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Lecture 7

BIO271 2014 Lecture 7.pdf

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Christopher Garside

  Lecture  7:  Respiratory  Systems   -­‐ ALL  respiratory  organs  HAVE  to  be  thin  and  moist     Two  Major  Animal  Lineages  have  Colonized  Terrestrial  Habitats   1) Arthropods:  Crustaceans,  Chelicerates,  Insects   2) Vertebrates:  Fish,  Amphibians,  Reptiles,  Birds,  Mammals     Birds   -­‐ parabronchial  lungs  are  stiff  and  change  little  in  volume   o lungs  themselves  do  not  change  in  volume   o lungs  are  parabronchi   -­‐ lungs  between  a  series  of  flexible  air  sacs  that  act  as  bellows   o increase  in  suction  to  decrease  pressure   § sacs  change  volume  in  birds,  not  in  the  lungs   o posterior  and  anterior  air  sacs   o no  alveoli   § almost  unidirectional  flow   § birds  have  high  metabolic  rates  (have  higher  body   temperature  compared  to  ours)  =  increases  requirement   for  energy   § making  this  an  energetically  efficient  system   -­‐ gas  exchange  occurs  as  air  flows  through  parabronchi  in  lungs   o air  flow  through  parabronchi  is  unidirectional   § air  goes  into  posterior  air  sacs   à  parabronchi  à  anterior   air  sacs  à  air  moves  out   § air  diffuses  into  air  capillaries  =  where  actual  diffusion  of   gases  occur  =  across  air  capillaries   § air  capillaries  are  surrounded  with  blood  in  capillaries   § massive  increase  in  surface  area,  very  thin  wall   o bird  lungs  do  not  change  in  volume  (parabronchi)   -­‐ blood  flow  is  cross  current  –  determined  by  a  change  of  direction  of  air  flow   =  air  will  be  crossing  over  the  capillaries  from  a  different  direction   o cross  current:  partial  pressure  of  oxygen  in  the  blood  exiting  the  respiratory  surface  can  be  higher  than  the   partial  pressure  of  oxygen  in  the  medium  exciting  the  respiratory  surface   § opposite:  concurrent   o birds  are  cross  current   -­‐ gas  exchange  occurs  in  air  capillaries   o passive  gas  exchange   o very  thin  walls     Bird  Ventilation   -­‐ bird  lungs  are  stiff  and  do  not   change  in  volume,  air  sacs  do   1) expansion  of  the  chest  (using   muscles  in  the  chest)  =   increases   the  sacs  =  decreased  pressure   -­‐ allows  fresh  air  to  flow   through  the  bronchi  to  the   posterior  air  sacs   -­‐ fresh  air  does  NOT  flow   directly  through  the  lungs,   flows  into  the  posterior  air   sacs   2) compression  of  the  chest  (mostly   elastic  recoil,  some  muscular  action)  pushes  fresh  air  from  the  posterior  air  sacs,  into  the  parabronchi   -­‐ fresh  air  diffuses  into  the  air  capillaries   -­‐ where  diffusion  of  gases  occur   3) expansion  of  the  chest  pulls  air  from  the  parabronchi  into  the  anterior  air  sacs       4) compression  of  the  chest  takes  the  air  from  the  anterior  air  sacs,  and  releases  it  to  the  environment   -­‐ requires  2  cycles  of  inhalation  and  exhalation   o steps  1  and  3  occurs  at  the  same  time;  steps  2  and  4  occurs  at  the  same  time   o when  you  have  inhalation  (fresh  air  to  the  posterio r  air  sacs)  the  air  (which  has  been  used  in  the   parabronchi)  go  into  anterior  air  sacs   o exhalation:  air  moves  from  the  posterior  air  sacs  into  the  parabronchi  AND  the  old  air  in  the  anterior  air   sacs  move  out   o not  exactly  2  cycles  of  inhalation  and  exhalatio n  for  ventilation,  but  for  a  single  breath  it  is     -­‐ air  does  mix  a  little  bit  à  fresh  air  as  its  moving  to  the  posterior  air  sacs  does  mix  