Functions : Thyroid hormones:
Increase Basal Metabolic Rate (BMR), the rate of O2 consumption under standard or basal conditions (awake, at rest, and fasting), by stimulating the use of cellular oxygen to produce ATP. As BMR increases, cellular metabolism of carbohydrates, lipids, and proteins increases. Stimulate the synthesis of additional Sodium-Potassium Pumps. As the Na/K pumps work and the cell uses more ATP, heat is produced, and body temperature rises. This is known as Calorigenic Effect . In this way, thyroid hormones play an important role in the maintenance of normal temperature. Examples: mammals can survive in freezing temperatures, but if the thyroid gland is removed, they cannot. Help regulate metabolism by stimulating protein synthesis and increase the use of glucose and fatty acids for ATP production. They also help to reduce blood cholesterol levels. Enhance some actions of Catecholamines (NE and Epi) because they up-regulate Beta receptors. Symptoms of hyperthyroidism include increased heart rate, palpatations, increased blood pressure. Together with eGH and Insulin, thyroid hormones accelerate body growth, particularly growth of the nervous system and skeletal system. Thyroid hormone deficiencies in neonates and young horses can cause mental retardation and stunted bone growth. Calcitonin helps regulate calcium homeostasis . Regulation: Levels of T3 & T4 in the blood control the secretion of TSH/TRH through a negative FB system. Blood calcium levels in a negative FB system regulate calcitonin release. High blood calcium levels stimulate calcitonin secretion which decreases the level of Ca++ in the blood by inhibiting the action of osteoclasts that do not involve the pituitary gland.
Clinical Diseases: Hyperthyroidism, hypothyroidism & goiter formation
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