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19: The Respiratory System

  • Page ID
    12539
  • Skills to Develop

    • List the structures that make up the respiratory system

    The Nose and its Adjacent Structures

    The major entrance and exit for the respiratory system is through the nose. When discussing the nose, it is helpful to divide it into two major sections: the external nose, and the nasal cavity or internal nose.

    The external nose consists of the surface and skeletal structures that result in the outward appearance of the nose and contribute to its numerous functions (Figure 19.1). The root is the region of the nose located between the eyebrows. The bridge is the part of the nose that connects the root to the rest of the nose. The dorsum nasi is the length of the nose. The apex is the tip of the nose. On either side of the apex, the nostrils are formed by the alae (singular = ala). An ala is a cartilaginous structure that forms the lateral side of each naris (plural = nares), or nostril opening. The philtrum is the concave surface that connects the apex of the nose to the upper lip.

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    Figure 19.1 Nose This illustration shows features of the external nose (top) and skeletal features of the nose (bottom).

    The nares open into the nasal cavity, which is separated into left and right sections by the nasal septum (Figure 19.2). The nasal septum is formed anteriorly by a portion of the septal cartilage (the flexible portion you can touch with your fingers) and posteriorly by the perpendicular plate of the ethmoid bone (a cranial bone located just posterior to the nasal bones) and the thin vomer bones (whose name refers to its plough shape). Each lateral wall of the nasal cavity has three bony projections, called the superior, middle, and inferior nasal conchae. The inferior conchae are separate bones, whereas the superior and middle conchae are portions of the ethmoid bone.

    Conchae serve to increase the surface area of the nasal cavity and to disrupt the flow of air as it enters the nose, causing air to bounce along the epithelium, where it is cleaned and warmed. The conchae and meatuses also conserve water and prevent dehydration of the nasal epithelium by trapping water during exhalation. The floor of the nasal cavity is composed of the palate. The hard palate at the anterior region of the nasal cavity is composed of bone. The soft palate at the posterior portion of the nasal cavity consists of muscle tissue. Air exits the nasal cavities via the internal nares and moves into the pharynx.

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    Figure 19.2 Upper Airway

    The conchae, meatuses, and paranasal sinuses are lined by respiratory epithelium composed of pseudostratified ciliated columnar epithelium (Figure 19.3). The epithelium contains goblet cells, one of the specialized, columnar epithelial cells that produce mucus to trap debris. The cilia of the respiratory epithelium help remove the mucus and debris from the nasal cavity with a constant beating motion, sweeping materials towards the throat to be swallowed. Interestingly, cold air slows the movement of the cilia, resulting in accumulation of mucus that may in turn lead to a runny nose during cold weather. This moist epithelium functions to warm and humidify incoming air. Capillaries located just beneath the nasal epithelium warm the air by convection. Serous and mucus-producing cells also secrete the lysozyme enzyme and proteins called defensins, which have antibacterial properties. Immune cells that patrol the connective tissue deep to the respiratory epithelium provide additional protection.

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    Figure 19.3 Pseudostratified Ciliated Columnar Epithelium Respiratory epithelium is pseudostratified ciliated columnar epithelium. Seromucous glands provide lubricating mucus. LM × 680. (Micrograph provided by the Regents of University of Michigan Medical School © 2012)

    Pharynx

    The pharynx is a tube formed by skeletal muscle and lined by mucous membrane that is continuous with that of the nasal cavities (see Figure 19.2). The pharynx is divided into three major regions: the nasopharynx, the oropharynx, and the laryngopharynx (Figure 19.4).

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    Figure 19.4 Divisions of the Pharynx The pharynx is divided into three regions: the nasopharynx, the oropharynx, and the laryngopharynx.

    Larynx

    The larynx is a cartilaginous structure inferior to the laryngopharynx that connects the pharynx to the trachea and helps regulate the volume of air that enters and leaves the lungs (Figure 19.5). The structure of the larynx is formed by several pieces of cartilage. Three large cartilage pieces—the thyroid cartilage (anterior), epiglottis (superior), and cricoid cartilage (inferior)—form the major structure of the larynx. The thyroid cartilage is the largest piece of cartilage that makes up the larynx. The thyroid cartilage consists of the laryngeal prominence, or “Adam’s apple,” which tends to be more prominent in males. The thick cricoid cartilage forms a ring, with a wide posterior region and a thinner anterior region. Three smaller, paired cartilages—the arytenoids, corniculates, and cuneiforms—attach to the epiglottis and the vocal cords and muscle that help move the vocal cords to produce speech.

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    Figure 19.5 Larynx The larynx extends from the laryngopharynx and the hyoid bone to the trachea.

