Respiratory Physiology Part III

1
Respiratory Physiology Part III

• Special Considerations Species Differences e.g.
  tracheal systems, air sacs, gills
• Extreme Conditions

2
Special Considerations Species Differences
Birds

• gas transfer takes place in small air capillaries
  that branch from tubes called parabronchi
  (functional equivalent to mammalian alveroli)
  they extend between larger dorsobronchi
  ventrobronchi both of which are connected to an
  even larger tube, the mesobronchus which joins
  the trachea anteriorly parabronchi their
  connecting tubes form the lung (contained within
  the thoracic cavity) since movement of the ribs
  forward is slight, volume of thoracic cage and
  lung change little during breathing the unique
  lung ventilation is related to the air-sac system
  connected to the lungs fig 13-31p.553

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Special Considerations Species Differences
Birds cont

• as air sacs are squeezed, air is forced through
  parabronchi system of air sacs, penetrates into
  adjacent bones between organs, reducing density
  of bird only thoracic abdominal sac show
  marked changes in volume during breathing
  volume changes in air sacs are achieved by a
  rocking motion of sternum against the vertebral
  column by lateral movements of the posterior
  ribs during inhalation, air flows into caudal
  air sacs through mesobronchus air also moves
  into the crainial air sacs via dorsobornchus
  parabronchi during exhalation, air leaving
  caudal air sacs passes through parbronchi
  through mesobronchus to trachea cranial air
  sacs, whose volume changes less than that of
  caudal air sacs, are reduce somewhat in volume by
  air moving via the ventrobronchi to the trachea
  during exhalation

4
Web Sites for Birds

• http//www.sonoma.edu/users/h/hanesda/B324/chap13.
  1.html - lecture notes on ventilation with
  sections on birds, insects and fish
• http//www.peteducation.com/article.cfm?cls15cat
  1829articleid2721 (pet bird site with diagram
  of air sacs)
• http//people.eku.edu/ritchisong/birdrespiration.h
  tml avian respiration link (EKYU link) from
  http//www.birdsnways.com/birds/artother.htmAnato
  my
• (has a large links on birds anatomy from main
  page http//www.birdsnways.com/birds/artother.htm
  )

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Special Considerations Species Differences
Insects

• Insect Tracheal System takes advantage of fact
  that O2 CO2 diffuse 10,000 x more rapidly in
  air than in water, blood or tissues tracheal
  system consists of a series of air-filled tubes
  that penetrate form body surface to cells act
  as a pathway for the rapid movement of O2 CO2
  thereby avoiding need to transport gases through
  the circulatory system these tubes are
  invaginations of the body surface their wall
  structure is similar to that of the cuticle
  tracheal entrances (spiracles) can be adjusted to
  control air flow into the tracheas, regulate
  water loss keep dust out the tracheas branch
  everywhere in the tissues the smallest, terminal
  branches (tracheoles) are blind-ended poke
  between into individual cells (without
  disrupting the cell membrane) delivering O2 to
  regions very close to the mitochondria

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Web Sites on Insects (Tracheal System)

• http//w3.dwm.ks.edu.tw/bio/activelearner/44/ch44c
  3.html diagram of insect tracheal system

7
Special Considerations Special Considerations
Gills

• Gas Transfer in Water usually a unidirectional
  flow of water water has much lower O2 content
  than air, H2O breathing animals require a much
  higher ventilation rate to achieve a given O2
  uptake than do air-breathing animals combined
  with the high density viscosity of H2O, the
  extraction of O2 is a energy costly exercise
  (cost offset somewhat by gills having a
  unidirectional rather than tidal flow of H2O
  lamprey sturgeons are exceptions have a tidal
  flow e.g. lampreys are attached to host )
  teleost fishes is maintain by action of skeletal
  muscle pumps in buccal opercular cavities
  water drawn into mouth, passes over gills exits
  through a cleft in operculum valves make sure
  its unidirectional operculum swings in out,
  enlarging reducing size of opercular cavity

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Special Considerations Species Differences
Gills cont

