Question Video: Completing a Table to Show the Structure of Each of the Main Blood Vessels | Nagwa Question Video: Completing a Table to Show the Structure of Each of the Main Blood Vessels | Nagwa

Question Video: Completing a Table to Show the Structure of Each of the Main Blood Vessels Biology • Second Year of Secondary School

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The table describes the structures of the main types of blood vessels in the human body. Which of the options correctly replace X, Y, and Z in the table? [A] X: artery, Y: vein, Z: capillary [B] X: vein, Y: capillary, Z: artery [C] X: capillary, Y: artery, Z: vein [D] X: capillary, Y: vein, Z: artery

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Video Transcript

The following table describes the structures of the main types of blood vessels in the human body. Which of the options correctly replace X, Y, and Z in the table? (A) X: artery, Y: vein, Z: capillary. (B) X: vein, Y: capillary, Z: artery. (C) X: capillary, Y: artery, Z: vein. Or (D) X: capillary, Y: vein, Z: artery.

This question asks us to complete a table describing different blood vessels in the human body. You might remember that there are three main types of blood vessels, and these are given in the various answer options. So let’s have a review of the structure and function of arteries, veins, and capillaries.

Arteries are blood vessels that carry blood away from the heart. We can remember this because the words artery and away both start with A. Due to the constant pumping of the heart, blood traveling through arteries is under high pressure. To withstand this high pressure, arteries have thick walls and a relatively small lumen, or inner space.

The blood pressure within arteries is also constantly changing as the heart contracts and relaxes. To deal with this variation, a layer of elastic fibers in the wall of arteries allows them to stretch and recoil. Damage to an artery carrying high-pressure blood can lead to rapid blood loss and can even be fatal. Because of this, arteries are located deeper in the body than other blood vessels to protect them from injury.

After being carried away from the heart, blood will pass through the smallest vessels in the body, the capillaries. Capillaries connect the arteries to the veins through networks called capillary beds, which surround all the tissues in the body. They have the critical role of allowing the exchange of gases and other materials with other tissues in the body.

As an adaptation for this function, capillary walls are permeable and extremely thin. In fact, if we zoom in on a capillary wall, we can see that it is made of a single layer of epithelial cells. Capillaries also have a very small lumen, which forces blood cells to flow through them in a single file line in order to exchange nutrients, gases, ions, and hormones.

After the blood has delivered oxygen and picked up carbon dioxide waste from the other cells of the body, it is transported back to the heart by the veins. Veins are under much less pressure than arteries. So they have thinner walls that contain less smooth muscle and fewer elastic fibers. They also have a relatively large lumen.

Veins tend to be located closer to the surface of the skin than arteries. Take a moment to see if you can figure out why. Hopefully, you concluded that damage to a vein carrying low-pressure blood will not cause as much blood loss as damage to an artery carrying high-pressure blood. So it is safer for veins to be closer to the surface than arteries.

A unique feature of veins is that they have flaps of tissue called valves that prevent the low-pressure blood from flowing backward. We can remember which of the three vessel types has valves because the words vein and valve both start with the letter V.

After discussing the three types of vessels in the body, we can now fill in our table correctly. The first column in our table describes the vessels that are only one-cell thick with a small lumen. We just learned that these vessels are capillaries. The second column describes vessels with relatively thin walls, a large lumen, and valves, which we now know are the veins. Finally, the vessels in the last column have thick elastic walls with no valves. We know that these are the arteries.

So the correct answer to our question is (D). In the table, X should be replaced with capillary, Y should be replaced with vein, and Z should be replaced with artery.

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