Final answer:
Capillaries are found throughout the human body and are the smallest blood vessels, connecting arterioles to venules. They form capillary beds for the efficient exchange of substances and have walls that allow selective permeability. The correct option is B. They are found in every square inch of the human body
Step-by-step explanation:
Characteristics of Capillaries
One characteristic of capillaries is that they are found in virtually every square inch of the human body. As the smallest blood vessels in the cardiovascular system, capillaries connect arterioles to venules and form extensive networks called capillary beds.
These networks provide a large surface area for the efficient exchange of substances like oxygen and nutrients between the blood and surrounding tissues.
The walls of capillaries consist of little more than a single layer of endothelial cells which, combined with a basement membrane, facilitate the permeability necessary for this exchange.
While they are permeable, they are selectively so; continuous capillaries have tight junctions which may be incomplete, and fenestrated capillaries possess pores.
These structures mean capillaries are selectively permeable to water, various small molecules, and under certain conditions, leukocytes, but not permeable to every substance. The correct option is B. They are found in every square inch of the human body