My answer to In Sympathetic Nervous System Why the digestion of food is slow? Where as in fight or flight we need m…
Answer by Connie b. Dellobuono:
There are hormones involved in preparation (norepineprine), during and after (acetylcholine) the fight/flight reaction.
The effect of norepinephrine on each target organ is to modify its state in a way that makes it more conducive to active body movement, often at a cost of increased energy use and increased wear and tear.
After the fight:
The acetylcholine-mediated effects of the parasympathetic nervous system, which modifies most of the same organs into a state more conducive to rest, recovery, and digestion of food, and usually less costly in terms of energy expenditure.
The fight and flight reaction begins in the amygdala, which triggers a neural response in the hypothalamus. The initial reaction is followed by activation of the pituitary gland and secretion of the hormone ACTH. The adrenal gland is activated almost simultaneously and releases the hormone epinephrine. The release of chemical messengers results in the production of the hormone cortisol, which increases blood pressure, blood sugar, and suppresses the immune system. The initial response and subsequent reactions are triggered in an effort to create a boost of energy. This boost of energy is activated by epinephrine binding to liver cells and the subsequent production of glucose.
Additionally, the circulation of cortisol functions to turn fatty acids into available energy, which prepares muscles throughout the body for response.
Catecholamine hormones, such as adrenaline (epinephrine) or noradrenaline (norepinephrine), facilitate immediate physical reactions associated with a preparation for violent muscular action. These include the following:
– Acceleration of heart and lung action
– Paling or flushing, or alternating between both
– Inhibition of stomach and upper-intestinal action to the point where digestion slows down or stops
– General effect on the sphincters of the body
– Constriction of blood vessels in many parts of the body
– Liberation of metabolic energy sources (particularly fat and glycogen) for muscular action
– Dilation of blood vessels for muscles
– Inhibition of the lacrimal gland (responsible for tear production) and salivation
– Dilation of pupil (mydriasis)
– Relaxation of bladder
– Inhibition of erection
– Auditory exclusion (loss of hearing)
– Tunnel vision (loss of peripheral vision)
– Disinhibition of spinal reflexes
Function of physiological changes
The physiological changes that occur during the fight or flight response are activated in order to give the body increased strength and speed in anticipation of fighting or running. Some of the specific physiological changes and their functions include:
– Increased blood flow to the muscles activated by diverting blood flow from other parts of the body.
– Increased blood pressure, heart rate, blood sugars, and fats in order to supply the body with extra energy.
– The blood clotting function of the body speeds up in order to prevent excessive blood loss in the event of an injury sustained during the response.
– Increased muscle tension in order to provide the body with extra speed and strength.
Norepinephrine is the main neurotransmitter used by the sympathetic nervous system, which consists of about two dozen sympathetic chain ganglia located next to the spinal cord, plus a set of prevertebral ganglia located in the chest and abdomen. These sympathetic ganglia are connected to numerous organs, including the eyes, salivary glands, heart, lungs, liver, gallbladder, stomach, intestines, kidneys, urinary bladder, reproductive organs, muscles, skin, and adrenal glands. Sympathetic activation of the adrenal glands causes the part called the adrenal medulla to release norepinephrine into the bloodstream, from which, functioning as a hormone, it gains further access to a wide variety of tissues.
The sympathetic effects of norepinephrine include:
In the eyes, an increase in production of tears, making the eyes more moist., and pupil dilation through contraction of the iris dilator.
In the heart, an increase in the amount of blood pumped.
In brown adipose tissue, an increase in calories burned to generate body heat.
Multiple effects on the immune system. The sympathetic nervous system is the primary path of interaction between the immune system and the brain, and several components receive sympathetic inputs, including the thymus, spleen, and lymph nodes. However the effects are complex, with some immune processes activated while others are inhibited.
In the arteries, constriction of blood vessels, causing an increase in blood pressure.
In the kidneys, release of renin and retention of sodium in the bloodstream.
In the liver, an increase in production of glucose, either by glycogenolysis after a meal or by gluconeogenesis when food has not recently been consumed. Glucose is the body's main energy source in most conditions.
In the pancreas, increased release of glucagon, a hormone whose main effect is to increase the production of glucose by the liver.
In skeletal muscles, an increase in glucose uptake.
In adipose tissue (i. e., fat cells), an increase in lipolysis, that is, conversion of fat to substances that can be used directly as energy sources by muscles and other tissues.
– In the stomach and intestines, a reduction in digestive activity. This results from a generally inhibitory effect of norepinephrine on the enteric nervous system, causing decreases in gastrointestinal mobility, blood flow, and secretion of digestive substances.