What is the Thyroid Gland

The thyroid derives its name from the Latin word meaning "Shield". It looks like an old shield but in its true state it looks more like a butterfly. The thyroid is located just in front of the wind pipe (trachea). The normal thyroid consists of 2 lobes the left and the right lobe, placed on either side of the wind pipe which is connected by a bridge of thyroid tissue called the isthmus. Sometimes there is an additional thyroid tissue in the form of a tail found jutting upwards on the mid-line from the isthmus this is called the pyramidal lobe. Each lobe is about 1.5 to 2 inches (4-5cm) tall, 0.6-0.8 inches (1.5-2 cm) wide and 0.8-1.2inches (2-3 cm) in thickness. The total weight of the adult thyroid gland ranges from 0.35-0.87 ounces (10-25gms) in weight. The thyroid gland is a very vascular organ and in general has a reddish brown color. If one were to look at the microscopic structure of the thyroid gland, it would look like tiny, hollow, micro-spheres called follicles. Each of these tiny ball like structures has a central core containing a proteineous material called colloid surrounded by an outer lining of epithelial (follicular) cells. Sparsely scattered among the follicles are para-follicular cells, or C-cells that comprise much less than 0.1% of the the total number of thyroid cells. 

The thyroid has 2 types of different cells and they have a different embryonic origins. The follicular cells develop from the endodermal pharyngeal pouch and the para-follicular (C-Cells) originate from the ectodermal neural crest tissue. This is the differentiation that leads to the clinically important distinctions in the types of thyroid cancers that are encountered. The well differentiated cancers of the thyroid gland called the papillary & follicular carcinoma of the thyroid gland (90% of all thyroid cancers) originate from the follicular cells. The medullary carcinoma of the thyroid originates from the par-follicular cells or the C-Cells of the thyroid gland and consists of about 5% of all thyroid carcinomas. The rarest types of thyroid cancers of the thyroid gland are, the anaplastic type (1%), lymphoma and other metastatic types.    

The thyroid functions as an endocrine organ or gland. That is the thyroid gland produces hormones and secretes them into the blood, where they circulate and later bind with specific target tissues. The thyroid secretes these hormones: L-thyroxine (T4), L-triiodothyronine (T3), and calcitonin. The follicular cells produce T4 & T3 and the para-follicular cells produce Calcitonin.   

Hypothyroidism: A disorder when the thyroid gland does not produce enough (or normal) levels of T4 & T3 as is required by the human body to function properly. Causes of hypothyroidism can be Thyroiditis (Hashimotos Thyroiditis, Lymphocytic Thyroiditis), Congenital Hypothyroidism, Post Partum (Pregnancy) Hypothyroidism, after thyroidectomy (thyroid surgery), or a simple Iodine deficiency Hypothyroid state. 

Hyperthyroidism: A condition when the thyroid gland produces excess thyroid hormones than what is required in normal conditions. Here the circulating T3 & T4 levels are much higher than what is required or normal. The gland generally is detached from the control of the brain and starts to function autonomously, and does not depend on the TSH (thyroid stimulating hormones) produced by the pituitary gland as the basis of T3 & T4 production. TSH levels in the circulation is normally suppressed and is in the range of 0.1 - 0.001 uIU/ml. 

Thyroid Cancer: A condition when the thyroid gland or a nodule or growth inside the gland starts to grow uncontrollably and becomes malignant and invades the sourrounding structures. Cancers originate from different cell types and are of the specified type as mentioned above.

Dr Ajith Joy k
Consultant Nuclear Medicine Physician
Thyroid Cancer Specialist
4A-4H Aster Square, Ulloor, Trivandrum,
 Kerala, India. PIN: 695011
joyajith@gmail.com, 
Clinic Number : +91 9633275251, 944777508

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