Endoplasmic Reticulum, or ER for short, are organelles found near the nucleus in many cells that form a network of complex sacs throughout the cell. They are important in the synthesis of proteins , special chemicals, and enzymes needed for the cell to function, and they transport materials through the inside of the cell. Endoplasmic Reticulum also come in two types, Rough ER and Smooth ER. In macrophages, Endoplasmic Reticulum are important in the production of enzymes needed to digest materials that it consumes.
The surface of rough ER is covered with Ribosomes, giving it a rough appearance, hence the name. Rough ER help synthesize, modify, and transport proteins.
Smooth ER do not have any ribosomes attatched to their surface, which gives them their smooth appearance. They contain enzymes for the production of lipids and other chemicals, and they transport molecules from the Rough ER to the Golgi Apparatus by pinching off small sections containing the molecules and forming transition vesicles.