Gas exchange


Gas exchange

Gas exchange or respiration takes place at a respiratory surface—a boundary between the external environment and the interior of the body. For unicellular organisms the respiratory surface is Fick's law we can predict that respiratory surfaces must have:
*a large surface area
*a thin permeable surface
*a moist exchange surface

Many also have a mechanism to maximise the diffusion gradient by replenishing the source and/or sink.

Control of respiration is due to rhythmical breathing generated by the phrenic nerve to stimulate contraction and relaxation of the diaphragm during inspiration and expiration. Ventilation is controlled by partial pressures of oxygen and carbon dioxide and the concentration of hydrogen ions. The control of respiration can vary in certain circumstances such as during exercise.

Gas exchange in humans and mammals

In humans and mammals, respiratory gas exchange or ventilation is carried out by mechanisms of the heart and lungs. The blood is subjected to a transient electric field (QRS waves of the EKG) in the heart which dissociates molecules of different charge. The blood, being a polar fluid, aligns dipoles with the electric field, is released, and then oscillates in a damped driven oscillation to form J or Osborn Waves, T, U, and V waves. The electric field exposure and subsequent damped driven oscillation dissociate gas from hemoglobin, primarily CO2, but more importantly BPG, which has a higher affinity for hemoglobin than does oxygen, due in part to its opposite charge. Completely dissociated hemoglobin (which will even effervesce if the electric field is too strong—the reason defibrillation joules are limited, to avoid bubble emboli that may clog vessels in the lung) enters the lung in red blood cells ready to be oxygenated.

Convection occurs over the majority of the transport pathway. Diffusion occurs only over very short distances. The primary force applied in the respiratory tract is supplied by atmospheric pressure. Total atmospheric pressure at sea level is 760 mmHg (101 kPa), with oxygen (O2) providing a partial pressure ("p"O2) of 160 mmHg, 21% by volume, at the entrance of the nares, a partial pressure of 150 mmHg in the trachea due to the effect of partial pressure of water vapor, and an estimated "p"O2 of 100 mmHg in the alveoli sac, pressure drop due to conduction loss as oxygen travels along the transport passageway. Atmospheric pressure decreases as altitude increases making effective breathing more difficult at higher altitudes. Higher BPG levels in the blood are also seen at higher elevations, as well.

Similarly CO2 which is a result of tissue cellular respiration also exchange. The "p"CO2 changes from 45 mmHg to 40 mmHg in the alveoli. The concentration of this gas in the breath can be measured using a capnograph. As a secondary measurement, respiration rate can be derived from a CO2 breath waveform.

Gas exchange occurs only at pulmonary and systemic capillary beds, but anyone can perform simple experiments with electrodes in blood on the bench-top to observe electric field stimulated effervescence.

Trace gases present in breath at levels lower than a part per million are ammonia, acetone, isoprene. These can be measured using selected ion flow tube mass spectrometry.

Diffusion

Blood carries oxygen, carbon dioxide and hydrogen ions between tissues and the lungs.

The majority (70%) of CO2 transported in the blood is dissolved in plasma (primarily as dissolved bicarbonate; 60%). A smaller fraction (30%) is transported in red blood cells combined with the globin portion of hemoglobin as carbaminohaemoglobin.

As CO2 diffuses into the blood stream 93% goes into red blood cells and 7% is dissolved in plasma. 70% is converted into H2CO3 by carbonic anhydrase. The H2CO3 dissociates into H+ and HCO3. The HCO3 moves out of the red blood cells in exchange for Cl (chloride shift). The hydrogen ions are removed by buffers in the blood (Hb).

External links

* [http://people.eku.edu/ritchisong/301notes6.htm Human Physiology Respiration at eku.edu]
*
* [http://www.rtcorner.net RT Corner (Educational Site for RT's and Nurses)] at rtcorner.net


Wikimedia Foundation. 2010.

Look at other dictionaries:

  • gas exchange — dujų apykaita statusas T sritis ekologija ir aplinkotyra apibrėžtis Dujinių medžiagų mainai gyvūnų ir žmogaus organizme. Atmosferos dujos patenka į organizmo vidinę terpę per kūno paviršių ir kvėpavimo organus (trachėjas, žiaunas arba plaučius).… …   Ekologijos terminų aiškinamasis žodynas

  • Gas exchange — The primary function of the lungs involving the transfer of oxygen from inhaled air into the blood and the transfer of carbon dioxide from the blood into the exhaled air …   Medical dictionary

  • Discontinuous gas exchange — Contents 1 Phases 1.1 Closed phase 1.2 Flutter phase 1.3 Ope …   Wikipedia

  • alveolar gas exchange — the passage of oxygen and carbon dioxide in opposite directions across the alveolocapillary membrane …   Medical dictionary

  • Gas chromatography-mass spectrometry — (GC MS) is a method that combines the features of gas liquid chromatography and mass spectrometry to identify different substances within a test sample. Applications of GC MS include drug detection, fire investigation, environmental analysis,… …   Wikipedia

  • Gas gangrene — Classification and external resources Photograph before right leg amputation (hemipelvectomy) of a patient with gas gangrene. The right thigh is swollen, edematous and discoloured with necrotic bullae (large blisters). An impressive crepitation… …   Wikipedia

  • Gas mask — A gas mask is a mask worn over the face to protect the wearer from inhaling airborne pollutants and toxic materials. The mask forms a sealed cover over the nose and mouth, but may also cover the eyes and other vulnerable soft tissues of the face …   Wikipedia

  • Exchange-traded fund — An exchange traded fund (ETF) is an investment fund traded on stock exchanges, much like stocks.[1] An ETF holds assets such as stocks, commodities, or bonds, and trades close to its net asset value over the course of the trading day. Most ETFs… …   Wikipedia

  • Gas — This article is about the physical properties of gas as a state of matter. For the uses of gases, and other meanings, see Gas (disambiguation). Ga …   Wikipedia

  • Gas Exporting Countries Forum — The Gas Exporting Countries Forum (GECF) is an organization of world s leading gas producers, which was established in Tehran in 2001. The aims of the GECF are: * to foster the concept of mutuality of interests by favouring dialogue between… …   Wikipedia


Share the article and excerpts

Direct link
Do a right-click on the link above
and select “Copy Link”

We are using cookies for the best presentation of our site. Continuing to use this site, you agree with this.