Heparin, histamine, and serotonin are secreted by Mast cells.

Mast cells are a type of white blood cell that plays a role in the body's immune system. They are found in connective tissue and mucous membranes, and are especially concentrated in areas of the body that are prone to infections, such as the nose, throat, and lungs. Mast cells are best known for their role in allergic reactions, but they also play a role in inflammation, wound healing, and protection against pathogens.

Heparin:
Heparin is a type of anticoagulant that prevents blood from clotting. Mast cells secrete heparin into the bloodstream to prevent blood clots from forming around an injury or inflammation.

Histamine:
Histamine is a chemical that is involved in the body's immune response. When mast cells are activated, they release histamine into the surrounding tissue. Histamine causes blood vessels to dilate, which increases blood flow to the area, and also causes inflammation, which helps to fight infections.

Serotonin:
Serotonin is a neurotransmitter that is involved in regulating mood, appetite, and sleep. Mast cells also secrete serotonin, which can cause blood vessels to constrict, reducing blood flow to the area. This can help to limit inflammation and prevent the spread of infections.

In conclusion, Mast cells are responsible for secreting heparin, histamine, and serotonin. These chemicals play a crucial role in the body's immune response, helping to fight infections and promote healing.

Mast cells is a type of granular basophil cells in the connective tissue