Spotlight on Internal Respiration

Published on 26th March 2021


Anyone studying for a qualification in Anatomy and Physiology, or indeed even researching the possibility of doing such a course, may be surprised at the variety of topics covered. As will become clear to budding therapists, it is not enough to learn the basics of anatomy. You need to know the ‘how’ and the ‘why’ too. The physiology.

Learning about the most microscopic of processes brings a fascinating depth to your knowledge of the human body and fortunately, there are many to choose from.

One such microscopic process covered on the Level 3 ITEC Anatomy and Physiology e-course is Internal Respiration. This is the continuous process of supplying oxygen and removing carbon dioxide from cells. Even though it is not visible to the human eye, it is critical to every single cell in the body.

Once oxygen has been taken in through the lungs (external respiration), it is transported around the body via a network of blood capillaries. Every single cell is in close contact with a blood capillary. This is its supply pipe.

Diffusion, high to low

As blood flows through the capillary in close proximity to a cell, the concentration of oxygen in the blood is high. On the other hand, the concentration of oxygen within the cell is low as it uses up its supply of oxygen constantly.

This inequality creates movement.

Oxygen moves from a place of high concentration (capillary) to a place of low concentration (cell) in order to gain homeostasis or equilibrium. Diffusion.

Oxygen in

Oxygen from the blood in the capillary diffuses through the capillary wall, through the interstitial fluid and into the cell.

The cell is now supplied with fresh oxygen which it can use as fuel. The use of this oxygen produces carbon dioxide as a waste product.  The concentration of carbon dioxide within the cell is now high. As the concentration of carbon dioxide within the neighbouring blood capillary is low, movement is once again created.

Carbon dioxide out

In a complete reversal of the movement of oxygen, carbon dioxide is diffused out through the cell wall into the blood capillary for removal from the body.

Internal Respiration at cellular level = the diffusion of oxygen in and the diffusion of carbon dioxide out.

A microscopic process, but important.

Learn more about Internal Respiration, and many other microscopic processes, on our Level 3 ITEC Anatomy, Physiology and Pathology online course.


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