Transport of Gases

You all must be knowing that oxygen is necessary for the survival of human beings. However, our body has a pre-defined mechanism for transporting oxygen to body parts that require it. Transport of gases in human beings is done via a well-developed system. Many small unicellular organisms do not need a transportation system as they directly diffuse gases via their cell membrane. The diffusion of gases in small organisms is caused due to the pressure difference inside and outside the cell. However, human beings have a complex yet functional system for the transport of gases. Read on to know more about the transport of gases in human beings.

Transport of oxygen

After the inspiration process, oxygen present in alveoli has to be transported to different tissues in the body. After inspiration, the air pressure of oxygen in alveoli is around 100 mmHg. The air pressure in the human blood is around 45 mmHg. We all know that gases travel to a low-pressure area from a high-pressure area. Due to the same reason, oxygen moves into the blood from the alveoli In our blood, haemoglobin is present in our red blood cells which is the main respiratory pigment. Haemoglobin has the power to attract the oxygen molecules coming from the alveoli. Each haemoglobin consists of four subunits and each one of them binds with an oxygen molecule. For one unit of haemoglobin, four oxygen molecules are required. When a unit of haemoglobin binds with four oxygen molecules, oxyhaemoglobin is formed. Due to the haemoglobin present in our blood, transport of gases becomes possible. Approximately 97% of oxygen in our body is transported through oxyhaemoglobin. Around 20 ml of oxygen is transported for every 100 ml of blood in our bodies. How the remaining 3% of oxygen is transported in our body? Well, the remaining 3% oxygen is transported to plasma in the form of dissolved gas. In such a manner, all the oxygen coming into our bodies after inspiration is transported to different parts of the body.

What is the oxygen dissociation curve?

After the oxygen starts combining with haemoglobin, an S-shaped curve is observed. The oxygen dissociation curve tells us about the amount of saturated haemoglobin in the body. Saturated haemoglobin is formed when oxygen molecules combine with haemoglobin. When the haemoglobin saturation in our body increases, the oxygen dissociation curve shifts to the left. When the haemoglobin saturation in our body decreases, the oxygen dissociation curve shifts to the right. Dissociation of oxygen from haemoglobin is an important step in the transport of gases in human beings. The criterion is our tissues which governs the dissociation of oxygen from haemoglobin are as follows:

• The pH (number of H⁺ ions) in our tissues increases due to an increase in the amount of carbon dioxide. Due to an decrease in pH of our tissues, the oxygen dissociation process is accelerated. This process is termed Bohr’s effect and the dissociation curve shifts to the right

• Besides the main respiratory process, cellular respiration also takes place in our body. Due to cellular respiration, tissues in our body experience a paucity of oxygen. Since there is a shortage of oxygen in tissues, the partial pressure decreases. The decrease in partial pressure of oxygen in tissues also prompts the dissociation of oxyhaemoglobin

• During the cellular respiration process, thermal heat is released from our tissues. Due to the increase in temperature, saturated haemoglobin dissociates and the oxygen dissociation curve moves to the right

• After cellular respiration, 2,3-BPG is formed as a by-product. When the concentration of 2,3-BPG (2,3-bisphosphoglycerate) increases after cellular respiration, it binds itself with the haemoglobin. Since the haemoglobin binds with 2,3-BPG, oxygen is dissociated from haemoglobin

Transport of carbon dioxide

The transport of gases classification in human beings also includes the transportation of carbon dioxide outside the body. Carbon dioxide is a by-product of cellular respiration and is discharged out of the body. Around 7% of carbon dioxide in our bodies is transported to plasma in dissolved form. It happens as carbon dioxide has a greater solubility than oxygen. When carbon dioxide enters our bloodstream, it meets with water. The presence of carbonic anhydrase in our blood binds the water and carbon dioxide to form carbonic acid. In a quick span, carbonic acid breaks down into bicarbonate ions and hydrogen ions. Through an antiport, chloride ions enter the bloodstream and bicarbonate ions enter the plasma. This process is termed chloride shift and approximately 70% of carbon dioxide is transported by this phenomenon. The remaining 23% of carbon dioxide in our body converts into carbaminohemoglobin. When the amino radical of haemoglobin combines with carbon dioxide, carbaminohemoglobin is formed. This phenomenon is known as the Haldane effect and supports the transport of carbon dioxide. When you state the transport of gases definition, make sure to discuss the transportation of oxygen and carbon dioxide also.