Vasoconstriction and Vasodilatation

[Energizer Bunny]

Okay, so I understand what vasoconstriction and vasodilatation mean. I get the definitions, but I'm not sure that I understand how they have anything to do with fevers, etc. Why does vasoconstriction occur and when (referring to body temp)? Why does vasodilatation occur and when (also referring to body temp)?

Test Monday and I'm a bit stuck on this.

[talaxandra]

How's this for a start?

Fever usually occurs in response to pyrogens (e.g. prostaglandins) which are released from inflammatory cells. These pyrogens act on the hypothalamus (the body's thermostat), resetting it to a higher temperature and in doing so invoking the body's temperature raising mechanisms and raising the body temperature to a level above normal. The body has a number of techniques to raise its temperature.

Shivering, which involves physical movement that produces heat.

Vasoconstriction, which entails the constriction of blood flow beneath the skin and thus reduces the amount of heat lost from the body.

from http:// http://en.wikipedia.org/wiki/Fever

Abnormal elevations of temperature are due to either hyperthermia or pyrexia (fever). Hyperthermia results from failure of thermal control mechanisms. In fever, thermoregulatory mechanisms are intact, but the hypothalamic set-point is elevated above normal by exogenous or endogenous pyrogens. There are 3 phases to fever. In the initiation phase, cutaneous vasoconstriction promotes heat retention and shivering generates additional heat. When the new (elevated) set-point is reached, heat production balances heat loss and shivering stops. With lowering of the set-point to normal, cutaneous vasodilatation promotes heat loss to the environment in the form of sweating. These same mechanisms maintain normal core body temperature in afebrile individuals.

from http://www.cancer.gov/cancerinfo/pdq/supportivecare/fever/healthprofessional/

I popped "fever" and "vasoconstriction" into Google and these were the first two hits, so you'll undoubtably find more info than you need with a little searching. Good luck :)

[Antikigirl, ASN, RN]

Okay..this is when I step back a bit and think..hmmmmm does the body like to open up circulation to extremities, or shunt it to the vital organs? That normally helps me to remember, but in some cases...like shock, you have to remember it may be the opposite!

During a generalized fever, your body wishes to increase temp to a premium temp for your immune system (which commonly is 101d F..but not exclusively because some people naturally run higher or lower normally)...well, what happens when you get warm...your vascular system opens and relaxes, and the skin becomes highly vascularized (flushing) to assist with sweating(conduction, covention..etc)! So stands to reason why people with fevers get flushed, diaphoretic, achy (increased temp in synovial fluids which joints are very sensitive to!)...the blood is being moved to the extremities! So we are talking vasodilitation here :)

So when I try to understand this, I think back to the basics and try to really take it to a simplistic level!

But in the cases of fever r/t septicemia..the opposite can happen! Your body struggles to keep temps high, but it has gotten to the point of your brain asying "hmmmm better protect my vital organs and myself!!!" so it increases circulation to vital organs by shunting extremities. Septic shock! And this can happen in eldery quite quickly (within hours!). So this is a factor too! So I tend to read my patient more than I read themometers :).

These are just two examples of the complex subject of vasodil/con and I suggest you just think of it in terms of..okay what is the body going to try to do with the blood...protect vital organs (constriction of extremities) or open up (dilitation of extremities) at first...you will make connections and understanding as they come along :).

That is very apple and orange...and a reason I really feel people need to know sympathetic vs parasympathic well, and fluid and electrolytes well too! That background will really help connect the pieces of the puzzle so you can work with it :).

Really think about these connections when you are dealing with the vital organs, especially lungs, brain and heart...and once you understand the physiology in regards to these well...it helps to discover (or make connections) to the underlying probelms...a cycle so to speak..but this comes with experience...so don't push yourself too hard...just think about these factors when you are studying :). Don't worry..you will get it

[Energizer Bunny]

Okay, this really helps! Thank God! I wasn't sure anyone would be around to answer. You both gave me a lot of information to explain it better. *huge sigh of relief* now, I can finally move on to BP. LOL!

[Energizer Bunny]

oh, and watch for more questions this weekend too!! LOL! Thanks a bunch, guys!