Respiratory System Anatomy

• The video is about the anatomy of the respiratory system and explains why we breathe

Specific Learning Objectives

• Understanding basic anatomy of respiratory tract from nasal cavity to alveoli
• Knowing the structure of lungs
• Listing the respiratory membrane's components
• Explaining the roles of the thoracic wall and pleura in respiration
• Detailing how respiratory muscle contraction impacts thoracic volume during breathing
• Understanding alveolar pressure changes and their connection to air movement
• Describing how surfactant and pleural pressure prevent lung collapse
• Knowing mechanism of gas exchange and transport
• Defining alveolar ventilation, lung (pulmonary) volumes, and capacities

Functions of Respiratory System

• Includes respiration, blood pH regulation, sound production, olfaction, and protection
• Respiration involves:
• Ventilation
• External respiration
• Respiratory gas transport
• Internal respiration

Organization of the Respiratory System

• Includes the nares, nasal cavity, pharynx, larynx, trachea, bronchi, bronchioles, alveolar duct, and alveoli
• Structural classification:
• Upper respiratory tract
• Includes the nose, nasal cavity, and pharynx
• Lower respiratory tract
• Includes the larynx, trachea, bronchi, bronchioles, and alveoli
• Functional classification:
• Conducting zone
• From nose to terminal bronchioles
• Respiratory zone
• From respiratory bronchioles, alveolar duct & alveoli

Nares and Nasal Cavity

• External nose forms the external structure
• The internal structure includes:
• Nares opening to the choana internally
• Vestibule of the nasal opening
• Septum dividing the nose
• Floor which consists of the hard palate, soft palate, and uvula
• Conchae and meatuses structures include:
• Superior, middle, and inferior conchae
• Superior, middle, and inferior meatuses
• Sinuses are present

Functions of the Nasal Cavity

• It acts as a passageway for air
• Hair filters coarse particles from inspired air
• Mucus traps dust, bacteria, and other debris from inspired air, and humidifies the air
• Cilia create a gentle current, moving contaminated mucus towards the throat to be swallowed
• Lysozyme kills bacteria
• A rich capillary network helps maintain the temperature of inhaled and exhaled air
• Conchae & meatuses increase mucosal surface, creating turbulence
• Olfactory epithelium contains olfactory receptors that aid olfaction
• Sinuses act as resonating chambers

Pharynx

• The pharynx, known as the throat, serves as a common passage for both food and air
• Three regions:
• Nasopharynx:
• Situated posterior to the nasal cavity
• Extends from the choana to the uvula
• Includes the Eustachian tube opening and pharyngeal tonsils
• Oropharynx:
• Located posterior to the oral cavity
• Extends from uvula to the hyoid bone
• Acts as a common passage for air and food
• Includes palatine and lingual tonsils
• Laryngopharynx:
• Situated posterior to the epiglottis
• Extends from the hyoid bone to the larynx/esophagus

Larynx

• Also called the voice box and serves as a passageway for air
• Consists of 9 cartilages
• Six are paired; arytenoid, corniculate, and cuneiform
• Three are unpaired; thyroid (Adam's apple), cricoid, epiglottis
• Ligaments extend from arytenoids to thyroid cartilage
• True vocal cords (vocal folds)
• Vestibular folds (false vocal cords)
• Opening between cords is known as the glottis

Functions of the Larynx

• Maintains an open passageway for air movement
• Directs food into the oesophagus away from the respiratory tract
• Facilitates sound production through the vocal folds
• Traps debris to prevent it from entering the lungs

Trachea (windpipe)

• Extends from the larynx to the carina
• Divides into two main bronchi at the carina
• Located anterior to the oesophagus and passes through the mediastinum
• About 10-12 cm long and 2 cm in diameter
• A tough, flexible membranous tube composed of dense regular connective tissue (CT) and smooth muscle
• Contains 15-20 C-shaped hyaline cartilage rings with smooth muscle in between
• Presence of trachealis muscle posteriorly
• The mucosa of the carina area is very sensitive, triggering a cough reflex

Trachea Functions

• Cartilage maintains an open airway
• Trachealis muscle facilitates ease of peristaltic movement in the oesophagus
• Contraction of the trachealis muscle causes expired air to rush out with greater force
• The sensitive nature of the carina triggers coughing to expel foreign particles

Tracheobronchial Tree

• Progressive changes occur throughout tracheobronchial tree
• Progressive changes
• Primary (main) bronchi → terminal bronchioles (<0.5mm in diameter)
• Decrease in passageway diameter as tree progresses
• Decrease in cartilage as tree progresses
• Rings in trachea replaced with irregular plates until completely replaced with elastic fiber
• Increase in smooth muscle as tree progresses
• From in between cartilage rings(trachea) to whole layer
• Epithelial changes
• Pseudostratified ciliated columnar to simple squamous epithelium

Respiratory System - Respiratory Zone

• Includes respiratory bronchioles, alveolar ducts, and alveoli
• Respiratory bronchioles consists of very few alveoli
• Alveolar ducts have more alveoli and end in alveolar sacs
• Alveoli are small bag-like structures, richly supplied by blood capillaries, and contain elastic fibers

Lungs

• Located in the thoracic cavity on either side of the mediastinum
• Cone-shaped with the base on the diaphragm
• Costal, medial, and diaphragmatic surfaces
• The right lung has three lobes
• Superior, middle, and inferior
• Separated by two fissures: horizontal and oblique
• The left lung has two lobes
• Superior and inferior
• Separated by one (oblique) fissure
• Hilum on the medial surface is the entry/exit point for blood vessels, nerves, lymphatic vessels & bronchi
• Cardiac notch medially on the left lung
• Bronchopulmonary segments
• Ten in the right lung and 8/9 in the left lung
• Lobules are key
• 25 orders of the branching from trachea to the alveolar ducts
• Primary (main) bronchi on the right and left supply each lung
• Secondary (lobar) bronchi supply the lobes
• Tertiary (segmental) bronchi supply the bronchopulmonary segments
• Terminal bronchi supply the lobule

Pleura/Pleural Membrane

• Consists of a double-layered serous membrane
• Parietal pleura is superficial, lining the inner wall of the thoracic cavity
• Visceral pleura is deep and covers the lungs
• Pleural cavity is the space between the two layers
• Pleural fluid is a lubricating fluid secreted by the pleura and fills the pleural cavity
• Pleural fluid reduces friction, causes the two membranes to adhere, protects, & reduces the impact of force

Respiratory System Epithelium

• Epithelium changes along the respiratory track to accommodate specific function of the structure
• Vestibule: Stratified squamous epithelium
• Nasal cavity: Pseudostratified ciliated columnar epithelium (PSCC)
• Nasopharynx: Pseudostratified ciliated columnar epithelium
• Oropharynx: Stratified squamous epithelium
• Laryngopharynx: Stratified squamous epithelium
• Trachea: Pseudostratified ciliated columnar epithelium with goblet cells
• Alveoli: Simple squamous epithelium
• Between trachea and alveoli, epithelium gradually changes from PSCC (bronchi) to ciliated simple columnar (larger bronchioles) to ciliated simple cuboidal (smaller bronchioles) to simple cuboidal (respiratory bronchioles)