ANIMAL PHYSIOLOGY
HUMAN CIRCULATION
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Question
[CLICK ON ANY CHOICE TO KNOW THE RIGHT ANSWER]
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veins and arteries
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trachea and bronchi
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capillaries and alveoli
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lymph vessels and stomach
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Detailed explanation-1: -These tiny air sacs in the lungs are only one cell thick and they are surrounded by capillaries that are also only one cell thick. Blood from the heart flows through these capillaries and collects oxygen from the alveoli. At the same time, carbon dioxide passes out of the capillaries and into the alveoli.
Detailed explanation-2: -Capillary walls are only one cell thick, allowing exchange of gases, nutrients, and wastes. Capillaries are so fine that RBCs must line up single-file to go through them.
Detailed explanation-3: -a) The alveoli wall (and the capillary wall) is only one cell thick so there is only a short distance over which diffusion takes place (short diffusion pathway) so there is a faster rate of diffusion of oxygen from alveoli into the blood.
Detailed explanation-4: -Capillary walls are composed of a single layer of endothelial cells.
Detailed explanation-5: -Final answer: One-cell thick vessels are called capillaries.