Question

Thyroid Hormone: Triiodothreonine (T3) & Thyroxine (T4). What gland secretes? What is the target tissue and what effect does this cause?

A) Thyroid gland - Target tissue: Almost all cells in the body - Effect: Increase metabolic rate
B) Adrenal gland - Target tissue: Liver - Effect: Stimulates insulin release
C) Pituitary gland - Target tissue: Muscles - Effect: Promotes bone growth
D) Pancreas

Answer 1

The thyroid gland secretes the hormones Thyroxine (T4) and Triiodothyronine (T3), targeting almost all body cells to increase the metabolic rate. This effect of raising metabolism is termed the calorigenic effect.

Step-by-step explanation:

The thyroid gland secretes two important hormones known as Thyroxine (T4) and Triiodothyronine (T3). These hormones play a critical role in regulating the body's metabolic rate. They are secreted in response to thyroid-stimulating hormone (TSH), which is released by the anterior pituitary gland. The target tissues for T3 and T4 are almost all cells in the body, with the primary effect of increasing the metabolic rate. This is achieved by transporting these hormones across the plasma membrane of target cells, where they bind to receptors on the mitochondria to increase ATP production, and in the nucleus, to activate genes involved in energy production and glucose oxidation. Enhanced metabolism and body heat production are known as the hormone's calorigenic effect.