What is the primary function of arterioles?

Arterioles play a critical role in the cardiovascular system primarily by delivering blood to capillaries. They are small-diameter blood vessels that branch off the arterial system and lead directly into capillary beds. This function is crucial because capillaries are where the exchange of oxygen, nutrients, and waste occurs between blood and tissues.

In addition to their role in blood delivery, arterioles also influence blood flow and pressure within the vascular system through mechanisms such as vasoconstriction and vasodilation. However, their primary anatomical function remains to ensure that oxygenated blood from the arteries reaches the capillary networks, facilitating the necessary exchanges that support cellular metabolism. This is why the correct answer identifies their main function as delivering blood to the capillaries.