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The gas exchange between air in an alveolus and blood circulating through
pulmonary capillariesRespiratory System
Questions Received:
Responses:
Can panic attacks make a person turn blue through lack of oxygen?
28th April 1999
One of the components of a panic attack is hyperventilation, or over-breathing. This means that the person is removing carbon dioxide from their blood more rapidly than it is being produced, upsetting the pH of the blood. The blood becomes increasingly alkaline, and this causes a number of changes which will affect brain function - the person experiences dizziness and may faint. Actually, the oxygen level in the blood is high so the problem is not a lack of oxygen, rather it is more to do with the distribution of blood and the imbalance in pH. So it is unlikely that a person will turn blue, but they may become paler initially as a result of the stress they are experiencing.
Panic attacks reach maximum intensity within a minute or two of onset. Rapid physiological changes occur associated with overwhelming feelings of dread and anxiety. They diminish slowly over the next 30 minutes or the next several hours. Treatment is now very effective, and includes the use of special breathing patterns and anti-depressant drugs.
For useful information about panic attacks, visit www.anxietypanic.com
14th March 2000
Surfactant is a family of phospholipids with detergent-like properties. It is produced by cells lining the air sacs in the lungs, and has the ability to lower the surface tension of the watery film that moistens the inside of the air sacs (alveoli). Without surfactant, the alveoli would be in constant danger of collapsing from surface tension. Surfactant is not produced in the developing lungs of the fetus until around the 24th week of pregnancy. Thus, premature babies may lack surfactant and have difficulty in establishing normal breathing. As a result they develop infant respiratory distress syndrome, also known as hyaline membrane disease (Clancy and McVicar, 1995). In this situation the alveoli fail to fill with air at birth - atelectasis. To overcome this problem, artificial pulmonary surfactants are given together with other measures to help the premature baby until it can produce its own surfactant in sufficient quantities.
Reference
Clancy, J., and McVicar, J. (1995) Physiology & anatomy: a homeostatic approach. London: Edward Arnold (The respiratory system, p 300).
What is the difference between inspired air and expired air? What is the difference between the oxygen content and carbon dioxide content in alveoli and pulmonary blood?
15th January 2001
The main difference between inspired air and expired air lies in gas composition: inspired air contains more oxygen than expired air, and expired air contains more carbon dioxide than inspired air. These differences reflect the use of oxygen by cells during metabolism and the release of the waste product carbon dioxide.
The partial pressure of oxygen in the air (PO2) at standard atmospheric pressure is 159 mm mercury (Hg), but this drops to 100-105 mm Hg when air is inhaled and enters the lungs. The inhaled air mixes with air already in the alveoli - air that is rich in water vapour and carbon dioxide and both of which contribute to the total pressure there.
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The gas exchange between air in an alveolus and blood circulating through
pulmonary capillaries
When blood circulates through the tissues it donates its oxygen to the cells that need it and later enters the pulmonary capillaries with its PO2 reduced to 40-45 mm Hg. This is about 60 mm Hg lower than the PO2 in the alveoli. As a consequence, a pressure gradient is set up for oxygen across the respiratory membrane. It is this pressure gradient which drives the oxygen from the alveolar air into the blood to balance the pressure of oxygen on each side of the membrane. The PO2 in the alveoli stays relatively stable at about 105 mm Hg. As the blood moves along the pulmonary capillary it begins to take up oxygen. By the time the venous end of the capillary is reached the partial pressure of oxygen in the blood equals that in the alveolus: 105 mm Hg. Thus the blood leaving the lungs via the pulmonary veins to the heart is rich in oxygen.
Carbon dioxide (CO2) exchange occurs in a similar way but in the opposite direction across the respiratory membrane. Blood passing through the pulmonary capillaries has a PCO2 of about 45 mm Hg. The alveoli air has a PCO2 of about 40 mm Hg. Although this results in a relatively small pressure gradient of about 5 mm Hg, it is more than adequate. This is because CO2 has a membrane solubility which is 20 times greater than that of O2 and diffuses across the respiratory membrane much more quickly.
Reference
Wilmore, J.H., and Costill, D.L. (1994) Physiology of sport and exercise. Published by: Human Kinetics.