Difference Between Internal and External Respiration

Main Difference – Internal Respiration vs External Respiration

During the gas exchange in animals, oxygen and carbon dioxide diffuse in and out of the blood in lungs and metabolizing tissues. Oxygen is used in the cellular respiration, produces metabolic energy in order to carry out cellular functions. During cellular respiration, carbon dioxide is produced as a waste. The gas exchange occurs at the respiratory membrane in lungs and in metabolizing tissues like skeletal muscles. The partial pressure gradient of each gas determines the direction and the rate of diffusion across the respiratory membrane. The main difference between internal respiration and external respiration is that internal respiration refers to the gas exchange across the respiratory membrane in the metabolizing tissues whereas external respiration refers to the gas exchange across the respiratory membrane of lungs.

This article examines,

1. What is Internal Respiration
      – Definition, Process, Function
2. What is External Respiration
      – Definition, Process, Function
3. What is the difference between Internal and External Respiration

What is Internal Respiration

The gas exchange between blood and the metabolizing tissue is referred to as internal respiration. Tissues like skeletal muscles require oxygen in order to carry out cellular respiration by which the cells produce energy in the form of ATP by burning food, mainly glucose. ATP is used to drive cellular functions. Cellular respiration occurs in the mitochondria. Carbon dioxide is produced as a waste during cellular respiration. So, metabolizing cells in the tissue have a high demand for oxygen while carbon dioxide is to be removed from the cells. That is, the partial pressure of oxygen is low and that of carbon dioxide is high in the tissue. But in the blood, the partial pressure of oxygen is high and that of carbon dioxide is low. Therefore, oxygen diffuses out of the blood into the tissue while carbon dioxide diffuses out from the tissue into the blood. The partial pressure of oxygen (PO₂) is 100 mmHg and it is 40 mmHg in the tissue cells. The oxygen exchange continues until equilibrium occurs on the either sides of the respiratory membrane in the tissue. Hence, the final PO₂ in the blood becomes 40 mmHg. The gas exchange occurs in blood capillaries of the tissue. This oxygen-depleted blood is carried out to the lungs through the heart by veins. Internal respiration at metabolizing tissue is shown in figure 1.

Figure 1: Internal respiration

What is External Respiration

The gas exchange in the lungs is referred to as external respiration. One side of the respiratory membrane, alveolar air is situated outside of the body. Oxygen-depleted blood, which is transported from metabolizing tissues, flows through the pulmonary capillaries where oxygen diffuses from the alveolar air into the blood. Carbon dioxide diffuses out of the blood into the alveolar air. The partial pressure of oxygen (PO₂) in the blood increases up to 100 mmHg. The partial pressure of carbon dioxide (PCO₂) in the blood is 45 mmHg while that of the alveolar air is 40 mmHg. Therefore, the exchange of carbon dioxide occurs from the blood into the alveolar air. Both exchanges of oxygen and carbon dioxide occur until the equilibrium of each gas is established. The final PO₂ is 100 mmHg and PCO₂ is 40 mmHg in the blood which leaves the lungs. Thus, the blood which leaves the lungs is called oxygen-rich blood. This oxygen-rich blood flows to the metabolizing tissues, responding to their high demands of oxygen. Both oxygen and carbon dioxide are transported through the blood by binding with hemoglobin, which is found in red blood cells. Some of the carbon dioxide is transported by dissolving in the plasma as well. The external respiration at lungs is shown in figure 2.

Figure 2: External respiration

Difference Between Internal and External Respiration

Definition

Internal Respiration: Internal respiration refers to the gas exchange across the respiratory membrane in the metabolizing tissues.

External Respiration: External respiration refers to the gas exchange across the respiratory membrane of lungs.

Oxygen Exchanging Direction

Internal Respiration: Oxygen diffuses out from the blood into tissue during internal respiration.

External Respiration: Oxygen diffuses from alveolar air into the blood during external respiration.

PO₂

Internal Respiration: The PO₂ in the blood is reduced from 100 mmHg to 40 mmHg during internal respiration.

External Respiration: The PO₂ in the blood is increased from 40 mmHg to 100 mmHg during external respiration.

Carbon Dioxide Exchanging Direction

Internal Respiration: Carbon dioxide diffuses into the blood from the tissue during internal respiration.

External Respiration: Carbon dioxide diffuses out from the blood into the alveolar air during external respiration.

PCO₂

Internal Respiration: The PCO₂ in the blood is increased from 40 mmHg to 45 mmHg during internal respiration.

External Respiration: The PCO₂ in the blood is reduced from 45 mmHg to 40 mmHg during external respiration.

Correlation with External Environment

Internal Respiration: Internal respiration only correlates with the internal environment.

External Respiration: External respiration correlates with both internal and external environment.

Conclusion

Internal and external respiration are two processes where the exchange of oxygen and carbon dioxide occur. Internal respiration occurs in the respiratory membrane of metabolizing tissue. Inside the mitochondria, cellular respiration, which produces energy in the form of ATP, occurs. Cellular respiration requires oxygen and carbon dioxide is produced as a waste. Thus, in order to maintain cellular processes in a balanced condition, continuous flow of oxygen should be maintained by blood. Oxygen is provided by the internal respiration from the blood into tissues. Oxygen-depleted blood is transported into lungs, where external respiration takes place. Oxygen diffuses from the alveolar air into the blood. The main difference between internal respiration and external respiration is in the direction of gas exchange and in the location where each of the processes takes place.

Reference:
1.”External and Internal Respiration in the Lungs: Definition & Process.” Study.com. N.p., n.d. Web. 28 May 2017. <http://study.com/academy/lesson/external-and-internal-respiration-in-the-lungs-definition-process.html>.

Image Courtesy:
1.”2320 Fig 23.20 NEW KGX” By OpenStax College – Anatomy & Physiology, Connexions Web site. Jun 19, 2013. (CC BY 3.0) via Commons Wikimedia
2.”2319 Fig 23.19″ By OpenStax College – Anatomy & Physiology, Connexions Web site. Jun 19, 2013. (CC BY 3.0) via Commons Wikimedia