Final answer:
Chemical mediators of itching originate from mast cells, which release histamine when irritated or damaged, causing inflammatory responses such as itching and swelling. Histamine plays a significant role in various hypersensitivity reactions and can be countered by antihistamines.
Step-by-step explanation:
The origin of chemical mediators of itching is from mast cells, which are found in connective tissue proper. Mast cells contain cytoplasmic granules laden with chemical signals, notably histamine and heparin. When mast cells are irritated or damaged, they release histamine, which is a potent inflammatory mediator. This release causes symptoms such as vasodilation, increased blood flow, itching, swelling, and redness, which are characteristic of an allergic response. It's worth noting that mast cells originate from hematopoietic stem cells and are an integral part of the immune system, aiding in the protection against pathogens.
Chemical mediators like histamine are also crucial in different types of hypersensitivity reactions. For example, type II hypersensitivity reactions involve antibodies as the main initiators. In type III hypersensitivity, the accumulation of immune complexes in tissues and small blood vessels induces the response, leading to inflammation.
Moreover, antihistamines are substances used to prevent the effects of histamines, including the itching and swelling of body tissues, confirming the role of histamines as chemical mediators of itching.