Final answer:
Granular leucocytes include neutrophils, eosinophils, and basophils, which are types of white blood cells with granules in their cytoplasm, originating from myeloid stem cells, and they play a pivotal role in the immune response.
Step-by-step explanation:
The granular leucocytes, which are a type of white blood cells (leucocytes), consist of neutrophils, eosinophils, and basophils. These cells are characterized by the presence of granules in their cytoplasm and a lobed nucleus. They play a significant role in the body's immune response as they are often the first-responders during injury or infection. Neutrophils, for instance, are phagocytic cells that can engulf and destroy bacteria and other harmful microorganisms. Eosinophils are mostly involved in combating parasites and allergens, and basophils release chemicals such as histamine in response to allergic reactions. All these granular leukocytes originate from myeloid stem cells.