Overview
The thyroid gland (glandula thyroidea) produces the thyroid hormones (thyroxine and triiodothyronine), which regulate metabolism, growth and fetal development, and calcitonin. Their synthesis needs dietary iodine.
Topography and shape
- Lobes: two, one on each side of the first tracheal rings, caudal to the larynx. They are flattened and lobulated on the surface.
- Isthmus: in cattle it is a band of glandular tissue joining the two lobes across the ventral surface of the trachea. In other species, such as the dog or horse, the isthmus is narrow, fibrous or absent.
- Relations: they are covered by the neck muscles, close to the common carotid artery and the vagosympathetic trunk; the esophagus lies dorsal to the trachea. The parathyroid glands lie near the thyroid.
Clinical relevance
- Goitre: enlargement of the thyroid caused by iodine deficiency or by goitrogenic substances in the diet, such as those of some Brassica plants. It is most obvious in newborn calves of dams fed a deficient diet.
- Congenital goitre: calves are born weak or dead, sometimes with little hair and with an enlarged thyroid palpable in the cranial neck. It is prevented by giving iodine to pregnant cows.
- Palpation: in a healthy animal the thyroid is usually hard to palpate; a symmetrical mass in the cranioventral neck of a calf suggests goitre.