Author: Deborah De Pablos  

Where is it located?

The thyroid gland is in the middle region of the neck, near the larynx. In dogs it is found on both sides of the trachea. It is a highly vascularized gland, compact and reddish in colour.

Image credit: Benipeixcar Veterinary Hospital

What is its function?

The thyroid is an endocrine gland, it secretes hormones into the bloodstream. The main function of the thyroid is the production of the thyroid hormones thyroxine (T4) and triiodothyronine (T3). The synthesis and secretion of thyroid hormones is mainly regulated by the thyroid-stimulating hormone, TSH, also called thyrotropin.

Functions of the thyroid hormones

The functions of thyroid hormones can be described in 3 categories: functions in cell differentiation and growth, effects on metabolic pathways, and specific effects on organs and systems of the body.

Pathologies associated with the thyroid gland

Hypothyroidism is common endocrine disease seen in dogs and is occurs when the thyroid glands fail to produce adequate amounts of the hormones thyroxine (T4) and triiodothyronine (T3). Primary hypothyroidism is the most common presentation, usually resulting from idiopathic thyroid gland atrophy or immune-mediated lymphocytic thyroiditis. Uncommon causes of canine hypothyroidism include congenital disease resulting from dyshormonogenesis of thyroid hormone, abnormal thyroid-stimulating hormone (TSH) production, or abnormal thyroid gland development.     Neoplasia is a rare cause.  In primary cases, the total T4 is low and the TSH is high. Occasional cases will have low total T4 and normal TSH. Free T4 by equilibrium dialysis (FT4D) may then be required to add further information on thyroid function. Thyroglobulin autoantibodies (TGAA) can also be measured and will give information on thyroid pathology and the presence of auto antibodies that may interfere with total T4 measurement.

In contrast, hyperthyroidism is a common endocrine condition in older cats. It is usually caused by hyperplasia of the thyroid gland. Neoplasia is a less common cause. Total T4 is produced in excess and is high. TSH may be low due to excess Total T4 suppressing TSH production.

Image credit: Medicina Veterinaria Practica

Conclusion

The thyroid gland plays an important role as a producer of thyroid hormones, which are necessary for cell differentiation and growth of the organism. The proper functioning of metabolic pathways depends on these hormones, which have specific effects on different organs, maintaining homeostasis among all tissues.

About the author

Deborah finished her studies in animal health in 2015 (Complutense University of Madrid). Right after finishing, she started working in the veterinary clinical hospital of Complutense University researching Clostridium Difficile. After that she worked in different departments being involved in clinical analysis, biochemistry, and microbiology. At the end of her contract, Deborah went to Scotland and gained experience in histology, working with pathologists. She also contributed to analysing COVID samples. Her aspiration to constantly evolve as a professional has led her to Cambridge and NationWide Specialist Laboratories. Deborah’s day-to-day work consists of working in the endocrinology department and analysing hormones.