This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Physiology
Macrophages in nervous system is known as: 
Select and explain. 
A. Schwann cells, B. Oligodendrocytes, C. Astrocytes, D. Microglia
D: Microglia
Answer: D: Microglia 
Explanation: Microglia are scavenger cells that resemble tissue macrophages and remove debris resulting from injury, infection, and disease (eg, multiple sclerosis, AIDS-related dementia, Parkinson disease, and Alzheimer disease). Microglia arise from macrophages outside of the nervous system and are physiologically and embryologically unrelated to other neural cell types. Ref: Ganong's Review of Medical Physiology 23rd edition, Chapter 4.