• Set Yourself Up For Success Webinar

    October 6, 2021 at 2 PM Eastern/11 AM Pacific
    SDN and Osmosis are teaming up to help you get set up for success this school year! We'll be covering study tips, healthy habits, and meeting mentors.

    Register Now!

  • Funniest Story on the Job Contest Starts Now!

    Contest starts now and ends September 27th. Winner will receive a special user banner and $10 Amazon Gift card!

    JOIN NOW
  • Site Updates Coming Next Week

    Site updates are coming next week on Monday, Wednesday, and Friday. Click the button below to learn more!

    LEARN MORE

Why lungs vasoconstrict during sympathetic stimulation?

pizza100

Full Member
Nov 25, 2011
15
0
1
Hi. I can't understand why lungs vasoconstrict during sympathetic stimulation. Hope someone can shed some light into this matter for me.

Here's some background: My school notes say 1) Pulmonary Parasympathetic Stimulation induces Vasodilation. 2) Pulmonary Sympathetic Stimulation by Norepinephrine causes mostly vasoconstriction through alpha receptors and slight Vasodilation through beta receptors.

I tend to assume Sympathetic stimulation as fight-or-flight stimulation. If my assumption is true, then the blood vessels in the lungs should dilate during fight-or-flight (sympathetic) stimulation to increase blood flow through the lungs to supply enough oxygen to the body. Why is my thinking wrong or inconsistent with my school notes?
 

Raisenbran

Full Member
Aug 20, 2010
68
0
51
Kirksville, MO
  1. Medical Student
It says that it both vasoconstricts AND dilates so I THINK (and I am sure someone will correct me if I am wrong) that the poorly ventilated alveoli/lobules will vasoconstrict while the highly ventilated alveoli/lobules (which I think are the ones closer to the base of the lung?) vasodilate. This will increase the ventilation/perfusion ratio so that you are getting blood to where there is the most air and not wasting it on places where there is little air.

Again going just off memory and the way it made sense in my head but I hope it at least helps you remember that there is both vasoconstriction and dilation even if the reasoning is wrong :p
 

Unzbuzzled

Full Member
Aug 12, 2011
287
8
61
The Windy City
  1. Medical Student
It says that it both vasoconstricts AND dilates so I THINK (and I am sure someone will correct me if I am wrong) that the poorly ventilated alveoli/lobules will vasoconstrict while the highly ventilated alveoli/lobules (which I think are the ones closer to the base of the lung?) vasodilate. This will increase the ventilation/perfusion ratio so that you are getting blood to where there is the most air and not wasting it on places where there is little air.

Again going just off memory and the way it made sense in my head but I hope it at least helps you remember that there is both vasoconstriction and dilation even if the reasoning is wrong :p

This.

You have to make sure you differentiate between bronchiolar dilation and vascular dilation as well.

Remember, as a general rule the bronchial passages of the lungs vasodilate with sympathetic innervation. If you are running away from a tiger, you want your lungs to be open so you can get more air. This is also why albuterol is a beta2 adrenergic agonist. When you have a sympathetic rush of adrenaline, your B2 pathway is triggered and you have vasodilation of the bronchioles. Also, when you have a sympathetic response, your breathing rate goes up and so does your O2/CO2 ratio.

However, in areas of the lung that have poor ventilation, you have hypoxic pulmonary vasoconstriction of the blood vessels, which as the previous poster explained, causes an effective shunt of blood from areas of low alveolar oxygen to areas of high oxygenation.

Ultimately, low tissue oxygenation causes two things: sympathetic bronchiolar dilation, and hypoxic pulmonary vasoconstriction via the Euler– Liljestrand mechanism. So sympathetic discharge doesn't necessarily cause direct vasoconstriction, although the two are related.
 
About the Ads

Smokemont

Full Member
May 23, 2012
359
119
91
In the mountains
  1. Medical Student
This.

You have to make sure you differentiate between bronchiolar dilation and vascular dilation as well.

Remember, as a general rule the bronchial passages of the lungs vasodilate with sympathetic innervation. If you are running away from a tiger, you want your lungs to be open so you can get more air. This is also why albuterol is a beta2 adrenergic agonist. When you have a sympathetic rush of adrenaline, your B2 pathway is triggered and you have vasodilation of the bronchioles. Also, when you have a sympathetic response, your breathing rate goes up and so does your O2/CO2 ratio.

However, in areas of the lung that have poor ventilation, you have hypoxic pulmonary vasoconstriction of the blood vessels, which as the previous poster explained, causes an effective shunt of blood from areas of low alveolar oxygen to areas of high oxygenation.

Ultimately, low tissue oxygenation causes two things: sympathetic bronchiolar dilation, and hypoxic pulmonary vasoconstriction via the Euler– Liljestrand mechanism. So sympathetic discharge doesn't necessarily cause direct vasoconstriction, although the two are related.

While I agree with all this, isn't it a local response mediated by the partial pressure of oxygen? Whereas the original question is about sympathetic innervation, a global response?
 

MadKanMan

New Member
Dec 1, 2012
4
0
1
  1. Medical Student
I'm just speculating here. But during a sympathetic response, heart rate is increased, so transit time through pulm vasculature is reduced, therefore compromising oxygen delivery. Maybe sympatheitc vasoconstriction happens to increase resistance and therefore slow down the blood flow through the lungs for optimal delivery of oxygen. Also, like mentioned above, NE or epi causes dilation of the airways not the pulmonary vasculature. I hope someone corrects me if I'm wrong.
 

CrimsonKing

Living the dream
7+ Year Member
Dec 31, 2012
465
378
191
  1. Attending Physician
As has been pointed out, the sympathetic response leads to bronchodilation and vasoconstriction.

Keep in mind, however, that this vasoconstriction is occuring at the arteriolar level, which does not play a very significant role in pulmonary circulation. While peripheral resistance will slightly increase through the pulmonary vasculature during a sympathetic response, it will not increase anywhere near enough to prevent adequate perfusion.

Also, the simultaneous bronchodilation increases the ventilation throughout the lungs which, as has also been pointed out above, can lead to VQ mismatch and an increase in dead space in the Upper Lobes (however, keep in mind that thanks to the increased pressure in the vasculature, this increase in dead space will be minimal).
 

raiaxunmucha02

New Member
Feb 8, 2013
7
0
0
nice job!
23.jpg
 
About the Ads
This thread is more than 8 years old.

Your message may be considered spam for the following reasons:

  1. Your new thread title is very short, and likely is unhelpful.
  2. Your reply is very short and likely does not add anything to the thread.
  3. Your reply is very long and likely does not add anything to the thread.
  4. It is very likely that it does not need any further discussion and thus bumping it serves no purpose.
  5. Your message is mostly quotes or spoilers.
  6. Your reply has occurred very quickly after a previous reply and likely does not add anything to the thread.
  7. This thread is locked.