Chapter_29_Respiratory_Anatomy_Physiology_Pathophysiology_and

Respiratory Anatomy: Nose

  • Olfactory Region: Located on the roof of the nasal cavity.
    • Contains olfactory epithelium with olfactory receptors, supporting cells, and basal cells.
    • Sensory nerve signals progress from the ethmoid bone to the olfactory bulb and then to the rhinencephalon.
  • Respiratory Mucosa: Lines the lower two-thirds of the nose.
    • Composed of pseudostratified ciliated columnar epithelium with goblet cells.
    • Cilia motion directs mucus towards nostrils or pharynx for expulsion/swallowing.
  • Arterial Supply:
    • Ophthalmic arteries (anterior and posterior ethmoid branches).
    • Internal maxillary artery (sphenopalatine arteries) - sometimes ligated to manage severe nosebleeds.
  • Venous Drainage:
    • Ethmoid veins drain into the superior sagittal sinus.
    • Nasal veins drain into ophthalmic veins and then into cavernous sinuses, facilitating potential spread of nasal infections to the brain, leading to meningitis.
  • Sensory Nerves: Ophthalmic and maxillary nerves (branches of cranial nerve V).
  • Lymphatic Drainage: Deep cervical lymph nodes adjacent to the internal jugular vein.
  • Functions of the Nose: Filtration, humidification, and heating of inspired air.
    • Warms air to near body temperature and 100% relative humidity, unless the air is extremely cold.
    • General anesthesia can impair these warming and humidifying functions.
    • Inspiration of cold, dry gas can cause a sore throat due to drying of nasal and pharyngeal mucosa.
  • Filtration:
    • Nasal hairs filter large particles.
    • Turbulent precipitation is more effective, where air direction changes force particles onto mucus-covered surfaces (septum, turbinates, pharyngeal wall).
    • Trapped particles are moved by cilia and swallowed or expectorated.
    • Nasal filtration is effective for particles > 10μ10 \mum and < 11 nm, with inverse efficiency between 1010 nm and 1μ1 \mum.

Pharynx

  • A muscular tube shared by the respiratory and alimentary canals.
  • Extends from the base of the skull to the C6 vertebra, where it connects to the esophagus.
  • Foreign objects can lodge at the C6 level.
  • Lined by a musculo-membranous coat and divided into:
    • Nasopharynx: From posterior nares (choanae) to the soft palate.
    • Oropharynx: From soft palate to the tip of the epiglottis, bounded anteriorly by tonsillar pillars and the oral cavity.
    • Hypopharynx (Laryngopharynx): From the tip of the epiglottis to C6 or the start of the esophagus.
  • Tonsils: Lymphoid tissue aggregations as a first line of defense against bacterial invasion of nasal, oral, and buccal passages, forming Waldeyer’s tonsillar ring.
    • Palatine tonsils (major tonsils): in the tonsillar fossae at the boundary of the oral cavity and oropharynx.
    • Lingual tonsils: across the tongue from the base of each palatine tonsil.
    • Tubal tonsils: on the roof of the nasopharynx inferior and lateral to the pharyngeal tonsils.
    • Pharyngeal tonsils (adenoids): in the center part of the nasopharyngeal roof; if inflamed, can obstruct airflow and require adenoidectomy.
    • Chronic tonsillitis may necessitate tonsillectomy.

Larynx

  • Located between C3-C6 vertebrae in adults, primarily for airway protection during swallowing; vocalization is a secondary function.
  • Composed of one bone (hyoid), nine cartilages, ligaments, muscles, and membranes.
  • Hyoid Bone:
    • Supports the larynx and doesn't articulate with other bones.
    • Palpable anteriorly and used for airway assessment during laryngoscopy.
  • Thyroid and Cricoid Cartilages: Form the main laryngeal framework.
  • Epiglottis: Protects vocal cords and trachea from foreign materials during swallowing.

Laryngeal Cartilages

  • There are three paired and three unpaired cartilages.
  • Epiglottis:
    • Near the tongue root and vertical to the larynx opening.
    • Attached to the thyroid cartilage via the thyroepiglottic ligament, tongue via glossoepiglottic folds, and hyoid bone via the hyoepiglottic ligament.
    • Vallecula epiglottica (furrow between glossoepiglottic folds and tongue base) is the site for curved laryngoscope blade placement.
    • Epiglottis is elevated during swallowing or laryngospasm to seal off the trachea.
  • Thyroid Cartilage:
    • Largest laryngeal cartilage formed by fused quadrangular plates.
    • Provides protection to the larynx, meeting at the laryngeal prominence (Adam’s apple), larger in males.
  • Cricoid Cartilage:
    • Palpable below the thyroid gland, level with trachea and esophagus beginning.
    • It is the only complete ring of cartilage encircling the airway.
    • Lies below the thyroid cartilage, connected by the cricothyroid membrane.
    • Most inferior laryngeal cartilage.
  • Arytenoid Cartilages: Located on the superior posterior aspect of the cricoid cartilage and are attached to the posterior ends of the vocal cords.
  • Corniculate and Cuneiform Cartilages: Embedded in aryepiglottic folds for support. *Clinical Significance of Larynx Size
    • Narrowest part of adult larynx: Opening between the true vocal cords (rima glottidis).
    • Narrowest part of child larynx (<8 years): Cricoid cartilage and subcricoid region. An adequate tube with adequate clearance through the vocal cords may create mucosal pressure at the level of the cricoid ring in children

