Cytoplasmic Deposits

Cytoplasmic deposits are usually transitory components of the cytoplasm, composed mainly of accumulated metabolites or other substances. The accumulated molecules occur in several forms, one of them being lipid droplets in adipose tissue, adrenal cortex cells, and liver cells (Figure 2–38). Carbohydrate accumulations are also visible in several cells in the form of glycogen. After impregnation with lead salts, glycogen appears as collections of electron-dense particles (Figure 2–39). Proteins are stored in glandular cells as secretory granules or secretory vesicles (Figure 2–29); under stimulation, these proteins are periodically released into the extracellular medium.

Figure 2-38

Section of adrenal gland showing lipid droplets (L) and abundant anomalous mitochondria (M). x19,000. Figure 2-39 Electron micrograph of a section of a liver cell showing glycogen deposits as accumulations of electron-dense particles (arrows). The dark structures with a dense core are peroxisomes. Mitochondria (M) are also shown. x30,000. Deposits of colored substances—pigments—are often found in cells (Figure 2–40). They may be synthesized by the cell (eg, in the skin melanocytes) or come from outside the body (eg, carotene). One of the most common pigments is lipofuscin, a yellowish-brown substance present mainly in permanent cells (eg, neurons, cardiac muscle) that increases in quantity with age. Its chemical constitution is complex. It is believed that granules of lipofuscin derive from secondary lysosomes and represent deposits of indigestible substances. A widely distributed pigment, melanin is abundant in the epidermis and in the pigment layer of the retina in the form of dense intracellular membrane-limited granules. Figure 2-40 Section of amphibian liver shows cells with pigment deposit (PD) in the cytoplasm, a macrophage (M), hepatocytes (H), and a neutrophil leukocyte (N). In this resin-embedded material it is possible to see mitochondria (pale red) and lysosomes (blue) in the cytoplasm of the hepatocytes. Only with resin embedding is it possible to obtain such information. Giemsa stain. Medium magnification. References Afzelius BA, Eliasson R: Flagellar mutants in man: on the heterogeneity of the immotile-cilia syndrome. J Ultrastruct Res 1979;69:43. [PMID: 501788] Aridor M, Balch WE: Integration of endoplasmic reticulum signaling in health and disease. Nat Med 1999;5:745. [PMID: 10395318] Barrit GJ: Communication Within Animal Cells. Oxford University Press, 1992. Becker WM et al: The World of the Cell, 4th ed. Benjamin/Cummings, 2000. Bretscher MS: The molecules of the cell membrane. Sci Am 1985;253:100. [PMID: 2416050] Brinkley BR: Microtubule organizing centers. Annu Rev Cell Biol 1985;1:145. [PMID: 3916316] Brown MS et al: Recycling receptors: the round-trip itinerary of migrant membrane proteins. Cell 1983;32:663. [PMID: 6299572] Cooper GM: The Cell: A Molecular Approach. ASM Press/Sinauer Associates, Inc., 1997. DeDuve C: A Guided Tour of the Living Cell. Freeman, 1984. DeDuve C: Microbodies in the living cell. Sci Am 1983;248:74. Dustin P: Microtubules, 2nd ed. Springer-Verlag, 1984. Farquhar MG: Progress in unraveling pathways of Golgi traffic. Annu Rev Cell Biol 1985;1:447. [PMID: 3916320] Fawcett D: The Cell, 2nd ed. Saunders, 1981. Krstíc RV: Ultrastructure of the Mammalian Cell. Springer-Verlag, 1979. Mitchison TJ, Cramer LP: Actin-based cell motility and cell locomotion. Cell 1996;84:371. [PMID: 8608590] Osborn M, Weber K: Intermediate filaments: cell-type-specific markers in differentiation and pathology. Cell 1982;31:303. [PMID: 6891619] Pfeffer SR, Rothman JE: Biosynthetic protein transport and sorting in the endoplasmic reticulum. Annu Rev Biochem 1987;56:829. [PMID: 3304148] Rothman J: The compartmental organization of the Golgi apparatus. Sci Am 1985;253:74. [PMID: 3929377] Simons K, Ikonen E: How cells handle cholesterol. Science 2000;290:1721. [PMID: 11099405] Tzagoloff A: Mitochondria. Plenum, 1982. Weber K, Osborn M: The molecules of the cell matrix. Sci Am 1985;253:110. [PMID: 4071030]