Final answer:
A macrophage is a type of connective tissue macrophage that plays a crucial role in the immune system by engulfing pathogens and cellular debris.
Step-by-step explanation:
A macrophage is a type of connective tissue macrophage. It is derived from a monocyte and enters the connective tissue matrix from the blood vessels. Macrophages are phagocytic cells that play a crucial role in the immune system, engulfing pathogens and cellular debris. Some examples of connective tissue macrophages include Kupffer cells in the liver, histiocytes in connective tissue, and alveolar macrophages in the lungs.