THE ARTERIES AND VEINS: THE ARTERIES & THE ARTERIOLES

The Arteries

Because your arteries transport blood under high pressure, they have strong elastic walls, and the blood flows rapidly through them. The flow of blood in the arteries is said to be pulsatile. This means that the amount of blood flowing constantly increases and decreases as a result of the heart pumping a new volume of blood into the arteries 70 times per minute. This effect is what causes the pulse that you feel over the arteries in your wrists and neck.

The Arterioles

The arterioles also have strong muscular walls that can close off the arteriole completely or dilate it greatly. This feature enables the arteriole to change the blood flow to the capillaries in response to the needs of your tissues. Muscles, for example, when active, may need as much as 20 to 30 times the blood flow that they need at rest. Because the heart can increase its output by only four to seven times, these tiny vessels continually monitor the needs in each tissue and control the blood flow in that portion of the body to the level required. When a large increase is needed in one area (for example, exercising muscles), the proportion of flow to other organs is temporarily decreased.

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Cardio & Blood