American Board of Surgery Qualifying Exam (ABS QE) Practice Test

What is the primary source of histamine in tissue?

1. Mast cells

2. Basophils

3. Eosinophils

4. Macrophages

The correct answer is: Mast cells

Mast cells are the primary source of histamine in tissues. These cells are strategically located in connective tissues, particularly near blood vessels and nerves, where they play a crucial role in immune responses and inflammation. Mast cells contain granules rich in histamine, which they release upon activation, particularly in allergic reactions or in response to certain stimuli. Histamine is a biogenic amine that contributes to various physiological functions, such as promoting vasodilation, increasing vascular permeability, and influencing gastric gastric acid secretion. This release of histamine from mast cells is a key event in allergic responses, leading to symptoms such as itching, swelling, and redness associated with conditions like hay fever and anaphylaxis. While other cell types, like basophils and eosinophils, can also produce or release histamine, especially in allergic contexts, mast cells are overwhelmingly recognized as the primary contributors to tissue histamine. Macrophages, while important immune cells, are not significant sources of histamine. Their roles involve phagocytosis and cytokine production rather than histamine secretion. Thus, the presence and activation of mast cells are central to the understanding of histamine's role in immunological responses and tissue inflammation.