The lung is an integral component of the human body's respiratory system responsible for one of the most vital functions - breathing. This complex organ facilitates the exchange of oxygen and carbon dioxide, with the oxygen being essential for the body's cells to live and function properly.

An average adult's lungs are roughly the size of a football and occupy a large portion of the chest cavity. They are predominantly divided into two parts: the right lung, slightly larger and divided into three lobes, and the left lung, divided into two lobes to accommodate the heart.

The lung's primary function is gas exchange, a process often referred to as respiration. When we breathe in, air travels through the mouth or nose, down the windpipe (also known as the trachea), and into two tubes known as bronchi, one each leading to the left and right lung. The bronchi branch out and get smaller, turning into bronchioles, akin to an inverted tree's branches. At the end of these tiny branches are minute air sacs called alveoli which consists of a thin, permeable membrane. It is here in these countless alveoli where the actual gas exchange occurs - oxygen from the air we breathe in passes into the bloodstream, and carbon dioxide, a waste product from the body's cells, is expelled from the bloodstream into the air, which we then breathe out.

Apart from respiration, the lungs play some lesser-known but vital roles. They filter small blood clots, aid in regulating blood pH by adjusting the blood's carbon dioxide levels and they also serve as a physical barrier against infection, with their lining secreting mucus that traps dust and germs.

Despite their robustness, the lungs can be severely affected by lifestyle choices, environmental factors, and genetic conditions, leading to diseases like Chronic Obstructive Pulmonary Disease (COPD), asthma, pulmonary fibrosis, and lung cancer.

Smoking, for instance, is significantly harmful to the lungs, causing upwards of 80% of all COPD deaths. Air pollution and occupational hazards like inhaling chemicals and dust are also notable causes of lung disease.

In conclusion, the lungs, while often overlooked in favor of the heart or brain, are an equally vital organ that serves some of our body's most essential and arduous tasks. By understanding their function and their importance, we can appreciate the need to protect and care for our lungs, ensuring a healthier and more robust life.