URT Notes (Lecture 14)

Lecture Objectives

  • Describe the structures of the respiratory system and state their functions
  • Describe the structures of the upper respiratory tract
  • Describe the epithelia of the upper respiratory tract
  • Pre-reading references: anatomy of URT and its epithelia (as per Martini Visual Anatomy & Physiology modules)

Main Components

  • URT (upper respiratory tract)
  • LRT (lower respiratory tract)
  • Thoracic cavity
  • Joints
  • Respiratory muscles
  • Link structure to function; cellular-level understanding of the respiratory mucosa is needed

Upper Respiratory Tract (URT)

  • Consists of: Nose, Nasal Cavity, Conchae, Paranasal Sinuses, Pharynx (Nasopharynx, Oropharynx, Laryngopharynx)

Functions of the URT

  • Conducts and conditions air for gas exchange: clean, warm, and moist air
  • Olfaction (smell)
  • Resonance for speech

Nasal Cavity & Nose

  • Nose: external nares, nasal bridge, nasal septum; anterior nasal cavity cartilage; vestibule lined with skin and hair follicles; vibrissae filter inhaled air
  • Nostrils separated by nasal septum; nasal bones form nasal bridge
  • Conchae (turbinates): superior, middle, inferior; swirl air to enhance contact with mucosa; humidify and warm air; aid in olfaction; lined by respiratory epithelium
  • Nasal Epithelium: predominantly respiratory epithelium (pseudostratified ciliated columnar with goblet cells); small area on roof lined by olfactory epithelium with olfactory receptors
  • Lamina propria beneath epithelium; thin-walled vascular plexus underneath
  • Functions of vascular plexus: warms incoming air; prone to nosebleeds when damaged
  • Goblet cells produce mucus; mucus traps debris and moistens air
  • Ciliated cells move mucus cephalad toward the pharynx; mucus swallowed and digested
  • Mucus components: mucins, lysozymes, immunoglobulins, glycoproteins, salts

Paranasal Sinuses

  • Sinuses are air-filled cavities within skull bones (frontal, sphenoid, ethmoid, maxillary) surrounding the nose
  • Lined with respiratory mucosa; drain into the pharynx
  • Functions: lighten the skull, increase surface area to humidify/clean air, sound resonance
  • Infection can block drainage (sinusitis)

Pharynx (shared air and food passage)

  • Three regions: Nasopharynx (air passage only), Oropharynx (air & food), Laryngopharynx (air & food)
  • Lined by respiratory mucosa in all regions except where protection is needed; oropharynx and laryngopharynx have stratified squamous epithelium to protect against abrasion
  • Nasopharynx: located posterior to nasal cavity; soft palate and uvula block nasopharynx during swallowing; auditory tubes drain here; pharyngeal tonsils present
  • Oropharynx: posterior to oral cavity; extends from soft palate to the hyoid; contains palatine and lingual tonsils
  • Laryngopharynx: extends from hyoid bone to the opening of the larynx/esophagus; ends where respiratory and digestive tracts diverge; during swallowing, food has right of way

Epithelium in the URT

  • Nasal epithelium sits on a mucosa that includes lamina propria
  • Two main epithelial types in the nasal region:
    • Respiratory epithelium: pseudostratified ciliated columnar with goblet cells
    • Olfactory epithelium: on the roof; contains olfactory receptor cells
  • Goblet cells produce mucus; ciliated cells help transport mucus toward pharynx
  • Olfactory region contains sensory receptors for smell; nerves project to olfactory bulb

Histology: Mucosa & Submucosa (brief)

  • Mucosa consists of epithelia + basement membrane + lamina propria (connective tissue)
  • Submucosa lies beneath, may contain glands
  • The mucosa + submucosa organization varies by region and function

Quick Notes on Snot & Mucus (contextual)

  • Mucus traps debris; protects against pathogens
  • Mucus composition includes mucins, enzymes, antibodies, salts
  • Snot (nasal mucus) vs sputum (lower respiratory mucus)

Quick Review Questions (Q1–Q3 prompts)

  • Why does the nose run on cold days? (temperature/warmth and mucus production balance)
  • Why do we cough up mucus when unwell? (clearing mucus and debris from airways)
  • Why do smokers cough frequently? (cilia fatigue/impairment and mucus buildup)

Summary of URT anatomy (key points)

  • URT includes nose, nasal cavity, conchae, paranasal sinuses, pharynx
  • Functions: air conditioning, olfaction, speech resonance
  • Epithelia: respiratory epithelium (ciliated + goblet cells) and olfactory epithelium on roof
  • Pharynx regions and their epithelial and functional characteristics
  • Sinuses: air-filled, drain to pharynx, functions in lightening skull and resonance