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Published in Henry J. Woodford, Essential Geriatrics, 2022
Thermoregulation becomes impaired as a consequence of frailty. Dysfunction of multiple physiological systems can contribute to this. Average core body temperature is estimated to be 0.4°C lower in older people compared to younger people.55 Core bodily temperature is a balance between heat creation from metabolism and heat loss from the skin, including evaporation of sweat. Blood flow to the skin is a key process in thermoregulation. The abilities to vasodilate and vasoconstrict are impaired in older people, making them more susceptible to hypothermia in cold conditions and overheating in hot settings. This is probably mediated by a reduction in sympathetic nervous system activity. Sweat production can be reduced when blood flow to the skin is impaired or with dehydration. Heat production is proportional to muscle mass, which declines with sarcopenia. Reduced activity can also result in less heat generation. There may be a reduced shivering response to hypothermia. Insulating fat conserves heat. There is a reduction in the subcutaneous fat layer in old age. Brown adipose tissue is important for thermogenesis in new-borns but probably not in adults. An underactive thyroid gland is a possible additional factor. Peripheral thermosensor receptors and central brain processing can be impaired in older age. There may also be cognitive aspects, such as wearing the appropriate clothing and home heating. Figure 22.1 summarises the aspects that promote hypothermia in frail older people. Paradoxical undressing can occur with hypothermia.56
Basic medicine: physiology
Published in Roy Palmer, Diana Wetherill, Medicine for Lawyers, 2020
Situated at the front of the neck, the thyroid gland controls the level of tissue metabolism. Its principal hormone, thyroxine, is rich in iodine. If the dietary intake of iodine is low, the thyroid enlarges to trap all the available supply; the resultant swelling is called a goitre. An overactive thyroid causes an increased metabolic rate manifested by weight loss, tachycardia, and sweating. An underactive thyroid slows down many bodily functions, causing patients to gain weight and lose full mental faculties.
Thyroid disease
Published in Judy Bothamley, Maureen Boyle, Medical Conditions Affecting Pregnancy and Childbirth, 2020
The thyroid is a butterfly-shaped gland located in the neck just below the larynx (seeFigure 10.1). It produces two hormones, tri-iodothyronine (T3) and thyroxine (T4), which regulate metabolism throughout the body.
Free thyroxine measurement in clinical practice: how to optimize indications, analytical procedures, and interpretation criteria while waiting for global standardization
Published in Critical Reviews in Clinical Laboratory Sciences, 2023
Federica D’Aurizio, Jürgen Kratzsch, Damien Gruson, Petra Petranović Ovčariček, Luca Giovanella
Thyroid dysfunction is among the most common endocrine disorders and accurate biochemical testing is needed to confirm or rule out a diagnosis. Notably, true hyper- and hypothyroidism in the setting of a normal TSH are highly unlikely, making the assessment of FT4 levels inappropriate in most cases. However, FT4 measurement is integral in both the diagnosis and management of relevant central dysfunctions (central hypothyroidism and central hyperthyroidism) as well as in monitoring therapy in hyperthyroid patients treated with anti-thyroid drugs or radioiodine. In such settings, accurate FT4 quantification is required. Significant progress has been made in the standardization of procedures for FT4 testing, but technical and implementational challenges, including the establishment of clinical decision limits in different patient populations and education of all stakeholders, remain. Accordingly, different assays and reference values cannot be interchanged. Two-way communication between laboratories and clinical specialists is pivotal to properly select a reliable FT4 assay, establish RIs, approaching discordant results, and monitor the analytical and clinical performance of this method over time.
Using the Biopsychosocial Approach to Identify Factors Associated with Major Depressive Disorder for Individuals with Hypothyroidism
Published in Issues in Mental Health Nursing, 2022
Kennedy S. Anderson, Krista J. Howard, Kelly B. Haskard-Zolnierek, Julia Pruin, Rebecca G. Deason
Hypothyroidism, or underactive thyroid, is described as a deficiency of thyroid hormones (American Thyroid Association, 2020). A diagnosis of hypothyroidism is made following a blood test to assess the function of thyroid stimulating hormone (TSH), and treatment typically consists of the thyroid hormone supplement thyroxine (T4) while some patients also are given the additional triiodothyronine (T3) supplement. Common physical symptoms of hypothyroidism include lethargy, sensitivity to cold, constipation, dry skin, weight gain, sexual dysfunction, and neck swelling (Ali et al., 2017; El Saide Sayyah et al., 2013). Hypothyroidism has also been implicated in changes in mood and cognition, such as poorer attention, memory, and executive function and increased rates of anxiety and depression (Samuels, 2014).
Low awareness and under-diagnosis of hypothyroidism
Published in Current Medical Research and Opinion, 2022
Ulrike Gottwald-Hostalek, Barbara Schulte
The diagnosis of overt hypothyroidism, where the TSH level is markedly elevated (>10 mIU/L), is straightforward once the patient has presented and undergone thyroid function testing. Measurement of smaller TSH elevations above the reference range is required for the diagnosis of subclinical hypothyroidism. Reference ranges for thyroid tests are assay-specific29, and vary according to region, particularly with regard to the local level of iodine depletion, and the success of strategies to achieve iodine repletion30. It has been noted recently that the use of different assays with different reference ranges might lead to different subsequent pathways for diagnosis and management for individual patients with suspected hypothyroid disease31. The use of age-specific reference ranges is important for optimizing the diagnosis of hypothyroidism, particularly for elderly patients15.