Adrenaline is a
catecholamine hormone and neurotransmitter secreted by the adrenal medulla, which is part of the endocrine system. Although the
adrenal cortex is often mentioned, it is actually the adrenal medulla that is responsible for the synthesis of adrenaline. Additionally, adrenaline is also secreted by the
endings of sympathetic nervous system fibers, making this hormone one of the fundamental transmitters responsible for
mobilizing the body in stressful situations, and not only.
It is chemically similar to
pyrocatechol (catechol). Moreover, its secretion can be stimulated by
testosterone, which means that individuals with higher levels of this hormone may show a
greater tendency for adrenergic reactions, thus intense emotions or a propensity to take risks.
Epinephrine plays an important role in regulating
glucose metabolism, acting antagonistically towards
insulin, thus combating it. This means that adrenaline
lowers insulin levels in the blood, leading to increased blood sugar levels, providing the body with
additional energy in stressful situations. Besides, adrenaline stimulates the secretion of
glucagon, causing the release of glucose from the liver into the bloodstream.
Adrenaline acts on
α-adrenergic and β-adrenergic receptors, which are responsible for activating the sympathetic system. This leads to
an acceleration of heart rate and dilation of the bronchi, and consequently, to an increased blood flow to the muscles. A similar effect is shown by
norepinephrine, however, unlike adrenaline, it does not significantly affect
metabolism, having little impact on digestion.
The most important effect of
adrenaline action is the acceleration of heart activity and an increase in its cardiac output, which
improves the transport of oxygen and nutrients to the body's tissues. Additionally, epinephrine causes
dilation of the pupils, which enhances visual acuity. It also causes
dilation of the larynx and bronchi, improving oxygen supply to the lungs. In turn,
increasing the rate of breathing facilitates oxygenation of the body.
Adrenaline also has a significant
impact on metabolism, as it activates lipases, enzymes responsible for
burning fat, which aids in the reduction of fat tissue. For this reason, it is a hormone that supports
metabolic processes, and thus is sometimes used in the
symptomatic treatment of some metabolic disorders.
Additionally, adrenaline
stimulates the secretion of saliva and digestive juices, which also affects digestion. Besides, epinephrine
reduces the tension of smooth muscles in the abdominal cavity. However, in stressful situations, adrenaline
inhibits intestinal peristalsis, which slows digestion.