Functional Anatomy of the Thyroid & Parathyroid Glands Innervation of the Pharynx & Larynx

1. Functional Anatomy of the Thyroid & Parathyroid GlandsInnervation of the Pharynx & Larynx Dr James Peerless June 2011

2. Objectives • The Thyroid Gland • Anatomy • Endocrine function • The Parathyroid Gland • Anatomy • Ca2+ metabolism • Pharynx & Larynx • Innervation

3. The Thyroid Gland • Largest endocrine gland in the body • Origin • Originates from the floor of pharynx • Thyroglossal duct sometimes persists in adults

4. 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

5. Highly vascular • Supplied by superior and inferior thyroid arteries • Drainage via superior, middle and inferior thyroid veins

6. 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

8. Functional Anatomy of Thyroid • Follicular structure lined by epithelial cells • Alter shape depending on amount of activity • Contain colloid • Parafollicular ‘C’ cells • Secrete calcitonin

9. Parafollicular Cells Thyroglobulin Colloid Follicular Cells

10. Thyroid Hormone Synthesis

11. 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

12. Sites of aberrant parathyroid glandular tissue

13. Parathyroid Hormone • Polypeptide produced in the chief cells • PreprohormonePrehormone PTH • Increases Ca2+ via three main actions: • Resorption • Reabsorption • Absorption

15. The Pharynx

16. The Pharynx • Nerve Supply Pharyngeal 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 velipalatini - 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

17. The Larynx • Muscles (6+3) • Intrinsic • Cricothyroid • Posterior cricoarytenoid • Lateral cricoarytenoid • Transverse arytenoid • Aryepiglottic • Thyroarytenoid • All paired except the tranversearytenoid • Extrinsic • Sternothyroid • Thyrohyoid • Inferior Constrictor

18. 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

19. Objectives • The Thyroid Gland • Anatomy • Endocrine function • The Parathyroid Gland • Anatomy • Ca2+ metabolism • Pharynx & Larynx • Innervation

20. Questions

21. 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