Respiratory Histo.

• Respiratory Epithelium

  Two portions: Conducting Portion - air pathway and air conditioning, Respiratory portion - gaseous exchange

  
• Conducting Portion

  1. Air conduit - presence of cartilage, collagen, elastic fibers, smooth muscle fibers (support and prevention of lumen collapsing)

  2. Air Conditioning - through: Vibrissae - thick, short hairs in inner surface of nostrils, remove coarse dust particles

  3. Layer of mucous and serous secretion - trap particles and gas impurities, moisten air, contain IgA

  4. Conchae - cause air flow turbulence

  5. Vascularate of lamina propria - loops of capillaries that warm up air
• Respiratory Epithelium

  • Pseudostratified ciliated columnar cells

  
• Cell types in Respiratory Epithelium

  • Ciliated columnar - most common
  • Goblet cells - contain mucous droplets
  • Brush cells - chemosensory receptors with microvill
  • Small granule cells - part of DNES
  • Basal cells - mitotically active, act as progenitor for other cells
• Organs lined by Respiratory Epithelium( these are also conducting)

  • Nasal cavity (except superior concha), paranasal sinuses, nasopharynx, larynx, trachea, bronchial tree up to bronchioles

  
• Nasal Cavity

  • Opens anteriorly into nares and posteriorly into nasopharynx. Two parts: Vestibule - dilated anterior part, lined by skin on the outside and resp. Epithelium on the inside
  • Nasal cavities - 2 cavities separated by nasal septum. There are 3 conchae (middle and inf. Are lined by resp. epith. the superior is lined by olfactory epith.)
• Olfactory Epithelium

  Mucous membrane specialized for sense of smell. Its lamina propria has large serous glands and olfactory Bowman's glands which secrete fluid and facilitate access to new odoriferous substances.

  
• Cell types in Olfactory Epithelium

  • Basal cells - Small, spherical, near basal lamina. They replace olfactory neurons and supporting cells every 2-3 months.
  • Olfactory neurons - bipolar shape, nuclei in middle. Their apical surface is the dendrite and has chemoreceptors for smell sensation. Their basal surface has axons which unite forming the olfactory nerve which passes to the brain.
  • Supporting cells - columnar, have microvilli on their broad apexes and narrow basal part, which nuclei at top of cell. They are connected to olfactory cells and support and protect them.
• Paranasal Sinuses

  Bilateral cavities in frontal, axillary, ethmoidal sphenoid bones. Lined by thin resp. Epith. And have a few goblet cells and few small glands. Communicate with nasal cavity through small openings where mucous pass.
• Nasopharynx

  Communicate with post. end of nasal cavities. Mucosa contains pharyngeal tonsils. Communicate with middle ear by auditory tube.

  
• Squamous metaplasia - change of pseudostratified ciliated columnar epithelium to stratified squamous epith. Due to chronic exposure to toxic materials. Caused by cilia immobilization and failure to clear mucous
• Immotile cilia syndrome - caused by def. of Dynein which is important in cilia movement. Can cause chronic resp. infection and male infertility
• Anosmia - loss of smell due to ethmoid bone or olfactory epithelium damage (temporary)

  
• Hyposmia - reduction of smell due to ethmoid/olfactory epithelium damage (temporary)

  
• Larynx

  Short passage for air between the pharynx and the trachea

  
• Larynx

  • Wall supported by hyaline and cartilages to maintain airway and help with sound production
  • Epiglottis - flat structure projecting from top of larynx to prevent swallowed food from entering larynx
  • Lingual surface - lined by strat. Squamous epith.
  • Laryngeal surface - lined by resp. epith.
  • Upper pair - vestibular fold - lined by resp. epith., below which is seromucous gl.
  • Lower pair - vocal folds - lined by strat. squamous epith.
  • Vocal ligament - dense elastic CT bundle supporting vocal cord free edge
  • Vocalis muscle - bundle of stratified muscles deep to mucosa of vocal fold

  
• Trachea

  Thin walled tube 10-12 cm long, 2.5cm diameter from larynx to thorax (divides into 2 primary bronchi)

  
• Trachea

  • Wall has 3 layers: Mucosa - Resp. epith., lamina propria
  • Submucosa - 16-20 C shaped hyaline cartilage rings
  • Adventitia - loose CT

  
• Bronchial Tree

  1. Trachea divides into 2 main bronchi

  2. Left primary bronchus divides into 2 secondary bronchi and the right primary bronchus divides into 3 secondary bronchi

  3. Secondary bronchi divide repeatedly into tertiary bronchi which give smaller branches (bronchioles)

  
• Bronchus

  • Primary - same histological structure as trachea, but complete cartilage rings
  • Secondary - same histological structure as trachea, but cartilage in isolated plates
  • Lamina propria rich in elastic fibers, mucous and serous glands, lymphocytes, lymphatics
  • Contains smooth muscle fibers as crisscrossing spiral bundles of smooth muscle fivers

  
• Bronchioles


  • Intralobular airways, 1mm or less diameter, no glands or cartilage
  • Large - lined by resp. epith.
  • Small - lined by simple ciliated columnar epithelium

  
• Terminal Bronchiole


  • Lined by simple columnar or simple cuboidal epithelium (ciliated) alternating with club cells
  • Club cells - non-ciliated, have apical secretory granules, secrete surfactant, detoxify and act as stem cells