Question

1. Describe in detail the two ways in which a hormone can deliver its message to a target cell. What characteristics of the hormone determine which mechanism is used?

2. List and briefly describe the chemical sequence of events in the fight-or-flight response to a threatening situation from the binding of epinephrine at the receptor site to readiness for another situation.

3. Compare the nervous system and the endocrine system with respect to chemical messengers used, and the messenger molecules' means of transport, specificity, and time lapse between release and effect.

Answer 1

1)

Steroid hormones, lipophilic signals, can diffuse across the plasma membrane and interact with intracellular receptors. The receptor-hormone complex then translocates to the nucleus and interacts with specific response elements, stimulating transcription.

Polypeptide hormones cannot diffuse across the plasma membrane as they are hydrophilic. Polypeptide hormones binds to cell surface receptors and enters the cell by receptor mediated endocytosis, that leads to the activation of nuclear transcription factors

Cortisol is a steroid molecule, hydrophobic molecule, diffuses across the plasma membrane and binds to the intracellular receptors. Once inside the cell they bind to intracellular receptors that are expressed by the hormonally responsive target cells. These receptors belongs to the nuclear receptor superfamily, are transcription factors that contain domains for ligand binding, DNA binding and transcriptional activation.