Epinephrine

     Epinephrine, which is also commonly known as adrenaline, is a hormone and neurotransmitter that is produced in the in inner part of the adrenal gland, called the medulla.  Epinephrine is a positive feedback loop, meaning that it increases system output in contrast to a negative feedback loop, which would decrease it.  Any hormone produced by the adrenal gland is called a catecholamine.  Epinephrine is derived from tyrosine, an amino acid.  Epinephrine is a hydrophilic, water-soluble hormone that can diffuse through the plasma of blood but not through plasma membranes of cells.  Instead, they attach to receptor proteins on the cell surface and activate secondary messengers.

     Our bodies use epinephrine in our “fight or flight response.” Fight or flight response occurs when a person is subjected to threat. This prompts a signaling process that causes our bodies to react to the danger. When a threat is received, a signal is sent to the brain, and the brain then sends impulses to the adrenal glands in the kidneys.  Once this signal reaches the adrenal glands, the medulla releases epinephrine into the bloodstream.  Carried around to various cells in the body, epinephrine initiates several responses, but the collective purpose is to provide energy so that our major body muscles can respond to the perceived threat.  The four main areas epinephrine affects are the liver, lungs, skin, and heart. In the liver, epinephrine, along with the hormone glucagon, breaks down glycogen and thus releases stored energy.  In the lungs, epinephrine causes smooth muscles and thus the bronchioles to relax, enabling intensified respiration. In the skin, epinephrine bonds to alpha-adrenergic receptors inhibiting blood supply to the skin and also contracts smooth muscle cells in skin to raise hairs on the skin’s surface. Finally, in the heart, epinephrine binds to beta-epinephrine receptors on heart muscle cells, increasing heart contraction rate and thus leading to increased blood supply to body tissues.