Sympathetic NS Function (EK Bio Lec 4 In-Class Exam, #76)

[futuredoctor10]

[shorted version of the question]

Epinephrine / Sympathetic nervous system functions include all except:
A. increased heart rate
B. elevated blood glucose levels
C. constricted pupils
D. increased basal metabolism

The answer is C. I understand sympathetic DILATES pupils (so you can see for "fight/flight" response).

Lets say C was not in the choices.
A is sympathetic.

Questions:
how is "elevated blood glucose levels" a sympathetic response?

if parasympathetic is "rest and digest" shouldn't increased metabolism - in other words increased digestion - be a parasympathetic response?

Maybe I need to differentiate metabolism vs digestion... please help!

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[Charles_Carmichael]

There is an elevated blood glucose level because the sympathetic nervous system prepares you for the fight or flight response. The increase in blood glucose is to provide your muscles and heart with energy for this response. This way the muscles don't run out of glucose as quickly as they would if they only used their glycogen stores. So, you can fight or run/escape for a longer period of time before tiring out.

This is sort of how I always thought about it. Does it make sense? What basically happens is that the body prepares itself for fight/flight and an increase in blood glucose levels provides more energy (because glucose is a primary source of energy) for the action you are about to take and you can sustain the physical activity for a longer period of time than you would without this preparation.

Edit: Yea, I think you need to differentiate between digestion and metabolism. Sympathetic activation constricts the blood vessles to the digestive tract and this slows down digestion and remember, the digestive tract is not really involved in regulation of the levels of body nutrients; it just maximizes nutrient absorption from food.

 

[futuredoctor10]

Does it make sense?

Wow that makes sense! I wish EK had explained it like that in the answer explanations.
You do a good job explaining concepts and should be an MCAT tutor/teacher

 

[futuredoctor10]

One more question (from my original post as well):
if parasympathetic is "rest and digest" shouldn't increased metabolism - in other words increased digestion - be a parasympathetic response?

 

[Charles_Carmichael]

Hey, no problem . I edited my previous post to answer your parasympathetic question but I'll recopy it here. Sympathetic activation constricts the blood vessels of the digestive tract and this slows down digestion. The key thing to remember about the digestive tract is that it's not really involved in regulating the blood levels of nutrients or anything like that; the main function of the digestive tract is to maximize the absorption of nutrients from the food you eat. Increased digestive activity doesn't necessarily mean increased metabolism; make sure you understand this difference.

Parasympathetic activation increases the blood flow to the digestive tract (via dilation of blood vessels) and thus, increases digestive activity. All this does is increase the rate of absorption of nutrients from the digestive tract. The blood levels of nutrients and other substances are regulated by other organs (ie. kidneys, liver, etc.) which respond differently to sympathetic/parasympathetic activation. Hope this helps.

 

[futuredoctor10]

Awesome response again!!! This really helped me understand the difference.

I should have been able to reason it out... but I find it much easier when some things in physiology are more verbally expressed/explained!

You should write an MCAT book for Bio!