Respiratory gas exchange is defined as exchange of two respiratory gases in the body. The exchange occurs between oxygen and carbon dioxide. Upon inhalation, oxygen is released into the bloodstream from the lung. Simultaneously, carbon dioxide is eliminated from the bloodstream.
- Gas exchange takes place between alveoli and capillaries into the lung.
- The alveoli is the primary site for gas exchange.
- However, exchange of O2 and CO2 also happens between blood and tissues.
- Respiratory gas exchange at this site happens through simple diffusion.
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Key terms: Respiratory gas exchange, Exchange of gases, Transport of gases, Oxygen, Carbon dioxide.
Also Read: Breathing and Exchange of Gases MCQs
Exchange of Gases
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Respiratory gas exchange is the process that occurs between oxygen and carbon dioxide during respiration. The two respiratory gases are exchanged after every inhalation and exhalation.
- The primary site to exchange oxygen and carbon dioxide is alveoli.
- The exchange happens between blood and tissue as well.
- During the exchange process, oxygen is released into the bloodstream.
- Carbon dioxide present in the blood is eliminated by the lung.
- This elimination and release of CO2 outside the body is called exhalation.
- Exchange of gases between blood and tissue occurs via simple diffusion.
- The rate of diffusion depends on the solubility of the gases.
- CO2 is 20–25 times more soluble than O2.
- Thus, the amount of CO2 diffusion is significantly more than that of O2.
- Diffusion is also dependent on the thickness of the membrane.
Exchange of gases in human lungs and tissue
When air reaches the alveoli, oxygen diffuses from the air into the capillaries' blood, while carbon dioxide diffuses from the blood into the alveolar lumen. These motions result from variations in partial pressures of these gases.
- A gas's partial pressure is its individual pressure within a gas mixture.
- It depends on the amount and concentration of gas present in the combination.
- Gases consistently diffuse from a higher partial pressure area to a lower one.
Pulmonary Gas Exchange
Transport of Gases
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The transport of respiratory gases occurs through the blood. The red blood cells (RBCs) carry 97% of oxygen and the rest 3% is carried by plasma.
- About 20-25% of carbon dioxide is carried by RBCs.
- 7% of the total CO2 is carried by plasma and almost 70% is transported by bicarbonate.
Transport of O2
At a high partial pressure of oxygen, haemoglobin absorbs almost all of the oxygen that enters the blood. A transient mixture known as oxyhaemoglobin is formed at this pressure.
- Oxyhaemoglobin is used to transport oxygen to the tissue level in this manner.
- Four molecules of oxygen can fit inside one Hb molecule.
- Oxygen is not used in the production of oxyhaemoglobin.
Transport of CO2
The three ways that carbon dioxide is delivered from tissues to lung alveoli are as follows:
In dissolved state
Due to its high solubility, roughly 5-7% of carbon dioxide dissolves in blood plasma and is transported to the lungs as a solution.
As bicarbonate ions
The RBCs receive around 70% of the carbon dioxide. It then interacts with the water to create carbonic acid in the presence of a carbonic anhydride.
- The carbonic acid splits into bicarbonate and hydrogen ions very quickly.
- HbO2 and hydrogen ions react to liberate oxygen and create H.Hb (haemoglobinic acid).
- The leftover bicarbonate ions leave the RBCs.
- In response to that, an equal quantity of chloride ions are taken up.
- It is known as a chloride shift.
- The processes are switched over at the tissue level, giving CO2 to the alveoli.
As carbamino compounds
The amine radicals (-NH2) of the globin (protein) portion of haemoglobin interact with carbon dioxide to create carbamino haemoglobin.
- This makes up around 20 to 23% of the carbon dioxide that enters erythrocytes (HbCO2).
- The partial pressure of carbon dioxide affects this reversible process.
- When carbamino haemoglobin dissociates, CO2 is released at the lung surface.
Things to Remember
- Respiratory gas exchange is an exchange of oxygen and carbon dioxide.
- This exchange takes place during respiration.
- Primary site for the exchange of gases is alveoli in the lung.
