About the Thyroid

According to Henry Gray, the thyroid gland is considered a ductless gland because it secretes hormones within the body; they have no external outlets.  A detailed draying of the thyroid and surrounding structures is can be seen in Figure #1174 of his book, Anatomy of the Human Body also known as Gray's Anatomy.

Location and Structure of the Thyroid Gland

• The thyroid is located in the neck, below the hyoid bone.  It sits atop the trachea, between the right and left jugular veins.  


• In females the gland is slightly heavier, but generally weighs approximately 30 grams.


• It is composed of two cone shaped lobes, each approximately five centimeters in length, two centimeters thick and not more than three centimeters at their widest point.  The isthmus connects the lobes.


• The thyroid gland is part of the endocrine system.

Function of the Thyroid Gland

• The thyroid gland manufactures the T3 and T4 hormones that the body uses in the functions of growth, development and metabolism. This includes regulating heart rate, maintaining fertility, brain and central nervous system development and function and metabolic cell rate.


• Hormone production is a process that begins with the absorption of iodine from food.  In the small intestine iodine is converted to iodide.  The iodide is carried to the thyroid by the blood.  Once in the thyroid the iodide adheres to thyroglobulin to form either monoiodotyrosine (MIT) or diiodotyrosine (DIT).  When an MIT and a DIT join, T3 hormone forms.  When two DITs join, T4 hormone forms.


• The pituitary gland produces thyroid stimulating hormone (TSH) which tells the body when and how much of the T3 and T4 hormones to release.  

Common Thyroid Disorders

• Iodine surplus or shortage


• Hypothyroidism (under active thyroid)


• Hyperthyroidism (over active thyroid)


• Thyroiditis


• Graves' Disease


• Hashimoto's Thyroiditis