4: Respiratory System: Pt. 1

Respiratory System: Introduction, Respiratory Tract, and Lungs

• Course Learning Objective: Describe gas exchange in the body by examining and identifying gross and microscopic anatomical structures in the respiratory system.

Lecture Learning Objectives

• Recall the components of the anatomical and functional divisions of the respiratory system.
• For each segment of the respiratory tract:
  • Identify its primary function (in green)
  • Identify its boundaries
  • Identify the bolded/labeled anatomical structure.
  • Link the epithelial lining to its function.
  • Innervation and blood supply, when identified.
• Describe the structures and mechanisms of sound production using the anatomical structures involved.
• Take three deep breaths visualizing air passage.
• Recall the difference between respiration and ventilation and describe the processes of each:
  • Explain Boyle's law and its role in ventilation.
  • Define inhalation and exhalation.
  • Detail the muscles of respiration and their actions.
  • Describe the steps of gas exchange.
• Use anatomical organization and function of the pleura to describe pulmonary collapse.

Organization and Function

• Provides gas exchange for living cells.
• Oxygen in, carbon dioxide out
• Partners with the cardiovascular system for gas transport between atmosphere and the body's cells.
• Categorization: anatomical (upper and lower respiratory tracts) and functional (conducting and respiratory portions).

Nose and Nasal Cavity Function

• Conduction: Opens to nasopharynx via choanae.
• Filtration: Vibrissae (hair) filter inhaled air. Lined with pseudostratified ciliated columnar epithelium (respiratory epithelium) with mucus-producing goblet cells (G).
• Conditioning: Highly vascularized layer deep to epithelial layer; 3 nasal conchae produce turbulence.
• Olfaction: Olfactory epithelium in superior portion. lined with pseudostratified columnar epithelium.
• Paranasal sinuses: Lined with pseudostratified columnar epithelium.

Nasal Cavity

• Structures: septal cartilage, perpendicular plate of ethmoid bone, nasal vestibule, naris, vomer and nasal septum.

Nose and Nasal Cavity Anatomy

• Nose: Structures include nares, frontal, nasal, cribriform plate, hard palate, maxillae, 3 nasal concha, nasal septum, and choanae (openings to nasopharynx).

Nose and Nasal Cavity Anatomy

• Nasal concha form nasal meatuses (superior, middle, inferior).
• Nasal cavity: roof (frontal, nasal, cribriform plate, sphenoid); floor (hard and soft palate, maxillae and palatine) walls (maxillae, 3 nasal conchae), divided by nasal septum, and opening to nasopharynx (choanae).

Nose and Nasal Cavity Anatomy (Paranasal Sinuses)

• Paranasal sinuses (frontal, ethmoidal, sphenoidal, maxillary) communicate with nasal cavity via openings in nasal meatuses.

Pharynx

• Extends from posterior nasal cavity to the larynx and esophagus.
• Common space for respiratory and digestive tracts (throat). Main function is conduction and defense (tonsils).
• Anatomical divisions: nasopharynx, oropharynx, laryngopharynx. Each division contains specific tonsils.

Pharynx Anatomy

• Nasopharynx: superior nasal cavity/soft palate; location of pharyngotympanic tube opening and pharyngeal tonsils; respiratory function (pseudostratified ciliated columnar epithelium).
• Oropharynx: soft palate to hyoid bone/epiglottis; contains palatine and lingual tonsils; respiratory and digestive function (nonkeratinized stratified squamous epithelium).
• Laryngopharynx: hyoid to superior border of esophagus; respiratory and digestive function (nonkeratinized stratified squamous epithelium).

Larynx (Voice Box)

• Start of the lower respiratory tract- 9 cartilaginous pieces held together by ligaments and muscles and suspended from hyoid bone, continuous with laryngopharynx and trachea (inferiorly) and anterior to esophagus.

Larynx

• Conducts air, produces sound, and guards airway passage.
• Cartilages: hyoid, thyroid, cricoid, epiglottis, corniculate, and cuneiform.
• Vocal folds, vestibular folds, epiglottis, and glottis.