- Oxygen is released into the bloodstream that is transported to other tissues.
- Carbon dioxide is eliminated from the bloodstream and exhaled outside the body.
- Transportation of carbon dioxide is achieved through 3 ways.
- The main reason for exchange of respiratory gases is to regulate respiration.
Sample Questions
Ques. What is Respiration? (2 marks)
Ans. Respiration is the catabolic process, which involves exchange of environmental oxygen and body's carbon dioxide. It is the oxidation of food for the production of energy.
Ques. Define the types of respiration? (3 marks)
Ans. Respiration can be divided into two categories based on the availability or lack of oxygen and the degree of fuel substance breakdown.
- Anaerobic respiration: Without oxygen, anaerobic respiration takes place. Anaerobic respiration resembles the fermentation of sugar. As well as bacteria, yeast cells, muscle cells, and parasites like Ascaris and tapeworms, it can also be found there. Anaerobic respiration is carried out by mammalian erythrocytes without mitochondria.
- Aerobic respiration: When there is oxygen present, aerobic respiration takes place. It entails total burning of glucose and other fuels to produce water and CO2. Aerobic respiration is a mechanism that produces a lot of energy. From protozoa to mammals, it is present in the majority of organisms.
Ques. Write the names of the respiratory organs present in human beings? (1 mark)
Ans. The main respiratory organ of human beings are called lungs. Besides accessory organs include nose, nasal cavity, pharynx, trachea, bronchi, bronchioles, alveoli, intercostal muscles, ribs and diaphragm.
Ques. How does the skin of earthworms help in respiration? (1 mark)
Ans. The skin of earthworm is highly vascular. The skin is moist. These two features help in the rapid exchange of gases through the skin. In this way skin acts as respiratory organs in earthworms.
Ques. How does haemoglobin help in the transport of oxygen from lung to tissue? (2 marks)
Ans. Haemoglobin, a pigment found in red blood cells, is capable of binding four oxygen molecules per molecule. Forming is oxyhaemoglobin. The oxygen molecules are transported to certain body tissue cells where they are released. Oxygen binding is a reversible process.
Ques. Define regulations of respiration? (5 marks)
Ans. The neurological system plays a major role in controlling breathing.
Respiratory centers in the brain's medulla oblongata and pons varolii control the rhythm of respiratory activity. There have been identified as three significant groupings of respiratory centers.
- Dorsal respiratory center
It is located in the dorsal medulla and communicates with the diaphragm to regulate breathing.
- Ventral respiratory center
It can be found in the ventral part of the medulla oblongata. While it is inactive during regular breathing, it becomes active during enhanced breathing and regulates the augmented respiratory motions.
- Pneumotaxic center
Located dorsally in the upper pons is the pneumotaxic center. It sends a signal to the inhalation region.
Ques. How does carbon dioxide transport from tissues to lung alveoli? (5 marks)
Ans. The three ways that carbon dioxide is delivered from tissues to lung alveoli are as follows: (i) in a dissolved state (ii) as bicarbonate ions (iii) as carbamino compounds.
(i) In dissolved state
Roughly 5-7% of carbon dioxide dissolves in blood plasma which is further transported to the lungs.
(ii) As bicarbonate ions
The RBCs carry around 70% of the carbon dioxide, which then interacts with the water to create carbonic acid in the presence of a carbonic anhydride. The carbonic acid splits into bicarbonate and hydrogen ions. These ions react to liberate oxygen and create H.Hb (haemoglobinic acid). The leftover bicarbonate ions leave the RBCs, and in response, an equal quantity of chloride ions are taken up.
(iii) As carbamino compounds
The amine radicals of the globin portion of haemoglobin interact with carbon dioxide and create carbamino haemoglobin, which makes up around 20 to 23% of the carbon dioxide that enters erythrocytes. The partial pressure of carbon dioxide affects this reversible process. CO2 is released at the lung surface when carbamino haemoglobin dissociates.
Ques. What is the significance of respiratory gas exchange? (1 mark)
Ans. Respiratory gases are exchanged and transported to maintain the regulation of respiration in the human body.
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