vasodilation vs. vasoconstriction?

Original post by fayemx

Today I got told that the sympathetic nervous system affects the skin by making hairs stand on end, increase sweating and vasoconstriction occurs.
But surely vasocontriction gives to opposite effect to the other two responses, and vasodilation would happen?
hmmmmmm...

Making hairs stand on end is a response when your body is cold and needs to preserve heat.

Sweating is when your body wants to lose heat.

Vasoconstriction is when your body is cold and wants to lose less heat to the environment via radiation.

Do you see now?

Reply 2

fayemx

OP

Original post by James A

Making hairs stand on end is a response when your body is cold and needs to preserve heat.

Sweating is when your body wants to lose heat.

Vasoconstriction is when your body is cold and wants to lose less heat to the environment via radiation.

Do you see now?

yeah, i know what they do but sweating contradicts the other two as it used to decrease temp. back to the optimum whereas the other two are used to increase temperature back to the optimum... why would they be used together when one contradicts the other two?

Reply 3

Original post by fayemx

yeah, i know what they do but sweating contradicts the other two as it used to decrease temp. back to the optimum whereas the other two are used to increase temperature back to the optimum... why would they be used together when one contradicts the other two?

That's what I was trying to get at, if sweating contradicts the other two, then your teacher must have made a mistake. It's impossible to have body cooling/heat gain methods contradicting each other at the same time.

Reply 4

fayemx

OP

Original post by James A

That's what I was trying to get at, if sweating contradicts the other two, then your teacher must have made a mistake. It's impossible to have body cooling/heat gain methods contradicting each other at the same time.

oh haha! I though so! he was so sure when i questionned him! do you know what effect the sympathetic nervous system would have on skin then? would it increase or decrease temperature?

Reply 5

Original post by fayemx

oh haha! I though so! he was so sure when i questionned him! do you know what effect the sympathetic nervous system would have on skin then? would it increase or decrease temperature?

I'm not sure :s-smilie:

It's not covered in my biology specification.

I'm doing AQA, wby?

Reply 6

nicatre

13

Original post by fayemx

oh haha! I though so! he was so sure when i questionned him! do you know what effect the sympathetic nervous system would have on skin then? would it increase or decrease temperature?

the sANS (sympathetic branch of the Autonomic Nervous System) is generally associated with 'Flight or Flight' responses thus diverts blood to the muscles and away from digestion for example.

So in the skin it increases sweating, to increases heat loss, and promotes vasoconstriction, as part of the diversion of blood towards the muscles.

Reply 7

Original post by James A

That's what I was trying to get at, if sweating contradicts the other two, then your teacher must have made a mistake. It's impossible to have body cooling/heat gain methods contradicting each other at the same time.

Not necessarily. The problem is that you are viewing all of these changes through the prism of thermoregulation, whereas these changes can be of broader physiological relevance.

I'm no expert in physiology, but vasoconstriction occurs with respect to some organs during sympathetic activation to prepare the body for the "flight or fight" response. Vessels supplying blood to the gut are vasoconstricted to reduce the blood supply to the gut, for example. Also, having your hairs stand on end is not always a consequence of cold weather but can result from fear/intense emotions. This probably has no function in H. sapiens but is a vestigial trait from a time when we had long hair and contraction of arrector pili could convey aggression during conflicts.

Reply 8

gummibear

I am assuming your teacher was refering to temperature homeostasis which is ANS mediated.

Basically, the stimulus (ie becoming too hot/too cold) will be picked up by receptors (skin, for example), then signals sent to the medulla oblongata in the brain which will co ordinate the effector response.

If the stimulus was being too hot, you will get vasodilation (to increase heat loss), stimulation of sweat glands and sometimes increased respiration rate. All ways of losing body heat.

If the stimulus was being too cold, you get vasoconstriction (to conserve heat), muscular contraction (the shivers to generate ATP release) and hairs standing on end (to trap air as a kind of a blanket). All ways of conserving body heat.

