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Controlled Release of Hormones by Pellet Implants
Published in Emmanuel Opara, Controlled Drug Delivery Systems, 2020
Thyroid hormones are hydrophobic compounds like steroids. These hormones are derivatives of the amino acid, tyrosine, produced by the follicular cells of the thyroid. The iodination of tyrosine is possible at maximum four positions namely 3, 3’, 5, 5’. However, it also produces iodinated product at three or two positions, which also can bind to the thyroid hormone receptor (TR) and carry out the biological action. Thyroid hormone has its receptor in almost every cell of the body making the whole body as target for this class of hormones. Apart from its pivotal role in controlling the basic metabolic rate (BMR) of body cells, these hormones regulate various other important functions. Thyroid hormone pellets are used to evaluate the physiological functions of this hormone ranging from embryonic development and growth to reproduction (Huffman et al. 2006, Nicolls et al. 2012, Al Husseini et al. 2013, Baliram et al. 2012, Chen, Weltman, et al. 2013). Listed in Table 6.6 are some of the commercially available pellets for thyroid hormones and their related products.
Biokinetic Models
Published in Shaheen A. Dewji, Nolan E. Hertel, Advanced Radiation Protection Dosimetry, 2019
Iodide is actively transported from blood plasma into thyroid follicular cells at the plasma membrane. A normal thyroid can concentrate the iodide ion to 20–40 times its concentration in blood plasma. Some of the trapped iodide leaks back into blood, but most of it diffuses across the follicular cell and enters the follicular lumen, where it is converted to organic iodine.
Nuclear Medicine in Oncology
Published in Computer Methods in Biomechanics and Biomedical Engineering: Imaging & Visualization, 2018
Carla Oliveira, Rui Parafita, Ana Canudo, Joana Correia Castanheira, Durval C. Costa
The basis of this therapy lies in the fact that iodine is an integral component of triiodothyronine and thyroxine hormones. During the process of biosynthesis for these hormones, iodine is taken up by the follicular cells in the thyroid – thyrocytes – by active transport (through sodium iodide symporter – NIS) and incorporated in the thyroglobulin (process known as organification), being stored in the glandular colloid until thyroid hormone secretion into the blood stream (Filetti et al. 1999).
Consumption of water contaminated by nitrate and its deleterious effects on the human thyroid gland: a review and update
Published in International Journal of Environmental Health Research, 2022
Edgar García Torres, Rebeca Pérez Morales, Alberto González Zamora, Efraín Ríos Sánchez, Edgar Héctor Olivas Calderón, José de Jesús Alba Romero, Esperanza Yasmín Calleros Rincón
It is the first endocrine gland developed in intrauterine life, and it begins functioning at 11–12 weeks of embryonic development (Sadler and Langman 2012). The thyroid follicle, formed by the circular union of thyrocytes, is the functional and structural part of the gland, which is composed of both follicular cells and C cells (Salgado et al. 2011). The TG requires iodine to synthesize and secrete thyroid hormones (THs), which have important roles in regulating physiology (De Escobar and Del Rey 2008; Ward 2012). THs include triiodothyronine, an active hormone known as T3, and thyroxine, a prohormone which is also known as T4. (Forrest and Visser 2013). The mechanism of regulation in THs synthesis occurs through a very finely tuned hypothalamic-pituitary-thyroid axis through which the hypothalamus generates thyrotropin-releasing hormone (TRH), which stimulates the synthesis and secretion of pituitary thyrotropin, also known as thyroid-stimulating hormone (TSH), which acts directly on the thyroid gland and initiates all the steps of the TH biosynthesis and secretion, this axis has a negative-positive feedback mechanism that can detect the presence of THs to maintain proper physiological levels of TRH and TSH in the body (Mendoza and Hollenberg 2017). THs have been described as influencing the following important physiological processes: cell proliferation and organism development, mainly throughout the embryonic stages; stimulation of the synthesis and degradation of proteins; and cell differentiation, THs are also required for the proper development of the central and peripheral nervous system during embryogenesis (Sadler and Langman 2012; Bursuk 2012). In addition, THs have been associated with energy metabolism, thermogenesis, the hepatic metabolism of nutrients, cardiovascular system function and the balance of corporal fluids (Ortiga‐Carvalho et al. 2016). To function correctly, the TG must have normal morphology and undergo normal biochemical processes, which require iodine, which enters the organism in the iodide form, and an adequate capacity to internalize it through the Na+/I− symporters (NISs) that are located in the plasma membranes of thyrocytes (Spitzweg and Morris 2002; De la Vieja et al. 2002; Bizhanova and Kopp 2009). These symporters are also present in other tissues, such as salivary glands, the small intestine and mammary glands (Chung 2014; Ravera et al. 2017). Any disruption in the synthesis of these hormones, in any stage of development, could lead to a malfunctioning of the entire organism (Chiovato et al. 2019).