Laryngeal Membranes

  • Thyrohyoid Membrane: Suspends larynx from the hyoid bone.
  • Cricothyroid Membrane: Between the cricoid and thyroid cartilages; site for emergency laryngotomy.
    • Cricothyrotomy: Emergency airway establishment when intubation and mask ventilation fail.
    • Transtracheal Block: Local anesthetic injection into the trachea via cricothyroid membrane puncture.

Interior of Larynx

  • Divided into three compartments by the false vocal cords (vestibular folds) and true vocal cords.
    • False vocal cords are involved with respiration, aspiration prevention, and phonation.
    • False vocal cords: Narrow bands of fibrous tissue covered by mucous membranes located to either side and superiorly to the true vocal cords.
      First compartment:
    • Supraglottic area/vestibule: From above the false cords to the tip of the epiglottis. Contains the pyriform sinus (pharyngeal sinus) for foreign body lodging.
      Second compartment:
    • Laryngeal Ventricles: Area between the false and true cords.
      Third compartment:
      *Infraglottic region: Below the true cords, above the trachea beginning.
    • Rima Glottidis (cricoid opening): Space between the true vocal cords.

Movements of the Vocal Cords

  • True vocal cords are attached anteriorly to the thyroid cartilage and posteriorly to arytenoids.
  • Laryngeal Vestibule Closure: Aryepiglottic, oblique arytenoid, and thyroepiglottic muscles close the laryngeal vestibule, pulling the epiglottis inferiorly.
  • Glottic Opening: Posterior cricoarytenoid muscles dilate (abduct) the glottic opening, while interarytenoid and lateral cricoarytenoid muscles close (adduct) it.
  • Vocal Cord Tension: Cricothyroid muscles increase tension (lengthen), and thyroarytenoid muscles decrease tension (shorten); regulates voice pitch. The laryngeal vestibule (i.e., laryngeal inlet) is closed, and the epiglottis pulled inferiorly to cover the laryngeal vestibule, by the aryepiglottic muscle, oblique arytenoid muscles, and thyroepiglottic muscle.

Nerve Supply to the Larynx

  • Superior Laryngeal Nerve: Branch of cranial nerve X (vagus nerve).
    • Internal Branch: Enters larynx through thyrohyoid membrane, sensory innervation from inferior epiglottis to true cords, and innervates interarytenoid muscles (phonation).
    • External Branch: Supplies inferior constrictor muscle of pharynx and cricothyroid muscles (lengthens vocal cords). Paralysis leads to weak, rough voice and vocal fatigue.
  • Inferior (Recurrent) Laryngeal Nerves: From bilateral vagus nerves at different levels.
    • Left Nerve: Loops around the aortic arch superiorly to the trachea.
    • Right Nerve: Loops around the right subclavian artery and ascends back up the neck.
    • Sensory innervation to larynx below vocal cord level and innervates intrinsic muscles (except cricothyroid and part of interarytenoid muscles). Damage causes vocal cord paralysis (hoarseness, dyspnea).
      *Blood Supply:
    • Superior thyroid artery (branch of external carotid artery).
    • Inferior thyroid artery (branch of thyrocervical trunk from the subclavian artery).

Trachea

  • Lined by pseudostratified ciliated columnar epithelium.
  • Extends from inferior larynx to the carina, which divides into two mainstem bronchi.
  • Distances are relatively constant in normal-sized adults:
    • Incisors to Larynx: approximately 13 cm.
    • Larynx to Carina: approximately 13 cm
    • Incisors to carina: approximately 26 cm (ETT length markings).
  • Blood supply:
    • Inferior thyroid artery (from thyrocervical branch of subclavian artery).
    • Some perfusion from superior thyroid, bronchial, and internal thoracic arteries.
    • Venous drainage via inferior thyroid veins.
      *Sensory Innervation:
    • Vagus nerve (parasympathetic and nociceptive stimuli).
  • Trachea Characteristics:
    • Diameter: approximately 2.5 cm.
    • Supported by incomplete cartilage rings providing posterior opening, prevent collapse during spontaneous respiration.
    • Extends to the T4-T5 level, where the carina is located. Corresponds anteriorly to the angle of Louis on the sternum.
    • Expands and contracts with head and neck movements.
      *ETT movement with head flexion /extension:
    • Flexion causes downward movement of a fixed ETT -> potential endobronchial intubation.
    • Extension causes upward movement of a fixed ETT -> potential extubation. (Mnemonic: "the hose follows the nose").
    • Neck rotation elevates trachea and may risk endobronchial intubation.

