Class 11 NEET Biology Structural Organisation in Animals

(a) : Mast cells are found in the matrix of areolar connective tissue and secrete histamine (vasodilator), serotonin (vasoconstrictor) and heparin (anticoagulant). These take part in allergic reactions and also help in a body defence. Fibroblasts and histiocytes are also found in the matrix of areolar tissue. Fibroblasts secrete ground substance while histiocytes engulf the microbes, foreign particles and damaged cells. Lymphocytes are the type of leucocytes present in blood and secrete antibodies.