The Lungs: Our Body's Air Pollution Filter

Air pollution is a mix of tiny solid and liquid particles in the air we breathe. These particles can be as small as one-tenth the diameter of a strand of hair, and many are invisible to the naked eye. While our body has natural defenses like coughing and sneezing to expel coarse particles, smaller fine and ultrafine particles can enter our bodies and cause serious health issues. The human nose acts as the first line of defense, filtering out some pollutants with the help of mucus and cilia. However, the nose doesn't filter out all pollutants, and the smallest particles can pass through the lungs into the bloodstream, affecting vital organs.

The nose filters out some air pollutants

The nose is an important organ in the respiratory system, and it serves as the first line of defence against air pollutants. While it doesn't filter out all pollutants, it does effectively trap large pollutants and allergens. The nose has narrow air passages, mucosal folds, and a mucous layer covering ciliated epithelial cells, which work together to trap and filter out particles.

The shape of the nose causes air to change direction rapidly as it passes through, slowing down as it moves from the nostril to the nasal cavity. This sudden change in airflow results in a deposition of particulate matter onto the sticky mucus surface inside the nose. The mucus then traps these particles, acting as a flytrap, and the tiny hairs or cilia, sweep the mucus away, pushing it towards the stomach where it is neutralised.

The nose is particularly effective at filtering out coarse particles, but it struggles with smaller fine and ultrafine particles. These smaller particles, such as cigarette smoke, smoke from forest fires, and viruses, can pass through the nose and enter the lungs. While the nose provides an important protective mechanism, it is not sufficient to protect against all harmful particles in the air.

To enhance the filtering process and protect against fine particles, individuals can take additional measures such as wearing FFP2 masks or using air purifiers with HEPA filters. Staying well-hydrated is also beneficial, as it helps to keep the mucus thin and fluid, aiding in the neutralisation of trapped pollutants.

Overall, the nose plays a crucial role in filtering out some air pollutants, but it is not a perfect defence system. Understanding the limitations of the nose's filtering capabilities is essential to taking the necessary steps to protect ourselves from harmful air pollutants.

Fine particles can enter the body through the respiratory system

The human respiratory system includes the nose, mouth, throat, voice box, windpipe, and lungs. Air enters the respiratory system through the nose or mouth. The nose filters out some air pollutants, but not all. Particles smaller than 0.5 µm, such as cigarette smoke, smoke from forest fires, viruses, and products of combustion, are generally not filtered by the nose. These fine particles can pass through the airway and enter the lungs.

The likelihood of particles entering the respiratory system depends on their mass and velocity. Particles with an aerodynamic diameter greater than 10 µm are usually deposited in the nose or throat and cannot reach the lower respiratory tract. However, smaller fine or ultrafine particles can get trapped in the lungs. The smallest particles can pass through the lungs and enter the bloodstream, similar to how oxygen molecules enter our bodies.

The mucociliary clearance mechanism is the pulmonary system's first line of defense against fine particles. It removes most of the inhaled particles deposited in the tracheobronchial airways. This mechanism is supported by the body's cough, immunologic, phagocytic, and enzymatic defenses. Phagocytosis is another clearance mechanism that removes foreign particles from the alveolar region. However, the efficiency of phagocytosis decreases with decreasing particle size, and particles smaller than 1 μm can be retained in the alveolar region for years.

Short-term exposure to high levels of fine particles can trigger cardiovascular events, hospitalisations, and even mortality. Long-term exposure can increase the risk of strokes, heart disease, and premature death. It can also cause respiratory issues such as asthma attacks, reduced lung development in children, and symptoms like coughing, wheezing, and shortness of breath.

Ultrafine particles can pass through the lungs into the bloodstream

The human body has a number of natural defenses against air pollution. The nose, for example, filters out some air pollutants, warming and humidifying the air before it reaches the lungs. The nose's narrow air passages, mucosal folds, and mucous layer trap large pollutants and allergens, which are then pushed into the stomach and neutralized.

