The Thyroid Gland: Physiology and Pathophysiology

Abstract

The thyroid gland contains many follicular cells that store the thyroid hormones within the thyroglobulin molecule until they are needed by the body. The thyroid hormones, often referred to as the major metabolic hormones, affect virtually every cell in the body. Synthesis and secretion of the thyroid hormones depend on the presence of iodine and tyrosine as well as maturation of the hypothalamic-pituitary-thyroid system. Interruption of this development, as occurs with premature delivery, results in inadequate production of thyroid-stimulating hormone and thyroxine, leading to a variety of physiologic conditions. Pathologic conditions occur in the presence of insufficient thyroid production or a defect in the thyroid gland. Laboratory tests are important in diagnosing conditions of the thyroid gland. A thorough history in combination with clinical manifestations and radiologic findings are also useful in diagnosing specific thyroid conditions. Nurses play an important role in identifying and managing thyroid disorders and in providing supportive care to infants and their families.

Thyroid Function and Dysfunction in Term and Premature Equine Neonates

“…TSH concentrations in human newborns have been reported to be 3–10X adult concentrations 12, 30, 31, 32. In humans, TSH concentration increases rapidly soon after birth, peaks at 12–36 hours, and then slowly decreases over the first few weeks of life.…”

“…In humans, TSH concentration increases rapidly soon after birth, peaks at 12–36 hours, and then slowly decreases over the first few weeks of life. It has been suggested that the initial TSH surge is caused by cold shock, and that the subsequent gradual decrease in TSH concentration is caused by increased TH concentrations and maturation of feedback control 12, 30. Possible explanations for higher TH concentrations in foals (compared to adults) without proportionally higher TSH concentrations include increased sensitivity of TSH receptors in the foal thyroid gland, decreased feedback inhibition by TH on the foal hypothalamus and pituitary gland, increased bioactivity of foal TSH compared to adult TSH, or some combination of the these factors.…”

“…NTIS and iodine deficiency also may contribute in some individuals 12, 14. The clinical relevance of THOP is that premature infants with low TH concentrations are at increased risk for neurodevelopmental abnormalities, respiratory disease, intraventricular hemorrhage, cerebral white matter damage, and higher morbidity and mortality 12, 30, 36, 37, 38. In the present study, TT4 and fT4D concentrations were not lower in sick foals than in normal foals, whereas premature foals had significantly lower concentrations of TT4 and fT4D compared to both sick and normal foals.…”

Association between Subclinical Hypothyroidism and Proliferative Diabetic Retinopathy in Type 2 Diabetic Patients: A Case-Control Study

“…Further, hypothyroidism can play a permissive role in the development of retinal neovascularization. Infants born very prematurely (27 weeks) were more likely to have low thyroxine levels, indicating an abnormal function of the hypothalamus-pituitary-thyroid axis (Kirsten 2000;Beeram and Wilson 2000). Premature infants with low serum thyroxine (hypothyroxinemia) were at risk for retinopathy of prematurity (Fisher 1990).…”

Association of Vitamin D Deficiency With Hypothyroidism in Nepalese Population: A Pilot Study.

“…Hypothyroidism is define as deficiency of thyroid function, reduced production of FT3 and FT4 that lead to hyper secretion of pituitary hormone TSH (Kirsten, 2000). Thyroid disorder is defined as the abnormal thyroid stimulating hormones (TSH) with normal or abnormal thyroid hormones, free tri-iodothyronine (fT3) and free tetraiodothyronine(fT4) (Smyth, 2009).…”