Blood flow is regulated in all three types of blood vessels through and dilation.

*contraction of blood vessels blood flow, while of blood vessels, or dilation, allows free flow of blood.

*muscle fibers control the constriction and dilation of vessels. in the capillaries, rings of muscle called capillary control blood flow.

*the directional flow of blood in the veins is controlled with , which prevent backward blood flow when closed, and allow blood to flow only the heart when open.

*Blood flow is regulated in all three types of blood vessels through constriction and dilation.

*Contraction of blood vessels slows blood flow, while relaxation of blood vessels, or dilation, allows free flow of blood.

*Muscle fibers control the constriction and dilation of vessels. In the capillaries, rings of muscle called capillary sphincters control blood flow.

*The directional flow of blood in the veins is controlled with valves , which prevent backward blood flow when closed, and allow blood to flow only toward the heart when open.

Vasoconstriction and vasodilatation allow blood vessels (arteries and veins) to control blood flow and thus control the blood pressure. This is possible because of the smooth muscle cells that surround the vessels. The contraction and dilatation of those muscles is controlled by chemical signals (e.g. norepinephrine constricts the vessels, while NO dilates them).

constriction

slows

relaxation

sphincters

valves

toward

Explanation:

c. live where it’s cold and icy

answer:

convection currents in the magma drive plate tectonics. heat generated from the radioactive decay of elements deep in the interior of the earth creates magma (molten rock) in the aesthenosphere. the aesthenosphere (70 ~ 250 km) is part of the mantle, the middle sphere of the earth that extends to 2900 km.