question

Investigate and explain how lungs inflate (what muscles are involved in the process of breathing?). Explain Boyle’s Law. Think about how air from the atmosphere is able to enter the lungs (describe the path it takes to the region of gas exchange) and ultimately describe the process of gas exchange.

answer

 

1. Introduction

The process of lung inflation, or ventilation, creates a flow of air into the alveoli of the lungs. Gas exchange mainly occurs in the alveoli and this is the site where oxygen and carbon dioxide are exchanged. This gas exchange is commonly described as occurring between the alveolar air and the blood in the capillaries that surround the walls of the alveoli. It is useful to understand the basic mechanisms of lung inflation and the maintenance of that inflation. There are also a number of basic physiological points to remember. First, when the lungs are inflated and the intra-alveolar pressure becomes greater than atmospheric pressure, air will flow into the alveoli. This is known as inspiration or inhaling. Muscles in the respiratory system contract to cause lung inflation. The muscles that run between the ribs, the intercostal muscles, are used in forceful breathing in that they can lift the ribs thereby aiding the muscle that forms the floor of the chest cavity. When the muscles between the ribs contract, the ribs are pulled upwards towards the neck. This has the effect of raising the rib cage and so increasing the volume of the chest from front to back. When the diaphragm muscle contracts, it becomes flattened and so increases the vertical dimension of the chest. When either the diaphragm or the intercostal muscles of the respiratory system contract, lung inflation will occur. Second, for gas exchange to occur, there must be a diffusion of gases from a region of high partial pressure to a region of lower partial pressure. In the lungs, alveolar air has a higher partial pressure of oxygen than the blood in the capillaries. Conversely, the blood in the capillaries has a higher partial pressure of carbon dioxide than the alveolar air. When the blood reaches tissues, the partial pressure of oxygen in the systemic arteriolar blood is lower than that in the tissues and so oxygen will diffuse into the tissues. The partial pressure of carbon dioxide in the systemic arteriolar blood is higher than that in tissues and so carbon dioxide will tend to diffuse from the tissues into the blood. When tissues have used up the oxygen and have a higher partial pressure of carbon dioxide, the blood returns its gases back to the heart to be pumped to the lungs for re-oxygenation and carbon dioxide removal.

1.1 Overview of lung inflation and gas exchange

When we start to inhale, the diaphragm contracts and moves downwards, and the external intercostal muscles, found between the ribs, move the ribs upwards and outwards. This then increases the volume of the thorax and the lungs. Boyle’s Law explains the relationship between the pressure (P) and volume (V) of a gas. At a constant temperature, the pressure of a given mass of gas is inversely proportional to its volume. As the lungs expand in inspiration, the pressure inside the lungs is decreased, and air flows into the lungs from the higher pressure outside the body. Conversely, as the lungs deflate in expiration, the pressure inside the lungs is increased, and air flows out of the lungs to the lower pressure outside the body. So this process is called inspiration and expiration. When we inhale, the oxygen passes from the alveoli into the blood in the capillaries, then the blood transports the oxygen to the cells and tissues of the body. At the same time, carbon dioxide passes from the blood into the alveoli, through diffusion, ready to be breathed out. This is the process of gas exchange. Aerobic respiration is the process of producing chemical energy in the form of ATP. In order to do this, oxygen, the acceptor of electrons in the final step of the electron transport chain is needed. Carbon dioxide is a waste product of respiration. So the gas exchange allows the removal of the carbon dioxide which has been produced in the reactions and the uptake of oxygen which is needed to enable respiration to occur.

2. Muscles Involved in Breathing

2.1 Diaphragm

2.2 Intercostal muscles

3. Boyle’s Law

3.1 Explanation of Boyle’s Law

4. Path of Air to the Lungs

4.1 Nasal cavity

4.2 Pharynx

4.3 Larynx

4.4 Trachea

4.5 Bronchi

4.6 Bronchioles

4.7 Alveoli

5. Gas Exchange Process

5.1 Diffusion of oxygen and carbon dioxide

5.2 Alveolar-capillary membrane

5.3 Oxygen transport in the blood

5.4 Carbon dioxide transport in the blood

6. Conclusion

How Lungs Inflate and Gas Exchange Process

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