How does oxygen enter the lungs?

Oxygen enters the lungs through the process of inhalation or breathing in. Here's a step-by-step explanation of how oxygen enters the lungs:

1. Diaphragm and Intercostal Muscles: When you inhale, the diaphragm, which is a dome-shaped muscle located at the bottom of the ribcage, contracts and moves downward. Simultaneously, the intercostal muscles between the ribs also contract, causing the ribcage to expand and move outward.

2. Increased Lung Volume: As the diaphragm contracts and the ribcage expands, the volume of the thoracic cavity (the space within the chest) increases. This creates a lower air pressure inside the lungs compared to the atmospheric air outside.

3. Airflow into Lungs: Due to the pressure difference, atmospheric air rushes into the lungs through the nose and mouth. The air passes through the pharynx, larynx, and trachea before reaching the lungs.

4. Trachea and Bronchi: Inside the lungs, the trachea branches into two large tubes called the bronchi. Each bronchus enters one of the lungs. The bronchi further divide into smaller branches called bronchioles.

5. Alveoli: The bronchioles end in tiny air sacs called alveoli. The alveoli are where the exchange of oxygen and carbon dioxide takes place. Oxygen from the inhaled air diffuses across the thin walls of the alveoli into the capillaries (tiny blood vessels) that surround them.

6. Capillaries and Oxygen Transport: Inside the capillaries, oxygen binds to hemoglobin, a protein in red blood cells, forming oxyhemoglobin. The oxygenated blood is then transported by the bloodstream to various tissues and organs in the body, where the oxygen is released to meet the metabolic demands of the cells.

This process of inhalation allows oxygen to enter the lungs and be transported throughout the body, while simultaneously removing carbon dioxide, a waste product of cellular respiration, which is exhaled during the process of exhalation or breathing out.