Larynx

INTRODUCTION:
  • The Larynx is an apparatus made up of cartilage, ligaments, muscles, and mucous membrane, which guards the entrance to the lower respiratory passages (trachea, bronchi, and lungs) and houses the vocal cords.
DEVELOPMENT OF LARYNX:
  •  Occur during the 4th week of intra uterine life
  • The respiratory primordium appears in the floor of the foregut in the 4th week of gestational life.
  • The larynx begins as a slit like diverticulum(laryngotracheal groove ) in the ventral wall of the primitive pharynx .
  • The groove gradually deepens and its edges fuse to form a septum,which separates the laryngotracheal tube from the pharynx and oesophagus.
  • The process of this fusion starts caudally and extend cranially
  • Between 5th & 6th weeks, — 3 swellings appear at the laryngeal aditus.
  • An anterior swelling , a derivative of the hypobranchial eminence from 4th arch—forms Epiglottis.
  • 2 lateral arytenoid swellings appear, derived from the 6th branchial arch, move medially and form a T-shaped aperture
  • Laryngeal lumen— temporarily occluded at 8 weeks gestational age as a result of epithelial proliferation.
  • By the 10th week of gestation, recanalization occurs and consequently pair of laryngeal ventricles are formed. 
  • The laryngeal ventricles are bound by mesenchyme tissue that condense and progress into false and true vocal cords.
  • Laryngeal cartilages develop from the mesenchyme of the branchial arches.
  • Thyroid cartilage-- from the 4th arch mesenchyme as two lateral plates meet in the midline.
  • Arytenoids , Corniculate , Cricoid & Tracheal cartilages-- 6th branchial arch
  • Epiglottis — develops from Hypobranchial eminence
  • Intrinsic laryngeal muscles develop from the mesoderm of the 4th and 6th arches
EXTERNAL FEATURES OF LARYNX:
  • Larynx is located anterior to the 3rd, 4th, 5th, and 6th cervical vertebrae.
  • Extends from the base of the tongue to the proximal portion of the trachea.
  • Laryngeal skeleton is suspended from the hyoid bone by the medial and lateral thyrohyoid membrane.
  • The lateral lobes of the thyroid gland lie anterolateral to the thyroid and cricoid cartilage.
  • Isthmus of the thyroid gland lies just below the cricoid cartilage and often covers the first 1 or 2 tracheal rings.
  • The carotid sheath and its contents lie just posterolateral to the larynx.
  • The recurrent laryngeal nerve ascends in the tracheoesophageal groove and enters the larynx just posterior to the cricothyroid articulation
  • The 3rd to 6th cervical vertebrae, prevertebral muscles, and fascia lie posterior to the larynx.
  • Laryngofissure is opening of larynx in midline
INTERNAL FEATURES OF LARYNX:
  • The cavity of the larynx extends
  • Above – from the area of the tip of the epiglottis,aryepiglottic folds, and interarytenoid folds
  • Below — to the 1st tracheal ring
  • Internal cavity of the larynx
  • Divided into 3 spaces:
  1. Supraglottic 
  2. Glottic
  3. Subglottic spaces
DIFFERENCE B/W ADULT & INFANT LARYNX:
  • Size- smaller in infants
  • Shape- funnel shaped in infants , cylindrical in adults
  • Softness-laryngeal cartilages are softer in infants
  • Superiorly placed in infants helps child to breathe & suckle at same time
  • Straighter and less oblique than in adults
  • Sensitivity is greater in infants more prone to spasm
  • Sub glottis is very narrow ,even a small swelling can lead to airway obstruction in infants
  • The narrowest part of the infantile larynx is the junction of subglottic larynx with trachea and this is because cricoid cartilage is very small
Exam Question
  • Superiorly placed larynx in infants helps child to breathe & suckle at same time
  • Larynx is funnel shaped in infant
  • Larynx is cylindrical shaped in adults
  • Cricoid is the narrowest part of infantile larynx
  • Laryngofissure is opening of larynx in midline

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