Final answer:
Histamine is the chemical mediator that is secreted onto the surface of the skin. It is released by mast cells in response to irritants or allergic reactions, and it plays a role in dilation of blood vessels, itching, and inflammation.
Step-by-step explanation:
The correct answer is c) Histamine.
Histamine is a chemical mediator that is secreted onto the surface of the skin. It is released by mast cells in response to irritants or allergic reactions, and it plays a role in dilation of blood vessels, itching, and inflammation.
Insulin is a hormone produced by the pancreas that helps regulate blood sugar levels. Melatonin is a hormone that regulates sleep and wake cycles. Serotonin is a neurotransmitter that affects mood, appetite, and many other functions in the body. These substances are not secreted onto the surface of the skin.