The level of glucose in the bloodstream drops. The person requires glucose in cells to meet the demand for ATP (glucose is broken down to create ATP). The body detects glucose levels with a particular receptor designed for this function. These receptors release hormones, chemical messages that initiate the start of the feedback mechanism. The hormones travel to their target tissue and initiate a corrective response. In this case, the corrective response is the secretion of more glucose into the bloodstream.

When you are cut, your cells begin to produce an enzyme called thrombin that forms the matrix of the blood clot. The presence of thrombin speeds up the production of still more thrombin. That is, it has a self- catalytic , self-accelerating effect, so that once the clotting process begins, it runs faster and faster.

Oxytocin is a hormone that intensifies the contractions that take place during childbirth. The stretching of the uterus triggers the secretion of oxytocin, which stimulates uterine contractions. These contractions further stretch the uterus, which cause the secretion of more oxytocin and speeds up labor.

An increase in blood pressure is detected by receptors in the blood vessels that sense the resistance of blood flow against the vessel walls. The receptors relay a message to the brain, which in turn sends a message to the effectors, the heart and blood vessels. The heart rate decreases and blood vessels increase in diameter, which cause the blood pressure to fall back within the normal range or set point. Conversely, if blood pressure decreases, the receptors relay a message to the brain, which in turn causes the heart rate to increase, and the blood vessels to decrease in diameter. Some set points become "reset" under certain conditions. 

Heart rate and respiratory rate increases in response to increased exercise or other increased muscle cell activity.  During exercise, the heart and breathing rates normally increases. This increase is not abnormal; it is the body's response to the increased demand of oxygen by muscle tissues. When the muscles require more oxygen, the body responds by increasing the blood flow to muscle tissues, thereby increasing blood pressure.

The human body maintains a blood pH within the very narrow range of 7.35 to 7.45. A pH below this range is called acidosis and a pH above this range is alkalosis. Either condition can be life-threatening. One can live only a few hours with a blood pH below 7.0 or above 7.7, and a pH below 6.8 or above 8.0 is quickly fatal. Yet the body's metabolism constantly produces a variety of acidic waste products that challenge its ability to maintain pH in a safe range. Individual blood cells, your kidneys, and even your lungs remove wastes to maintain pH at appropriate levels.

The death of a small area of heart tissue triggers a heart attack (myocardial infarction), the heart pumps an inadequate amount of blood. Thus, the heart muscle itself is deprived of blood flow, and more begins to die. This can lead to a rapid worsening of cardiac function until a person dies.