Biology STAAR (State of Texas Assessments of Academic Readiness) Practice Test

The thyroid gland secretes thyroxin, also known as levothyroxine or T4, which plays a crucial role in regulating metabolism. This hormone influences the metabolic rate of cells throughout the body, affecting how quickly they use energy and produce proteins. Increased levels of thyroxin lead to a higher metabolic rate, whereas decreased levels can result in a slower metabolism. This regulation is essential for maintaining overall energy balance and supporting growth, development, and various bodily functions.

Insulin, although important for glucose metabolism, is produced by the pancreas and primarily regulates blood sugar levels rather than general metabolism. Adrenaline, released by the adrenal glands, is involved in the body's fight-or-flight response, affecting heart rate and energy mobilization, but it does not directly regulate metabolism like thyroxin does. Estrogen is a hormone associated with reproductive functions and plays a role in several bodily processes but is not primarily involved in metabolic regulation by the thyroid gland.