The adrenal medulla (internal part) produces two hormones that are called adrenaline (epinephrine) and noradrenaline (norepinephrine) Noradrenaline controls circulation. If the blood pressure falls, more hormones are excreted. This makes the peripheral blood vessels contract, and this in turn causes the blood pressure to rise. The heart rate slows, but the output remains constant.
Adrenaline also influences the heart and circulation, but it is related more to a response to stress situations. The so-called “fight or flight” mechanism occurs. In moments of sudden danger, this is an inbuilt and automatic response designed to prepare the individual for immediate action.
It is aimed at preserving life. The whole body is geared to cope with an emergency situation, be it attacking an adversary or running for safety. For this reason, adrenaline immediately raises the blood-sugar levels (to provide more food for activity) by converting glycogen stored in the liver to glucose available in the bloodstream. Oxygen consumption increases, making the muscles ready for activity. The air passageways dilate, ready to cope with greater demands and the intake of more oxygen. (This is why it is so effective in asthma where there is a constriction of the air-passages making respiration difficult.
By opening the airways, breathing is immediately made much easier.) There is a marked increase in the heart rate and output, enabling more blood (and oxygen, food and supplies) to be pumped around to the body, supplying all organs with essential requirements. The blood pressure tends to rise.
The body’s reaction by increasing production of this hormone is amazing.
Most are well aware of the symptoms that can occur, for simple events, such as a sudden fright, can produce symptoms. For instance, the “hair stands on end” (you might feel this on the back of the neck or on the legs). Sweating, thumping heart, quicker respiration, muscle tension, general alertness and an improvement in mental acuity all take place. If you do have to run, then the ability to do this is usually accelerated.
Abnormalities can occur in the medulla, and although rare, a significant growth called a phaeochromocytonza can arise. This is usually noncancerous, but it may be malignant. It is said to occur in only one of every 1000 persons with high blood pressure.