    Trachea

    The trachea (windpipe) extends from the larynx toward the lungs (Figure 19.6a). The trachea is formed by 16 to 20 stacked, C-shaped pieces of hyaline cartilage that are connected by dense connective tissue. The trachealis muscle and elastic connective tissue together form the fibroelastic membrane, a flexible membrane that closes the posterior surface of the trachea, connecting the C-shaped cartilages. The fibroelastic membrane allows the trachea to stretch and expand slightly during inhalation and exhalation, whereas the rings of cartilage provide structural support and prevent the trachea from collapsing. In addition, the trachealis muscle can be contracted to force air through the trachea during exhalation. The trachea is lined with pseudostratified ciliated columnar epithelium, which is continuous with the larynx. The esophagus borders the trachea posteriorly.

    Bronchial Tree

    The trachea branches into the right and left primary bronchi at the carina. These bronchi are also lined by pseudostratified ciliated columnar epithelium containing mucus-producing goblet cells (Figure 19.6b). The carina is a raised structure that contains specialized nervous tissue that induces violent coughing if a foreign body, such as food, is present. Rings of cartilage, similar to those of the trachea, support the structure of the bronchi and prevent their collapse. The primary bronchi enter the lungs at the hilum, a concave region where blood vessels, lymphatic vessels, and nerves also enter the lungs. The bronchi continue to branch into bronchial a tree. A bronchial tree (or respiratory tree) is the collective term used for these multiple-branched bronchi. The main function of the bronchi, like other conducting zone structures, is to provide a passageway for air to move into and out of each lung. In addition, the mucous membrane traps debris and pathogens.

    A bronchiole branches from the tertiary bronchi. Bronchioles, which are about 1 mm in diameter, further branch until they become the tiny terminal bronchioles, which lead to the structures of gas exchange. There are more than 1000 terminal bronchioles in each lung. The muscular walls of the bronchioles do not contain cartilage like those of the bronchi. This muscular wall can change the size of the tubing to increase or decrease airflow through the tube.

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    Figure 19.6 Trachea (a) The tracheal tube is formed by stacked, C-shaped pieces of hyaline cartilage. (b) The layer visible in this cross-section of tracheal wall tissue between the hyaline cartilage and the lumen of the trachea is the mucosa, which is composed of pseudostratified ciliated columnar epithelium that contains goblet cells. LM × 1220. (Micrograph provided by the Regents of University of Michigan Medical School © 2012)

    Respiratory Zone

    In contrast to the conducting zone, the respiratory zone includes structures that are directly involved in gas exchange. The respiratory zone begins where the terminal bronchioles join a respiratory bronchiole, the smallest type of bronchiole (Figure 19.7), which then leads to an alveolar duct, opening into a cluster of alveoli.

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    Figure 19.7 Respiratory Zone Bronchioles lead to alveolar sacs in the respiratory zone, where gas exchange occurs.

    Alveoli

    An alveolar duct is a tube composed of smooth muscle and connective tissue, which opens into a cluster of alveoli. An alveolus is one of the many small, grape-like sacs that are attached to the alveolar ducts.

    An alveolar sac is a cluster of many individual alveoli that are responsible for gas exchange. An alveolus is approximately 200 μm in diameter with elastic walls that allow the alveolus to stretch during air intake, which greatly increases the surface area available for gas exchange. Alveoli are connected to their neighbors by alveolar pores, which help maintain equal air pressure throughout the alveoli and lung (Figure 19.8).

    The alveolar wall consists of three major cell types: type I alveolar cells, type II alveolar cells, and alveolar macrophages. A type I alveolar cell is a squamous epithelial cell of the alveoli, which constitute up to 97 percent of the alveolar surface area. These cells are about 25 nm thick and are highly permeable to gases. A type II alveolar cell is interspersed among the type I cells and secretes pulmonary surfactant, a substance composed of phospholipids and proteins that reduces the surface tension of the alveoli. Roaming around the alveolar wall is the alveolar macrophage, a phagocytic cell of the immune system that removes debris and pathogens that have reached the alveoli.

    The simple squamous epithelium formed by type I alveolar cells is attached to a thin, elastic basement membrane. This epithelium is extremely thin and borders the endothelial membrane of capillaries. Taken together, the alveoli and capillary membranes form a respiratory membrane that is approximately 0.5 mm thick. The respiratory membrane allows gases to cross by simple diffusion, allowing oxygen to be picked up by the blood for transport and CO2 to be released into the air of the alveoli.

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    Figure 19.8 Structures of the Respiratory Zone (a) The alveolus is responsible for gas exchange. (b) A micrograph shows the alveolar structures within lung tissue. LM × 178. (Micrograph provided by the Regents of University of Michigan Medical School © 2012)

    LAB 19 EXERCISES 19-1

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    A

    Label the following: Nasal vestibule * Nasal

    cavity * Esophagus * Pharynx * Larynx.

