THYROID AND PARATHYROID GLANDS Dr.Lubna Nazli

Objectives To list the various endocrine glands Site, size of thyroid and parathyroid Coverings or capsules Presenting parts Relations Blood supply Development of thyroid and parathyroid Applied anatomy

The human endocrine glands

Location of Thyroid Gland

The thyroid gland is the largest endocrine gland of the body. It is located in the neck at the level of C5-T1 vertebrae. It lies deep to the strap muscles of the neck. (sternothyroid and sternohyoid). The gland is enclosed with in the pretracheal fascia of the deep cervical fascia.

It is a butterfly shaped gland having two lateral lobes connected with a central region called isthmus, which has an extension above as pyramidal lobe. Levator glandulae thyroidae is a musculofibrous extension from pyramidal lobe.

Thyroid & Parathyroid glands

Coverings or capsules True False In between the two capsules PARATHYROID glands are situated.

Presenting parts Apex Base 3 surfaces: antero-lat, posterolat & medial 2 borders: ant & post

Relations Apex: towards oblique line of thyroid cartilage. Related to sup thyroid artery and ext laryngeal nerve Base: at level of 5th & 6th tracheal rings Related to inf thyroid artery and recurrent laryngeal nerve

Anterolat surface: strap muscles Posterolat surface: carotid sheath Medial surface: larynx & pharynx, their muscles & ext laryngeal and recurrent laryngeal nerves

Blood supply

Development of Thyroid Gland It is developed from endodermal cells of floor of pharynx (area of developing tongue). It begins a diverticulum at dorsum of tongue between tuberculum impar and hypobranchial eminence.

Elongation of thyroid diverticulum forms thyro-glossal duct Elongation of thyroid diverticulum forms thyro-glossal duct. It elongates downwards in front of hyoid and thyroid cartilage where it ends by dividing into 2 parts.

Fate of Thyro-glossal Duct Upper end of the duct remains as foramen cecum on dorsum of tongue. The duct degenerates from foramen cecum and hyoid bone. The duct from the hyoid to divisions of the duct form levator glandulae thyroidae and may be pyramidal lobe. Divisions of the duct form lobes of thyroid gland with isthmus in between.

Congenital Anomalies Thyroid agenesis: Failure of its formation. Lingual thyroid: Failure of thyroid descend. Aberrant thyroid (Retrosternal goiter): over-descend of thyroid gland in the thorax. Thyroglossal cyst: It is persistence of a part of the thyroglossal duct. Thyroglossal fistula: Thyroglossal duct opens to skin.

Ectopic thyroid During its descent thyroid gland can get arrested at the following points: 1. In the substance of tongue—lingual thyroid. 2. Posterior to the hyoid bone. 3. Anterior to the hyoid bone. 4. In the retrosternal space.

The parathyroid glands The superior parathyroid glands arise from the endoderm of fourth pouch. The inferior parathyroid glands develop from the endoderm of III pouch.

PARATHYROID GLANDS Tiny glands embedded in the posterior aspect of the thyroid PTH (parathormone) regulates calcium balance in the blood

Parathyroid Glands Chief (principal) cells secrete PTH It is supplied by inf thyroid artery. Figure 15.10a

Applied anatomy Goiters, Thyrotoxicosis, exophthalmos, Myxedema hypoparathyroidism

Goiter is an enlargement of thyroid gland

Large sized goiter causes dysphagia & hoarseness of voice Thyrotoxicosis is a clinical condition of excessive thyroid hormones release