When a star is fusing iron in its core, it's still giving off insane amounts of energy. ... Iron cannot be fused into anything heavier because of the insane amounts of energy and force required to fuse iron atoms. The atomic structure of iron is very stable, more so than most other elements.
That's what is called competitive enzymatic regulation. If there are more of that substance than the enzyme substrate, then most of the enzyme, if not all depending on the substance's concentration, will be inhibited on its action. If there are more substrate then the competitive substance, the expected reaction for that enzyme will happen at an expected rate. If the ratio substrate:substance is 1:1 then the reaction enzyme-substrate is very slowed down.
Nicotine on direct application in humans causes irritation and burning sensation in the mouth and throat, increased salivation, nausea, abdominal pain, vomiting and diarrhea. Predominant immediate effects consist of increase in pulse rate and blood pressure. Nicotine also causes an increase in plasma free fatty acids, hyperglycemia, and an increase in the level of catecholamines in the blood. There is reduced coronary blood flow but an increased skeletal muscle blood flow. The increased rate of respiration causes hypothermia, a hypercoagulable state, decreases skin temperature, and increases the blood viscosity.
For amphetamine the immediate effects are quicker reaction times, feelings of energy/wakefulness, excitement, increased attentiveness and concentration, feelings of euphoria. Side effects of amphetamines can include heart palpitations, dry mouth, headache, hostility, nausea, cognitive impairment, severe anxiety, lack of appetite, teeth grinding, dizziness, increased heart rate, heart palpitations, rapid breathing rate, hypertension (high blood pressure), increased body temperature, erectile dysfunction, irregular heartbeat.
Cocaine causes a short-lived, intense high that is immediately followed by the opposite intense depression, edginess and a craving for more of the drug the side effects are Loss of appetite increased heart rate, blood pressure, body temperature, contracted blood vessels increased rate of breathing, dilated pupils, disturbed sleep patterns, nausea, hyperstimulation, bizarre, erratic, sometimes violent behavior hallucinations, hyperexcitability, irritability, tactile hallucination that creates the illusion of bugs burrowing under the skin, intense euphoria, anxiety and paranoia, depression, intense drug craving, panic and psychosis, convulsions, seizures and sudden death from high doses (even one time)
