Why are capillaries and not arteries or veins found in alveoli, nephrons, and villi?
1.Vessels must be narrow so that only very small molecules can reach these tissues
2.Vessels must be lightweight so that they do not interfere with the movements of these tissues.
3.Vessel walls must be thin to allow ease of transfer of molecules to these tissues.
4.Vessels must be small so that very little blood enters these tissues.
looks like #3 to me.
The others really make no sense when you think about them.
The correct answer is 3. Vessel walls must be thin to allow ease of transfer of molecules to these tissues.
In order to understand why capillaries are found in alveoli, nephrons, and villi, it's important to understand the function of these structures. Alveoli are small air sacs in the lungs responsible for oxygen exchange, while nephrons are the functional units of the kidneys involved in filtering waste products from blood and forming urine. Villi are finger-like projections found in the small intestine that are responsible for absorbing nutrients from digested food.
Capillaries are the smallest and most numerous blood vessels in the body. They have thin walls, consisting of a single layer of endothelial cells, which allows for easy exchange of molecules between the blood and surrounding tissues. This is essential in tissues like alveoli, nephrons, and villi, where efficient transfer of molecules is necessary.
Arteries and veins, on the other hand, have thicker walls and are responsible for carrying blood away from and towards the heart, respectively. They are not present in these specific tissues because their thicker walls would impede the exchange of molecules and interfere with the function of these tissues.
Therefore, the preference for capillaries in alveoli, nephrons, and villi is due to the need for thin vessel walls that facilitate the efficient transfer of molecules between blood and surrounding tissues.