Does that help?

Reply 9

Dynamo123

7

Both occur at tje same time to achieve a common purpose of warming or cooling body. Like if vadodilation occurs in skin, vasoconstriction is in gut. Both have same effect to dissipate heat under control of epi and norepinephrine

Posted from TSR Mobile

Reply 10

Original post by Dynamo123

Both occur at tje same time to achieve a common purpose of warming or cooling body. Like if vadodilation occurs in skin, vasoconstriction is in gut. Both have same effect to dissipate heat under control of epi and norepinephrine

Posted from TSR Mobile

Again, the problem is that you guys are speaking as if the sympathetic nervous system and vasoconstriction/vasodilation exist only to effect thermoregulation. This really is not the case, and the perceived contradictions that you see break down when you realise this. The blood vessels beneath the skin actually do become vasoconstricted during sympathetic activation, and this has been hypothesised to reduce potential blood loss during conflict.

Also, the way that the sympathetic nervous system works means that it does not act in mass all other the body (e.g. we don't orgasm whenever our pupils dilate). So this means we don't automatically sweat (sympathetic) whenever skin vasoconstriction (sympathetic) occurs.

Reply 11

Dynamo123

7

We were dealing with the SNS because it was what had been specifically mentioned in the thread. :smile:

Reply 12

Original post by Dynamo123

We were dealing with the SNS because it was what had been specifically mentioned in the thread. :smile:

Oh yeah I know; I'm not disputing the fact that the SNS is the subject of the thread. :smile:

I was just saying that there is a problem with trying to interpret the actions of the SNS from the perspective of thermoregulation only. There also seems to be an implicit (and erroneous) assumption that the SNS acts on all of its targets simultaneously.

Edit: Neg rep... I don't understand. Was there something factually wrong with what I said?

Edit 2: Nevermind; I think this is actually revenge rep from a subscribed user.

(edited 11 years ago)

Reply 13

ash92:)

22

Original post by fayemx

Today I got told that the sympathetic nervous system affects the skin by making hairs stand on end, increase sweating and vasoconstriction occurs.
But surely vasocontriction gives to opposite effect to the other two responses, and vasodilation would happen?
hmmmmmm...

I don't know if you feel your issue has been cleared but:

sympathetic NS:

piloerection? yup, methinks

increased sweating? yup, homeostatic, regulates body temp

vasoconstriction? in some areas, prioritises blood flow to other areas, which may have vasodilation (eg, when lifting weights, less blood flow in the digestive system by vasoconstriction, but more in arms by vasodilation).

It's been a while since I did anything on the CV system, but this seems to be the logical answer.

Hope I helped.

Reply 14

Eloades11

17

Original post by Ashnard

Oh yeah I know; I'm not disputing the fact that the SNS is the subject of the thread. :smile:

I was just saying that there is a problem with trying to interpret the actions of the SNS from the perspective of thermoregulation only. There also seems to be an implicit (and erroneous) assumption that the SNS acts on all of its targets simultaneously.

Edit: Neg rep... I don't understand. Was there something factually wrong with what I said?

Edit 2: Nevermind; I think this is actually revenge rep from a subscribed user.

Weird, this was a very good post as well as your others on this thread pointing out good points. +rep :smile:

Reply 15

Original post by Eloades11

Weird, this was a very good post as well as your others on this thread pointing out good points. +rep :smile:

Thanks a lot. :smile:

What happened was that I neg-repped a user on a completely unrelated thread due to an obnoxious post. Presumably, he saw my neg-rep (as he is a subscribed user) and then decided to "retaliate" on my most recent post (on this thread). I can't be certain that this is what happened (as I'm not a subscriber), but this seems to be the most likely explanation.

Reply 16

fayemx

OP

Original post by Eloades11

Weird, this was a very good post as well as your others on this thread pointing out good points. +rep :smile:

Right that clears it up for me :biggrin:

thank you!

Reply 17