Mechanics of Breathing

• some components:
  • diaphragm -
  • external & internal intercostals - expand to allow more air in
• *during inhalation, diaphragm moves down
  contracts, forcing air into lungs
  • diaphragm relaxes, forcing air out.
• labored breathing recruits intercostals to increase/decrease size of thoracic cavity

Natural movements of air & pressure flow

• respiration takes advantage of diffusion
• air naturally flows into lungs
  • diaphragm contracts, lungs - low pressure, environment pressure rushes into lungs
• exhale - increase lung pressure - forcing out
• human body uses diffusion in # of ways (eg. digestion)
• passive transport

Collapsed Lung

• surfacant (lipoprotein) - produced in aveolar epithelium
  • used- help reduce surface tension
  • result - adheration of visceral pleura to parietal pleura
  • helps prevent abrasion & keeps lungs inflated briefly
  • works like 2 wet sheets of glass
• elastic recoil (sprung elastic fibers) lost
  (ie - hole in balloon)
  [point where lung injured - have to make area arond stronger - to keep capacity]
• when this happens - surface tension between surfacant & parietal plura is lost
  • larger the hole - harder to make contact with surfacant
  • large enough - fills with water from moist air
  • thus decreasing amount of volume
    • if body does counteract, lung can become dried and shriveled
      
    • (positive feedback)

Gas Exchange

• respiratory membranes
• exchange of gas between blood & air - takes place largely in aveolies
• air in other respiratory passages - dead air space
• Alveolie
       ~ 300 million - surface area = 1/2 tennis court
• Respriatory membranes
  • increase thickness of fluid / decrease rate of exchange of gases
  • decrease surface area - decrese area for exchange
  • partial pressure -
    • if liquid contains less O2 than air, O2 will move into liquid
    • but if total pressure is greater than pressure inside cell -
           no diffusion takes place
  • when O2 is less in alveolar cappilaries than in alveoli, O2 moves toward cappilaries

O2 in Blood

• 97% of O2 combines with heme group in hemoglobin
  (other 3% dissolved in plasma)
• O2 & hemoglobin = oxyhemoglobin

Factors Influencing O2 Release from Oxyhemoglobin
  *  pH out of balance (blood is slightly basic) - affects O2 release
  *  partial pressure of O2
  *  if temperature is too high
          needs increase O2
  *  exercise
  *  partial pressure of CO2

How to get CO2 from cells out of body?

• 8% of CO2 dissolved in plasma
• 20% transported by blood protein hemoglobin
• 72% transported by bicarbonate ions

 Reaction

CO2 + H2O -> H2CO3 (carbonic acid)

H2CO3 -> H + HCO3 (dissociated carbonic acid)

* carbonic anhydrase - increased rate

• CO2 reacts with H2O to get H+ and bicarbonate ions
  in the tissue capillaries

• so can be diffused into alveoli & exhaled

• decreases blood pH - making more acidic
• CO2 goes up, pH goes down

Nervous Control of Respiration

• Medulla Oblongata & lower pons - make up respiratory center
• Phrenic nerves carry action potentials
  nbsp;    nbsp;    diaphragm to respiratory centers
  • - action potentials fatigue quickly
    • so don't hyperventalate or inflate lung too strongly - pop
    • saves energy
    • this controls rhythmn of breathing - inhalation & exhalation
  • - if fatigue of normal respiratory center takes place
    • pons then takes over phythmic breathing
      nbsp;    but not long-term & barely functional at best

• Hering-Breuer reflex
  • mechanism - senses inhalation
    • & sends message to medulla oblongata
    • inhalation stopped - causing expiration
    • very important in infants (& adults during exercise)
      • controls rhythmic breathing
    • (could be possible reason for SIDS)
    • ***skin contains receptors - also stimulates respiratory centers

Chemical Control of Respiration

• chemoreceptors in medulla detect even small changes in CO2 & O2 in blood
  • (more O2 - inhale / get rid of CO2 - exhale)
• fainting - can also be a result of exaggerated breathing
  • CO2 becomes low & blood vessels in periphery dialate
  • causes blood to pool in lower abdomin & lower legs
    nbsp;    (long term lowers blood pressure causing fainting)