ANATOMY OF THE THYROID GLAND

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ANATOMY OF THE THYROID GLAND

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Friday, 11 December 2009 08:39

Definition:
Butterfly gland, 15-25 gm in weight, composed of 2 lobes, isthmus and pyramidal lobe.
Extent:
upper pole extends to middle of thyroid cartilage and lower pole extends to 6th tracheal ring

Thyroid gland from the front

Attachment:
(1) To the trachea by loose areolar tissue.
(2) Enclosed in the pre tracheal fascia (which is an extension from the deep fascia of the neck) giving false capsule. The capsule is attached to the thyroid cartilage by the suspensory ligament of Berry. Hence the thyroid moves up and down with deglutition.
Blood Supply:
(1) Superior thyroid artery from external carotid artery.
(2) Inferior thyroid artery from thyrocervical trunk.
(3) Thyroidaima artery from the innominate A or Aortic arch.
Venous Drainage:
[I] Sup. thyroid vein ® Internal Jagular vein
[2] Middle thyroid vein ® Internal Jagular vein
[3] Inf. thyroid vein ® Innominate vein
Lymphatic drainage:
(1) Lat. parts to deep cervical lymph nodes.
(2) Isthmus and medial parts to the pre tracheal and pre laryngeal lymph nodes.
(3) Posteromedial parts to lymph nodes in the tracheo-oesophageal groove extending downwards into the superior mediastinum.
Hormones Secreted by Thyroid:
a) Tetra-iodothyronin (T4) or thyroxin
b) Tri-iodo thyronin (T3)
c) Thyrocalcitonin from the parafollicular "C" cells
Hormones acting on the thyroid:
a) T.S.H (Thyroid Stimulating Hormone) from the anterior pituitary.
b) T.R.H (Thyrotropin Releasing Hormone) from the hypothalamus.
c) L.A.T.S.H (Long acting TSH) (Ig G)
Histology of the Thyroid Gland:
[1] Thyroid follicles:
Ordinary cubical cells Parafollicular "C" cells
[2] Inter-follicular cells: between the follicles
Biosynthesis of Thyroid Hormones:
1) Iodide trapping.
2) Oxidation of Iodide to Iodine.
3) Iodination of tyrosine to iodotyrosine.
4) Coupling of iodotyrosine to give Tri-iodothyronine (T3) and Tetra-iodothyronine (T4) or thyroxine.
Effects of Thyroxine:
(1) Enhance neuromuscular actions of catecholamines:
a) Increase all cardiac functions.
b) Nervousness, insomnia, tremors & hyper-reflexia.
(2) Increase cholinergic activity causing diarrhea, polyurea, & increase sexual desire.
(3) Activation of energy producing process:
Increase metabolic rate & increase oxygen consumption.
(4) Increase glycogenolysis : Increase blood sugar (Diabetogenic effect)
(5) Deposition of mucopolysaccharide and round-cell infiltration in the tissues give skin manifestations of toxic goitre.
SOURCE: Prof. AYMAN SALEM'S BOOK
Copyright: (Vascular Society of Egypt ) & (Medical Educational web)
Not to be reproduced without permission of Vascular Society of Egypt

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