Question

Understand the basic organization of the respiratory system and how that structure leads to it’s function, both in terms of the mechanics of breathing (getting the air to the alveoli) and in terms of gas exchange at the alveolar- pulmonary capillary interface.

Answer 1

The respiratory system is divided into two parts:
Upper and lower respiratory tract.
Upper respiratory tract includes the nose, mouth, and the beginning of the trachea (the section that takes air in and lets it out).
Lower respiratory tract includes the trachea, the bronchi, broncheoli and the lungs (the act of breathing takes place in this part of the system).

The organs of the lower respiratory tract are located in the chest cavity. They are delineated and protected by the ribcage, the chest bone (sternum), and the muscles between the ribs and the diaphragm.
The trachea – the tube connecting the throat to the bronchi.

The bronchi – the trachea divides into two bronchi (tubes). One leads to the left lung, the other to the right lung. Inside the lungs each of the bronchi divides into smaller bronchi.

The broncheoli - the bronchi branches off into smaller tubes called broncheoli which end in the pulmonary alveolus.

Pulmonary alveoli – tiny sacs (air sacs) delineated by a single-layer membrane with blood capillaries at the other end.

The exchange of gases takes place through the membrane of the pulmonary alveolus, which always contains air: oxygen (O2) is absorbed from the air into the blood capillaries and the action of the heart circulates it through all the tissues in the body. At the same time, carbon dioxide (CO2) is transmitted from the blood capillaries into the alveoli and then expelled through the bronchi and the upper respiratory tract.

The inner surface of the lungs where the exchange of gases takes place is very large, due to the structure of the air sacs of the alveoli.

Mechanism of breathing includes inspiration and expiration.

In the process of inspiration, there would be a contraction of muscles attached to the ribs on the outer side which pulls out the ribs and results in the expansion of the chest cavity .The expansion of the chest cavity produces a partial vacuum which sucks air into the lungs and fills the expanded alveoli.

The expiration process is considered once after the gaseous exchange occurs in the lungs and the air is expelled out. This expulsion of air is called expiration. Here muscles attached to the ribs contract, the muscles of the diaphragm and the abdomen relax which leads to a decrease in the volume of the chest cavity and increases the pressure of the lungs, causing the air in the lungs to be pushed out through the nose.