Editing Thyroid (section)

===Microanatomy===
[[File:Thyroid-histology.jpg|thumb|Section of a thyroid gland under the microscope. 1 colloid, 2 follicular cells, 3 [[Endothelium|endothelial]] cells]] 
At the [[histology|microscopic level]], there are three primary features of the thyroid—[[thyroid follicle]]s, [[thyroid follicular cell]]s, and [[parafollicular cell]]s, first discovered by Geoffery Websterson in 1664.<ref>{{Cite book|last1 = Fawcett|first1 = Don| last2 = Jensh | first2 = Ronald | name-list-style = vanc |title = Bloom & Fawcett's Concise Histology|publisher = Arnold Publishers|year = 2002|location = New York|pages = 257–258|isbn = 978-0-340-80677-7}}</ref>

;Follicles
[[Thyroid follicular cell#Location|Thyroid follicles]] are small spherical groupings of cells 0.02–0.9mm in diameter that play the main role in thyroid function.{{sfn|Gray's Anatomy|2008|pp=462–4}} They consist of a rim that has a rich blood supply, nerve and lymphatic presence, that surrounds a core of [[colloid]] that consists mostly of thyroid hormone precursor proteins called [[thyroglobulin]], an [[iodine|iodinated]] [[glycoprotein]].{{sfn|Gray's Anatomy|2008|pp=462–4}}<ref name="Wheaters2006">{{cite book| first1 = Paul R | last1 = Wheater | first2 = Barbara | last2 = Young | name-list-style = vanc |title=Wheater's functional histology : a text and colour atlas|url=https://archive.org/details/wheatersfunction00youn|url-access=limited|date=2006|publisher=Churchill Livingstone|location=Oxford|isbn=978-0-443-06850-8|pages=[https://archive.org/details/wheatersfunction00youn/page/n741 333]–335|edition=5th}}</ref>

;Follicular cells
The core of a follicle is surrounded by a single layer of follicular cells. When stimulated by thyroid stimulating hormone (TSH), these secrete the thyroid hormones T<sub>3</sub> and T<sub>4</sub>. They do this by transporting and metabolising the thyroglobulin contained in the colloid.{{sfn|Gray's Anatomy|2008|pp=462–4}} Follicular cells vary in shape from flat to cuboid to columnar, depending on how active they are.{{sfn|Gray's Anatomy|2008|pp=462–4}}<ref name=Wheaters2006 />

;Follicular lumen
The ''follicular lumen'' is the fluid-filled space within a follicle of the thyroid gland. There are hundreds of follicles within the thyroid gland. A follicle is formed by a spherical arrangement of [[thyroid follicular cell|follicular cells]]. The follicular lumen is filled with ''colloid'', a concentrated solution of [[thyroglobulin]] and is the site of synthesis of the thyroid hormones [[thyroxine]] (T4) and [[triiodothyronine]] (T3).<ref>[http://www.expertconsultbook.com/expertconsult/ob/book.do?method=display&type=bookPage&decorator=none&eid=4-u1.0-B978-1-4160-5583-9..00072-1--s0040&isbn=9781416055839 The Thyroid Follicle] {{Webarchive|url=https://archive.today/20130123031837/http://www.expertconsultbook.com/expertconsult/ob/book.do?method=display&type=bookPage&decorator=none&eid=4-u1.0-B978-1-4160-5583-9..00072-1--s0040&isbn=9781416055839 |date=2013-01-23 }}, ''Endocrinology'' by J. Larry Jameson, MD, PhD and Leslie J. De Groot, MD, chapter 72</ref>

;Parafollicular cells
Scattered among follicular cells and in spaces between the spherical follicles are another type of thyroid cell, parafollicular cells.{{sfn|Gray's Anatomy|2008|pp=462–4}} These cells secrete [[calcitonin]] and so are also called C cells.<ref>{{cite journal | vauthors = Hazard JB | title = The C cells (parafollicular cells) of the thyroid gland and medullary thyroid carcinoma. A review | journal = The American Journal of Pathology | volume = 88 | issue = 1 | pages = 213–50 | date = July 1977 | pmid = 18012 | pmc = 2032150 }}</ref>