Turnover rate mucosa

Because many antineoplastic drugs affect DNA synthesis, any cell with a high turnover rate will be more sensitive to the toxic effects of chemotherapy. Cancer cells do not necessarily proliferate faster than normal cells. Normal tissues that consist of rapidly proliferating cells are targets for the toxicities of many anticancer drugs.The bone marrow, intestinal mucosa, and hair follicles are such tissue sites where drug effects are manifested. 

To increase retention time. When intended for a part of the body with high tissue turnover rate, such as intestinal mucosa, a drug linked to a mucoadhesive polymer can increase adhesion to the site and increase bioavailability of a drug that has low residence time. 

Among these thiolated chitosans, chitosan-MNA showed the highest mucoadhesive features [33]. Even though thiolated chitosans have shown excellent mucoadhesive properties, the adhesion of the polymers is sloughed off by the natural mucus turnover due to a continuous process of mucus secretion. In the human intestine, for instance, the mucus turnover rate is typically about 12—24 h this is very rapid and makes it difficult for the polymers to interact with the mucosa for a prolonged period of time [34]. 

The process of maturation from basal cell through to desquamation (shedding) has been estimated at 13 days for the buccal epithelium and this process is probably representative of the oral mucosa as a whole. Thus the rate of cell turnover in the oral cavity is considerably faster than that of skin, which takes approximately 30 days (see Section 8.2.1). 

Most dietary folate is reduced and methylated to methyl-tetrahydro-folate in the intestinal mucosa (Section 10.2.1). Intestinal mucosal ceUs have a rapid turnover, typicaUy 48 hours from proliferation in the crypt to shedding at the tip of the vUlus. This means that an unstable variant of the enzyme, which loses activity over a shorter time than the normal enzyme, is probably irrelevant in ceUs that have such a rapid turnover. A high intake of folate would therefore result in a relatively high rate of supply of methyl-tetrahydrofolate to cells, arising from newly absorbed folate, so that impaired turnover of folate within cells would be less important. 

VITAMIN Bj2 deficiency Vitamin Bj deficiency is recognized by its impact on the hematopoietic and nervous systems. The sensitivity of the hematopoietic system relates to its high rate of cell turnover. Other tissues with high rates of cell turnover (e.g., mucosa and cervical epithelium) also have high requirements for the vitamin. 

If the phosphatide molecules of carcinomatous tissue were replaced at a high rate by labeled molecules, and such molecules were given off by the tumor to the circulation shortly after the administration of labeled phosphate, the presence of carcinomatous tissue could possibly be diagnosed by determination of the activity of plasma phosphatides. The facts, however, that the phosphatide turnover of neoplastic tissue is much slower than turnover in liver and intestinal mucosa and that phosphatide molecules in the circulation were to a very large extent built up in the liver frustrate this possibility. 

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