THE RESPIRATORY SYSTEM Respiration In this sense is exchange of gases occuring across a moist membra

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Respiratory System
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THE RESPIRATORY SYSTEM

• Respiration - The exchange of gases occurring
  across a moist membrane in close contact with
  blood vessels.
• Better referred to as external respiration.

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I. Aquatic Respiration

• A. Integument1. Protochordates - common in
  protochordates2. Amphibians - used by many as
  secondary function of skin - common among
  salamanders - but - requires moist
  skin3. Reptiles - fresh-water turtles have
  paired Cloacal bursae - evaginate from the
  cloaca
• Bladder-like sacs that draw water in and out for
  gas exchange - permits respiration while
  submerged for long periods, e.g., hibernation

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B. Gills

• Stages in evolution
• 1. Pharyngeal slits - alterations of pharyngeal
  slits
• Pharyngeal feeding
• Pharyngeal respiration
• Tetrapod adaptation
• 2. Gill structurea. Early stages - First
  stagger internal and external slits

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• Second - canal becomes bag-like with folded and
  vascularized walls producing a gill chamber
• Folds lamellae - narrow and closely spaced with
  inner ends lying close to pharyngeal bar.septum
  with cartilagenous raysGill rakers are
  extensions which protect internal openings

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• b. Later stages
• c. Final stages - loss of septum resulting in
  filamentous gill

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3. Modifications of gills in higher vertebrates

• a. Reduction - 8 is primitive number
• reduced to 3-5 and finally 0 in
  tetrapodsb. Protection - formation of
  protective operculum - single covering which
  eliminates separate gill slits

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4. Fate of gill slits

• a. 0 - lost or fused with mouth
• b. I - lost or transformed into spiracle in
  shark and Eustachian tube in tetrapods
• c. II, III, IV - gills of modern bony fish
• d. V, VI - gills in some fish or lost
• e. VII, VIII - lost
• f. III - VIII - completely lost in tetrapods
• g. Embryos of tetrapods (5 pouches persist in
  embryos of reptiles, 4 pouches persist in
  embryos of birds and mammals)

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5. Pouch wall derivatives

• a. Thymus gland4 pairs in jawed fishes3 pairs
  in amphibians - tailed1 pair in frogs1-2 pairs
  in amniotes
• b. Palatine tonsils - not sure which pouch gives
  rise
• c. Parathyroid glands - outpockets of 2-3 pairs
  of pouches. Imbedded in thyroid in mammals or
  situated closely in others
• d. Carotid bodies - sense organs of O2 in blood
  and blood pressure (endotherms)

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II. Terrestrial Respiration A. Integument

• Exchange gases across moist integument
  infiltrated by capillary beds.

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B. Air bladders

• 1. Early history - paired - derived from rear
  pair of arches (VII, IX or X)Outer slit became
  closed leaving pouch in pharynx for storing
  gases
• 2. Modificationsa. Utilized for gas exchange
  first
• b. Later used as hydrostatic organ
• c. physostomous - (hydrostatic)d. physoclistous
  -
• with red gland
• typical of higher bony
• fish

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Examples of modifications of the air or swim
bladder
Physo- stomous
Lungs
Physo- clistous
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c. Tetrapod lungs

• 1. primitiveshort tracheabronchi lead to
• sac-like lungs
• 2. more advancedlung pockets

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3. most advanced - alveoli with capillaries in
mammals
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Air capillaries of birds
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• Air sacs of birds
• Function in cooling rather than for respiration
• 1/4 of air for respiration
• 3/4 for cooling
• 5 of internal volume is respiratory in humans
• 20 of internal volume is respiratory in ducks

Lung
Air Sacs
Air Sacs
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III. The Breathing Mechanism

• A. Fishes - Branchiomeric muscles move gills to
  circulate H2O over the gills
• B. Amphibians - Buccopharyngeal movements
  changing volume of buccal cavitydepress floor
  of mouth
• fill buccal cavityclose external narescontract
  buccal cavity force air into lungs Some
  amphibians especially
• have vascularized buccal
• cavity for gas exchange.Ribs do not move

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• C. Reptiles - movement of ribs with
  buccopharyngeal movement
• D. Birds - contraction of hypaxial muscles that
  exert and relax pressure on air sacs.

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• E. Mammals - intercostal, muscles, diaphragm,
  abdominal muscles - change volumn of thoracic
  cavity
• 1. Mechanisms -
• 2. Pleural membranesparietal pleura - inner
  surface of thoracic walldiaphragmatic
  pleuravisceral pleura

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3. Nares

• External nares - Closed and used for olfaction
  only in most fishesOpen to mouth in lobe -
  finned fishes and tetrapods for lung respiration

Shark
Human
Fig. 13.7