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Endocrine system
Published in A Stewart Whitley, Jan Dodgeon, Angela Meadows, Jane Cullingworth, Ken Holmes, Marcus Jackson, Graham Hoadley, Randeep Kumar Kulshrestha, Clark’s Procedures in Diagnostic Imaging: A System-Based Approach, 2020
A Stewart Whitley, Jan Dodgeon, Angela Meadows, Jane Cullingworth, Ken Holmes, Marcus Jackson, Graham Hoadley, Randeep Kumar Kulshrestha
The principal function of the thyroid gland is production of the thyroid hormones tri-iodothyronine (T3) and thyroxine (T4), which control the basal metabolic rate of the body. The hormones also interact with and influence the effect of adrenaline and sex hormones. Adequate levels of thyroid hormones are essential for proper development of the nervous system in utero and early childhood, and for maintenance of brain function in adults. An essential component of the thyroid hormones is iodine, there being three iodine atoms in T3, and four in T4.
Eating behaviours related to psychological stress are associated with functional hypothalamic amenorrhoea in exercising women
Published in Journal of Sports Sciences, 2020
Nicole C.A. Strock, Mary Jane De Souza, Nancy I. Williams
Much of the FHA literature in exercising women support a metabolic aetiology as the driving force for reproduction dysfunction. Prolonged energy deficiency prompts physiological adaptations, as the body redirects available metabolic fuels towards the physiological processes essential for survival, i.e., locomotion, cellular maintenance, and thermoregulation, while simultaneously suppressing growth and reproduction (Schneider & Wade, 1990, 1989; Wade et al., 1996). In an energy deficient state, suppressed hypothalamic-pituitary-thyroid signalling can be indicated by reduced thyroxine (T4), total triiodothyronine (T3) (MJ De Souza et al., 2008; Loucks et al., 1992), and the peripheral conversion of T4 to T3 (Agnihothri et al., 2014), ultimately leading to a reduced metabolic rate (RMR) (Koehler et al., 2016; Myerson et al., 1991). Other indications of downstream physiologic disruption are reflected in altered LH pulsatility (Loucks & Thuma, 2003; Loucks et al., 1985), reduced insulin-like growth factor-1 (IGF-1) (Kaufman et al., 2002), and uncoupled bone turnover (MJ De Souza et al., 2008; Ihle & Loucks, 2004). Appetite-regulating hormones involved in energy homoeostasis are also altered with energy deficiency, as fasting concentrations of peptide YY (PYY) and ghrelin remain elevated in exercising women with FHA (MJ De Souza et al., 2004; Scheid et al., 2009) and anorexic women (Misra et al., 2006). Importantly, evidence exists in both human (Williams et al., 2015) and animal studies (Williams, Caston-Balderrama et al., 2001; Williams, Helmreich et al., 2001), proving that energy deficiency is a causal factor in the induction of FHA.
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).