Question

Regarding the sympathetic nervous system regulation of blood vessels

Select one:

a. Beta adrenergic receptors have a higher affinity for norepinephrine compared to epinephrine

b. Beta adrenergic receptors are located on all arterioles throughout the circulation

c. Norepinephrine activation of alpha-adrenergic receptors on the smooth muscle of arterioles causes a vasoconstrictor signal

d. Sympathetic nerves release equal amounts of norepinephrine and epinephrine

e. Simultaneous activation of both alpha and beta adrenergic receptors will lead to a stronger vasoconstriction than if just 1 receptor type was activated

Answer 1

Answer) option C - Norepinephrine activation of alpha-adrenergic receptors on the smooth muscle of arterioles causes a vasoconstriction signal.

Explanation -

Alpha adrenergic receptors which are on located on blood vessels are associated with most of the excitatory functions on smooth muscles of arterioles causing constriction of smooth muscles leading to vasoconstriction.

Other options are incorrect -

Option A is incorrect - As beta adrenergic receptors respond to epinephrine with higher affinity.

These beta adrenergic receptors in general are relatively insensitive to norepinephrine.

So beta adrenergic receptors have high affinity to epinephrine than norepinephrine.

Option B is incorrect - As beta adrenergic receptors are not located all arterioles. They are located in arterioles of skin, heart, skeletal muscles and brain.

Option D is incorrect - As catecholamines (epinephrine and norepinephrine) are synthesized by chromaffin granules of adrenal medulla.

In humans, approximately 80 to 90 percent percent of chromaffin granules in adrenal medulla synthesize epinephrine (adrenaline), the remaining 10 to 20 percent synthesize norepinephrine (noradrenaline).

So sympathetic release more epinephrine than norepinephrine.

Option E is incorrect - As alpha adrenergic receptors cause vasoconstriction and beta adrenergic receptors causes vasodilatation.

So, simultaneous stimulation of both alpha and beta adrenergic receptors will not lead to vasoconstriction.