Exchange of Gas

The process of oxygen and carbon dioxide exchange is referred as gas exchange. Carbon dioxide is removed from the bloodstream and oxygen is transferred from the lungs to the bloodstream. Gas exchange occurs in the lungs between the alveoli and capillaries, that are small blood vessels that line the alveolar walls. The rate of diffusion is determined by the thickness of the biological membrane, that serves as a barrier between the outside world and living organisms. 

Exchange Of Gases

Whereas the alveoli are the principal sites of gas exchange, O2and CO2are also exchanged between blood and tissues. At these regions, gas exchange is accomplished through simple diffusion based on a concentration/pressure gradient. The rate of diffusion is determined by the thickness of the membranes engaged in gas exchange as well as the solubility of the gases.

The pressure exerted by a single gas in a mixture of gases is referred as partial pressure. It’s denoted as pO2 (oxygen) and pCO2 (carbon dioxide). 

Diffusion Membrane

There are three main levels to the diffusion membrane:

• The alveolar squamous epithelium is a thin squamous epithelium.
• Alveolar capillaries are contained inside the endothelium.
• Between the epithelium and the endothelium, there is a substance called the basement substance.
• The diffusion membrane has a total thickness of less than a millimetre. All of these components in our bodies enhance O2 diffusion from alveoli to tissues and CO2diffusion from tissues to alveoli.

Gas exchange

Gas exchange is a physical process in which gases travel across a surface in a passive manner. This surface can be found in a water body’s air/water interface, a gas bubble’s surface in a liquid, a gas-permeable membrane, or a biological membrane separating an organism from its extracellular environment. Because most living things constantly consume and create gases as a result of cellular and metabolic activities, an effective system for gas exchange between the inside of the cell(s) and the external environment is required. Bacteria and protozoa, for example, are small, unicellular organisms with a high surface-area-to-volume ratio. 

The gas exchange membrane is usually the cell membrane in these organisms. Some microscopic multicellular organisms, including flatworms, can also exchange enough gas through the skin or cuticle which covers their bodies. In most bigger species with low surface-area-to-volume ratios, specialised structures with complicated surfaces, like gills, pulmonary alveoli, and spongy mesophyll, offer the enormous area required for successful gas exchange.

Internalization of these convoluted surfaces into the organism’s body is possible. This is characteristic of the alveoli, which make up the inner surface of the human lung, the spongy mesophyll found inside some plant leaves, and the gills found in the mantle cavity of those molluscs with them.

Respiratory gases, such as oxygen and carbon dioxide, are exchanged between the air and the blood through the lungs’ respiratory exchange surfaces. The human lung’s anatomy provides an enormous interior surface for gas exchange between the alveoli and blood in the pulmonary capillaries. In an adult human, the alveolar surface covers roughly 20 to 50 square metres.

The thin nature of the membrane between the alveoli and capillaries, around 0.5 m, or 1/100of the diameter of a human hair, enhances gas exchange across the membranous barrier between the alveoli and capillaries.

Transport Of Gases

O2 and CO2are transported by the bloodstream. RBCs in the blood carry 97 % of the oxygen, whereas plasma transports the remaining 3 %  in dissolved form. Whenever it comes to CO2, RBCs transport about 20 to 25 %, plasma carries 7 % in a dissolved condition, and the rest 70 %  is transported as bicarbonate.

Transport Of Oxygen

Oxyhaemoglobin is formed when oxygen binds reversibly to haemoglobin in the blood. Haemoglobin is an iron-containing crimson pigment found in RBCs. The fundamental determinant of this binding is the partial pressure of O2. The partial pressure of CO2, the temperature, and the concentration of hydrogen ions are all parameters which can affect this binding.

Transport Of Carbon Dioxide

Aside from oxygen, haemoglobin also transports about 20 to 25 % CO2 as carbamino-haemoglobin. Although the partial pressure of CO2 is the most important element influencing this binding, pO2  is also important. Whenever the pCO2 is high and the pO2 is low, more CO2 binding occurs in the tissues. CO2 dissociates from carbamino-haemoglobin produced in the tissues and is released in the alveoli if pCO2is low and pO2 is high in the alveoli.

What is the swapping of gases called?

The ‘swapping’ of gases – taking oxygen into the blood and expelling carbon dioxide from the blood – is referred as gas exchange. Diffusion is the process by which oxygen leaves the alveoli and enters the bloodstream.

Conclusion

This surface can be found in a water body’s air/water interface, a gas bubble’s surface in a liquid, a gas-permeable membrane, or a biological membrane separating an organism from its extracellular environment.

Although gas exchange takes place mostly in the alveoli, O2 and CO2 are also transferred between blood and tissues. Gas exchange occurs in these areas by simple diffusion depending on a concentration/pressure gradient.