Larynx - Anterior/Lateral View

• Structures: hyoid, thyroid cartilage, thyroid notch, cricoid cartilage, trachea, cricothyroid ligament, and thyrohyoid membrane.

Larynx - Posterior View

• Epiglottis, thyrohyoid ligament, thyroid cartilage, cricoid cartilage, cornuculate cartilage, arytenoid cartilage.

Internal Laryngeal Structures

• Laryngeal inlet continuous with the vestibule.
• Vestibule is bound inferiorly by vestibular folds (false vocal folds).
• Laryngeal ventricles open laterally, bounded inferiorly by vocal folds (true vocal folds) and are continuous with laryngeal saccule.
• Vocal folds create rima glottidis, vestibular folds create rima vestibuli.
• Folds are mucosa overlying ligaments
• Conus elasticus creates infraglottic space.

Intrinsic Laryngeal Muscles

• Oblique arytenoid, transverse arytenoid.
• Posterior and lateral cricoarytenoid.
• Transverse arytenoid.
• Lateral cricoarytenoid/ and superficial/ deep.

Intrinsic Muscles of the Larynx

• Change shape of internal structures (vestibule and rima vestibuli).
• Help close the laryngeal inlet (oblique arytenoid).
• Cause arytenoid cartilage to abduct or adduct (pivot).
• Open and close rima glottidis.
• Adjust tension in vocal ligaments.

Larynx - Sound Production

• Epiglottis, vestibular fold, vocal fold, rima glottis, thyroid cartilage, arytenoid cartilage, cricoid cartilage.
• Vocal ligaments and conus elasticus.

Laryngeal Innervation

• Branches of vagus nerve:
  • Superior laryngeal n. (internal branch-sensory; external branch - cricothyroid mm.)
  • Recurrent laryngeal n. (all other muscles).

Trachea

• Continuous with larynx superiorly, anterior to esophagus.
• Conducts air, provides defense via cilia and mucus production in goblet cells.
• Lined with pseudostratified ciliated columnar epithelium.
• Cartilage: 15-20 "C" shaped tracheal cartilages connected by CT and annular ligaments, inferior most C shaped cartilage called the carina.
• Trachealis muscle located at open portion of "C", allows expansion for swallowing and contraction for coughing

Lungs

• Located within pleural cavities, one on each side of the mediastinum.
• Left lung has 2 lobes, right lung has 3 lobes; lobes divided by fissures
• Root or hilum of lungs (passage for primary bronchi, pulmonary arteries, and veins).

Lungs (Lateral View)

• Oblique and horizontal fissures divide lungs into lobes (superior, middle, inferior).

Left Lung

• Structures: root of lung (pulmonary arteries, pulmonary veins, bronchi), groove for esophagus, groove for aorta, cardiac notch.

Right Lung

• Structures include root of lung, pulmonary arteries, pulmonary veins, bronchi, groove for esophagus, groove for superior vena cava and cardiac notch/impression

Pleura of the Lungs

• Visceral pleura directly on lungs, parietal pleura on internal thoracic walls and superior surface of diaphragm; pleural cavity potential space between each layer.
• Costodiaphragmatic recess where serous fluid collects in pleural effusion.

Blood Supply to Lungs

• Bronchial arteries directly from anterior aorta and form capillary beds (left superior and inferior bronchial; right bronchial branches).
• Bronchial veins drain into azygos and accessory hemiazygous veins.
• Alveoli and alveolar ducts exchange gas directly using pulmonary system, instead of bronchial circulation.

Bronchial Tree

• Bronchial tree in lungs begins with primary bronchi which end in terminal bronchioles.
• Location for conduction and respiration; made of cartilaginous rings that become less numerous and smaller. Eventually, the rings become scattered cartilage pieces.
• Surrounded by a complete ring of smooth muscle.
• From largest to smallest branches transitioning from pseudostratified ciliated columnar epithelium to simple columnar to simple cuboidal, to simple squamous

Bronchial Tree (Primary, Secondary, Tertiary)

• Primary bronchi (right and left): enter each lung at the hilum with vessels and nerves.
• Secondary (lobar) bronchi: to each lobe (three on right, two on left).
• Tertiary (segmental) bronchi: to each broncopulmonary segment.

