**Experimental Advances**

342 Thyroid Hormone

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**Chapter 13** 

© 2012 Spinel et al., licensee InTech. This is an open access chapter distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

and reproduction in any medium, provided the original work is properly cited.

© 2012 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution,

The thyroid is an endocrine gland formed by two lobes (Figure 1A L) located on each side of the trachea and the larynx; they are joined by an isthmus (ultimo-branchial origin) (Figure 1A clear arrow) located between the trachea's second and third cartilage rings (Figure 1A

A fibrous connective tissue capsule covers each lobe from where the septa go inside, partially dividing the glandular parenchyma containing a very developed network of capillaries surrounding the follicles and irrigating the glandular parenchyma. The gland also contains adipocytes, nerve fibres, mastocytes and occasionally lymphocytes and macrophages [2].

The thyroid parenchyma mainly consists of follicles which are the thyroid's functional unit (Figure 1B). It has an oval or spherical structure whose wall consists of a layer of cubic epithelial cells (thyrocytes) (Figure 1B black arrow) surrounding a viscous solution of proteins called colloid (Figure 1B Co) [2,3] containing 80% thyroglobulin (Tg) or thyroid hormone [4,5]. Follicle size varies according to an individual's age, its localisation in the gland and animal species; for example, diameter varies from 50 to 150 μm in rats and mice where peripheral follicles are larger than the central ones (Figure 1A L), whilst diameter varies from 150 to 500 μm in humans and pigs, the largest ones occurring towards the inside of the gland, even though their location could vary [6,2]. As well as follicle cells or thyrocytes, it has been found that 1% to 2% of neural crest cells in different mammals' thyroids are parafollicular or clear cells, appearing clearer in different types of histological staining. These are located at the base

of follicles but do not come into contact with the colloid and secrete calcitonin [7].

**Thyroid Culture from Monolayer** 

Clara Spinel, Magnolia Herrera and Jhon Rivera

Additional information is available at the end of the chapter

**to Closed Follicles** 

http://dx.doi.org/10.5772/45968

**1. Introduction** 

**1.1. Morphology** 

black arrow).

*1.1.1. Histology* 