    Match the following: Naris * Ala (of nose) *

    B

    Bridge (of nose) * Philtrum.

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    Where did these arrows come from?

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    LAB 19 EXERCISES 19-2

    Identify the following components of the upper respiratory tract:

    Superior nasal conchae * Middle nasal conchae * Inferior nasal conchae * Hard palate * Soft palate * Eustachian tube * Nasopharynx * Oropharynx * Laryngopharynx * Epiglottis * Uvula * Sphenoid sinus * Frontal sinus.

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    LAB 19 EXERCISES 19-3

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    UPPER RESPIRATORY TRACT

    A

    B

    5

    1

    1

    Label the following: All of the lobes of the lungs * all the fissures of the lungs * apex * base * diaphragm.

    Label these components of the larynx: Epiglottis * Vestibular fold * Vocal cord * Thyroid cartilage * Cricoid cartilage * Tracheal cartilages.

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    LAB 19 EXERCISES 19-4

    LABEL THE CARTILAGES AND LIGAMENTS

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    LAB 19 EXERCISES 19-5

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    UPPER  LOWER RESPIRATORY TRACT

    A

    B

    Label the following: Vocal cords * Vestibular folds * Epiglottis * Glottis * Arytenoid cartilage.

    Label the following: Thyroid cartilage * Cricoid cartilage * Trachea * Carina *

    R. primary bronchus * L. primary bronchus * secondary bronchi * Tertiary bronchi.

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    "Stroboscopy: Normal Female Vocal Cords" by James P Thomas * MD is licensed under CC BY 4.0

    LAB 19 EXERCISES 19-6

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    LOWER RESPIRATORY TRACT

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    B

    Label the following: Cardiac notch *

    2

    Pulmonary artery * Pulmonary vein * Abdominal aorta

    Label the following: Bronchiole * Alveoli * Alveolar sac * Pulmonary venule * Pulmonary arteriole * Capillary network

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    oxygenated

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    De-oxygenated

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    LAB 19 EXERCISES 19-7

    HISTOLOGY

    A

    BImage_437.png

    Label the tracheal histology:

    Pseudostratified ciliated columnar epithelium *

    LAB 19 EXERCISES 19-8

    Goblet cell * Cilia

    Label the tracheal cartilage histology:

    Hyaline cartilage * Mucosa * Submucosa *

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    Lumen * Mucous gland.

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    LABEL THE FOLLOWING LUNG HISTOLOGY COMPONENTS: SIMPLE SQUAMOUS EPITHELIUM * SMOOTH MUSCLE * ALVEOLI * ALVEOLAR SAC * BRONCHIOLE * ARTERIOLE.

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    Low power Med. power

    MODELS: Bronchial Tree, Lungs & Heart, Trachea, Torsos and Mid-Sagittal Head

     Pleura

    • parietal & visceral

     Pleural cavity

     Right lung

    • Lobes: upper * middle * lower

    • Horizontal fissure

    • Oblique fissure

    • Hilus

       Left Lung:

    • lobes: upper * lower

    • Oblique fissure

    • Cardiac notch

    • Hilus

       Philtrum

       Nose

      • Bridge

      • Ala

      • Nares

         Nasal cavity

    • Vestibule

    • Nasal conchae:

       superior * middle * & inferior

    • Nasal meatuses:

       superior * middle * & inferior

    • Nasal septum

    • Pharyngotympanic tube (Eustachian)

     Sinuses (Sphenoid * frontal)

     Hard palate

     Soft palate

    • Uvula

       Hyoid bone

       Pharynx:

    • Nasopharynx

    • Oropharynx

    • Laryngopharynx

       Larynx:

    • Epiglottis

    • Thyroid cartilage

    • Cricoid cartilage

    • Crico-thyroid ligament

    • Crico-tracheal ligament

    • Hyo-thyroid ligament

    • Vestibular folds (false vocal cords)

    • True vocal cords

    • Arytenoid cartilage

    • Corniculate cartilage

       Trachea:

    • Tracheal cartilages

    • Carina

       Bronchial tree:

    • L * R primary (main) bronchi

    • Secondary (lobar) bronchi

    • Tertiary (segmental) bronchi

    oLung tissue:

    oBronchioles oAlveolar sac oAlveoli

    • Muscles:

      • Diaphragm

      • External intercostals

      • Internal intercostals

    • Vasculature

      • Pulmonary arteries

      • Pulmonary veins

        oLung Histology: (2 slides)

        oTrachea

        oAdventitia

        oTracheal cartilage (hyaline)

        oTrachealis muscle

        oMucosa (pseudostratified ciliated columnar epithelium)

        oLungs

        oAlveoli (Simple squamous epithelia)

        oBronchioles

        oPulmonary arterioles * venules * & capillaries