• Blood flow through fish described as sheet flow
  as pressure increases, the thickness, but not the
  other dimensions, of the blood sheet increases
  in this respect, circulation through gills is
  similar to pulmonary circulation blood flow
  relative to flow of water in aquatic animas can
  be concurrent, countercurrent or some combination
  of the 2 advantage of countercurrent flow of
  blood water is that a larger difference in PO2
  can be maintained across the exchange surface
  allowing more transfer of gases

9
Special Considerations Species Differences
Gills cont

• Fig 14-38 shows comparative anatomy of teleosts
  elasmobranchs gills using teleost gills 4
  branchial arches on either side of head separate
  opercular buccal cavities area has 2 rows of
  filaments, each filament, flattened
  dorsoventrally has an upper lower row of
  lamellae lamellae of successive filaments I a
  row are in close contact tips of filaments of
  adjacent arches are juxtaposed, so that the whole
  gill forms a sieve-like structure in path of
  water flow gills are covered by mucus secreted
  from mucous cells within the epithelium (protects
  gills creates a boundary layer between water
  epithelium) water flows through slit-like
  channels between neighboring lamellae

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Special Considerations Species Differences
Gills cont

• Thus water flows in thin sheets between the
  lamellae, which represent the respiratory portion
  of the gill lamellae are covered by thin sheets
  of epithelial cells which are joined by tight
  junctions diffusion distance between center of
  a RBC flowing water is much greater than
  diffusion distance across mammalian lung
  epithelium (remember gills are NB ion regulation
  carry out many functions of mammalian kidney)
  when exposed to air, gills collapse become
  nonfunctional, so a fish out of H2O becomes
  hypoxic, hypercapnic (excessive CO2) acidotic

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Web Sites for Gills

• http//www.fishdoc.co.uk/disease/gill20disease/ht
  m
• Anatomy, blood water flow, histographs of
  lamellae
• http//www.erin.utoronto.ca/w3bio325/Fish20gill
  20ventilation.htm
• Cross-sectional view of gill ventilation
• http//www.biology.ualberta.ca/facilities/multimed
  ia/uploads/zoology/fishgill.html
• Graphs of models for freshwater sea water ion
  acid-base regulation
• (if you type fish gill into your internet
  browser, these are the 1st 3 pages)

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Special Considerations Species Differences
SwimBladders

• Fish are denser than surrounding H2O must
  generate upward hydrodynamic forces if they are
  to maintain their position in the water column
  not sink to the bottom
• Generate lift by swimming using their fins
  bodies as hydrofoils
• Some fish must swim continuously to maintain
  their position
• Regardless, there is an energetic cost to
  maintaining position that can be reduced by
  incorporation of a buoyancy device

13
Special Considerations Species Differences
SwimBladders cont

• Various devices may be employed depending on the
  species e.g. ammonium chloride solutions
  (squids), lipid layers or air-filled swimbladders
  
• Hydrostatic pressure increases by approximately 1
  atm for every 10 m of depth in water (if a fish
  is swimming just below surface suddenly dives
  to 10 m, the total pressure in its swimbladder
  doubles form 1 to 2 atm swimbladder volume is
  reduced by ½ increasing the density of the fish
  the fish should continue to sink because its
  more dense than H2O, however a means to prevent
  this volume change is for gas to be added (or
  removed) as the fish descends (or ascends)

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Special Considerations Species Differences
Swim Bladders cont

• Fishes with swimbladders spend most of time in
  upper 200 m of lakes, seas oceans pressure in
  swimbladder ranges from 1 atm at surface to 21
  atm at 200 m
• Gases dissolved in H2O are generally in
  equilibrium, with air, neither the gas partial
  pressure not the gas content in water varies with
  depth, because H2O is virtually incompressible
• Swimbladder gas in most fishes consists of O2
  (but some are filled with CO2 or N2)
• If fish dives to depth of 100 m, O2 must be added
  to swimbladder to maintain buoyancy the aquatic
  environment is the source of this O2 which is
  moved form surrounding water into swimbladder
  against a pressure difference

