Respiratory System

1
Respiratory System

• If cells are not directly exposed to the outside
  environment, then some mechanism must provide gas
  exchange to internal cells, delivering O2 and
  removing waste CO2

2
Gas exchange mechanisms

• Direct with environment
• Phylum Porifera, Phatyhelminthes
• Typically have large surface areas, and every
  cell either is exposed to the outside environment
  or is close enough that gases are avialable by
  diffusion through adjacent cells
• In larger animals, such as Annelida, gas exchange
  through the skin is augmented by the circulatory
  system just inside the skin.

3
Gas exchange mechanisms

• Gills
• Countercurrent exchange
• Tracheae
• Insects have chitin-lined tubes, or tracheae,
  that permeate their bodies
• Oxygen enters (or CO2 exits) the tracheae through
  openings called spiracles
• Diffusion occurs across moistened tracheal
  endings
• Lungs

4
Gas exchange in Humans

• 1. Mouth
• 2. Pharynx
• 3. Larynx (contains the vocal cords)
• 4. Trachea
• 5. Bronchi, bronchioles
• 6. Alveolus (alveoli)
• 7. Diffusion between alveolar chambers and blood
• 8. Bulk flow of oxygen

5
Gas exchange in Humans

• 7. Diffusion between blood and cells
• 8. Bulk flow of CO2
• Most CO2 is transported as dissolved bicarbonate
  ions (HCO3-) in plasma
• CO2 H2O ? H2CO3 ? H HCO3-
• The formation of HCO3- occurs in RBC where the
  fromation of carbonic acid is catalyzed by the
  enzyme carbonic anhydrase
• 9. Bulk flow of air into and out of the lungs
• Diaphragm and intercostal muscles

6
Gas exchange in Humans

• 10. Control of respiration
• Chemoreceptors in the carotid arteries monitor
  the pH of the blood
• Blood pH drops as CO2 enters the blood
• In response, the chemoreceptors send nerve
  impulses to the diaphragm and intercostal mucles
  to increase respiratory rate.
• This results in a faster turnover in gas
  exchange, which returns blood pH to normal
• Homeostasis in maintained by negative feedback