Anatomy & Physiology: The Unity of Form and Function, 7th Edition

Published by McGraw-Hill Education
ISBN 10: 0073403717
ISBN 13: 978-0-07340-371-7

Chapter 17 - Section 17.3 - Other Endocrine Glands - Before You Go On - Page 650: 12

Answer

Thyroid hormones, primarily thyroxine (T4) and triiodothyronine (T3), have a calorigenic effect because they play a key role in regulating the basal metabolic rate (BMR) of the body. The basal metabolic rate refers to the amount of energy (calories) the body needs to maintain essential functions while at rest. Thyroid hormones exert their calorigenic effect through several mechanisms: 1. **Stimulation of Cellular Respiration:** Thyroid hormones increase the metabolic activity of cells by stimulating cellular respiration. This means that cells consume more oxygen and produce more adenosine triphosphate (ATP), which is the primary energy currency of cells. The increased metabolic activity results in greater utilization of nutrients, especially glucose and fatty acids, to produce energy. 2. **Enhancement of Heat Production (Thermogenesis):** Thyroid hormones promote thermogenesis, which is the production of heat by the body. This is achieved through increased energy expenditure and heat production by cells. The elevated metabolic rate leads to more heat being generated as a byproduct of energy metabolism. 3. **Maintenance of Sodium-Potassium Pump:** Thyroid hormones help maintain the activity of the sodium-potassium pump, an essential cellular process that regulates the balance of sodium and potassium ions across cell membranes. This activity requires energy in the form of ATP. Since the sodium-potassium pump is crucial for maintaining cellular integrity and proper nerve and muscle function, its energy demands contribute to the overall calorigenic effect of thyroid hormones. 4. **Regulation of Gene Expression:** Thyroid hormones affect the transcription of various genes involved in metabolism. They increase the expression of genes related to energy metabolism, protein synthesis, and other metabolic processes. This leads to increased synthesis of enzymes and proteins necessary for these metabolic pathways. The calorigenic effect of thyroid hormones helps ensure that the body has sufficient energy to carry out its various functions. It also plays a role in maintaining body temperature and overall metabolic homeostasis. Disorders of thyroid function, such as hyperthyroidism (excessive thyroid hormone production) or hypothyroidism (insufficient thyroid hormone production), can lead to significant alterations in metabolism and energy balance, with corresponding effects on body weight and overall health.

Work Step by Step

Thyroid hormones, primarily thyroxine (T4) and triiodothyronine (T3), have a calorigenic effect because they play a key role in regulating the basal metabolic rate (BMR) of the body. The basal metabolic rate refers to the amount of energy (calories) the body needs to maintain essential functions while at rest. Thyroid hormones exert their calorigenic effect through several mechanisms: 1. **Stimulation of Cellular Respiration:** Thyroid hormones increase the metabolic activity of cells by stimulating cellular respiration. This means that cells consume more oxygen and produce more adenosine triphosphate (ATP), which is the primary energy currency of cells. The increased metabolic activity results in greater utilization of nutrients, especially glucose and fatty acids, to produce energy. 2. **Enhancement of Heat Production (Thermogenesis):** Thyroid hormones promote thermogenesis, which is the production of heat by the body. This is achieved through increased energy expenditure and heat production by cells. The elevated metabolic rate leads to more heat being generated as a byproduct of energy metabolism. 3. **Maintenance of Sodium-Potassium Pump:** Thyroid hormones help maintain the activity of the sodium-potassium pump, an essential cellular process that regulates the balance of sodium and potassium ions across cell membranes. This activity requires energy in the form of ATP. Since the sodium-potassium pump is crucial for maintaining cellular integrity and proper nerve and muscle function, its energy demands contribute to the overall calorigenic effect of thyroid hormones. 4. **Regulation of Gene Expression:** Thyroid hormones affect the transcription of various genes involved in metabolism. They increase the expression of genes related to energy metabolism, protein synthesis, and other metabolic processes. This leads to increased synthesis of enzymes and proteins necessary for these metabolic pathways. The calorigenic effect of thyroid hormones helps ensure that the body has sufficient energy to carry out its various functions. It also plays a role in maintaining body temperature and overall metabolic homeostasis. Disorders of thyroid function, such as hyperthyroidism (excessive thyroid hormone production) or hypothyroidism (insufficient thyroid hormone production), can lead to significant alterations in metabolism and energy balance, with corresponding effects on body weight and overall health.
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