The major function of the respiratory system is to supply the body with oxygen and dispose of carbon dioxide.
To accom-plish this function, at least four processes, collectively called respiration, must happen:
- Pulmonary ventilation: movement of air into and out of the lungs so that the gases there are continuously changed and refreshed (commonly called breathing).
- External respiration: movement of oxygen from the lungs to the blood and of carbon dioxide from the blood to the lungs.
- Transport of respiratory gases: transport of oxygen from the lungs to the tissue cells of the body, and of carbon dioxide from the tissue cells to the lungs.
- This transport is accomplished by the cardiovascular system using blood as
the transporting fluid.
- Internal respiration: movement of oxygen from blood to the tissue cells and of carbon dioxide from tissue cells to blood.
- Only the first two processes are the special responsibility of the respiratory system (Figure 22.1),
- but it cannot accomplish its primary goal of obtaining oxygen and eliminating carbon dioxide unless the third and fourth processes also occur.
- As you can see, the respiratory and circulatory systems are closely cou- pled, and if either system fails,
- the body’s cells begin to die from oxygen starvation.
- The actual use of oxygen and production of carbon dioxide by tissue cells, known as cellular respiration,
- is the cornerstone of all energy-producing chemical reactions in the body.
- We discuss cellular respiration, which is not a function of the respiratory system, in the metabolism section of Chapter 24.
- Because it moves air, the respiratory system is also involved
with the sense of smell and with speech.
of the Respiratory System
Identify the organs forming the respiratory passageway(s)
In descending order until the alveoli are reached
Describe the location, structure, and function of each of
the following: nose, paranasal sinuses, pharynx, and larynx.
List and describe several protective mechanisms of the respiratory system.
The respiratory system includes the nose, nasal cavity, and paranasal sinuses; the pharynx; the larynx; the trachea; the bronchi and their smaller branches; and the lungs, which contain the terminal air sacs, or alveoli (Figure 22.1). Functionally, the system consists of two zones.
The respiratory zone, the actua site of gas exchange, is composed of the respiratory bronchioles, alveolar ducts, and alveoli, all microscopic structures.
The conducting zone includes all other respiratory passageways, which provide fairly rigid conduits for air to reach the gas ex-change sites.
The conducting zone organs also cleanse, humid- ify, and warm incoming air.
As a result, air reaching the lungs has fewer irritants (dust, bacteria, etc.)
than when it entered the system, and it is warm and damp, like the air of the tropics.
The functions of the major organs of the respiratory system are summarized in Table 22.1.
In addition to these organs, some authorities also include the respiratory muscles (diaphragm, etc.) as part of this system.
Al-though we will consider how these skeletal muscles bring about the volume changes that promote ventilation, we continue to classify them as part of the muscular system.
The Nose and Paranasal Sinuses The nose is the only externally visible part of the respiratory sys-tem. Unlike the eyes and lips, facial features often referred to po- etically, the nose is usually an irreverent target.
We are urged to our nose to the grindstone and to keep it out of other peo- ple’s business.
The nose (1) provides an airway for res- piration, (2) moistens and warms entering air, (3) filters and cleans inspired air, (4) serves as a resonating chamber for speech, and (5) houses the olfactory (smell) receptors.
The structures of the nose are divided into the external nose and the internal nasal cavity for ease of consideration.
The surface features of the external nose include the root (area between the eyebrows), bridge, and dorsum nasi (anterior margin), the latter terminating in the apex (tip of the nose) (Figure 22.2a).
Just inferior to the apex is a shallow vertical groove called the philtrum (fil-trum).
The external openings of the nose, the nostrils or nares (na-re-z), are bounded laterally by the flared alae.
The skeletal framework of the external nose is fashioned by the nasal and frontal bones superiorly (forming the bridge and root, respectively),
the maxillary bones laterally, and flex-ible plates of hyaline cartilage (the alar and septal cartilages, and the lateral processes of the septal cartilage) inferiorly (Figure 22.2b).
The skin covering the nose’s dorsal and lateral aspects is thin and contains many
sebaceous glands. The internal nasal cavity lies in and posterior to the external
The nasal cavity is divided by a midline nasal septum, formed anteriorly by the septal cartilage and posteriorly by the vomer bone and perpendicular plate of the ethmoid bone (see Figure 7.14b, p. 213).
“The nasal cavity is continuous posteriorly with the nasal por-tion of the pharynx through the posterior nasal apertures, also called the choanae (ko-a-ne; “funnels”)”.
The roof of the nasal cavity is formed by the ethmoid and sphenoid bones of the skull.
The floor is formed by the palate, which separates the nasal cavity from the oral cavity below.
An- teriorly, where the palate is supported by the palatine bones and processes of the maxillary bones, it is called the hard palate.
The unsupported posterior portion is the muscular soft palate.
The part of the nasal cavity just superior to the nostrils,called the nasal vestibule, is lined with skin containing seba-ceous and sweat glands and numerous hair follicles.
The hairs, or vibrissae (vi-bris-e; vibro – to quiver), filter coarse particles (dust, pollen) from inspired air.
The rest of the nasal cavity is lined with two types of mucous membrane.
The olfactory epithelium (mucosa), lining the slitlike superior region of the