What is the Mechanism of Breathing?

In this article we're going to look at the mechanism of breathing.  Before we start it is very important to understand the concept of gases and pressure .The rule to know is that gases travel from an area of higher pressure to an area of low pressure. 

So it's similar like diffusion gas is moved from an area of high pressure to an area of low pressure. Anyways what is the mechanism behind breathing.

Pathway:

Well here I'm drawing a guy with his respiratory tract, the nose ,the mouth, the larynx, the trachea, the bronchi and the lungs . Here are the lungs surrounding the lungs we have visceral pleura which is a type of serous membrane. Then we have another pleura around it called the parietal pleura . The parietal and visceral prolog pleura are actually part of the same serous membrane ,it just folds on itself .

Pleural Cavity:

But we don't have to really understand that for this article in between the visceral and parietal pleura we have what's called a pleural cavity and it's important to know just the names of these three we're dealing with the lungs .

Intercoastal Muscle:

Now these things I'm drawing around the right lung,  here partially are the ribs connecting in between the ribs  we have muscles known as intercostal muscles and we have three intercostal muscles. These intercostal muscles are muscles used for respiration. 

We also have another important muscle used in respiration the one you probably all know about called the diaphragm , so the two important muscles for respiration of the diaphragm and the intercostal muscles.

Pressures

Now that we know the muscles , let's learn about the pressures. Now outside our body there is atmosphere pressure which we measure to be 760 millimeters of mercury in our lungs there is pressure that we call intra pulmonary pressure which complements the atmospheric pressure . 

So it's balanced at 760 millimeters mercury we also have this other pressure called the intrapleural pressure which is the pressure in the pleural cavity.

Now in this article we will focus only on the atmospheric pressure and the intra pulmonary pressure which will try to balance out and remember the rule that gasses air travels from an area of higher pressure to an area of lower pressure .

So the air the gas here, for example outside will only travel into the lungs when the intra pulmonary pressure drops.

How does the intra pulmonary pressure in our lungs decrease?

So how does the intra pulmonary pressure in our lungs decrease drops. Let's have a look so again just quickly here are the ribs surrounding the lungs and here are the intercostal muscles that run between the ribs then you have the diaphragm here the intercostal muscles and the diaphragms are the two important muscles.

Normal Respiration:

In normal respiration then you have the two important pressures the atmospheric pressure which is 760 and the intra pulmonary pressure which in this case is also 760 so the atmospheric pressure and the intra pulmonary pressure are balanced there is a difference of zero millimeters mercury in respect with the atmospheric pressure.

Intra pulmonary Volume and Pressure:

One more thing to know is the intrapulmonary volume which is basically the volume within the lungs. Now if the intrapulmonary volume changes this would mean that the intra pulmonary pressure will change as well . Right because there is a relationship between pressure and volume and this is also important to understand. 

Now before we continue the ribs I have drawn here are a bit misleading because most of the ribs actually wrap around the lungs correct .

Diagram from a superior view:

So if we were to look at this diagram from a superior view it looks it can look something like this, so here is the back the vertebrae and then the ribs which actually circulate around the whole lungs and connects to a bone in the center known as a sternum with College.

And then in between the ribs running in between the ribs we have the intercostal muscles and of course in the center which I have not drawn we have the lungs. 

So let's look at inspiration. The mechanism of inspiration so here again we have the lungs and the pleura and then we have the diaphragm below the lungs what happens it inspiration is that the volume within the lungs will actually increase .

So here this is due to the constriction of the two important muscles the intercostal muscles and the diaphragm during inspiration the diaphragm contracts and moves down ,this will allow the intrapulmonary volume to increase .

Because the intrapulmonary volume increases the intra pulmonary pressure will decrease to about 759 millimeters mercury so in respect to the atmospheric pressure there is a difference of negative one millimeters mercury .

Rule:

The intra pulmonary pressure is one below the atmospheric pressure and because we know the rule of gases the air the gas oxygen will flow into the lungs down it's pressure gradient from an area  whrere there is of high pressure to an area of  a lower pressure .

Mechanism of Exhalation

And so after inspiration we have automatically exploration when we breathe out air what happens here is that the intercostal muscles and the diaphragm muscle will relax the diaphragm will move back up to its original place.

And this will cause the intra pulmonary volume to decrease again a decrease in intrapulmonary volume will mean that the intra pulmonary pressure will increase and the intra pulmonary pressure will increase to 761 millimeters of mercury one above the atmospheric pressure.

Cycling:

And so  knowing the rule of  gases will move out from the lungs into the air outside down it's pressure gradient hope that makes sense then from expiration we have inspiration again and the cycle continues of course .

We have some voluntary control over our breathing and we can hold our breath but this is this only lasts a short time before our brain overrides our voluntary control .Now that we get the gist of what's happening in inspiration exploration .