Download Adrenal Medulla Chromaffin Cells Epinephrine Threat: Real or

System Interactions
Stress Response
Threat:
Real or Perceived
Hypothalamus
Adrenal
Gland
Adrenal Medulla
Chromaffin Cells
Epinephrine
Fight or Flight Stress Response
The fight-or-flight response (also called the fight, flight, freeze, or fawn response, hyper arousal, or the acute stress response) is a physiological reaction that occurs
in response to a perceived harmful event, attack, or threat to survival.
The hypothalamus of the brain triggers a cascade of events that effect every system
in the body as the body prepares to fight or run away in order to survive. The
hypothalamus is connected to the adrenal glands sitting on top of the kidneys by a
set of neurons. The adrenal medulla releases adrenalin known as epinephrine.
This response is recognized as the first stage of a general adaptation syndrome that
regulates stress responses among vertebrates and other organisms.
As many as 30 different chemical messengers are involved, but epinephrine begins the spreading out of these
chemicals and responses. Epinephrine is released into the blood stream and circulates to every cell in the body with
1-2 minutes. Epinephrine has different effects on different cells. It does not enter the cells, but instead binds to
receptors on cell surfaces. The binding is a warning to the cell to perform its specific functions and processes in
response to an emergency. In the next few paragraphs these cell responses will be explained.
As epinephrine reaches the respiratory system, cells are forced to cause a faster breathing rate by making the diaphragm muscles increase inhaling and exhaling. This increases oxygen intake necessary to increase ATP production
in the mitochondria. Reaching the heart muscle, the muscles beat faster increasing the flow of gases and glucoesthroughout the body. More energy is needed to meet the demand of all the muscle stimulation. Blood flow is
increased to the skeletal muscle.
Epinephrine stimulates muscle to remain tense in anticipation of action. By this point some muscles are already
working faster. In the digestive system, epinephrine slows down muscles and enzyme production to stop the digestive process. The rectal muscles may cause the evacuation of the solid waste so running faster is possible. Likewise
in the excretory system, the muscle relax so that liquid wastes stored in the bladder can be eliminated.
The immune system is depressed for the present time, but may increase once the danger passes in order to defend
against germs in wounds. Other endocrine organs such as the pancreas and liver are stimulated to increase blood
levels of glucose which in turn produce the ATP necessary for all the increased activity.
The skin of the integumentary system begins producing sweat to cool down the body so muscles can work better.
Also, erectopilli muscles cause the hair to stand upright. This is an attemp to also regulate body temperature, but
has a warming effect, not so much in humans though. The muscles also cause the goose bumps, another attempt to
conserve heat by having lees skin exposed. The action of the muscles, small as they are, also add heat to the skin.
The circulatory system respond in various ways depending on the cells involved. Blood pressure is increased. Some
veins and arteries are dilated to increase flow of gases, wastes and glucose. Blood stickiness is increased to help clot
blood faster in the event of a wound causes bleeding. The nervous system itself is on increased alertness. Eyes dilate to focus sight. Other senses such as touch are set to fell the slightest pressure or movement. The reproductive
system becomes suppressed which diverts much needed energy reserves to other systems of the body.
While the skeletal system may not be actively involved, it is passively involved by providing protection for major
organs of circulation, respiration and digestion. It can release calcium which is essential for nutrient absorption and
hormone production. Production of osteocalcin increases insulin secretion and sensitivity.