The diagram below illustrates two key pathways by which different types of hormones interact with their target cells:
Aldosterone is a lipid-soluble steroid hormone synthesized in the adrenal cortex, whereas glucagon is a hydrophilic polypeptide hormone synthesized in the pancreas.
Using Pathway A as a reference, suggest where the receptor proteins for aldosterone are situated within a target cell, and explain how aldosterone is able to reach these receptors.
Using Pathway B as a reference, state the location of glucagon receptors and explain why glucagon cannot access the same intracellular compartment as aldosterone.
Once glucagon binds to its target receptor on the cell-surface membrane, it triggers a cascade of intracellular events without entering the cytosol. Explain the mechanism by which this extracellular binding event leads to the activation of intracellular enzymes, such as glycogen phosphorylase.
