Give examples of a negative feedback system and the mechanism that regulates it.
1) Regulation of body temperature: When body temperature rises beyond the normal range, a negative feedback system is activated to bring it back to normal. The mechanism involves the release of sweat by sweat glands onto the skin's surface. As sweat evaporates, it cools the body and lowers its temperature. The cooling effect then triggers a decrease in the release of sweat, halting the cooling process.
2) Regulation of blood glucose levels: After a meal, blood glucose levels rise. This increase activates a negative feedback system to bring glucose levels back to normal. The hormone insulin is released from the pancreas, which facilitates the uptake of glucose by cells for energy production. As more glucose is taken up by cells, its concentration in the blood decreases. Consequently, the release of insulin decreases, preventing blood glucose from dropping too low.
3) Regulation of blood pressure: High blood pressure triggers a negative feedback system. Arterial baroreceptors, located in blood vessels, sense the increased pressure and send signals to the brain. This leads to a decrease in sympathetic nervous system activity, causing blood vessels to dilate and reducing heart rate. As a result, blood pressure is brought back to a normal range.
4) Regulation of hormone secretion: In the endocrine system, hormone levels are tightly regulated through negative feedback mechanisms. For example, cortisol, a stress hormone, is regulated by the hypothalamus-pituitary-adrenal (HPA) axis. When cortisol levels are too high, the hypothalamus secretes corticotropin-releasing hormone (CRH), which stimulates the pituitary gland to release adrenocorticotropic hormone (ACTH). ACTH then stimulates the adrenal glands to produce cortisol. However, when cortisol levels rise, it signals the hypothalamus and pituitary gland to reduce the secretion of CRH and ACTH, respectively, thus reducing cortisol production and maintaining balance.