Half head anatomy model of respiration

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half head anatomy model respiration sagittal section respiratory tract anatomy

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half head respiratory model anatomy structures

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I now have everything I need for a comprehensive, well-illustrated answer. Here is the full breakdown of the half-head anatomy model of respiration:

Half-Head Anatomy Model: Respiration

The half-head (midsagittal section) model shows the upper respiratory tract in its entirety - from the external nares down to the larynx and upper trachea. Below is the labeled model:

Half-head anatomy model showing labeled respiratory structures

Structures Identified on the Model

Nasal Cavity

External Nares - the openings of the nose through which air enters
Superior, Middle, and Inferior Nasal Conchae (turbinates) - scroll-like bony projections that increase surface area, warm, humidify, and filter inspired air
Nasal septum - divides the cavity into left and right sides
Opening of the Pharyngotympanic (Auditory/Eustachian) tube - connects middle ear to nasopharynx, visible on the lateral wall

Sinuses

Frontal Sinus - paired air-filled cavities in the frontal bone; drain into the nasal cavity; warm and humidify air
Sphenoid Sinus - posterior to the nasal cavity, within the sphenoid bone

Palate

Hard Palate - bony anterior roof of the oral cavity; separates oral from nasal cavities
Soft Palate - muscular posterior continuation; the levator palati, tensor palati, palatopharyngeus, and palatoglossus muscles keep it from collapsing against the posterior pharynx during breathing
Uvula - the dangling projection at the posterior margin of the soft palate

Pharynx (3 Divisions)

The pharynx connects the nasal and oral cavities to the larynx and esophagus.

Division	Location	Function
Nasopharynx	Behind the nasal cavity, above the soft palate	Air passage only; contains pharyngeal tonsil (adenoid)
Oropharynx	Behind the oral cavity, from soft palate to epiglottis	Air and food passage; contains palatine tonsils
Laryngopharynx (Hypopharynx)	From epiglottis to esophageal opening	Air to larynx, food to esophagus

Pharyngeal Tonsil (Adenoid) - lymphoid tissue on the posterior wall of the nasopharynx; part of Waldeyer's ring of immune defense.

Palatine Tonsil - lymphoid tissue at the oropharynx, between the anterior and posterior tonsillar pillars.

Tongue and Epiglottis

Tongue - occupies the floor of the oral cavity; the genioglossus muscle maintains its forward position, preventing posterior airway obstruction
Epiglottis - leaf-shaped cartilage at the root of the tongue; deflects over the laryngeal inlet during swallowing to protect the airway
Vallecula - the depression between the base of the tongue and the lingual surface of the epiglottis; the landmark for Macintosh laryngoscope blade placement during intubation

Larynx

The larynx consists of:

Hyoid Bone - the only bone with no articulation to another bone; serves as anchor for tongue and laryngeal muscles
Thyroid Cartilage - the largest laryngeal cartilage; forms the "Adam's apple"
Cricoid Cartilage - the only complete cartilaginous ring; the narrowest part of the adult airway (~17 mm diameter in men, ~13 mm in women)
Vestibular Folds (False Vocal Cords) - superior folds; involved in vocalization support and protection
Vocal Folds (True Vocal Cords) - inferior folds; vibrate to produce sound; the glottis is the space between them

Into the Lower Airway

Trachea - begins at the inferior border of the cricoid, extends ~10-13 cm to the carina; composed of C-shaped cartilaginous rings connected posteriorly by the membranous wall
Esophagus - visible posterior to the trachea; receives food from the laryngopharynx

Airway Zones: Conducting vs. Respiratory

Tracheobronchial tree showing dichotomous branching generations from trachea to alveolar sac, and segmental bronchi of right and left lungs

The airway undergoes ~23 generations of dichotomous branching from trachea to alveolar sacs. The conducting zone (generations 0-16, trachea to terminal bronchioles) carries air but does not exchange gas - this is anatomical dead space (~150 mL). The respiratory zone (generations 17-23, respiratory bronchioles to alveolar sacs) is where gas exchange occurs across ~300-500 million alveoli, with a total surface area of 50-100 m².

Muscles of Respiration (Not Visible on Half-Head Model)

The half-head model shows the upper airway, but breathing is driven by:

Diaphragm - principal muscle; accounts for ~75% of chest volume change; descends 1.5-7 cm during inspiration
External intercostals - assist inspiration by lifting ribs upward and outward
Accessory muscles (sternocleidomastoid, scalenes) - recruited during increased respiratory effort
Abdominal muscles - active during forced expiration
Pharyngeal muscles - genioglossus, levator/tensor palati, palatopharyngeus keep the upper airway patent during both waking and sleep

Functional Summary of Upper Airway Structures

Structure	Respiratory Function
Nasal conchae & sinuses	Filter, warm, humidify inspired air
Soft palate & pharyngeal muscles	Maintain patent airway, prevent collapse
Epiglottis	Directs air to larynx; closes over airway during swallowing
Vocal cords / glottis	Airway gatekeeper; phonation
Trachea	Conduit; mucociliary clearance of secretions

Sources: Morgan & Mikhail's Clinical Anesthesiology, 7e (Ch. 23); Fishman's Pulmonary Diseases and Disorders (Ch. 145); Indiana University A215 Half-Head Model Lab

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