What is the Difference Between Perfusion and Diffusion

The main difference between perfusion and diffusion is that perfusion is the delivery of blood to the pulmonary capillaries, whereas diffusion is the movement of gases from the alveoli to plasma and red blood cells. Furthermore, ventilation and perfusion occur simultaneously, facilitating the diffusion.

Perfusion and diffusion are two mechanisms which occur during the gas exchange through the lungs. Here, the gas exchange of animals occurs through the respiratory membrane of the alveoli of the lungs.

Key Areas Covered

1. What is Perfusion
     – Definition, Process, Importance
2. What is Diffusion
     – Definition, Process, Importance
3. What are the Similarities Between Perfusion and Diffusion
     – Outline of Common Features
4. What is the Difference Between Perfusion and Diffusion
     – Comparison of Key Differences

Key Terms

Alveoli, Carbon Dioxide, Diffusion, Gas Exchange, Oxygen, Perfusion, Ventilation

What is Perfusion

Perfusion is the process which delivers blood to the pulmonary capillaries. Therefore, the main function of perfusion is to supply blood efficiently as required by the gas exchange. Generally, the two factors responsible for the efficient gas exchange are the air volumes inside the alveoli and the volumes of blood inside the pulmonary capillaries. Here, ventilation is the process responsible for the movement of air into the space of alveoli.

Figure 1: Alveoli

Furthermore, the volume of air that enters the alveolus depends on the diameter of airways. Here, the increased partial pressure of carbon dioxide inside alveoli causes the dilation of bronchioles. On the other hand, the volume of blood that enters the blood capillaries depends on the diameter of the blood vessels. Also, a higher partial pressure of oxygen inside alveoli causes the dilation of pulmonary arteries, allowing the entrance of relevant amounts of blood volumes required for the efficient exchange of respiratory gases.

What is Diffusion

Diffusion is the movement of respiratory gases through the respiratory membrane of alveoli. Here, oxygen, which is the gas required for cellular respiration, enters into the blood from the air inside the alveoli. On the contrary, carbon dioxide, which is a metabolic waste, moves the air inside the alveoli from the blood. However, diffusion is a passive process, which allows the movement of different molecules through a concentration gradient.  

Figure 2: Diffusion of Respiratory Gases

The two main types of diffusion are the primary diffusion and secondary diffusion. Simple diffusion, facilitated diffusion, osmosis, and filtration are the four main types of passive diffusion. Moreover, secondary diffusion is the type of diffusion which uses energy for the movement of molecules. Primary active diffusion and secondary active diffusion are the two types of active diffusion.

Similarities Between Perfusion and Diffusion

• Perfusion and diffusion are two mechanisms which occur in lungs during gas exchange.
• Both occur in the alveoli in lungs.

Difference Between Perfusion and Diffusion

Definition

Perfusion refers to the passage of fluid through the circulatory system or lymphatic system to an organ or a tissue, usually referring to the delivery of blood to a capillary bed in tissue, while diffusion refers to the physical process of the net movement of molecules from a high concentration region to a lower concentration region. Thus, this is the main difference between perfusion and diffusion.

During Gas Exchange

Moreover, perfusion is the movement of blood to the pulmonary capillaries, while diffusion is the movement of respiratory gases through the respiratory membrane of alveoli.

Importance

Another difference between perfusion and diffusion is that perfusion helps in the efficient supply of blood to the alveoli needed by the gas exchange, while diffusion allows oxygen to enter into the blood, and thus, removing carbon dioxide from the blood.

Conclusion

Perfusion is the delivery of blood into the capillary bed. During the gas exchange, perfusion refers to the delivery of blood into the pulmonary capillaries. On the other hand, diffusion is the exchange of the respiratory gases through the respiratory membrane of alveoli. However, diffusion also refers to the movement of molecules through a concentration gradient. Therefore, the main difference between perfusion and diffusion is the type of process and its importance.

References:

1. 149 22.4 Gas Exchange. BCcampus, 6 Mar. 2013, Available Here

Image Courtesy:

1. “Alveolus diagram” By LadyofHats – self-made(extracted from Image:Respiratory system complete.svg) (duplicate of Image:Respiratory system complete en.svg) (Public Domain) via Commons Wikimedia  
2. “Alveoli” By helix84 – en:Image:Alveoli.jpg (CC BY 2.5) via Commons Wikimedia