What are the hormones secreted by the adrenal medulla? What are their respective functions?
The medullary portion of the adrenals secretes hormones of the catecholamine group: adrenaline (also called as epinephrine) and noradrenaline (also called as norepinephrine). Besides their hormonal function, adrenaline and noradrenaline act as neurotransmitters too. The neurons that use them as neurotransmitters are known as adrenergic neurons.
Adrenaline increases the glycogen breaking into glucose (glycogenolysis) therefore increasing glycemia and the basal metabolic rate of the body. Adrenaline and noradrenaline are released during situations of danger (fightfight or flight response) and they intensify the strength and rate of the heartbeat and selectively modulate the blood irrigation in some tissues by selective vasodilation and selective vasoconstriction. By vasodilation they enhance the blood supply to the brain, the muscles and the heart and by vasoconstriction they decrease the blood supply to the kidneys, the skin and the gastrointestinal tract.
Substances like adrenaline and noradrenaline that promote vasodilation or vasoconstriction are known as vasoactive substances.