Which of the following hormones can cross the cell membrane?
glucagon
epinephrine
insulin
cortisol
The correct answer and explanation is:
The correct answer is cortisol.
Cortisol is a steroid hormone produced by the adrenal glands. Being a lipid-soluble molecule, it can easily cross the cell membrane, which is made of a lipid bilayer. Steroid hormones, including cortisol, are able to pass through cell membranes because they are nonpolar and hydrophobic. Once inside the cell, cortisol binds to specific intracellular receptors, usually located in the cytoplasm or nucleus, to initiate changes in gene expression. This leads to various physiological effects, such as regulating metabolism and the body’s response to stress.
On the other hand, glucagon, epinephrine, and insulin are water-soluble hormones and cannot cross the lipid membrane directly. These hormones must bind to specific receptors on the surface of the target cell. Once bound to their receptors, they trigger signaling pathways inside the cell via second messengers like cyclic AMP (cAMP) or calcium ions. These signaling cascades alter cellular functions, such as activating enzymes or modifying protein activity, without the hormone itself entering the cell.
Glucagon, produced by the pancreas, primarily stimulates the liver to release glucose into the bloodstream. Epinephrine (adrenaline), produced by the adrenal medulla, is involved in the “fight or flight” response and affects various organs, including the heart and lungs. Insulin, also produced by the pancreas, helps regulate blood glucose levels by promoting the uptake of glucose into cells.
To summarize, cortisol is the only one of the listed hormones that can directly cross the cell membrane due to its lipophilic nature, while glucagon, epinephrine, and insulin rely on membrane-bound receptors to exert their effects.