The sER consists of short anastomosing tubules that are not associated with ribosomes.
Cells with large amounts of smooth-surfaced endoplasmic reticulum may exhibit distinct cytoplasmic eosinophilia (acidophilia) when viewed in the light microscope. The sER is structurally similar to the rER but lacks the ribosome-docking proteins. It tends to be tubular rather than sheetlike, and it may be separate from the rER or an extension of it. The sER is abundant in cells that function in lipid metabolism (i.e., cells that synthesize fatty acids and phospholipids), and it proliferates in hepatocytes when animals are challenged with lipophilic drugs. The sER is well developed in cells that synthesize and secrete steroids such as adrenocortical cells and testicular Leydig (interstitial) cells (Fig. 2.31). In skeletal and cardiac muscle, the sER is also called the sarcoplasmic
FIGURE 2.31 • Electron micrograph of the sER. This image shows numerous profles of sER in an interstitial (Leydig) cell of the testis, a cell that produces steroid hormones. The sER seen here is a complex system of anastomosing tubules. The small, dense objects are glycogen particles. 60,000.
reticulum. It  sequesters Ca2 , which is essential for the contractile process and is closely apposed to the plasma-membrane invaginations that conduct the contractile impulses to the interior of the cell.
The sER is the principal organelle involved in detoxification and conjugation of noxious substances.
The sER is particularly well developed in the liver and contains a variety of detoxifying enzymes related to cytochrome P450 that are anchored directly into sER plasma membranes. They modify and detoxify hydrophobic compounds such as pesticides and carcinogens by chemically converting them into water-soluble conjugated products that can be eliminated from the body. The degree to which the liver is involved in detoxification at any given time may be estimated by the amount of sER present in liver cells. The sER is also involved in:  lipid and steroid metabolism,  glycogen metabolism, and  membrane formation and recycling.
Because of these widely disparate functions, numerous other enzymes—including hydrolases, methylases, glucose-6phosphatase, ATPases, and lipid oxidases—are associated with the sER, depending on its functional role.
The Golgi apparatus is well developed in secretory cells and does not stain with hematoxylin or eosin.
The Golgi apparatus was described more than 100 years ago by histologist Camillo Golgi. In studies of osmium-impregnated nerve cells, he discovered an organelle that formed networks around the nucleus. It was also described as well developed in secretory cells. Changes in the shape and
FIGURE 2.32 • Photomicrograph of plasma cells. This photomicrograph of a plastic-embedded specimen showing the lamina propria of the small intestine is stained with toluidine blue. The plasma cells, where appropriately oriented, exhibit a clear area in the cytoplasm near the nucleus. These negatively stained regions (arrows) represent extensive accumulation of membranous cisternae that belong to the Golgi apparatus. The surrounding cytoplasm is deeply metachromatically stained because of the presence of ribosomes associated with the extensive rER. 1,200.