Bronchial Tree (Structures)

• Based on anatomy, the right primary bronchus is more likely to be blocked during aspiration

Bronchial Tree (After Bronchi)

• Conducting bronchioles, terminal bronchioles (last conduction portion).
• Lined by simple columnar or simple cuboidal epithelium with no surrounding cartilage.
• Thicker layer of smooth muscle to maintain integrity to aid in bronchoconstriction and bronchodilation

Respiratory Portion

• Respiratory bronchioles, alveolar ducts, alveolar sacs, alveoli (plural of alveolus).
• Lined by simple cuboidal and simple squamous epithelium with no cartilage.
• Openings in walls allow for respiration.

Respiration and Ventilation

• Gas exchange between alveoli and pulmonary circulation, and movement of gases.

Pulmonary Ventilation - Breathing

• Caused by muscular actions, atmospheric pressure, and intrapulmonary (lung) pressure.
• Boyle's law: Pressure of a gas decreases if volume of the container increases and vice versa.

Pulmonary Ventilation - Breathing (Inhalation/Exhalation)

• Inhalation: Thoracic wall expansion increases thoracic cavity volume, decreasing intrapulmonary pressure. Air moves from higher to lower pressure.
• Exhalation: Thoracic wall compression decreases thoracic cavity volume, increasing intrapulmonary pressure. Air moves from higher to lower pressure.

Muscles of Respiration (Diaphragm)

• Diaphragm contraction flattens diaphragm causing expansion of thoracic cavity.

Muscles of Respiration (Transversus Thoracis)

• Depresses ribs,

Muscles of Respiration (Serratus Posterior Superior/Inferior, Scalenes, External/Internal Intercostals)

• Role in inhalation and exhalation, forced inhalation/exhalation and elevation/depression of ribs.

Blood Supply and Gas Exchange

• Gas enters bronchopulmonary segments via respiratory bronchioles and alveolar ducts lined by simple squamous epithelium.
• 300-400 million alveoli where gas exchange occurs between respiratory and cardiovascular systems. Low oxygen-containing blood enters lungs via pulmonary arteries (from right ventricle); oxygenated blood exits via pulmonary veins to the left atrium.

Lungs - Blood Supply

• Pulmonary circulation conducts blood to and from gas exchange surfaces in the lungs, replenishing oxygen and ridding blood of carbon dioxide.
• Deoxygenated blood travels through pulmonary trunk to pulmonary arteries and pulmonary capillary systems in lungs.
• Oxygenated blood travels back through pulmonary veins to the pulmonary capillary system to the left atrium.

Pleura and Pulmonary Collapse

• Lungs and internal thoracic wall are covered in pleura. Visceral pleura directly on lungs, parietal pleura lines internal thoracic walls. Pleural cavity is a potential space between them, and costodiaphragmatic recess is where serous fluid may accumulate.

External Lung Structures

• Lungs and internal thoracic wall covered in pleura; visceral pleura directly on lungs; parietal pleura on internal thoracic walls and superior surface of diaphragm; pleural cavity between each layer; costodiaphragmatic recess.

Clinical Correlation: Pulmonary Collapse

• Lungs similar to inflated balloons, if distention not maintained, inherent elasticity makes them collapse.
• Parietal and visceral pleura attached to the thoracic wall and lungs; surface tension, fluid filled pleural cavity, adheres lungs to the thoracic wall, preventing collapse.

Clinical Correlation: Pulmonary Collapse (Atelectasis)

• Primary atelectasis: collapse failure of a lung to inflate at birth.
• Secondary atelectasis: collapse of a previously inflated lung due to loss of negative pleural pressure.