Quiz 38: Immunity


Veins function as low resistant transport tubes carrying blood to the heart, and have a large diameter. Veins are the main blood volume reservoirs. The largest of blood volume and pressure is seen in the ventricles and it gradually reduces as it flows through the arteries, arterioles, capillaries, and venules. These large blood vessels (veins) are also provided with valves to avoid backflow of blood. The neighboring muscles also help in raising the fluid pressure inside the vein. When moved, these muscles contract and bulge into the vein and increase the pressure that keeps blood flowing continuously in the veins. When people periodically take a walk during flight, they can lower the risk of clot formation.

Cells directly exchange substances with interstitial fluid. Blood makes exchanges with fluid in tissue spaces around cells which are called as the interstitial space. This is the place where the actual exchange of substances takes place. Hence, blood and the interstitial spaces is a functionally inseparable pair. Hence the correct option is C. Option A is incorrect as blood vessels are the transport system, transporting nutrients and gas besides maintaining the flow volume. Based on their size they are of different types. They are arteries, arterioles, capillaries, venules and veins. Option B is incorrect as lymph vessels or the lymph vascular system functions mainly to return the excess of tissue fluid to blood. Though these also consists of many tubes that help in transportation, these tubes collect and deliver solutes from the interstitial fluid to the ducts of the circulatory system. Its components are the lymph capillaries and lymph vessels. Option D is incorrect as both A and B is incorrect.

I say that the blood cells are passing through a capillary in the picture. And the cells are red blood cells and these cells can pass only one after the other in the capillaries. Only then does this squeeze put oxygen transporting red blood cells and solutes in plasma in direct contact with the capillary wall for exchange. The blood vessel-capillary is a cylindrical tube which is one cell thick. Based on all these facts I conclude that the blood vessels are capillaries.

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