The vessels that exhibit the lowest level of permeability are the __________.

• A. venules
• B. sinusoidal capillaries
• C. fenestrated capillaries
• D. continuous capillaries

Answer: (D)

Verified step by step guidance

1. Step 1: Understand the concept of capillary permeability. Capillaries are small blood vessels that allow the exchange of substances between the blood and surrounding tissues. Their permeability depends on the structure of their walls.
2. Step 2: Learn about the types of capillaries. There are three main types: continuous capillaries, fenestrated capillaries, and sinusoidal capillaries. Each type has different levels of permeability based on its structure.
3. Step 3: Examine the structure of continuous capillaries. Continuous capillaries have tightly joined endothelial cells with very few gaps, making them the least permeable. They are commonly found in the brain, lungs, and muscles.
4. Step 4: Compare continuous capillaries to fenestrated and sinusoidal capillaries. Fenestrated capillaries have small pores (fenestrations) that increase permeability, while sinusoidal capillaries have large gaps, making them the most permeable.
5. Step 5: Conclude that continuous capillaries exhibit the lowest level of permeability due to their tightly joined endothelial cells and lack of fenestrations or large gaps.