Damaged cells

Cell Cycle Control. Figure 3 The DNA damage checkpoint. In response to DNA damage cells activate p53 dependent and independent checkpoint pathways leading to cell cycle arrest at G1/S and G2/M allowing DNA repair. If the cellular damage cannot be repaired, cells can initiate apoptosis. 

FIGURE 19.27 A DNA molecule is very large, even in bacteria. In this micrograph, a DNA molecule has spilled out through the damaged cell wall of a bacterium. 

Living cells are delicately balanced chemical machines. The ionization track generated by a nuclear particle upsets this balance, almost always destroying the cell in the process. Although the body has a remarkable ability to repair and replace damaged cells, exposure to radiation can overload these control mechanisms, causing weakness, illness, and even death. 

Inflammation is a non-specific reaction which can be induced by a variety of agents apart fiom microorganisms. Lymphokines and derivatives of arachidonic acid, including prostaglandins, leukotrienes and thromboxanes are probable mediators of the inflammatory response. The release of vasoactive amines such as histamine and serotonin (5-hydroxytryptamine) firm activated or damaged cells also contribute to inflammation. 

Drugs frequently bind to blood elements directly (e.g. penicillin to erythrocytes) and the antibodies to the resultant complex react with, and damage, cells coated with the drug. Viruses, especially those that bud, become associated with the host cell surface antigens with the resultant generation of Tc cells. 

Cell culture tests show that dental silicate cement is strongly cytotoxic - that is it severely damages cells - even after set (Spangberg et al., 1973). This effect has been attributed to the hydrogen and fluoride ions present (Helgeland Leirskar, 1972, 1973 Tyas, 1979). 

The well-known fact that in irreversibly damaged cells, respiratory control is lost and is accompanied by oxidation of cytochromes a and as, as well as NADH (Taegtmeyer et al., 1985), was originally thoug it to be due to substrate deficiency (Chance and Williams, 1955) but may be due to an enzymatic defect resulting in an inability to metabolize NADH-linked substrates (Pelican etal., 1987). It seems likely therefore that return of function is dependent on preservation of mitochondrial membrane integrity, and the structure and activities of respiratory chain (R.C) complexes I-IV (Chance and Williams, 1955). 

The fluidity of blood is a result of the inhibition of a complex series of enzymic reactions in the coagulation cascade (see Fig. 10). When triggered either intrinsically (by contact with foreign surfaces ), or extrinsically (by tissue factors from damaged cells), inactive proenzymes (factors XII, XI, IX, and X) are transformed into activated pro-teinases (XHa, XIa, IXa, and Xa, respectively). Each proteinase catalyzes the activation of the following proenzyme in the sequence, up to formation of thrombin (Factor Ha), another proteinase that catalyzes partial... 

In general, normally aging erythrocytes and slightly damaged cells are sequestered in the spleen, whereas those heavily damaged or modified are removed from circulation by the liver [101]. This along with a short... 

Mailer An analogous event occurs in Nenopus, Low-level irradiation results in a few damaged cells being removed into the blastocoel, and development proceeds normally without apoptosis. 

Prostaglandins Arachidonic acid/ damaged cells Cyclooxygenase Sensitization Non-steroidal anti-inflammatory drugs (e.g. aspirin, ibuprofen)... 

Leukotrienes Arachidonic acid/ damaged cells Lipoxygenase Sensitization ... 

CytoTox One Homogeneous LDH released by cells with damaged Cell membrane No [34]... 

Free radical Highly reactive species (atoms or molecules with an unpaired electron) which can damage cells in a variety of ways. Oxygen containing hydroxyl and... 

Damaged cell morphology due to excessive antigen retrieval... 

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