De Histology

Warming Up

noreply@blogger.com (deztroyer28) — Wed, 29 Jun 2011 13:29:00 +0000

When The Doctor was preparing a drug that would be injected to the patient, suddenly, the patient who was lying in bed screaming out. The Doctor was surprised, so he asked to the patient:

The Doctor : Well...why are you screaming out ? What is the fear of injections ?
Patients : No...Sir, I screamed just for warming up. So that, when I'm shot I will not scream anymore... :D
The Doctor : ?!!?!!?!?!

Cytosol

noreply@blogger.com (deztroyer28) — Tue, 28 Jun 2011 13:06:00 +0000

At one time, it was believed that the cytoplasm intervening between the discrete organelles and deposits was unstructured. This belief was reinforced by the use of homogenization and centrifugation of the homogenates to yield fractions consisting of recognizable membrane-bound organelles. The final supernatant produced by this process, after the separation of organelles, is called the cytosol. The cytosol constitutes about half the total volume of the cell. Homogenization of cells disrupts a delicate microtrabecular lattice that incorporates filaments of actin, microtubules, intermediate filaments, enzymes, and other soluble constituents into a structured cytosol. The cytosol coordinates the intracellular movements of organelles and provides an explanation for the viscosity of the cytoplasm. Soluble (not membrane-bound) enzymes, such as those of the glycolytic pathway, for example, function more efficiently when organized in a sequence instead of having to rely on random collisions with their substrates. The cytosol provides a framework for this organization. It contains thousands of enzymes that produce building blocks for larger molecules and break down small molecules to liberate energy. All machinery to synthesize proteins (rRNA, mRNA, tRNA, enzymes, and other factors) is contained in the cytosol.

Cell Components & Diseases

Many diseases are related to molecular alterations in specific cell components. In several of these diseases, structural changes can be detected by light or electron microscopy or by cytochemical techniques. Table 2–5 lists some of these diseases and emphasizes the importance of understanding the many cell components in pathobiology.

Table 2–5. Some Human and Animal Diseases Related to Altered Cellular Components.

Cell Component Involved	Disease	Molecular Defect	Morphological Change	Clinical Consequence
Mitochondrion	Mitochondrial cytopathy	Defect of oxidative phosphorylation	Increase in size and number of muscle mitochondria	High basal metabolism without hyperthyroidism
Microtubule	Immotile cilia syndrome	Lack of dynein in cilia and flagella	Lack of arms of the doublet microtubules	Immotile cilia and flagella with male sterility and chronic respiratory infection
Microtubule	Mouse (Acomys) diabetes	Reduction of tubulin in pancreatic cells	Reduction of microtubules in cells	High blood sugar content (diabetes)
Lysosome	Metachromatic leukodystrophy	Lack of lysosomal sulfatase	Accumulation of lipid (cerebroside) in tissues	Motor and mental impairment
Lysosome	Hurler disease	Lack of lysosomal -L-iduronidase	Accumulation of dermatan sulfate in tissues	Growth and mental retardation
Golgi complex	I-cell disease	Phosphotransferase deficiency	Inclusion-particle storage in several cells	Psychomotor retardation, bone abnormalities

References

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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]

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Simons K, Ikonen E: How cells handle cholesterol. Science 2000;290:1721. [PMID: 11099405]

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Cytoplasmic Deposits

noreply@blogger.com (deztroyer28) — Sun, 26 Jun 2011 12:34:00 +0000

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.