta p/d
   R= rate
   D= diffusion constant
   A= area diffusion occurs
   Delta p= difference in concentration btw
    interior of organism and external
    environment
   d= distance across diffusion occurs
 Evolution has optimized R via increased
  surface area, decreased distance and
  increased concentration difference.
 Levels of O2 required can’t be obtained
  by diffusion alone over distances
  greater than 0.5 mm.
 Vertebrates decreased this distance
  through the development of respiratory
  organs and bringing the external
  environment closer to the internal fluid
 Dry air is composed of 78.09% N,
  20.95% O2, 0.93% Ar and other inert
  gases, and 0.03% CO2.
 This composition remains constant at
  altitudes of at least 100 km but the
  amount of air decreases as the altitude
  goes up.
 Humans don’t survive long over 6000
  meters, though the same composition
  of O2 is there, the atmospheric
  pressure brings it to only half the
  amount of 02 than what’s at sea level.
 Though gills are effective in aquatic
 environments, there are two reasons
 terrestrial animals replaced gills with
 other respiratory organs.
   1. Air is less buoyant than water. Gills
    collapse out of water while internal air
    passages remain open because the body
    provides structural support.
   2. Water diffuses into air via evaporation.
    Terrestrial animals are constantly
    surrounded by air and therefore lose H2O.
    Gills would provide a large surface area for
    H2O loss.
    Terrestrial respiratory
           organs
 Trachae – used by insects and is a
  network of air-filled tubular passages.
 Lung – moves air through branched
  tubular passages. Air is saturated with
  H2O before reaching a thin, wet
  membrane that allows gas exchange.
   All but birds use a uniform pool of air
      Moves in and out of the same airway passages
 Mammals have higher metabolic rates
  so they require a more efficient
  respiratory system.
 Lungs are packed with tiny, grape-like
  sacs called alveoli. Air is inhaled
  through mouth/nose, past the pharynx
  to the larynx where it then passes
  through the glottis and into the trachea.
 The trachea splits into right and
  left bronchi which enter into each
  lung and subdivide into bronchioles
  that deliver air into the alveoli.
 All gas exchange btw air and blood
  occurs across walls of alveoli.
          QuickTime™ and a
TIFF (Un compressed) decompressor
   are neede d to see this picture.
 Visceral pleural membrane – a thin membrane
  that covers the outside of each lung.
 Parietal pleural membrane – lines the inner
  wall of the thoracic cavity.
 Pleural cavity – the space between these two
  membranes, very small and filled with fluid.
   Fluid allows membranes to adhere to each other,
    coupling the lungs to the thoracic cavity.
 Pleural membranes package each lung
  separately so if one should collapse, the other
  can function.
   Mechanics of breathing
 In all terrestrial vertebrates but
  amphibians, air is drawn into the lungs
  by subatmospheric pressure.
   Boyle’s Law – when the volume of a given
    quantity of gas increases, its pressure
    decreases.
 When inhaling, volume of thorax is
  increased and the lungs expand.
  Lowered pressure in lungs allows air to
  enter.
 Diaphragm – a muscle that increases
 thoracic volume by contracting.
   When it contracts, it assumes a flattened
    shape and lowers, expanding the volume of
    the thorax and lungs while adding pressure
    onto the abdomen.
 External intercostal muscles – also
 contributes in increasing thoracic
 volume.
   These muscles between the ribs contract,
    causing the ribcage to expand.
         QuickTime™ an d a
TIFF (Uncompressed) decompressor
   are need ed to see this p icture .
 The thorax and lungs have a
 degree of elasticity.
   They resists distension and recoil
   when distending force subsides.
 Breathing measurements
 At rest, each breath moves a tidal
 volume of 500 mL of air in and out of
 the lungs.
   150 mL in trachea, bronchi and bronchioles
    where no gas exchange occurs.
      Anatomical dead space, air here mixes with fresh
      air during inhalation.
 Maximum amount of air expired after a
 maximum inhalation is called the vital
 capacity.
   Averages 4.6 liters in young men and 3.1
    liters in young women.
 Hypoventilating - when breathing is
  insufficient to maintain normal blood
  gas measurements.
 Hyperventilating – when breathing is
  excessive for a particular metabolic
  rate.
   Increased breathing after exercise isn’t
    necessarily hyperventilating because faster
    breathing is matched to faster metabolic
    rate and blood gas measurements remain
    normal.
   Mechanism regulating
        breathing
 Each breath initiated by a
 respiratory controntrol center in
 the medulla oblongata.
   Neurons send impulses that stimulate
    muscles to contract and expand the
    chest cavity.
   Though controlled automatically,
    these controls can be overridden by,
    for example, holding one’s breath.
 A fall in blood pH stimulates neurons in
 aortic and carotid bodies
   These are sensory structures known as
    peripheral chemoreceptors in the aorta and
    carotid artery.
   Send impulses to the respiratory control
    center in the medulla oblongata, which
    stimulates increased breathing.
   responsible for immediate stimulation when
    the blood partial CO2 pressure rises.
 Central chemoreceptors –
 responsible for sustained increase
 in ventilation if partial CO2
 pressure remains elevated.
 Increased respiratory rate acts to
 eliminate extra CO2, bringing
 blood pH to normal.
     Hemoglobin and gas
         transport
 When O2 diffuses from alveoli into
 blood, the circulatory system then
 delivers the O2 to tissues for respiration
 and carries away the CO2.
   Amount of O2 dissolved in blood plasma
    depends directly on the partial O2 pressure
    or the air in the alveoli.
 When lungs function normally, the
 blood plasma leaving the lungs have
 almost as much DO as possible.
   Whole body carries almost 200 mL/L of O2,
    most is bound to molecules of hemoglobin
 Hemoglobin - protein composed of
 four polypeptide chains and four
 organic compounds (heme
 groups).
   Each heme group has an iron atom at
    the center, able to bind to a molecule
    of O2.
   Allows hemoglobin to carry four
    molecules of O2.
 Hemoglobin loaded with O2 forms
 oxyhemoglobin.
   Bright red, tomato juice color
 As blood passes capillaries, some
 oxyhemoglobin releases oxygen,
 becoming deoxyhemoglobin
   Dark red but gives tissues a bluish tinge.
 Red color,
  oxygenated
                             QuickTime™ and a

