Post on 05-Jan-2016
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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