The lungs are part of the respiratory system, but they also play a role in excretion. Excretion is the process of removing waste products from the body. When the cells in the body use oxygen to produce energy, they release carbon dioxide as a waste gas. The lungs remove this waste gas from the blood and release it into the air when we exhale. This is why the lungs are considered excretory organs.
Path of Air and Function of Each Part
Nasal Cavity
Air enters the body through the nasal cavity. This cavity is lined with tiny hairs (called cilia) and mucus. These work together to filter out dust, dirt, pollen, and germs from the air. The nasal cavity also warms and moistens the air, making it suitable for the lungs. This initial filtering step is important to prevent harmful particles from reaching deeper parts of the respiratory system.
Throat (Pharynx) and Windpipe (Trachea)
After the air passes through the nasal cavity, it moves into the pharynx (throat), and then into the trachea (windpipe). The trachea is a strong, flexible tube supported by rings of cartilage, which keeps it open. The inside of the trachea is also lined with mucus and cilia, which trap and move particles upward toward the throat. This debris is usually swallowed or coughed out. The presence of mucus and cilia helps to further clean the air before it reaches the lungs.
Breathing Tubes (Bronchi and Bronchioles)
The trachea divides into two main bronchi, one for each lung. These bronchi further branch into smaller tubes called bronchioles. These tubes distribute the air to all parts of the lungs. Like the trachea, the bronchi and bronchioles also contain mucus and cilia to continue filtering the air.
Alveoli – The Site of Gas Exchange
At the ends of the bronchioles are millions of tiny air sacs called alveoli. These are very small, balloon-like structures surrounded by thin blood vessels called capillaries. Here, oxygen from the air moves into the blood, and carbon dioxide from the blood moves into the alveoli. This exchange happens through the thin walls of the alveoli. The carbon dioxide is then carried out of the lungs when we exhale.
Role of the Diaphragm
The diaphragm is a large, dome-shaped muscle located below the lungs. It plays a key role in breathing. When we inhale, the diaphragm moves downward, increasing space in the chest and allowing the lungs to expand and fill with air. When we exhale, the diaphragm moves upward, helping to push air out of the lungs. This muscular movement makes breathing efficient and automatic.
Filtering of Dust Particles and Phlegm Production
The respiratory system has several layers of protection to keep dust and harmful particles from reaching the lungs. The nasal hairs, mucus, and cilia work together to trap and remove particles. When these particles mix with mucus, the body produces a sticky substance called phlegm. This phlegm traps the particles and is then expelled through coughing or swallowing. This is a natural cleaning process that protects the lungs.
Composition of the Air We Breathe
The air we breathe contains a mixture of gases:
Approximately 78% nitrogen
About 21% oxygen
Around 0.04% carbon dioxide
Small amounts of water vapor and other gases
When we inhale, only the oxygen is used by the body. The remaining gases, including nitrogen and carbon dioxide, are exhaled without change.
Importance of Nitrogen
Even though nitrogen is the most abundant gas in the air, it is not used directly in the breathing process. However, nitrogen has important roles:
It helps maintain pressure balance in the lungs.
It keeps the oxygen concentration stable, which prevents oxygen from becoming too reactive or damaging to tissues.
It is also used by the body to build proteins and DNA, but this nitrogen is obtained from food, not from the air.
Thus, while nitrogen is not involved in respiration, it is still essential for overall body function.
Conclusion
The lungs are vital excretory organs that remove carbon dioxide from the body. This is made possible by the careful coordination of several structures: the nasal cavity, pharynx, trachea, bronchi, bronchioles, alveoli, and the diaphragm. The system also includes built-in cleaning mechanisms like cilia, mucus, and phlegm production to protect the lungs. The air we breathe is mostly nitrogen, which plays a supporting role in maintaining the proper balance in our respiratory system, even though it is not used directly in breathing.
