Basophils are the least numerous of the leukocytes, consisting less than 1% of the total leukocytes.
Basophils are about 10- 12 μm in diameter.
Figure18. EM of a human basophil; B, basophilic granules, M, myelin figures
The nucleus is divided into irregular lobes, but the division usually obscured by the overlying specific granules.
Specific granules in basophils are fewer and more irregular in size and shape than the granules of the other granulocytes.
Basophilic specific granules contain heparin and histamine and are capable of generating leukotriens. They cause slow contraction of smooth muscles.
Histamine and slow-reacting substance of anaphylaxis are vasoactive agents that bring on the dilation of small blood vessels.
Main functions are:
-basophils may supplement the function of mast cells in immediate hypersensitivity reactions by migrating into connective tissues
-basophils have also a very weak phagocytic activity
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