The part of the respiratory system affected by asthma is primarily the bronchial tubes (airways) within the lungs. Asthma causes inflammation, swelling, and tightening of the muscles around these airways, along with increased mucus production. These changes narrow the airways, making breathing difficult. This condition mainly affects the lower respiratory tract, including the bronchi and smaller bronchioles, leading to symptoms like wheezing, coughing, chest tightness, and shortness of breath. Other parts such as the trachea and even the vocal cords can also be involved in some cases, but the key area is the bronchial tubes inside the lungs.