Tissue homeostatic mechanisms

Maintenance of red cell volume is critical to having an adequate oxygen supply to the tissues [10]. Healthy individuals finely balance erythropoiesis and erythrocyte loss and maintain constant hematocrit. The glycoprotein hormone erythropoietin is the principal controller of the homeostatic mechanism that links tissue oxygen delivery to red cell production. While hypothesized as early as 1863, unequivocal evidence of erythropoietin was first published in 1953. A few years later, scientists showed that animals subjected to bilateral nephrectomy were unable to mount an erythropoietin response to hypoxia. Indeed, the kidneys produce about 90% of circulating erythropoietin. 

The reversal of the pH gradient at tumor cells has been known for quite some time. While, in normal tissue, the extracellular medium is slightly basic, the opposite situation is observed in tumor tissues [104]. The intracellular pH, on the other hand, is almost the same for both kinds of cells due to homeostatic mechanisms. Therefore triggering MRI contrast agents by pH variation seems like a promising method for highlighting tumors. Several pH sensitive MRI contrast agents have already been developed. 

The chemical analysis of biologic tissues is a reflection of biologic activity. The human body tries to maintain itself in a state of homeostasis. Homeostasis is a dynamic equilibrium and not a chemical stagnation. Homeostatic mechanisms tend to keep the chemical makeup of the body constant. Chemical analysis of various human tissues will, therefore, yield relatively consistent findings in healthy tissues. 

Up to 30% of ingested zinc is absorbed from the small intestine however, a homeostatic mechanism controls the absorption. Nutritional status also influences zinc absorption deficiency of pyridoxine or tryptophan somewhat inhibits absorption. Zinc induces a zinc metallothionein, the form in which it is bound to the liver and other tissues. The pancreas is high in zinc, and in males the prostate gland contains the greatest store of zinc. Zinc is excreted in the feces. 

Pain can be described as a complex experience consisting of aphysiological response to a noxious stimulus followed by an affective (emotional) response to that event. Pain, in the context of a homeostatic mechanism, is a warning signal that helps to protect an organism by influencing it to withdraw from harmful stimuli it is primarily associated with injury, or the threat of injury, to the body tissue. 

A further difficulty in interpretation of changes in or a constant level of P02, as indicated by electrode current, is presented by tissue homeostatic mechanisms. The rate of tissue change and the electrode response... 

As with other essentiai nutrients there are homeostatic mechanisms which maintain a constant tissue concentration of zinc in spite of fiuctuations in dietary suppiy. The total dietary intake is 10-15 mg per day. The bioavailability of zinc from different foodstuffs varies. Some 40% of zinc is absorbed from the average diet. Inside the intestinai mucosai ceil zinc enters a metabolic pooi in equiiibrium with zinc-thionein. The synthesis of this metal binding protein is induced by various metals, and it appears to reguiate their intracellular transport. Zinc leaves the intestinal mucosal cell across the plasma membrane and is taken up by albumin in the portal circulation. The liver extracts zinc with a high... 

The test usually conducted to determine body zinc is the measurement of plasma zinc concentration. However, plasma zinc concentrations do not seem to reflect the concentration found in the liver parenchyma (Goksu Ozsoylu, 1986 Sato et al., 2005). This may be explained by the fact that there are very efficient homeostatic mechanisms to correct plasma or serum zinc deficiencies, which makes it difficult to diagnose marginal deficiency by using this method. Therefore, the investigation of zinc concentration in liver tissue is important. 

---