 Blue color,      TIFF (Un compressed) decompressor
                      are neede d to se e this picture.



 oxygen-depleted
 Hemoglobin is used by all
  vertebrates, and also by many
  invertebrates
 Other invertebrates use
  hemocyanin as an oxygen-carrier
   O2 binds to copper rather than iron.
   Not found in blood cells but rather
   dissolved in circulating fluid of
   invertebrates
       Oxygen transport
 As blood travels through the systemic
 blood capillaries, O2 leaves the blood
 and diffuses into tissues.
   1/5 of O2 is unloaded in tissues, 4/5 in
    blood as a reserve.
 The reserve allows the blood to supply
 the body O2 during exercise.
   Also ensures enough O2 to maintain life 4-5
    minutes if breathing is interrupted or the
    heart stops.
 O2 transport affected by
   CO2: produced by metabolizing tissues, it
    combines with H2O forming carbonic acid.
    This dissociates into bicarbonate and H+,
    lowering blood pH.
      Also reduces hemoglobins affinity for O2 and
       causes it to release O2 more readily.
      This is all called the Bohr effect.
   Increase in temperature has a similar
    effect.
      Skeletal muscles produce CO2 quicker during
       exercise, producing heat.
 Carbon Dioxide Transport
 Systemic capillaries deliver O2 and
 remove CO2 from tissues
   Majority diffuses into red blood cells where
    it’s catalyzed with water to form carbonic
    acid (H2CO3)
   Disassociates into bicarbonate and H+ and
    moves into the plasma, exchanging a
    chloride ion for a bicarbonate (chloride
    shift).
      Removes large amounts of CO2 from plasma,
      facilitating diffusion of additional CO2 into plasma
      from surrounding tissues.
 Blood carries CO2 to the lungs in
 this form.
   CO2 diffuses out of red blood cells,
   into the alveoli and then leaves the
   body with exhalation.
   Nitric Oxide Transport
 Nitric oxide acts on many cells to
 change their shape/functions.
   Causes blood vessels to expand by
    relaxing surrounding muscle cells.
   Blood flow/pressure regulated by
    nitric oxide in bloodstream.
 One hypothesis proposes hemoglobin
 carries super nitric oxide which is able
 to bind to cysteine in hemoglobin
   Dumps CO2 and picks up O2 and NO in the
    lungs
 To increase blood flow, hemoglobin can
  release super NO into blood, making
  blood vessels expand
 Can also trap excess NO on vacant iron
  atoms, making blood vessels constrict.
 Red blood cells return to lungs,
  hemoglobin dumps CO2 and regular
               Disease
 Emphysema - usually caused by
  cigarette smoking, the vital capacity of
  the lungs is reduced and alveoli are
  destroyed.
 Bronchitis - a respiratory infection
  affecting nose, sinus and throat, then
  moves on into the lungs. Cough
  produces an excess of mucus.
 Pneumonia - inflammation of the lungs
  that can be caused by bacteria, viruses
  or fungi. Causes coughing, fever and it
  will likely make it harder to breathe.
         QuickTime™ an d a
TIFF (Uncompressed) decompressor
  are need ed to see this p icture .

								
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