Mast cells are made in our bone marrow and travel to various areas of the body where they live for 2-4 years and serve as a sentinel to protect against assaults that might cause harm to the body. They concentrate in the areas of the body where there is an interface between the body and the external environment such as the mucosal surfaces of the gastrointestinal tract, the genitourinary tract, the respiratory tract, and they are also in the connective tissue and the skin. Unfortunately, Mast cells’ efforts to protect us is a reason why we feel allergic and experience inflammation when they are activated. 
 

Mast cells contain granules that secrete multiple chemicals such as:

neurotransmitters histamine, and serotonin

Serine proteases such as tryptase, and chymase

Proteoglycans such as heparin (an anticoagulant)

Lysosomal enzymes such as B-hexsamineidase, B-glucuronidase, and arylsulfatases Cytokines such as TNF alpha, interleukin four, stem cell factor, chemokines, and eosinophil chemotactic factor

Lipid mediators (eicosanoids) such as thromboxane, prostaglandin D2, leukotriene C4, platelet activating factor...