Organs for Respiration
Mechanism of breathing:
The organs involved in the mechanism of breathing are nostrils, windpipe, lungs, ribs and diaphragm (Figure 7.3.2). Humans inhale the atmospheric air rich in oxygen through our nostrils. Inside our nostrils, we contain small hairs that filter the air from other dust particles. The air moves up the nasal cavity, passes along the windpipe and reaches the lungs present in the chest cavity. Our chest cavity consists of lungs enclosed by ribs. The diaphragm is a sheet of muscle which forms the floor of the chest cavity separating lungs from the stomach in the abdominal cavity.
As we inhale air through the nostrils, the ribs move up and outwards of the chest cavity and the diaphragm moves downward creating a space in the chest cavity. The air inhaled rushes and reaches the lungs, thus filling the lungs with pure oxygen. As we exhale and force out the air through our nostrils the diaphragm and ribs relax as the diaphragm moves up and ribs move down. This result in decreasing the space created previously in the chest cavity and contraction of lungs. This increases the air pressure inside the lungs resulting in the flow of the air from the lungs to different organs of the body.
Figure 7.3.2 Mechanism of breathing:
Path of the air inside the lungs:
The air inhaled through the nasal cavity is passed on to the windpipe and then to pharynx, larynx, and trachea which branches into the left and right bronchi of the lungs. From the bronchi, the air enters either into both left and right lungs. The bronchi are divided into numerous tiny tube-like structures called bronchioles ending up in air sacs called the alveoli. The alveoli consist of blood vessels and play an important role in the exchange of gasses. The oxygen-rich air travels to alveoli, from where it is absorbed by the blood vessels and transported to different organs of the body. At the same time, the blood vessel releases carbon dioxide and water collected from different parts of the body into the alveoli. This carbon dioxide rich air is then expelled through the nostrils bypassing the respiratory tract of the lungs.
The percentage of oxygen and carbon dioxide in inhaled and exhaled air:
All organisms inhale about 21% oxygen and 0.04% carbon dioxide from the atmospheric air. As this air passes through the lungs and is expelled out again through nostrils the percentage of oxygen decreases proportionately to the percentage of carbon dioxide increased. Therefore, the percentage of oxygen in exhaled air is about 16.4% and that of carbon dioxide is 4.4%.