Hormone receptor location — Which hormone listed requires a cell surface receptor to exert its action?

Introduction:Hormones differ in chemistry and therefore in receptor location. This question asks which listed hormone requires a receptor at the cell surface to initiate its effects.

Given Data / Assumptions:

• Hydrophilic hormones cannot freely cross membranes and use surface receptors.
• Lipophilic hormones and gases often use intracellular receptors or direct diffusion targets.
• Choices include both hormones and general growth factors.

Concept / Approach:Adrenaline (epinephrine) is a catecholamine that is hydrophilic and signals through G protein coupled adrenergic receptors at the plasma membrane. In contrast, steroid hormones (e.g., progesterone) and thyroid hormones (T4/T3 after transport) signal via intracellular receptors; nitric oxide diffuses and activates soluble guanylyl cyclase inside cells. Many growth factors bind surface receptors but are not hormones in the classical endocrine sense.

Step-by-Step Solution:

Verification / Alternative check:Beta adrenergic agonists rapidly stimulate cAMP production via surface β adrenergic receptors, consistent with surface receptor dependence.

Why Other Options Are Wrong:

• Nitric oxide: diffuses and activates soluble guanylyl cyclase in the cytosol.
• Progesterone: lipophilic steroid, binds intracellular nuclear receptors.
• Growth factors: usually act at the surface but are not hormones in the strict endocrine sense as framed by the question.
• Thyroxine (T4): enters cells via transporters and binds nuclear receptors after conversion to T3.

Common Pitfalls:Choosing any molecule that binds a surface receptor without considering whether it is a hormone in the sense posed by the question.

Final Answer:Adrenaline (epinephrine).