Triiodothyronine (T3)

Definition

Triiodothyronine, commonly known as T3, is a thyroid hormone that plays a crucial role in regulating metabolism, energy production, and overall growth and development in the body. It is produced by the thyroid gland and is more potent than its counterpart, thyroxine (T4), despite being present in smaller amounts. T3 influences various physiological processes, including heart rate, digestion, and muscle function, making it an essential hormone in maintaining homeostasis.

5 Must Know Facts For Your Next Test

1. T3 is synthesized from thyroxine (T4) by the removal of one iodine atom, making it a more active form of thyroid hormone.
2. The levels of T3 in the blood are regulated by the hypothalamus and pituitary gland through a feedback mechanism involving Thyroid-Stimulating Hormone (TSH).
3. T3 has a half-life of approximately 1 day, which is shorter than that of T4, leading to more rapid physiological effects.
4. This hormone is essential for normal growth and development in children, particularly for brain development and maturation.
5. Abnormal levels of T3 can lead to conditions such as hyperthyroidism, where excessive amounts can cause symptoms like increased heart rate and anxiety.

Review Questions

• How does triiodothyronine (T3) influence metabolic processes in the body?
  • Triiodothyronine (T3) plays a significant role in regulating metabolic processes by enhancing cellular respiration and energy production. It increases the basal metabolic rate (BMR), promoting the consumption of glucose and fatty acids for energy. Additionally, T3 stimulates protein synthesis, thus contributing to growth and development while also impacting heart rate and digestive function.
• Discuss the relationship between T3 and thyroxine (T4) in terms of their synthesis and physiological effects.
  • T3 and thyroxine (T4) are both produced by the thyroid gland, with T4 being converted into T3 in various tissues. While T4 serves as a storage form of thyroid hormone, T3 is the more biologically active form that exerts immediate effects on metabolism. This conversion process ensures that tissues receive an adequate supply of the more potent hormone when needed, allowing for fine-tuning of metabolic regulation according to the body's requirements.
• Evaluate the implications of abnormal triiodothyronine (T3) levels on health, considering both hyperthyroidism and hypothyroidism.
  • Abnormal levels of triiodothyronine (T3) can significantly impact health, manifesting as either hyperthyroidism or hypothyroidism. In hyperthyroidism, elevated T3 levels lead to increased metabolism, causing symptoms like rapid heart rate, anxiety, and unintended weight loss. Conversely, low levels of T3 characteristic of hypothyroidism result in reduced metabolic activity, leading to fatigue, weight gain, and sensitivity to cold. Understanding these conditions highlights the critical role of T3 in maintaining overall health and metabolic balance.

Related terms

Thyroid Gland: A butterfly-shaped gland located in the neck that produces thyroid hormones, including T3 and T4, which regulate metabolism.

Thyroxine (T4): Another primary hormone produced by the thyroid gland, T4 is converted into the more active form T3 in target tissues and plays a significant role in metabolic regulation.

Hypothyroidism: A condition characterized by an underactive thyroid gland leading to insufficient production of thyroid hormones like T3 and T4, resulting in symptoms such as fatigue and weight gain.