12.5.2 Human Circulation: Blood Vessels

Question 1

Human Circulation: Blood Vessels

Answer 1

• The three major types of blood vessels are veins, arteries, and capillaries.
• An artery branches into many small capillaries, which have a greater total cross-sectional area than the artery. This movement of blood from arteries to capillaries results in a decrease in the rate of blood flow. As blood flows from the capillaries into the veins, the total cross sectional area decreases and the rate of blood flow increases.
• Veins depend on skeletal muscle activity to propel blood back to the heart. Veins have one-way valves that keep blood flowing towards the heart.

Question 2

arteries

Answer 2

• Arteries are blood vessels that carry blood away from the heart, while veins carry blood to the heart. Veins and arteries both have an inner lining of endothelium, which consists of tissue made of smooth flattened cells. Surrounding the endothelial lining is a cylinder of smooth muscle, which, in turn, is surrounded by a layer of connective tissue.

Question 3

capillaries

Answer 3

• Capillaries are microscopic blood vessels that allow for the exchange between blood and the interstitial fluidin tissues. Capillaries have an inner lining of endothelial cells and a basement membrane.

Question 4

law of continuity

Answer 4

• The law of continuity explains why the speed of blood slows down when it enters the capillaries. The law of continuity explains that as the diameter of a pipe becomes smaller, the fluid flowing through it travels more quickly than it does through sections with a larger cross sectional area (as seen with the hoses to the left). The volume of the fluid per second remains the same, but the speed of the fluid increases.

Question 5

note

Answer 5

• As fluid travels from the arteries into the capillaries, the total cross sectional area increases. This increase in cross sectional area results in a decreased rate of blood flow in the capillaries.
• Note that even though the individual capillaries have a smaller diameter than the artery, when put together, the total cross sectional area of all of the capillaries is larger than that of the artery.
• As blood flows from the capillaries to the veins, the rate of blood flow increases because of the decrease in total cross sectional area.
• Veins have a lower pressure than arteries, so the action of skeletal muscles helps to propel blood from the veins to the heart. As muscles contract, blood is squeezed through the veins. One-way valves in the veins help to prevent the back flow of blood, as seen in the diagram to the left.

Question 6

Which has the greatest total cross-sectional area?

Answer 6

• capillaries

Question 7

Which of the following is not a type of blood vessel?

Answer 7

• lacteal

Question 8

As the blood travels away from the heart and into the capillaries

Answer 8

• the speed decreases because the total cross-sectional area increases.

Question 9

Veins are to venules as

Answer 9

• arteries are to arterioles.

Question 10

Every living body cell is located close to a capillary, with the exception of:

Answer 10

• those in the lens of the eye.

Question 11

Which tissue layer differs the most drastically between arteries and veins?

Answer 11

• smooth muscle layer

Question 12

Endothelium is best defined as

Answer 12

• an inner layer of tightly packed, tightly joined flattened cells.