Question

Which of the following statements concerning control of blood flow through arterioles is true?

Select one:

a. There are more beta-adrenergic receptors than alpha-adrenergic receptors on arteriolar smooth muscle

b. Binding of epinephrine to alpha-adrenergic receptors causes vasodilation.

c. Stimulation of vascular smooth muscle by the parasympathetic nervous system causes vasodilation.

d. If blood pressure/flow within an organ increases, arterioles in the organ will autoregulate using the myogenic response

e. None of the choices are true

Answer 1

Option	Response	Reason
a	Wrong	There are more Alpha receptors on arteriolar smooth muscles than beta receptors. Alpha receptors are alpha1 and alpha 2. Beta receptors are only Beta2. Both act in response to Noradrenaline and Epinephrine. Vasoconstriction occurs in most of the blood vessels in the body by alpha receptors. Beta 2 stimulation causes vasodilation.
b	Wrong	Binding of epinephrine (adrenaline) to alpha receptors causes vasoconstriction. Beta 2 receptors cause vasodilation
c	Right.	The blood vessels in the body doesn't have parasympathetic innervation except in some blood vessels in salivary gland, git. They cause vasodilation through release of Nitric oxide.
d	RIGHT	Arterioles are called resistance vessels because they provide resistance to the blood flow. When the blood flow increases, the smooth muscles sense it and undergo vasoconstriction due to calcium action and this increases the pressure and decreases the volume flowing through it. This is called myogenic response. With this feature, blood flow to the organ is autoregulated.

As options c and d are right. But in Option c, the parasympathetic innervation to most of the blood vessels is very very less. Therefore it can be neglected.

If you have to choose one, choose option D.