PATHOLOGY

Detailed explanation-1: -Receptor sites can be found within the plasma membrane of a cell, which acts as a boundary between the cell’s internal and external environment. Molecules that bind to receptor sites are known as ligands. Hormones, neurotransmitters, and drugs are examples of ligands.

Detailed explanation-2: -1: Second messenger systems: The amino acid-derived hormones epinephrine and norepinephrine bind to beta-adrenergic receptors on the plasma membrane of cells.

Detailed explanation-3: -Intracellular receptors are located in the cytoplasm of the cell and are activated by hydrophobic ligand molecules that can pass through the plasma membrane. Cell-surface receptors bind to an external ligand molecule and convert an extracellular signal into an intracellular signal.