FACTS & HINTS

High-Yield Facts

Anatomic Points

The piriform fossa is a common site for fish bones to lodge. It is also a site where pharyngeal tumors can grow undetected for a period of time.

Aggregations of lymphoid tissue in the nasopharynxare called adenoids. Theycan become enlarged in children, causing obstruction of the nasopharynxand forcing the child to breathe through the mouth.

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Clinical Points

Pharyngitis

Also called a sore throat

Usuallycaused byviral infection

In children, common cause of bacterial pharyngitis is beta hemolytic streptococcus

If infection is severe, auditorytubes can become blocked, predisposing to otitis media

Patient maycomplain of pain on swallowing and pain referred to the ear

On examination, the throat maybe reddened and cervical lymph nodes maybe enlarged

Clinical Points

Tonsillectomy

Surgical removal of the palatine and lingual tonsils

Tonsillectomyis advised if the patient has experienced recurrent attacks of tonsillitis, particularlyif theyresulted in airwayobstruction and hearing difficulties

Amajor and common surgical procedure performed in children in the USA

Recoveryusuallywithin 2 weeks, although for adults this maytake longer and can have a higher complication rate

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8 Thyroid Gland and Larynx

STUDYAIMS

At the end of your study, you should be able to:

Know the general anatomyof the larynx

Describe the cartilaginous skeleton of the larynx

Describe the membranes of the larynx

Know the internal anatomyof the larynx

List the intrinsic and extrinsic muscles of the larynxand their function

Describe the arterial supply, venous and lymphatic drainage, and innervation of the larynx

Describe the structure of the thyroid gland

Describe the structure of the parathyroid glands

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GUIDE

Head and Neck: Thyroid Gland and Larynx

Larynx: General Anatomy

Organ of phonation and sphincter guarding lower respiratorytract

Approximately8 cm long

Connects oropharynxwith trachea

Lies anterior to prevertebral muscles, fascia, and the bodies of C3-C6 vertebrae

Laryngeal skeleton

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Comprised of three paired and three nonpaired cartilages Epiglottic cartilage (epiglottis)

Leaf-shaped elastic cartilage

Posterior to root of tongue and hyoid bone, anterior to laryngeal inlet

Broad superior end is free

Inferior end attached in midline to angle of thyroid laminae bythyroepiglottic ligament

Quadrangular membranes run between lateral sides of epiglottic cartilage and arytenoid cartilages on either side

Upper free margin of quadrangular membrane + covering mucosa = aryepiglottic fold

During swallowing overlies laryngeal inlet Thyroid cartilage

Composed of two flat laminae

Lower two thirds of laminae fuse in midline to form laryngeal prominence (Adam's apple)

Upper one third of laminae diverge to form superior thyroid notch

Posterior superior border of each plate projects superiorlyas superior horns

Posterior inferior border of each plate projects inferiorlyas inferior horns

Superior horns and superior borders of laminae attach to hyoid bone bythyrohyoid membrane Cricoid cartilage

Signet ring shaped, signet (lamina) facing posteriorly

Strong, thick, complete circle of cartilage

Attached to inferior thyroid bymedian cricothyroid ligament

Attached to first tracheal ring bycricotracheal ligament Arytenoid cartilages (paired)

Pyramid shaped with three sides

Articulate with lateral superior parts of cricoid lamina Has three processes:

a.Apexat superior end

b.Vocal process projects anteriorly

c.Muscular process projects laterally

Apex: Corniculate cartilage sits atop; attaches to aryepiglottic fold

Vocal process: posterior attachment for vocal ligament

Muscular process: attachment for posterior and lateral cricoarytenoid muscles

Corniculate and cuneiform cartilages

Nodules in posterior aryepiglottic folds

Cuneiforms do not attach to other cartilages

Corniculates attach to apices of arytenoids

Membranes of the laryngeal skeleton

Cricothyroid ligaments

Median cricothyroid ligament

Lateral cricothyroid ligaments (conus elasticus)

Both attach to cricoid cartilage to inferior border of thyroid cartilage

Medial free edge of lateral cricothyroid ligaments = vocal ligaments, basis of true vocal cords

Quadrangular membrane

Inelastic connective tissue

Attaches lateral aspects of arytenoids and epiglottis

Lower free border = vestibular ligament (false vocal cord)

Covered byvestibular fold

Above vocal fold

Extends from thyroid cartilage to arytenoid cartilage

Upper free border forms aryepiglottic ligament

Covered with mucosa

Called aryepiglottic fold

Thyrohyoid membrane

Bridges gap between superior border and superior horns of thyroid cartilage and

Pierced bysuperior laryngeal vessels and internal laryngeal nerve

Mucous membrane

Respiratoryepithelium except over true and aryepiglottic folds

This is composed of stratified squamous epithelium

Internal anatomy of the larynx

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Laryngeal cavity

From laryngeal inlet to tracheal cavity

Can be divided into three parts

Vestibule-above vestibular folds

Ventricle-sinus between vestibular folds above and vocal folds below

Infraglottic cavity-from below vocal folds to inferior border of cricoid cartilage

Vocal folds

Paired, project into laryngeal cavityon either side

Consist of

Vocal ligament-medial free edge of lateral cricothyroid ligament (conus elasticus)

Vocalis muscle-medial fibers of thyroid arytenoids muscle

Overlying mucosa

Source of sound

Produce audible vibrations when free edges of folds closelyapproximate each other

