Answer:

The endoplasmic reticulum (ER) is a TYPE of organelle found in eukaryotic cells that forms an interconnected network of flattened, membrane-enclosed sacs or tube-like structures known as cisternae. The membranes of the ER are continuous with the outer nuclear membrane. The endoplasmic reticulum occurs in most TYPES of eukaryotic cells, but is absent from red blood cells and spermatozoa.

Cell biology

The animal cell

Animal Cell.svg

Components of a typical animal cell:

Nucleolus

Nucleus

Ribosome (little dots)

Vesicle

Rough endoplasmic reticulum

Golgi apparatus (or "Golgi body")

Cytoskeleton

Smooth endoplasmic reticulum

Mitochondrion

Vacuole

Micrograph of rough endoplasmic reticulum network around the nucleus (shown in lower right-hand side of the PICTURE). Dark small circles in the network are mitochondria.

There are two types of ER: rough endoplasmic reticulum and smooth endoplasmic reticulum. The outer (cytosolic) face of the rough endoplasmic reticulum is studded with ribosomes that are the sites of protein synthesis. The rough endoplasmic reticulum is ESPECIALLY prominent in cells such as hepatocytes. The smooth endoplasmic reticulum lacks ribosomes and functions in lipid synthesis but not metabolism, the production of steroid hormones, and detoxification.[1] The smooth ER is especially abundant in mammalian LIVER and gonad cells