Gas exchange

Jump to: navigation, search

WikiDoc Resources for Gas exchange

Articles

Most recent articles on Gas exchange

Most cited articles on Gas exchange

Review articles on Gas exchange

Articles on Gas exchange in N Eng J Med, Lancet, BMJ

Media

Powerpoint slides on Gas exchange

Images of Gas exchange

Photos of Gas exchange

Podcasts & MP3s on Gas exchange

Videos on Gas exchange

Evidence Based Medicine

Cochrane Collaboration on Gas exchange

Bandolier on Gas exchange

TRIP on Gas exchange

Clinical Trials

Ongoing Trials on Gas exchange at Clinical Trials.gov

Trial results on Gas exchange

Clinical Trials on Gas exchange at Google

Guidelines / Policies / Govt

US National Guidelines Clearinghouse on Gas exchange

NICE Guidance on Gas exchange

NHS PRODIGY Guidance

FDA on Gas exchange

CDC on Gas exchange

Books

Books on Gas exchange

News

Gas exchange in the news

Be alerted to news on Gas exchange

News trends on Gas exchange

Commentary

Blogs on Gas exchange

Definitions

Definitions of Gas exchange

Patient Resources / Community

Patient resources on Gas exchange

Discussion groups on Gas exchange

Patient Handouts on Gas exchange

Directions to Hospitals Treating Gas exchange

Risk calculators and risk factors for Gas exchange

Healthcare Provider Resources

Symptoms of Gas exchange

Causes & Risk Factors for Gas exchange

Diagnostic studies for Gas exchange

Treatment of Gas exchange

Continuing Medical Education (CME)

CME Programs on Gas exchange

International

Gas exchange en Espanol

Gas exchange en Francais

Business

Gas exchange in the Marketplace

Patents on Gas exchange

Experimental / Informatics

List of terms related to Gas exchange

Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]


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 simply the cell membrane, but for large organisms it usually is carried out in respiratory systems.

This name can cause problems - in biology the word "respiration" can mean cellular respiration or metabolism (ATP generation inside cells), however sometimes (such as here) it can also refer to breathing (which is how the word is most often used by non-biologists).

Gases cross the respiratory surface by diffusion, so from 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

File:Alveoli.svg

In humans and other mammals, respiratory gas exchange or ventilation is carried out by mechanisms of the lungs. The actual exchange of gases occurs in the alveoli.

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 mm Hg, with oxygen (O2) providing a partial pressure (pO2) of 160 mm Hg, 21% by volume, at the entrance of the nares, and an estimated pO2 of 100 mm Hg 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.

Gas exchange occurs only at pulmonary and systemic capillary beds.

CO2 is a result of cellular respiration. 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.

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.

Transporting of oxygen, carbon dioxide, and hydrogen ions

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 carbaminohemoglobin.

AS CO2 diffuses into the blood stream 93% goes into RBCs and 7% is dissolved in plasma. 70% is converted into H2CO3 by Carbonic Anhydrase. The H2CO3 dissociates into H+ and HCO-3. The HCO-3 moves out of the RBC in exchange for CL-(chloride shift). The hydrogen is removed by buffers in the blood (Hb).

External links


nl:Gaswisseling no:Gassutveksling nn:Gassutveksling simple:Breath ta:வாயுப் பரிமாற்றம் uk:Газообмін


Linked-in.jpg