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Special Considerations Species Differences
Swim Bladders cont

• Animals capable of moving O2 into swimbladder
  against a high pressure gradient have a rete
  mirabile consisting of several bundles of
  capillaries in close apposition arranged so
  that there is countercurrent blood flow between
  arterial venous blood
• The rete structure allows blood to flow into the
  swimbladder wall without a concomitant large loss
  of gas from swimbladder blood passes first
  through arterial capillaries of rete, then
  through secretory epithelium (gas gland) in
  swimbladder wall back through venous
  capillaries in the rete

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Special Considerations Species Differences
Swim Bladders cont

• Anaerobic metabolism of glucose to lactate CO2
  in gas gland, located in wall of swimbladder,
  leads to decrease in RBC pH a release of O2
  from Hb therefore O2 in blood flowing through gas
  gland becomes greater than PO2 in lumen of
  swimbladder so O2 diffuses into the lumen (called
  Root-off shift)

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Web Sites for Swimbladder

• http//floridafisheries.com/Fishes/anatomy.html
  external and internal fish anatomy

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Respiratory Responses to Extreme Conditions
(varying levels of respiratory gases, diving by
air-breathing animals exercise)

• Hypoxia (reduced O2 levels) aquatic animals are
  subjected to more frequent rapid changes in O2
  levels than air-breathing animals
• Photosynthesis occurs during day results in
  very high O2 levels O2 consumption by both
  biological chemical process can produce
  localized hypoxic regions especially at night
  (may or may not be accompanied by changes in CO2
  levels)
• Many aquatic animals can withstand very long
  periods of hypoxia e.g some fishes such as carp
  over-winter in the bottom mud of lakes where PO2
  is very low many limpets bivalve mollusks
  close their shells during exposure at low tide to
  avoid desiccation are subjected to periods of
  hypoxia

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Respiratory Responses to Extreme Conditions
Hypoxia cont

• In general, animals reduce energy expenditures
  utilize a variety of anaerobic metabolic pathways
  to survive periods of reduced O2 availability
• Animals also adjust their respiratory CVS to
  maintain O2 delivery in face of reduced O2
  availability (aquatic hypoxia causes an increase
  in gill ventilation in many fishes, as a result
  of stimulation of chemoreceptors on gills
  increase in water flow offsets reduction in O2
  content of gill water maintains delivery of O2
  to fish

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Respiratory Responses to Extreme Conditions
Hypoxia cont

• Compared with aquatic environments, O2 CO2
  levels are relatively stable in air local
  regions of low O2 or high CO2 are rare easily
  avoided
• Is a gradual reduction in PO2 with altitude
  animals vary in their capacity to climb to high
  altitudes withstand accompanying reduction in
  ambient O2 levels (high altitudes are associated
  with low temperatures as well as low pressures
  marked effect on animal distribution)
• Highest human habitation 5800m, where PO2 is
  80 mmHg (compared to 150 mm Hg at sea level)

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Respiratory Responses to Extreme Conditions
Hypoxia cont

• Remember from assignment on migration, many birds
  migrate over long distances at altitudes gt 6000
  m, where atmospheric pressures would cause severe
  respiratory distress in many mammals (related to
  differences in mechanism of lung gas transfer
  between birds mammals?)
• In mammals, a reduction n PO2 of ambient air
  results in a decrease in blood PO2, which in turn
  stimulates the carotid aortic body
  chemoreceptors, causing an increase in lung
  ventilation rise in lung ventilation then leads
  to increase in CO2 elimination a decrease in
  blood PCO2, which causes a reduction in PCO2 of
  CSF and thus an increase in its pH