Are sphincter of larynxwhen folds are tightlyapproximated

Rima glottidis

Space between vocal folds

Varies in size with activity

During normal breathing: narrow wedge

During forced respiration: wide apart

During phonation: slit-like

Vestibular folds (false vocal cords)

Folds of mucous membrane over vestibular ligaments superior to vocal folds

Extend between thyroid and arytenoids cartilages

Protective in function

Ventricle of larynx: lateral outpocketings between vocal and vestibular folds on either side

Muscles of the larynx

Extrinsic muscles

Are muscles attached to hyoid bone and thus move thyroid

Infrahyoid muscles: lower larynxand hyoid bone

Sternohyoid

Omohyoid

Sternothyroid

Thyrohyoid

Suprahyoid muscles: Fixhyoid or elevate hyoid bone and larynx

Stylohyoid

Digastric

Mylohyoid

Stylopharyngeus-elevates hyoid bone and larynx

Intrinsic muscles

Alter length and tension of vocal cords

Alter rima glottides

Adductors

Lateral cricoarytenoid muscles

Transverse arytenoids

Abductors: posterior cricoarytenoid muscles

Sphincters

Transverse arytenoids muscles

Oblique arytenoids muscles

Aryepiglottic muscles

Tensors: cricothyroid muscles

Relaxers

Thyroarytenoid muscles

Vocalis muscles

All except cricothyroid supplied byrecurrent laryngeal nerve

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Joints of the larynxand movements at the joints

Cricothyroid joints

Thyroid cartilage glides and rotates here

Changes length of vocal folds

Cricoarytenoid joints: movement of the arytenoids cartilage on the lamina of the cricoid

Slide towards each other and awayfrom each other

Rotate

Tilt forward and back

Arterial supply to larynx

[Plate 69, Arteries of Oral and Pharyngeal Regions]

Superior laryngeal artery

Through gap in thyrohyoid membrane

Supplies internal larynx

Accompanies bysuperior laryngeal nerve

Inferior laryngeal artery

Supplies inferior internal larynx

Accompanied byrecurrent laryngeal nerve

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Venous drainage of larynx

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[Plate 70, Veins of Oral and Pharyngeal Regions]

Superior laryngeal vein to internal jugular vein

Inferior laryngeal vein → inferior thyroid vein or thyroid venous plexus (left brachiocephalic)

Lymphatic drainage of larynx

Above folds: to deep cervical nodes

Below folds: to paratracheal nodes to deep cervical nodes

Innervation of larynx

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[Plate 71, Nerves of Oral and Pharyngeal Regions]

Sensory

Above vocal folds: internal laryngeal nerve (branch of superior laryngeal)

Below vocal folds: inferior laryngeal nerve (branch of recurrent laryngeal nerve)

Motor:

Recurrent laryngeal nerve to all intrinsic muscles except cricothyroid

External laryngeal nerve to cricothyroid

Thyroid Gland

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H-shaped endocrine gland Produces two hormones

Thyroid hormone-controls metabolic rate

Calcitonin-controls calcium metabolism Overlies anterior and lateral surface trachea Enclosed in thin fibrous capsule with septa into gland

Surrounded bypretracheal fascia (therefore moves on swallowing) Two lateral lobes linked byisthmus

Lobes extend from second to fifth tracheal ring

Isthmus lies at third tracheal ring

Occasionallya pyramidal lobe extends superiorlyfrom isthmus on left side Anatomic relationships

Anteriorly: sternohyoid and sternothyroid muscles jugular vein

Anterolaterally: infra-hyoid muscles sternocleidomastoid

Posterolaterally: carotid sheath

Posteromedially: trachea larynx

esophagus Innervation

Parasympathetic: external branch superior laryngeal nerve (branch vagus n.) Sympathetic

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From: superior, middle, and inferior cervical ganglia

Vasomotor, not secretomotor

Arterial supply

Superior thyroid artery

Branch of external carotid artery

Divides into anterior and posterior branches

Anterior branch

Supplies anterior thyroid

Anastomoses with opposite anterior branch

Posterior branch

Supplies posterior thyroid

Anastomoses with inferior thyroid artery

Inferior thyroid artery

Branch thyrocervical trunk from subclavian artery

Supplies inferior pole of thyroid

Thyroid ima artery

Branch of aorta

Occurs in 10% of all people

Unpaired, on left of midline

Supplies isthmus

Venous drainage

Three pairs of thyroid veins

Superior thyroid vein

Drains superior region of thyroid

Tributaryof internal jugular

Middle thyroid veins

Drain middle of gland

Tributaries of internal jugular

Inferior thyroid veins

Drain inferior region of thyroid

Tributaries of brachiocephalic vein

Lymphatic drainage

Lymphatic vessels run with arteries

Drain to capsular network of lymphatics

→ prelaryngeal, pretracheal, or paratracheal nodes

→ deep cervical nodes

Innervation: sympathetic from cervical sympathetic ganglia

Parathyroid Gland

Small, oval endocrine glands

On medial half of posterior surface of lateral lobes of thyroid, external to capsule

Two pairs of glands

Superior glands slightlyabove entrance of inferior thyroid arteries

Inferior glands slightlybelow entrance of inferior thyroid arteries

Arterial supply

Superior thyroid artery

Inferior thyroid artery

Thyroid ima artery

Venous drainage

Parathyroid veins

→ thyroid plexus of veins

Lymph drainage: paratracheal and deep cervical lymph nodes

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