Bronchi

*Cellular Structure:
* Begins to change at the point from columnar to cuboidal epithelium.
*Carina:
* Cellular structure begins changing from columnar to cuboidal epithelium.
* Cartilaginous rings thin into plates once the bronchi penetrate the lungs.
*From the Carina:
* Right bronchus is wider, shorter (2 cm), and branches off at approximately 25 degrees (more vertical).
*Left bronchus is narrower, longer (4 cm), and branches off at approximately 45 degrees.
*Foreign Materials More Likely To Enter Right Side - greater tendency for ETTs, suction catheters, or aspirated foreign materials to enter the right side.
*Murphy Eye Function: located at distal end of ETT allows gas delivery if beveled tip opposed right side main bronchus.
*Lobar Divisions:
* Right: Three lobar bronchi (RUL, bronchus intermedius before RML and RLL bronchus).
*Left: Two lobar bronchi (LUL and LLL bronchus).
*Segmentary Divisions:
* Each division referred to as a generation (mainstem bronchi 1st gen., lobar bronchi 2nd gen.).
* Lobar bronchi divide into 3rd generation (segmental/bronchopulmonary, 10 in each lung, but fewer on the left).
*Segments with "basal" in name are diaphragm adjacent.
*Airway Changes::
* Each subsegmental bronchus divides several times -> numerous bronchioles.
* Increasing no. of airways lead to decrease velocity air velocity.
*20-25 generations b4 alveoli. >7th diameter of bronchioles is ~ 2mm.
*Terminal Bronchioles: Last structures perfused by the bronchial circulation and the end of the conducting airways (anatomical dead space).
*Gas Diffusion.
* Gas moves largely by diffusion as compared to bulk flow, in later airway division generations.
* Respiratory bronchioles: first location of gas exchange with pulmonary circulation and have occasional alveoli pockets.
*Closing Volume: Lung volume at which small airways tend to close during exhalation.
* Pores of Kohn: small pores in alveoli allow collateral gas flow and relieve gas stagnancy if airway closes.

Respiratory Zone

*Constituents: respiratory bronchioles, alveolar ducts, sacs, and alveoli.
*Function: gas exchange.
*All parts of the airway prior prior to this are: (nose -> terminal bronchioles) =
*Conducting Zone = conduct gas w/o gas exchange.
*Transitional Zone Respiratory: bronchioles/alveolar ducts w/ some gas exchange, conduct gas.
*Alveoli: air sacs that tightly packed w/ pulmonary capillaries, and have thin walls (squamous epithelium).

Alveoli

  • ~300 million alveoli reached ~9 yo average alveolar diameter ≈ 250 mcm, surface area ≈ 60 to 80 m2 Squamous epithelium walls Cell Types:
    • Type I pneumocytes: structural cells
    • Type II pneumocytes: surfactant production
    • Type III pneumocytes: macrophages
      *The cells also contain Nonciliated Bronchiolar Cells:
    • Club Cells (or Clara Cells): metabolic and anti-inflammatory processes and serve as progenitor cells (i.e., sim- ilar to stem cells) for themselves and the other pneumocytes.
      *Produce and secrete proteins and cytochrome P450 enzymes that are involved in: biotransformation of many inhaled harmful and toxic substances (i.e., tobacco smoke, ozone, hydrocarbons, and numerous other substances).
      *Uteroglobin (or CCSP): Primary protein secreted in the pregnant uterus. Along with other proteins, lipids, and glycoproteins secreted by club cells, binds with and helps to protect pulmonary surfactant (stabilize the lipoprotein secreted by type II alveolar cells).

Pulmonary Hilum and Pleura

Pulmonary Hilum and Contents

  • Nerve supply to the bronchi and lungs comes from sympathetic nerves and vagus nerve.
  • Structures entering hilum: mainstem bronchus, pulmonary artery and vein, bronchial arteries and veins, lymphatics, lymph nodes, pulmonary nerve plexuses, and pulmonary ligament.

Pleura

  • Serous membrane lining thoracic wall/ lungs.
  • Parietal Pleura lines the chest wall, mediastinum, and diaphragm.
    • It is then reflected back to cover the lungs as the visceral pleura (connection called hilum).
  • The potential space between these two layers that touching, slippery surfaces maintained by capillary-thin serous fluid.
    *Various conditions can disrupt liquid/fluid capacity (Table 29.2 in text), air/gas:
    *Liquids may affect ventilation/lung expansion. Infected intrapleural blood clots and is organized to form a fibrothorax that must be peeled to allow more expansion. The touching surfaces of the two layers of pleura remain slippery and are facilitated by the small amount of serous fluid

Mediastinum Divisions & Mechanics of Breathing

Mediastinum Divisions:

  • Region located between the two pleural sacs, centered in the thoracic cavity
  • Therefore: Left lung accounts for 45% of total lung capacity (TLC) while the right lung accounts for 55%.
    Perforation of the larynx, trachea, pharynx, or esophagus, which sometimes occurs during esophagoscopy, bronchoscopy, or traumatic intubation, can produce mediastini