Final answer:
Mast cells are the connective tissue cell type that secretes histamine.
Step-by-step explanation:
The connective tissue cell type that secretes histamine is the mast cell. Mast cells are a type of white blood cell that are involved in the body's immune response. When a mast cell reacts to an irritation, it releases chemicals such as histamine. Histamine is a compound that causes vasodilation and increased permeability of blood vessels, leading to the characteristic symptoms of inflammation.