Functional Anatomy of the Thyroid & Parathyroid Glands

Innervation of the Pharynx & Larynx

Dr James PeerlessJune 2011

Objectives

• The Thyroid Gland– Anatomy– Endocrine function

• The Parathyroid Gland– Anatomy– Ca2+ metabolism

• Pharynx & Larynx– Innervation

The Thyroid Gland

• Largest endocrine gland in the body

• Origin– Originates from the

floor of pharynx– Thyroglossal duct

sometimes persists in adults

The Thyroid Gland

• Relations– Deep to sternothyroid and

sternohyoid muscles– Level of C5 –T1– Bilobular; joined by the isthmus– Anterolateral to the larynx and trachea (2nd & 3rd

rings)– Bound by a loose connective tissue capsule which is

anchored to the cricoid cartilage and tracheal rings

• Highly vascular• Supplied by

superior and inferior thyroid arteries

• Drainage via superior, middle and inferior thyroid veins

The Thyroid Gland

• Nerve Supply– Derived from superior, middle and inferior cervical

sympathetic ganglia (from the sympathetic trunk)– Fibres are vasomotor– No secretomotor parasympathetic innervation:

the gland is hormonally regulated

Functional Anatomy of Thyroid

• Follicular structure lined by epithelial cells– Alter shape depending

on amount of activity– Contain colloid

• Parafollicular ‘C’ cells– Secrete calcitonin

Thyroglobulin Colloid

Follicular Cells

Parafollicular Cells

Thyroid Hormone Synthesis

The Parathyroid Glands

• Four disc-like glands, embedded in the thyroid gland (dorsal surface)

• Contain two cell types:• Chief cells

producing PTH• Oxyphil cells:

function unknown

Sites of aberrant parathyroid glandular tissue

Parathyroid Hormone

• Polypeptide produced in the chief cells• Preprohormone Prehormone PTH

• Increases Ca2+ via three main actions:– Resorption– Reabsorption– Absorption

The Pharynx

The Pharynx

• Nerve SupplyPharyngeal plexus provides motor and most of sensory– Motor:

• All muscles – fibres from nucleus ambiguus of the accessory nerve carried via the vagus nerve

• Stylopharyngeus – CN IX• Tensor veli palatini - CN V3

• Lower pharynx also receives some motor fibres from recurrent laryngeal nerve

– Sensory:• Glossopharyngeal (CN IX) – most of mucosa• Maxillary (CN V2) – anterior nasopharynx• Vagus (CN X)

– Branches from the cervical sympathetic chain

The Larynx

• Muscles (6+3)– Intrinsic

• Cricothyroid• Posterior cricoarytenoid• Lateral cricoarytenoid• Transverse arytenoid• Aryepiglottic• Thyroarytenoid

– All paired except the tranverse arytenoid

– Extrinsic• Sternothyroid• Thyrohyoid• Inferior Constrictor

The Larynx

• Innervation– Mucous membranes• Above cords: internal laryngeal nerve• Below cords: recurrent laryngeal nerve

– Muscles of the larynx• Cricothyroid: superior/external laryngeal nerve• All others: recurrent laryngeal nerve

Objectives

• The Thyroid Gland– Anatomy– Endocrine function

• The Parathyroid Gland– Anatomy– Ca2+ metabolism

• Pharynx & Larynx– Innervation

Questions

Reference

• Smith T, Pinnock C, Lin T (2009). Fundamentals of Anaesthesia, 3rd Edition. Cambridge: Cambridge University Press

• Moore K, Dalley A (1999). Clinically Oriented Anatomy, 4th Edition. Philadelphia: Lippincott Williams & Wilkins