Gas exchange

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Gas exchange
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Key concepts

• Gas exchange occurs across specialized
  respiratory surfaces
• Gills in aquatic animals
• Tracheal systems in insects
• Lungs
• Breathing ventilates the lungs
• Amphibian breathing
• Bird breathing
• Control of breathing in humans
• Respiratory pigments bind and transport gases
• Diffusion and partial pressure
• Respiratory pigments
• O2 and CO2 transport

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Vocabulary words

• respiratory surface
• tracheal system
• larynx
• bronchi (bronchus)
• breathing
• vital capacity
• partial pressure
• dissociation curve for hemoglobin

• ventilation
• lungs
• vocal cords
• bronchioles
• diaphragm
• residual volume
• respiratory pigments
• Bohr shift

• countercurrent exchange
• gills
• trachea
• alveoli (alveolus)
• tidal volume
• breathing control centers
• hemoglobin
• carbon dioxide transport

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Respiratory surfaces and gas exchange

• Gas exchange uptake of O2 from environment and
  discharge of CO2
• Mitochondria need O2 to produce more ATP, CO2 is
  the by-product
• C6H12O6 6O2 ? 6CO2 6H2O 36 ATP
• Diffusion rate
• a SA ? large
• a 1/d2 ? thin
• Moist so gases are dissolved first

DIFFUSION
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Respiratory surfaces and gas exchange

• Respiratory surface
• Size of organism
• Habitat
• Metabolic demands
• Unicellular organisms
• Entire surface area for diffusion

• Simple invertebrates
• Sponges, cnidarians, flatworms
• diffusion

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Respiratory surfaces and gas exchange

• More complex animals
• Thin, moist epithelium
• Separates medium from capillaries
• Entire outer skin ? small, long, thin organisms
• Specialized respiratory organs that are
  extensively folded and branched

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Gills in aquatic animals

• Outfoldings of the body surface suspended in
  water
• Sea stars
• Segmented worms or polychaetes
• Molluscs and crustaceans
• Fishes
• Young amphibians
• Total surface area is greater than the rest of
  the body

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Water as a respiratory medium

• Surfaces are kept moist
• O2 concentrations in water are low
• Ventilation increasing flow of respiratory
  medium over the surface
• Countercurrent exchange process in which two
  fluids flow in opposite directions, maximizing
  transfer rates
• Why are gills impractical for land animals?

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Air as a respiratory medium

• Air has a higher concentration of O2
• O2 and CO2 diffuse much faster in the air ? less
  ventilation
• Difficulty of keeping surface moist
• Solution respiratory infolding inside the body

• Tracheal system of insects network of tubes
  that bring O2 to every cell

Spiracles
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Lungs

• Heavy vascularized invaginations of the body
  surface restricted to one location
• Found in spiders, terrestrial snails, vertebrates
• Amphibians supplement lung breathing with skin
• Turtles supplement lung breathing with moist
  surfaces in mouth and anus

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Mammalian respiration
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Lung ventilation through breathing

• Positive pressure breathing in frogs
• Gulping in air

• Negative pressure breathing in reptiles and
  mammals
• Rib muscles and diaphragm change lung volume and
  pressure

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Lung volumes

• Tidal volume
• Volume of air inhaled and exhaled with each
  breath
• Vital capacity
• Maximum volume inhaled and exhaled during forced
  breathing
• Residual volume
• Air left in alveoli after forced exhalation

• Factors
• Sex
• Height
• Smoking
• Physical activity
• Altitude

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Avian breathing
Air sacs act as bellows to keep air flowing
through the lungs.
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Control centers in the brain regulate breathing
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Gases diffuse down pressure gradientsconcentrati
on and pressure drives the movement of gases into
and out of blood
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Respiratory pigments

• O2 transport
• Low solubility of O2 in H2O
• Respiratory pigments are proteins with metal
  atoms
• Hemoglobin Fe
• Hemocyanin Cu
• Allow reversible binding of O2
• Drop in pH results in a lowered affinity of
  hemoglobin for O2

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Respiratory pigments

• CO2 transport
• 7 in plasma
• 23 bound to hemoglobin
• 70 as HCO3-
• buffer

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Fetal hemoglobin

• HbF has greater affinity to O2 than Hb
• low O2 by time blood reaches placenta
• fetal Hb must be able to bind O2 with greater
  attraction than maternal Hb

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Deep-diving mammals

• Seals, whales, dolphins are capable of long
  underwater dives
• Weddell seal ? 5 O2 in lungs, 70 in blood
• Huge spleen stores huge volumes of blood
• Large concentrations of myoglobin in muscles
• Heart rate and O2 consumption rate decrease
• Blood is redirected from muscles to brain spinal
  cord and eyes