1 THYROID AND PARATHYROID GLANDS Dr.Lubna Nazli. 2 Objectives To list the various endocrine glands Site, size of thyroid and parathyroid Coverings or.

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THYROID AND PARATHYROID GLANDS

Dr.Lubna Nazli

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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

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The human endocrine glands

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Location of Thyroid Gland

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• 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.

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• 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.

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Thyroid & Parathyroid glands

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Coverings or capsules

• True

• False

• In between the two capsules PARATHYROID glands are situated.

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Presenting parts

• Apex

• Base

• 3 surfaces: antero-lat, posterolat & medial

• 2 borders: ant & post

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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

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• Anterolat surface: strap muscles

• Posterolat surface: carotid sheath

• Medial surface: larynx & pharynx, their muscles & ext laryngeal and recurrent laryngeal nerves

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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.

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• 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.

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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.

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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.

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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.

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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.

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PARATHYROID GLANDS

• Tiny glands embedded in the posterior aspect of the thyroid

• PTH (parathormone) regulates calcium balance in the blood

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Parathyroid Glands

• Chief (principal) cells secrete PTH

• It is supplied by inf thyroid artery.

Figure 15.10a

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Applied anatomy

• Goiters,

• Thyrotoxicosis, exophthalmos,

• Myxedema

• hypoparathyroidism

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Goiter is an enlargement of thyroid gland

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• Large sized goiter causes dysphagia & hoarseness of voice

• Thyrotoxicosis is a clinical condition of excessive thyroid hormones release