he arteries with walls that are mostly smooth muscle areMultiple Choicemedium-size (distributing) arteries.arterioles.elastic arteries.capillaries.

Break Down the Problem

1. Identify the types of arteries listed in the options:

   • Medium-size (distributing) arteries
   • Arterioles
   • Elastic arteries
   • Capillaries

2. Determine which type of artery has walls mostly made of smooth muscle.

Relevant Concepts

1. Medium-size (distributing) arteries: These arteries distribute blood to various parts of the body and have a thick layer of smooth muscle to regulate blood flow.

2. Arterioles: These are the smallest arteries that lead to capillaries and also have muscular walls but are not primarily defined by muscle.

3. Elastic arteries: These large arteries (such as the aorta) contain more elastic tissue in their walls to accommodate the high pressure of blood coming directly from the heart.

4. Capillaries: These are the smallest blood vessels and consist only of endothelial cells with no smooth muscle or elastic tissue.

Analysis and Detail

• Medium-size (distributing) arteries are designed to regulate blood flow and pressure through smooth muscle contraction and relaxation.
• Arterioles do have smooth muscle but are considered a further division of arteries.
• Elastic arteries maintain a different structure, focusing on elasticity rather than muscular strength.
• Capillaries lack muscular walls entirely.

Verify and Summarize

Based on the analysis, medium-size (distributing) arteries predominantly consist of smooth muscle, allowing them to play a crucial role in blood distribution and pressure regulation in the body's various regions.

Final Answer

The arteries with walls that are mostly smooth muscle are medium-size (distributing) arteries.