1. THYROID AND PARATHYROID GLANDS
Dr.Lubna Nazli

2. 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

3. The human endocrine glands

4. Location of Thyroid Gland

5. 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.

7. 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.

8. Thyroid & Parathyroid glands

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

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

11. 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

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

13. Blood supply

14. 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.

16. 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.

20. 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.

21. 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.

25. 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.

26. 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.

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

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

29. Applied anatomy Goiters, Thyrotoxicosis, exophthalmos, Myxedema
hypoparathyroidism

30. Goiter is an enlargement of thyroid gland

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