Lower Respiratory System

• Lower Respiratory System Anatomy


  consists of:

  larynx

  trachea

  bronchi

  lungs

  
• Larynx


  larynx (voice box) attaches superiorly to the hyoid bone + opens into the laryngopharynx

  inferiorly, it is contionus w the trachea

  
• Functions of the Larynx


  provide a patent (open) airway

  act as a switching mechanism to route air + food into the proper channels

  voice production cos it houses the vocal cords
• Larynx Structure


  the framwork of the larynx is an intricate arrangement of 9 cartilages connected by membranes + ligaments

  except for the epiglottis, all laryngeal cartilages = hyaline cartilages

  
• Larynx Structure - Thyroid Cartilage


  the large, shiled-shaped thyroid cartilage is formed by the fusion of 2 cartilage plates at the midline

  typically larger in males than in females cos male sex hormones stimulates its growth during puberty

  
• Larynx Structure - Cricoid Cartilage


  inferior to the thyroid cartilage = ring-shaped cricoid cartilage, perched atop + anchored to the trachea inferiorly

  
• Larynx - Epiglottis


  the 9th cartilage, flexible epiglottis is composed of elastic cartilage + is almost entirely covered by a taste bud containing mucosa

  extends from the posterior aspect of the tongue to its anchoring point on the anterior rim of the throid cartilage

  when only air is flowing into the larynx, the inlet to the larynx is wide open + the free edge of the epiglottis projects upward

  during swallowing, the larynx is pulled superiorly + the epiglottis tips to cover the laryngeal inlet

  = keeps food out of the lower respiratory passages
• Larynx - Vocal Cords & Glottis


  lying under the laryngeal mucosa on each side r the vocal ligaments, which attach the small cartilages of the larynx to the thyroid cartilage

  these ligaments, composed largely of elastic fibres, form the core of mucosal folds = vocal cords

  the vocal cords vibrate, producing sound as air rushes up from the lungs

  the vocal cords + the medial opeining between them thru which air passes r called the glottis
• Trachea


  trachea descends from the larynx thru the neck + into the mediastinum

  it ends by dividing into the 2 main bronchi at midthorax

  
• Structure of Tracheal Wall


  the tracheal wall consists of several layers:

  mucosa

  submucosa

  adventitia

  layer of hyaline cartilage

  
• Tracheal Wall - Mucosa


  the mucosa has the same goblet cell-containing pseudostratified epithelium that occurs thru out most of the respiratory tract

  its cilia continually propel debris-laden mucus toward the pharynx

  this epithelium rests on a fairly thick lamina propria that has a rich supply of elastic fibres
• Tracheal Wall - Submucosa


  the submucosa = connective tissue layer deep to the mucosa

  contains seromucous glands that help produce the mucus sheets w in the trachea

  supported by 16-20 C-shaped rings of hyaline cartilage encased by the adventitia
• Flexibility of the Trachea During Breathing


  the trachea's elastic elements make it flexible enough to stretch + move inferiorly during inspiration + recoil during expiration, but the cartilage rings prevent it from collapsing + keep the airway patent despite the pressure changes that occur during breathing
• Flexibility of Trachea During Swallowing


  the open posterior parts of the cartilage rings, which lie next to the oesophagus, r connected by smooth muscle fibres of the trachealis + by soft connective tissue

  cos this portion of the tracheal wall is flexible, the oesophagus can expand anteriorly as swallows food passes thru it
• Terminal of the Trachea


  the last tracheal cartilages is expanded = terminal/carina of the trachea

  = projects posteriorly from its inner face, marking the point where the trachea branches into the 2 main bronchi