Final answer:
The line indicating that mental stress causes blood vessels to narrow provides the meaning of constricted; it refers to the process of vasoconstriction, the narrowing of blood vessels. Vasoconstriction increases resistance and pressure, decreasing blood flow.
Step-by-step explanation:
The line from paragraph 4 that provides a clue to the meaning of the word constricted is: "This supports earlier scientific findings, which indicated that mental stress causes blood vessels to narrow." This line suggests that constricted means the narrowing of the blood vessels, thereby reducing blood flow.
Vasoconstriction is the term used to describe the narrowing process, which increases resistance and pressure in blood vessels but decreases the flow of blood. This is the opposite of vasodilation, where blood vessels widen, reducing resistance and allowing more blood to flow through. Vasoconstriction can be a response to various stimuli such as cold temperatures, stress, or certain hormonal changes and is controlled by the autonomic nervous system. The arterioles adjust their diameter to help regulate blood pressure, much like an adjustable nozzle on a garden hose.
Understanding the mechanisms of vasoconstriction and vasodilation is crucial for grasping many physiological responses and can have significant implications for medical treatments, such as those for stroke or cardiovascular diseases where blood flow dynamics are critical.