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Midterm

BIO271H1 Study Guide - Midterm Guide: Gas Exchange, Partial Pressure, Blood Pressure


Department
Biology
Course Code
BIO271H1
Professor
Christopher Garside
Study Guide
Midterm

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Lecture'7:'Respiratory'Systems'
" ALL!respiratory!organs!HAVE!to!be!thin!and!moist!
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Two!Major!Animal!Lineages!have!Colonized!Terrestrial!Habitats!
1) Arthropods:!Crustaceans,!Chelicerates,!Insects!
2) Vertebrates:!Fish,!Amphibians,!Reptiles,!Birds,!Mammals!
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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!"!parabronchi!"!anterior!
air!sacs!"!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!
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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!

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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!posterior!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!exhalation!for!ventilation,!but!for!a!single'breath'it!is!!
" air!does!mix!a!little!bit!"!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!partial!pressure!of!O2!in!the!exhaled!
medium!
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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!
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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!themselves!
! parietal!membrane:!directly!attached!to!the!thoracic!wall!
itself!
! in!between!visceral!and!parietal!membranes:!pleural!
cavity!(a!small!amount!of!liquid!here:!pleural)!

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as!the!chest!expands,!the!lungs!follow,!there!needs!to!be!a!connection!"!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!"!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!"!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!"!keeps!lung!opened)!
o intrapleural!pressure!is!subatmospheric!
! keeps!lung!expanded!
! any!change!in!thoracic!cavity!will!be!transferred!to!change!in!the!lungs!"!changes!of!pressure!in!
the!lungs!(Boyle’s!Law)!"!how!air!gets!into!the!lungs!
! also!reduces!friction!between!the!visceral!!
! without!the!fluid!between!the!2!membranes,!pressure!differences!cannot!be!transferred!
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!
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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!"!Boyle’s!law!"!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!PT!increases!
Because!intrapleural!has!been!decreased!
! Lungs!expand!
Because!of!a!greater!transpulmonary!pressure!
! Air!is!pulled!in!(because!of!the!pressure!gradient)!
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Mammalian!Tidal!Ventilation!–!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!"!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!
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