Which endocrine hormone promotes the breakdown of protein in muscle cells?

• A. Thyroxine
• B. Glucagon
• C. Insulin
• D. Cortisol

Answer: (D)

Verified step by step guidance

1. Understand the role of cortisol: Cortisol is a glucocorticoid hormone produced by the adrenal cortex. It plays a crucial role in the body's response to stress and has several metabolic functions.
2. Recognize the function of cortisol in protein metabolism: Cortisol promotes the breakdown of proteins in muscle cells, a process known as proteolysis. This is part of its role in mobilizing energy resources during stress.
3. Differentiate cortisol from other hormones: Thyroxine primarily regulates metabolism and energy levels, glucagon increases blood glucose levels by promoting glycogen breakdown, and insulin facilitates glucose uptake into cells. None of these directly promote protein breakdown in muscle cells.
4. Identify the physiological context: During stress or fasting, cortisol levels increase, leading to protein breakdown in muscles to provide amino acids for gluconeogenesis, which is the production of glucose from non-carbohydrate sources.
5. Conclude that cortisol is the hormone responsible for promoting the breakdown of protein in muscle cells, distinguishing it from the other hormones listed.