The thyroid gland is part of and a major organ of the endocrine system. This gland is composed of two cone-like lobes connected together forming a butterfly shape ( shown in figure 1).The isthmus is a thin band of connective tissues which connects the two lobes of the thyroid gland is located between the pyramidal lobe and the trachea. (Cohen and Wood 2000) The thyroid gland is situated on the anterior part of the lower neck, below the larynx (voice box) and in front of the trachea (windpipe) (Britannica online 2011) where it could easily be palpated during a physical examination by a doctor. (Kumar and Clark 2005).
Due to it being the largest endocrine gland in the body, as it weighs approx 20g, it receives an extensive blood supply from thyroid arteries which gives it a deep red colour. (Cohen and Wood 2000) The two parathyroid glands are located between two layers of the capsule that covers the thyroid gland. It is an important feature as it monitors the circulating concentration of calcium ions in the blood. (Martini 2004)
The functional unit of the thyroid gland is the follicle, a spherical group of cells that form a colloid from a casing protein-rich storage material. (Nussey and Whitehead 2001) Thyroglobulin is a protein synthesised by follicle cells which contain amino acid tyrosine and are building blocks of thyroid hormones. Iodine is then needed for formation of the hormones by its absorption from the diet and then carried via bloodstream to the thyroid gland which is then secreted into the colloid and oxidised into iodine ions. The attachment of iodine ions to tyrosine molecules triggers the pairing process performed by the thyroid peroxidise. This leads to production of thyroxine hormone T4 (containing four iodine ions) and triiodothyronine T3 (containing three iodine ions). (Martini 2004)
Figure 1: The
References: Lab Tests Online (2011) Hashimoto’s Thyroiditis [online] available from <http://www.labtestsonline.org/understanding/conditions/hashimoto.html> [10 March 2011] Kumar, P., Clark, M Martini, F. (2004) Fundamentals of Anatomy and Physiology. 6th edn. San Francisco: Pearson Benjamin Cummings Martini, F., Welch, K Michael, J., Rovick, A. (1999) Problem solving in Physiology. USA: Prentice-Hall Nussey, S.,Whitehead, S.(2001) Endocrinology: An Integrated Approach