a  little  with  the  parabronchi   -­‐ air  flow  is  unidirectional  =  allows  cross  current  and/or  counter  current  flow   -­‐ air  moving  into  the  parabronchi  do  not  change  in  volume  (stiff)   -­‐ air  capillaries  are  covered  in  blood  vessels  =  very  efficient  exchange   -­‐ PO2  if  blood  leaving  is  higher  than  PO2  of  exhaled  air   • cross  current:  partial  pressure  of  O2  leaving  the  blood  is  higher  than  the  pa rtial  pressure  of  O2  in  the  exhaled   medium     Mammals   -­‐ two  main  parts  to  respiratory  system:   1) conduction  zone:  mouth,  nasal  cavity,  pharynx,  larynx,  trachea,  bronchi,  bronchioles   -­‐ allows  fresh  air  to  get  into  the  lungs  –  NOT  involved  in  gas  exchange   -­‐ tends  to  be  large  in  diameter  =  low  resistance  =  don’t  have  to  develop   a  big  pressure  difference  to  move   air     2) respiratory  zone:  respiratory   bronchioles,  alveolar  ducts,  alveoli   -­‐ gas  exchange  zone   -­‐ 90%  of  gas  exchange  occurs   across  the  alveoli   -­‐ respiratory  sacs  on  respiratory   bronchioles  and  alveolar  ducts   –   some  gas  exchange     -­‐ alveoli  are  the  primary  site  of  gas  exchange   o type  I  alveolar  cells:  thin  walled   § primary  alveolar  cells   § where  gas  exchange   occurs   o type  II  alveolar  cells:  relatively   thick  walled   § not  efficient  in  allowing   diffusion   § not  involved  in  diffusion   § monitors  fluid  balance  across  the  walls  of  the  alveoli   § surfactant  secretion   o outer  surface  of  alveoli  are  covered  in  capillaries   § 80-­‐90%  of  surface   § very  thin  wall  capillaries,  very  thin  wall  alveoli,  very   closely  together  =  reducing  diffusion  distance  =  efficient   system     Pleural  Sac  –  Lung  Environment*   -­‐ thoracic  cavity  houses  the  lungs   -­‐ each  lung  is  surrounded  by  a  pleural  sac   o two  membranes  with  small  space  between  them   § visceral  membrane:  directly  surrounds  lungs  thems elves   § parietal  membrane:  directly  attached  to  the  thoracic  wall   itself   § in  between  visceral  and  parietal  membranes:  pleural   cavity  (a  small  amount  of  liquid  here:  pleural)       • as  the  chest  expands,  the  lungs  follow,  there  needs  to  be  a  connection   à  no  fluid  in  the   pleural  sac?  Lungs  would  collapse   o pleural  cavity  contains  a  small  volume  of  pleural  fluid   § has  cohesive  forces   § resist  in  external  force   • lung  has  elastic  recoil  à  pulls  on  visceral  membrane  of  the  pleural  sac  when  chest  expands   o chest  wants  to  go  out,  lung  wants  to  go  in  =  negative  intrapleural  pressure     o transpulmonary  gradient   § transpulmonary  pressure  =  atmospheric  pressure  (alveolar  pressure)   –  intrapleural  pressure   § will  always  be  positive   à  keeps  the  lungs  open  =  alveoli’s  and  bronchioles  do  no  collapse   o if  you  puncture  lungs  =  allows  intrapleural  pressure  to  equalize  to  atmospheric  pressure  =  lung   collapses  (do  not  have  positive  transpulmonary  gradient  anymore   à  keeps  lung  opened)   o intrapleural  pressure  is  subatmospheric   § keeps  lung  expanded   § any  change  in  thoracic  cavity  will  be  transferred  to  change  in  the  lungs   à  changes  of  pressure  in   the  lungs  (Boyle’s  Law)  à  how  air  gets  into  the  lungs   § also  reduces  friction  between  the  visceral     § without  the  fluid  between  the  2  membranes,  pressure  differences  cannot  be  t ransferred   o as  chest  expands,  lung  follows   –  need  to  be  a  connection  between  the  lungs   § lungs  would  collapse  without  the  fluids   § water  is  very  cohesive   –  resistant  