By respiratory system we usually mean the passages that transport incoming air to the lungs and to the microscopic air sacs called alveoli where gases are exchanged. The term respiration refers to the whole chain of processes from the inhalation of air to the use of oxygen in the cells. Index. Reference.
Phagocytes are the white blood cells that protect the body by eating (phagocytosing) dirt, bacteria and dead or dying cells. They are important for fighting infections. They are also important for becoming immune. Phagocytes are important in all animals and are very complex in vertebrates.
This function is important for the normal brain, during brain development, and in pathology and regeneration. In the CNS development microglial phagocytosis is instrumental in removing apoptotic cells and may be involved in synapse removal during development and potentially in pruning synapses in the postnatal brain.