Glucose is one of the major nutrients for maintaining metabolic homeostasis. Its deficiency can lead to cell death, but the exact mechanism remains unclear. The authors showed that glucose deprivation resulted in significant necrosis of MCF-7 cells, which was promoted by mitochondrial impairment with the generation of mitochondrial ATP.
They further demonstrated that glucose deficiency disrupted mitochondrial proton homeostasis to provoke a compensatory lysosomal proton efflux; this lysosomal proton efflux increased lysosomal pH, which might trigger apoptosis or necrosis of the cells. Oxford University Press is a department of the University of Oxford. It furthers the University's objective of excellence in research, scholarship, and education by publishing worldwide. Sign In or Create an Account.
Sign In. Advanced Search. Search Menu. Article Navigation. Close mobile search navigation Article Navigation. Volume 9. Article Contents. Positive feedback is a mechanism in which an output is enhanced in order to maintain homeostasis. Positive feedback mechanisms are designed to accelerate or enhance the output created by a stimulus that has already been activated. Positive feedback mechanisms are designed to push levels out of normal ranges.
To achieve this, a series of events initiates a cascading process that builds to increase the effect of the stimulus. This process can be beneficial but is rarely used because it may become uncontrollable. A positive feedback example is blood platelet accumulation and aggregation, which in turn causes blood clotting in response to an injury of the blood vessels. Negative feedback mechanisms reduce output or activity to return an organ or system to its normal range of functioning.
Regulation of blood pressure is an example of negative feedback. Blood vessels have sensors called baroreceptors that detect if blood pressure is too high or too low and send a signal to the hypothalamus.
The hypothalamus then sends a message to the heart, blood vessels, and kidneys, which act as effectors in blood pressure regulation. If blood pressure is too high, the heart rate decreases as the blood vessels increase in diameter vasodilation , while the kidneys retain less water.
These changes would cause the blood pressure to return to its normal range. The process reverses when blood pressure decreases, causing blood vessels to constrict and the kidney to increase water retention. In turn, ACTH directs the adrenal cortex to secrete glucocorticoids, such as cortisol. Glucocorticoids not only perform their respective functions throughout the body but also prevent further stimulating secretions of both the hypothalamus and the pituitary gland.
Temperature control is another negative feedback mechanism. Nerve cells relay information about body temperature to the hypothalamus. The hypothalamus then signals several effectors to return the body temperature to 37 degrees Celsius the set point. The effectors may signal the sweat glands to cool the skin and stimulate vasodilation so the body can give off more heat.
If body temperature is below the set point, muscles shiver to generate heat and the constriction of the blood vessels helps the body retain heat. Both internal and external events can induce negative feedback mechanisms. Homeostatic Control : This image illustrates the feedback mechanisms of homeostatic controls. If positive and negative feedback loops are affected or altered, homeostatic imbalance and resultant complications can occur.
Disease is any failure of normal physiological function that leads to negative symptoms. While disease is often a result of infection or injury, most diseases involve the disruption of normal homeostasis.
Aging is a general example of disease as a result of homeostatic imbalance. As an organism ages, weakening of feedback loops gradually results in an unstable internal environment.
This lack of homeostasis increases the risk for illness and is responsible for the physical changes associated with aging. Heart failure is the result of negative feedback mechanisms that become overwhelmed, allowing destructive positive feedback mechanisms to compensate for the failed feedback mechanisms. This leads to high blood pressure and enlargement of the heart, which eventually becomes too stiff to pump blood effectively, resulting in heart failure.
Severe heart failure can be fatal. Diabetes, a metabolic disorder caused by excess blood glucose levels, is a key example of disease caused by failed homeostasis. In ideal circumstances, homeostatic control mechanisms should prevent this imbalance from occurring. However, in some people, the mechanisms do not work efficiently enough or the amount of blood glucose is too great to be effectively managed.
In these cases, medical intervention is necessary to restore homeostasis and prevent permanent organ damage.
The human body maintains constant levels of glucose throughout the day, even after fasting. During long periods of fasting, glucose levels are reduced only very slightly. The cells convert excess glucose to an insoluble substance called glycogen to prevent it from interfering with cellular metabolism.
Because this ultimately lowers blood glucose levels, insulin is secreted to prevent hyperglycemia high blood sugar levels. Another hormone called glucagon performs the opposite function of insulin, causing cells to convert glycogen to glucose and stimulating new glucose production gluconeogenesis to raise blood sugar levels.
0コメント