Lung: Cell Types Composing the Tissue

Respiratory Zones

The thorax is the part of our body that extends from the neck to a dome-like muscle called the diaphragm. It is enclosed by the ribs and contains the heart and the lungs. There are two lungs in the chest, one on the right side and one on left. The lungs are spongy organs located inside the rib cage, and their basic function is gas exchange. They perform this task by absorbing oxygen (O2) from air during inhalation. Once O2 comes in contact with blood in microscopic capillaries enveloping the air sacs of lungs, it is ready to be transported to the whole body mixed with blood. In the meantime, carbon dioxide (CO2), which is the waste product of metabolism, is carried via the bloodstream away from the body to the lungs and then exhaled. The process of gas exchange is spontaneous and is intricately regulated by the brainstem. Normal respiratory rate ranges between 12 and 18 breaths per minute at rest. However, it can increase during exercise or while under stress. The respiratory system is comprised of two primary zones: a respiratory zone and a conducting zone. The conducting zone, also called the dead zone, refers to the area through which air moves but no gas exchange takes place. The conducting zone is composed of the nose, pharynx, larynx, trachea, bronchi, bronchioles, and terminal bronchioles. The respiratory zone comprises the areas of the respiratory system that are involved in gas exchange. The alveoli are the basic units of the lung and represent the actual respiratory zone. Lungs have both conducting and respiratory zones.

Upper Respiratory Tract

The process of inhalation starts from the nose or mouth. Most of the air is inhaled through the nose, where it is warmed and moistened and later enters the upper part of the pharynx (located at the back of nose and mouth), and makes its way to the trachea (also known as wind pipe). The pharynx and trachea act as passage ways for the air to pass into the lower respiratory tract. The trachea lies in front of the esophagus (the tube through which food travels). The larynx, or voice box, is located between the pharynx and trachea and assists in vocalization, as its name suggests. The human airway is protected from oncoming food by a flap-like structure called the epiglottis. During normal respiration, the epiglottis does not cover the larynx; however, when we eat, the epiglottis automatically covers the larynx and prevents food particles from entering the lower respiratory tract. The larynx consists of different cartilages and muscles that are fastened by elastic tissues. The larynx contains a tough, flexible cartilaginous structure called the Adam’s apple, which is present in front of the neck. The inner surface of the Adam’s apple has two stretched fibrous sheets of tissues, the vocal cords. Speech is produced with the help of the tongue, palate, and lips, which manage the vibrations of the vocal cords.

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