Anatomy Practice Exam

How do protein hormones interact with target cells?

1. They dissolve the cell membrane

2. They bind to internal receptors

3. They bind to surface receptors

4. They enter the nucleus directly

The correct answer is: They bind to surface receptors

Protein hormones primarily interact with target cells by binding to surface receptors. This is due to the hydrophilic nature of protein hormones, which prevents them from easily crossing the lipid bilayer of the cell membrane. Instead, these hormones must attach to specific receptors located on the surface of the target cells. Once a protein hormone binds to these surface receptors, it activates intracellular signaling pathways, often involving second messengers. This process initiates a series of biochemical reactions that lead to the desired physiological response. The significance of surface receptors is that they enable the hormone to exert its effects rapidly, as the signaling cascades can lead to changes in cellular function without the hormone needing to enter the cell itself. Other mechanisms of hormone action, such as binding to internal receptors or entering the nucleus directly, are more characteristic of steroid hormones or other lipophilic substances, which can diffuse through the membrane due to their chemical properties. Therefore, the interaction of protein hormones with surface receptors is a key aspect of their function within the endocrine system.