Final answer:
The rapid and immediate vasoconstriction by smooth muscle contraction is an example of a baroreflex mechanism, rather than autoregulation. Baroreflex involves neural responses to changes in blood pressure through receptors and neural pathways.
Step-by-step explanation:
Rapid and immediate vasoconstriction by contraction of smooth muscles is controlled by neural, endocrine, and autoregulatory mechanisms. This process is a vital part of the body's ability to regulate blood pressure and ensure adequate perfusion of tissues.
When blood vessels constrict, it is the arteriolar smooth muscles that contract to narrow the lumen of the vessels, which can lead to an increase in blood pressure upstream of the constriction. This is often in response to sympathetic nervous system activity, where neurotransmitters like norepinephrine can induce vasoconstriction. However, in the context of the options provided, the correct answer is D) Baroreflex, which is an example of a neural mechanism that often involves the cardiovascular centers in the medulla oblongata, baroreceptors, and chemoreceptors to regulate blood pressure amidst changes in the body.