in  external  force     Mammalian  Tidal  Ventilation   –  Inspiration   -­‐ Inhalation   o Somatic  motor  neuron  firing  stimulates  inspiratory  muscles   § 2  primary  sets  of  inspiratory  muscles:  diaphragm   (separates  thoracic  and  abdominal  cavity)  and  external   intercostals  (between  ribs)   1) Contraction  of  the  external  intercostals  and  the  diaphragm   2) Ribs  move  outwards  (and  up)  and  the  diaphragm  moves  down   § Volume  of  the  thorax  increases   § Intrathoracic  pressure  decreases  à  Boyle’s  law  à  volume   increases,  pressure  must  decrease   • Intrathoracic  pressure  =  intrapleural  pressure   • Intrapleural  pressure  decreases  (at  rest  its   already  subatmospheric,  but  now  its  even  lower)   § Transpulmonary  pressure  gradient  P increasT    • Because  intrapleural  has  been  decreased   § Lungs  expand   • Because  of  a  greater  transpulmonary  pressure   § Air  is  pulled  in  (because  of  the  pressure  gradient)     Mammalian  Tidal  Ventilati on  –  Expiration     -­‐ Exhalation  (usually  passive  –  no  muscles  involved,  but  elastic  recoil  of  the  chest  wall)   o Don’t  need  muscles  to  expire,  just  elastic  recoil   o Nerve  stimulation  of  inspiratory  muscles  stops   o Somatic  motor  neurons  stops  firing   à  Muscle  relax,  ribs  and  diaphragm  return  to  original  positions   o Volume  of  the  thorax  decreases,  Intrathoracic  pressure  increases  (intrapleural  pressure  increases)   o Passive  recoil  of  the  lungs  pushes  air  out   -­‐ during  rapid  and  heavy  breathing,  exhalation  is   active  via  contraction  of  the  internal  intercostal  muscles   (abdominal  muscles  also  involved)   o need  rapid  air  exchange  during  exercise   o motor  neurons  stimulated  during  exercise   o energy  required  will  depend  on  elastic  properties  and  resistance  (for  both  inhalation  and  exhalation   during  exercise)   § compliance  –  how  easy  to  stretch   • how  much  pressure  to  cause  the  expansion   • the  more  compliant,  less  pressure  gradient  needed,  the  more  easy  to  stretch       o because  of  surface  tension   § elastance  –  how  readily  returns  to  original  shape;  if  low,  acti on   • elastic  recoil   • in  healthy  people,  there  is  high  elastance,  and  a  bit  low  compliance   • emphysema:  elastin  destroyed  =  must  use  muscles  for  normal  exhalation     Mammalian  Ventilation   -­‐ intra-­‐alveolar  pressure:  only  changes  1mmHg   Inhalation   -­‐ 1mmHg  is  all  that’s  required  to  pull  our  tidal  volume   (~500mL  of  air)  into  our  lungs   -­‐ inspiration:  alveolar  pressure  drops  =  air  moves  in   down  its  pressure  gradient   -­‐ reduction  in  intrapleural  pressure   -­‐ greater  transpulmonary  gradient   -­‐ increase  water  diameter  of  the  conducting  zone  is   important  à  don’t  have  much  of  a  pressure   difference  between  outside  and  inside  to  pull  all  that   air  in   Exhalation   -­‐ only  need  1mmHg  to  push  the  air  back  out   § intrapleural  pressure  as  we  expire:  diaphragm   moves  down,  increasing  thoracic  cavity  volume,   increasing  transpulmonary  gradient,  intrapleural   pressure  decreases  (pulling  on  the  wall  =  decreasing   pressure)  à  returns  back  to  normal     Work  Required  for  Ventilation  Depends  On   1) Lung  Compliance  (ΔV/  ΔP)   • How  easily  the  lungs  stretch  during  inhalation   • Surface  tension  in  alveolar  fluid  lowers  compliance   o Can  exert  a  force  on  water   à  water  resists  to  this  force   o Surface  tension  important  in  lungs;  within  the  alveoli,  there  are  fluid,  if  it  was  only  water,  the   alveoli  would  collapse  (water  wants  