What is vasoconstriction and is there a treatment?
Answer
vasoconstriction is when some blood vessels (arteries, arterioles, etc) constrict and essentially increase the impedance to blood flow. This is known as vascular resistance, and is a major contributor to blood pressure (hypertension).
Blood vessels are usually in a state of relative constriction, but can constrict further in respone to cold (thermoregulation), to low blod volume or low blood pressure (shock/maintaining a normotensive state/maintaining perfusion pressure) or to signals from the nervous system, which can be replicated by the administration of drugs (e.g. adrenalin).
Treatment for vasoconstriction would include the use of vasodilators- alpha adrenoceptor antagonists, or calcium-channel blockers. The latter group of drugs is often used in the treatment of hypertension.
Does systemic vasoconstriction decrease blood pressure?
No. Vasoconstriction is a squeezing of the veins. This is like putting your thumb at the end of a garden hose. The constriction of the flow increases the pressure. The water shoots out faster from the hose when your thumb is blocking the way. If the entire hose were to tighten, as in vasoconstriction, the same effect happens. -- From Wikipedia: Vasoconstriction "Generalized vasoconstriction usually results in an increase in systemic blood pressure..."
Does the sympathetic nervous system cause vasoconstriction?
Yep! The sympathetic nervous system causes both vasoconstriction & vasodilation. During "fight or flight" you need more O2/blood delivered to your skeletal muscles. The SNS causes vasodilation in skeletal muscles. The other organs, of the body (like digestive organs) are not needed for "fight or flight" survival. The SNS causes vasoconstriction in these organs.