During perceived danger the fight-or-flight response includes faster heart beat, quickened breath, tense muscles and thought speed up. This co-ordinated set if physiological changes is triggered by two hormones of the adrenal gland, epinephrine and norepinephrine.
The major activities of these hormones is to increase the amount of chemical energy available for immediate use, increase the heart rate and stroke volume and dilate the bronchioles in the lungs, action the raise the rate of oxygen delivery to the cell.
Selective permeable means it selects what goes out and comes into the cell. If the cell membrane wasnt selective then things could enter the cell and destroy it.