to  stay  so  it  pulls  itself  together,  collapsing  the  alveoli)   2) Surfactants   • Type  II  cells  in  the  alveoli  secretes  surfactants   • Phospholipoproteins,  amphipathic  =  can  associate  with  water   • Reduces  surface  tension  by  disrupting  the  cohesive  forces  between  water  molecules  à  break  up  cohesive   forces  of  the  water  (cohesive  forces  will  collapse  the  alveoli   ß  surfactant  inhibits  this)   • Without  surfactant,  alveoli’s  will  collapse   • ↑  lung  compliance   • in  humans,  surfactant  synthesis  does  not  begin  until  late  gestation   o premature  baby:  will  not   produce  surfactant  yet  à  need  artificial  ventilation,  or  spray  surfactant   into  the  lungs     Airway  Resistance   -­‐ airway  diameter  affects  resistance  to  air  flow  (recall  Poiseuille’s  equation)   o as  diameter  decreases,  resistance  increases   o higher  resistance  requires  a  large  PT   o parasympathetic  nerve  stimulation  causes  bronchoconstriction   § parasympathetic  system  innervates  the  bronchiolar  muscles  for  bronchoconstriction   § at  rest  we  don’t  need  that  much  air  =  so  we  reduce  the  diameter  of  the  vessels   o sympathetic  nerve  stimulation  causes  bronchodilation  (fight  or  flight  response)   § epinephrine  innervates  the  bronchioles     -­‐ asthma:  asthmatic  allergic  reactions  can  cause  a  reduction  in  the  diameter  of  the  tubes  (bronchioles   à  alveoli)=   increase  in  pressure  gradient   o inhalers:  increases  diameters  of  bronchioles  to  reduce  resistance         Dead  Space   -­‐ tidal  volume  (V T   o volume  of  air  moved  in  one  ventilatory  cycle     o amount  of  air  breathed  in  OR  out  in  1  breathe     o includes  dead  space  (conducting  zone  à  air  that  does  not  participate  in  gas  exchan ge)   o next  inhalation,  first  air  that  goes  in  is  actually  stale  air   o tidal  breathers  can  never  have  respiratory  surface  beside  fresh  air   -­‐ dead  space  (V D   o air  that  does  not  participate  in  gas  exchange   o two  components   § anatomical  dead  space   • volume  of  conducting  zone   § alveolar  dead  space   • fresh  air  in  alveoli  must  be  perfused  with  blood  (capillaries  surround  alveoli),  or  else  it   will  be  dead  space  as  well  à  physiological  dead  space/alveoli  dead  space   • volume  of  alveoli  that  are  not  perfused   • important  for  some  animals  à  esp.  giraffe  –  has  a  very  long  trachea,  how  does  it  get   around  the  dead  space  volume  problem?   -­‐ alveolar  ventilation  volume  (V )  A o volume  of  fresh  air  that  enters  alveoli  with  each  respiratory  cycle   o V =  V  -­‐  V   A   T D -­‐ alveolar  minute  ventilation   o volume  of  fresh  air  that  enters  alveoli  each  minute   o V =  A  (V  T­‐  D )   § f  =  breathing  rate  in  breaths  per  minute   o alveolar  minute  ventilation  is  different  from  the  lung  ventilation     o lung  ventilation  includes  dead  space,  alveolar  minute  ventilation  is  to  get  the  maximal  amount  of  fresh  air   into  lungs   § tidal  volume  of  frequency  of  ventilation  can  be  varied   § take  bigger  breaths?  Or  more  breaths?   § Increase  tidal  volume  is  the  best  way  to  get  the  maximal  amount  of  fresh  air  into  the  lungs   § Every  breath  you  take  you  must  take  into  account   the  dead  space  volume  (never  leaves)   -­‐ conducting  zone  =  air  that  does  not  participate  in  gas  exchange     Lung  Volumes  and  Capacities  *   -­‐ V (tidal  volume)  =  500ml  inspiration  OR   T     expiration   -­‐ IRV  (inspiratory  reserve  volume):     maximum  amount  of  air  that  can  be  i nhaled   above  tidal  volume  (>500ml)   • V T      =  inspiratory  capacity  (IC)   -­‐ ERV  (expiratory  reserve  volume):   maximum  amount  of  air  that  can  be  exhaled   above  the  tidal  volume  (>500ml)   • IC  +  ERV  =  Vital    capacity  (VC)  à  maximum   amount  of  air  you  can  inhale/exhal e  in  a   single  breath   -­‐ RV  (residual  volume)  =  this  volume  results   from  the  stretch  against  the  chest  walls  by   the  pleural  sac  à  can  never  get  out  à   ~1200ml  à  because  of  intrapleural   pressure  à  lungs  can  never  fully  collapse   due  to  this  low,  transpulmonary  pr essure   -­‐ TLC  (total  lung  capacity)  =  VC  +  RV     Ventilation  Perfusion  Matching   -­‐ efficient  gas  exchange  at  respiratory  surface  requires  matching  of   ventilation  and  blood  flow       -­‐ arterioles  dilate  or  constrict  to  distribute  blood  to  well -­‐ventilated  alveoli   o for  ex.  Low  PO2  in  alveolus  causes  constriction  of  arteriole   -­‐ during  vasoconstriction,  capillaries  increases  in  pressure  =  pushes  more  fluid  across   à  can  lead  to  pulmonary   edema  –  more  fluid  covering  respiratory  surface  =  increases  diffusion  distance  =  difficult  to  get  fresh  oxygen  into   system     Gas  Transport   -­‐ sponges,  cnidarians,  and  insects  rely  on  simple  diffusion   -­‐ larger  animals  use  circulatory  systems   o transport  of  gases  in  blood     § must  create  pressure  difference  to  move  fluid  around  the  body     Oxygen  Transport  in  Bl ood   -­‐ solubility  of  oxygen  in  aqueous  fluids  is  low   -­‐ cannot  carry  that  much  oxygen  in  blood   à  have  to  utilize  respiratory  pigments   -­‐ metalloproteins  (respiratory  pigments)   o have  a  colour  when  they  bind  or  release  oxygen   o associated  with  some  type  of  metal  ion   o proteins  containing  metal  ions  which  reversibly  bind  to  oxygen   o any  respiratory  pigment  must  be  able  to  reversibly  bind  oxygen  (pick  it  up  in  one  place,  then  release  it   where  its  required)   o increase  oxygen  carrying  capacity  of  blood  by  50-­‐fold  (98%  of  O2  carried  in  blood  is  bound  to   hemoglobin)   o gives  us  our  active  lifestyle   o does  not  contribute  to  ΔP  (partial  pressure  gradient)   § as  soon  as  O2  bind  hemoglobin,  it  no  longer  contributes  to  the  partial  pressure  gradient  in  the   blood     § maintains  high  partial  pressure  gradient  from  alveoli  into  the  blood   -­‐ 3  major  types  of  respiratory  pigments   o hemoglobins   o hemocyanins   o hemerythrins     Oxygen  Transport  –  Hemoglobins   -­‐ found  in  many  animals  -­‐  vertebrates,  nematodes,  some  annelids,  crustaceans,  and   insects   -­‐ made  of  a  metallic  porphyrin  ring  (heme  group)   -­‐ globin  protein  bound  to  a  heme  molecule  containing  iron   o we  have  2  alpha-­‐globins,  and  2  beta-­‐globins   o non-­‐covalently  bond  to  heme   o oxygen  is  NOT  covalently  bond  either   à  that’s  why  its  reversible   -­‐ heme  group  binds  the  oxygen   -­‐ usually  within  blood  cells   -­‐ appear  red  when  oxygenated   -­‐ myoglobin  is  a  type  of  hemoglobin  found  in  muscles     o hemoglobin:  at  least  one  heme  +  one  globin  à  myoglobin  has  one  heme   and  one  globin     Hemocyanins  and  Hemerythrins   -­‐ hemocyanins   § arthropods  and  molluscs   § contain  copper   • copper  directly  bound  to  protein   • different  from  hemoglobin   • not  contained,  but  dissolved   § usually  dissolved  in  the  hemolymph   § appears  blue  when  oxygenated   -­‐ hemerythrins       § sipunculids,  priapulids,  brachiopods,  some  annelids   § contains  iron
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