However, the nose cannot filter out all pollutants. Particles smaller than 0.5 µm, such as cigarette smoke, wildfire smoke, viruses, and products of combustion, pass through the airway and into the lungs. These fine particles are generally referred to as particulate matter (PM) and are the principal component of air pollution.

While some of these fine particles are trapped in the lungs, the smallest ultrafine particles can pass through the lungs and enter the bloodstream, just like essential oxygen molecules. Ultrafine particles are defined as those with diameters of less than 0.1 µm, and they are found to a large extent in urban air. They are often generated as byproducts of fossil fuel combustion, condensation of semivolatile substances, or industrial emissions.

Once ultrafine particles enter the bloodstream, they can be transported to other organs, including the liver, spleen, kidneys, heart, and brain. This has been demonstrated in animal studies, where a small fraction of insoluble ultrafine particles deposited in the lungs were found in the blood within an hour. However, human studies have not identified insoluble particle translocation in organs, possibly due to the relatively small amount translocated into the blood.

The health effects of ultrafine particles can be detrimental. Inhaling these particles can aggravate respiratory illnesses such as asthma, trigger the production of reactive oxygen species, and cause cellular and DNA damage. Long-term exposure can lead to lung scarring and increase the risk of strokes, coronary heart disease, and premature death.

Coarse particles can be coughed or sneezed out of the body

Air pollution is a mix of tiny solid and liquid particles in the air we breathe. These particles are often categorised as coarse, fine, or ultrafine. Coarse particles are generally larger than 2.5 micrometres and smaller than or equal to 10 micrometres in diameter.

Coarse particles can be naturally coughed or sneezed out of the body. Our airways are lined with sticky mucus that acts as a flytrap to trap large pollutants and allergens. The nose also plays a crucial role in filtering out coarse particles. Due to the shape of the nose, air changes direction abruptly as it passes from the nostril to the nasal cavity, resulting in the deposition of particulate matter onto the sticky surface inside the nose. This trapped mucus is then swept away by tiny hairs called cilia, which push it into the stomach where it is neutralised.

However, our natural defences are not effective against smaller fine and ultrafine particles. These particles can bypass our body's natural filters and get trapped in the lungs. The smallest particles can even pass through the lungs and enter the bloodstream, just like the oxygen molecules we need to survive.

The impact of particle pollution on human health has been extensively studied. Both short-term acute exposure to high levels and long-term chronic exposure to low levels of particle pollution are linked to serious health issues. Short-term exposure to fine particles can trigger cardiovascular events, hospitalisations, and even mortality. Long-term exposure can increase the risk of strokes, coronary heart disease, and premature death. Respiratory symptoms such as coughing, wheezing, and shortness of breath are also associated with fine particle exposure.

To protect ourselves from particle pollution, we can take measures such as wearing masks or using air purifiers. Maintaining a healthy nose by staying well-hydrated can also help limit the number of particles that reach our lungs.

The lungs are the body's filters

Fine particles, such as cigarette smoke, smoke from forest fires, and viruses, can evade the nose's filtration system due to their small size. These particles can easily enter the body through the respiratory system and access the bloodstream, impacting vital organs like the brain and heart. Once in the bloodstream, they can have serious health consequences, including respiratory issues and cardiovascular events.

The lungs act as a critical barrier, trapping fine and ultrafine particles that escape the nose's defences. While the lungs can capture and prevent the passage of these particles into the body, prolonged exposure to high levels of particle pollution can overwhelm the lungs' filtering capacity. This overload can lead to serious health issues, including asthma, cardiovascular disease, and even premature death.

The impact of particle pollution on the lungs is particularly concerning for children. Their developing lungs are more susceptible to damage, and the irreversible effects can persist through adolescence. Additionally, children are more likely to suffer from asthma, and their higher activity levels result in increased exposure to particle pollution.

It is important to note that the lungs are not infallible in their filtering capacity. While they serve as a crucial defence mechanism, it is essential to minimise exposure to particle pollution and prioritise breathing clean air to maintain overall health and reduce the risk of adverse effects on the lungs and other organs.

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