Gas exchange in Mammals

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Gas exchange in Mammals
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Gas Exchange in Mammals

• Delivery of O2 to gas exchange surface (alveoli)
  and removal of CO2 from capillaries and out of
  the body (ventilation).

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In Larger Organisms

• Diffusion alone cannot meet the needs of the
  inner-most cells of larger organisms. They have a
  higher demand for O2 and removal of CO2.
• Larger organisms must have some form of internal
  transport system for gases.

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Pathway

• Air (outside) ? nasal passages (or mouth) ?
  pharynx ? larynx ? trachea ? bronchus ?
  bronchiole ? alveoli ? bloodstream

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• Nasal passages
• - Air is warmed and moistened. Dust and
  bacteria removed by mucous and nasal hairs
  (cilia).

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Cilia - creates wave-like movement to sweep
mucous upwards to be expeled at the mouth/nose
(along with trapped debris)
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Cilia animation

• http//www.bioscope.org/taste/cd1/a0255a.htm

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Trachea

• Hollow tube held open by C shaped bands of
  cartilage.
• It branches into the two bronchi (one bronchus)
  which also have cartilaginous rings.

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Alveolus

• Bronchus then branch into smaller tubes called
  bronchioles which lead into grape-like clusters
  of thin-walled air sacs called alveoli (one
  alveolus) which are surrounded by blood
  capillaries.

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• Oxygen diffuses across the moist lining of the
  alveoli into the capillaries.
• CO2 diffuses out of the capillary and into the
  air in the alveoli.

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Surfactant

• Lipoprotein produced by alveolar cells
• Reduced surface tension (if no surfactant lung
  cannot inflate normally)

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Pigment

• Oxygen is picked up by a red pigment called
  haemogoblin (in red blood cells) and is carried
  around the body in the circulatory system .
• As the blood carrying the oxygen (oxygenated
  blood) passes through the body the haemoglobin
  releases oxygen which diffuses into the cells.

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Other bits

• Diaphragm is a sheet of muscle at bottom of
  these cavities
• Pleural membrane lines each cavity and covers
  each lung, and encloses pleural space (which
  contains fluid to help membranes slide past each
  other during breathing)

www.tcnj.edu/mckinney
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Breathing/Ventilation
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Inhalation Breathing In

• Diaphragm contracts (lowered), intercostal
  muscles contract - lifts ribs up and out.
• Increases volume of chest cavity ? cause the air
  from outside to rush in and fill up the increased
  space.

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Exhalation Breathing out

• Diaphragm and intercostal muscles relaxes
• Diaphragm moves up and the ribs down
• Air is forced out as the volume in the chest
  cavity returns to normal.

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• The breathing action (diaphragm etc.) uses
  considerable energy but allows the animal to
  change the rate of gas exchange quickly to suit
  activity/environment requirements.

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Increased Surface Area for Gas Exchange

• Alveoli ?s surface area exposed for diffusion of
  O2 into capillaries and CO2 out into alveoli.
• 300 million alveoli creates 40x the surface area
  of the body.

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Moist Surfaces

• Moist surface within nasal passages, alveoli and
  capillaries help O2 in air to dissolve into the
  watery substance for diffusion into capillaries.

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Thin Exchange Surface

• Thin surface of alveoli and capillaries ?s
  barrier for diffusion of O2 into capillaries and
  CO2 out.

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• A more specialised system is required for the
  increased size of the animal to deal with
• ? the inefficiency of diffusion over longer
  distances
• ? higher demand for O2 and removal of CO2.
• Internal lungs are well protected from
• ? physical damage
• ? drying out in a dry environment. Enables
  mammals to have a wider range of habitats e.g.
  dry, wet, water on land.
• Lungs have a higher surface area to maximise rate
  of diffusion of O2 into capillaries and removal
  of CO2.
• Then the O2 and CO2 is transported around the
  body in the bloodstream of the circulation system.

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Blood vessels in the lung
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Some more interesting info/pictures

• Warning some pictures are a bit gory so stop
  here if you are sensitive to blood and gore.

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Cross-section of the lung and heart
Figure 238
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Cilia can be immobilized by smoking
Smokers lung tissue
Normal lung tissue
www.orangeusd.k12.ca.us/date/
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Cystic fibrosis

• Faulty chloride channel leads to thick mucus ?
  difficult to clear ? blockage and infection

Normal lung tissue
Lung tissue from cystic fibrosis patient
www.pathguy.com/lectures
www.orangeusd.k12.ca.us/date/
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Black lung disease
An electron micrograph scan of coal dust (marked
by dark patches) in lung tissue infected with
black lung disease. A disease found primarily in
older coal workers, black lung is characterized
by thickening and scarring of lung tissue.
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Pneumothorax air trapped in the chest cavity.
Pneumothorax air trapped in the chest cavity.
(Tension pneumothorax life-threatening)
(Tension pneumothorax life-threatening)
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