Title: The human respiratory system
Course: Non-Communicable Diseases, Emergency Care and Mental Health Part 1 - Ethiopia (Full)

The human respiratory system

Before we can teach you about respiratory diseases, you need to know more about the respiratory system and how it works. Look carefully at Figure 4.1. The air that you breathe in (inhale) passes down your windpipe (its medical name is trachea) into tubes in your lungs called bronchi, which branch into fine bronchioles that carry air into all parts of the lungs.

Trachea is pronounced 'trak-ee-yah'; bronchi is pronounced 'bronk-ee' and bronchioles are 'bronk-ee-oles'.

Figure 4.1 The human respiratory system (also known as the pulmonary system). (Source: The Open University, Chronic Obstructive Pulmonary Disease, SDK125, Case Study 5, Figure 3.3)

The bronchioles end in bunches of tiny round air sacs called alveoli ('al-vee-ole-eye', the singular is alveolus). The airways and alveoli are elastic (stretchy). When you breathe in, each air sac fills up with air like a small balloon, and when you breathe out, it gets smaller again as the air leaves.

Small blood vessels called pulmonary capillaries cover the walls of the alveoli (Figure 4.2). When air enters the air sacs, the oxygen in the air passes through the very thin walls of the alveoli into the blood in the capillaries. At the same time, carbon dioxide (a waste gas) moves from the capillaries into the alveoli and is breathed out (exhaled). This process is called gas exchange.

Figure 4.2 A cross-section of a bronchiole and clusters of alveoli (air sacs) showing the blood capillaries covering their surfaces. (Source: The Open University, Chronic Obstructive Pulmonary Disease, SDK125, Case Study 5, Figure 3.6)

With this information in your mind, we can move on to describe how the respiratory system is affected in COPD first and then in bronchial asthma.