Raynaud phenomenon is a phenomenon where there’s vasoconstriction of arteries near the skin that make a body part, often the fingers, turn white, then blue, and then red in response to a trigger like cold weather.
The phenomenon is named after Auguste Gabriel Maurice Raynaud, a French physician, who first described it.
To clear up some potentially confusing terminology, it’s called Raynaud disease or primary Raynaud phenomenon where the condition occurs alone and is not associated with any other disease, and it’s called Raynaud syndrome or secondary Raynaud phenomenon when it is associated with diseases like systemic lupus erythematosus or scleroderma.
Normally blood flows from large arteries into medium-sized or muscular arteries, and then into small arterioles which carry the blood to capillary beds.
All arterial vessels have three layers: from inside moving out, there’s the endothelium, then the media layer which contains smooth muscle, and finally the adventitia layer which has loose connective tissue and nerves.
Some nerve fibers in the skin function as thermoreceptors, which sense changes in temperature.
When stimulated, they cause the nerve to fire, sending signals up through the spinal cord to the hypothalamus, which is at the base of the brain.
The hypothalamus serves as the body’s thermostat because it coordinates the brain’s response to temperature changes.
The hypothalamus is what triggers the thought – “Hey, it’s pretty cold here. Maybe I should find a friendly llama to snuggle with for warmth.”
The hypothalamus also coordinates changes in the sympathetic and parasympathetic nervous system.
For example, normally, there’s a lot of heat energy in the blood, that gets lost to the environment.
When the sympathetic nervous system gets stimulated it causes contraction of smooth muscle that wraps around arterioles causing vasoconstriction and a reduction of blood flow to the skin.