22
Respiratory Responses to Extreme Conditions
Hypoxia cont

• Decreases in blood PCO2 increase in CSF pH tend
  to reduce ventilation thereby attenuating the
  hypoxia-induced increase in lung ventilation (if
  hypoxic conditions are maintained, as occurs when
  animals move to high altitudes, both blood CSF
  pH are returned to normal levels by the excretion
  of HCO3 takes a few days-1 week in humans)
• Long-term adaptations occur during prolonged
  exposure to hypoxia most vertebrates respond by
  increasing of RBCs blood Hb content (thus, O2
  capacity of blood) by stimulating production of
  hormone erythropoietin in kidney liver which
  acts on bone marrow to increase production of RBCs

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Respiratory Responses to Extreme Conditions
Diving

• Air-breathing vertebrates live in H2O dive for
  varying periods of time dolphins whales rise
  to surface to breathe but spend most of their
  lives submerged
• Time between breathes varies with species but is
  around 10-20 min.
• Diving mammals birds ar subjected to periods of
  hypoxia during submerence themammaliam CNS
  cannot withstand anoxia must be supplied with O2
  through the dive diving animals solve this
  problem by utilizing O2 stores in lungs, blood
  tissues

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Respiratory Responses to Extreme Conditions
Diving cont

• Many diving animals have high Hb myoglobin
  levels their total O2 stores generally are
  larger than those in non-diving animals
• O2 is preferentially delivered to brain heart
  during the dive blood flow to other organs may
  be reduced these tissue may adopt anaerobic
  metabolic pathways
• There is a marked slowing of HR (bradycardia) a
  reduction of CO during a prolonged dive
• Must have sufficient O2 stores to sustain aerobic
  metabolism, because they cannot tolerate the
  large amount of lactic acid that accumulates
  during anaerobic metabolism

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Respiratory Responses to Extreme Conditions
Diving cont

• Receptors that detect presence of H2O that
  inhibit inspiration during a dive are situated
  near the glottis near the mouth/nose (depending
  on species) thus, decrease in blood O2 levels
  increase in CO2 levels that occur during a dive
  do not stimulate ventilation because inputs from
  the chemoreceptors of the carotid aortic bodies
  are ignored by the respiratory neurons while the
  animal is submerged -increased chemoreceptor
  activity during a dive, generates bradycardia

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Respiratory Responses to Extreme Conditions
Exercise

• Exercise increases O2 utilization, CO2 production
  metabolic acid production
• CO increases to meet the higher demands of the
  tissues
• O2 levels in blood leaving lung remain in
  equilibrium with those in alveolar gas because
  ventilation volume increases
• Increase in ventilation in mammals is rapid,
  coinciding with onset of exercise (this initial
  sudden increase in ventilation volume is followed
  by a more gradual rise until a steady state is
  obtained both for ventilation volume O2 uptake)

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Respiratory Responses to Extreme Conditions
Exercise cont

• When exercise is terminated, there is a sudden
  decrease in ventilation rate, followed by a
  gradual decline in ventilation volume
• During exercise, O2 levels are reduced CO2 and
  H levels are raised in venous blood, but the
  mean PO2 PCO2 in arterial blood do not vary
  markedly (except in sever exercise)
• Exercise covers a range from slow movements up to
  maximum exercise capacity (moderate exercise
  exercise above resting levels that is aerobic,
  with only minor energy supplies derived from
  anaerobic glycolysis severe exercise exercise
  in which O2 uptake is maximal further energy
  supplies are derived from anaerobic metabolism)

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Respiratory Responses to Extreme Conditions
Exercise cont

• Several receptor systems involved in respiratory
  responses to exercise muscle contractions
  stimulate stretch, acceleration position
  mechanoreceptors in muscles, joints tendons
  activity of these receptors reflexly stimulates
  ventilation this system probably causes the
  sudden changes in ventilation that occur at the
  beginning end of a period of exercise
• Increase in ventilation varies with the group of
  muscles being stimulated (e.g. leg muscles
  results in larger increase in ventilation than
  arm exercise also true for bicycle vs. treadmill)

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Respiratory Responses to Extreme Conditions
Exercise cont

• Muscle contraction generates heat raises body
  temperature increasing ventilation via action
  on temperature receptors in hypothalamus (
  increase in ventilation is more pronounced in a
  hot environment)