III. Respiratory System
The respiratory system is responsible for the exchange of oxygen and carbon dioxide between
the body and the environment, allowing for gas exchange and maintaining acid-base balance.
A. Anatomy of the Respiratory System
● The respiratory system includes the upper respiratory tract (nose, nasal cavity, pharynx)
and the lower respiratory tract (larynx, trachea, bronchi, lungs).
● The nose and nasal cavity filter, warm, and moisten inhaled air, and are lined with cilia
and mucus to trap foreign particles.
● The pharynx is a common passage for both air and food, and it serves as a pathway for air
to enter the lower respiratory tract.
● The larynx, commonly known as the voice box, contains the vocal cords and is
responsible for producing sound during speech.
● The trachea, also known as the windpipe, is a rigid tube lined with cilia and mucus that
transports air from the larynx to the bronchi.
● The bronchi are the main branches of the trachea that lead to the lungs, where they
further divide into smaller bronchioles.
B. Gas Exchange
● The main function of the respiratory system is gas exchange, which occurs in the alveoli
of the lungs.
● Alveoli are small air sacs with thin walls that are surrounded by a network of capillaries.
● Oxygen from inhaled air diffuses across the thin walls of the alveoli and into the
capillaries, where it binds to hemoglobin in red blood cells and is transported to body
tissues.
● Carbon dioxide, a waste product of cellular metabolism, diffuses from body tissues into
the capillaries, where it is carried back to the lungs and exhaled.
C. Breathing and Ventilation
● Breathing, also known as ventilation, involves the movement of air in and out of the
lungs.
● Inspiration (inhaling) and expiration (exhaling) are controlled by the diaphragm and other
respiratory muscles.
● During inspiration, the diaphragm contracts and moves downward, while the intercostal
muscles between the ribs also contract, causing the ribcage to expand and air to be drawn
into the lungs.
The respiratory system is responsible for the exchange of oxygen and carbon dioxide between
the body and the environment, allowing for gas exchange and maintaining acid-base balance.
A. Anatomy of the Respiratory System
● The respiratory system includes the upper respiratory tract (nose, nasal cavity, pharynx)
and the lower respiratory tract (larynx, trachea, bronchi, lungs).
● The nose and nasal cavity filter, warm, and moisten inhaled air, and are lined with cilia
and mucus to trap foreign particles.
● The pharynx is a common passage for both air and food, and it serves as a pathway for air
to enter the lower respiratory tract.
● The larynx, commonly known as the voice box, contains the vocal cords and is
responsible for producing sound during speech.
● The trachea, also known as the windpipe, is a rigid tube lined with cilia and mucus that
transports air from the larynx to the bronchi.
● The bronchi are the main branches of the trachea that lead to the lungs, where they
further divide into smaller bronchioles.
B. Gas Exchange
● The main function of the respiratory system is gas exchange, which occurs in the alveoli
of the lungs.
● Alveoli are small air sacs with thin walls that are surrounded by a network of capillaries.
● Oxygen from inhaled air diffuses across the thin walls of the alveoli and into the
capillaries, where it binds to hemoglobin in red blood cells and is transported to body
tissues.
● Carbon dioxide, a waste product of cellular metabolism, diffuses from body tissues into
the capillaries, where it is carried back to the lungs and exhaled.
C. Breathing and Ventilation
● Breathing, also known as ventilation, involves the movement of air in and out of the
lungs.
● Inspiration (inhaling) and expiration (exhaling) are controlled by the diaphragm and other
respiratory muscles.
● During inspiration, the diaphragm contracts and moves downward, while the intercostal
muscles between the ribs also contract, causing the ribcage to expand and air to be drawn
into the lungs.
