The correct pathway for blood flow from the heart to the tissues of mammals is?

Analyze the question: It asks for the order of vessels that carry blood away from the heart to the tissues.

Concept: Blood vessels are named by the direction of flow:

• Arteries carry blood away from the heart. They are thick-walled and carry blood under high pressure.
• Arterioles are smaller branches of arteries. They lead into the capillaries.
• Capillaries are very thin-walled and are where exchange of materials with the tissues takes place.
• Venules collect blood from the capillaries.
• Veins carry blood back to the heart.

Step-by-step solution:

1. Blood leaves the heart through a large artery (the aorta for the body, the pulmonary artery for the lungs).
2. The artery divides into smaller arterioles.
3. The arterioles divide into capillaries, which supply the tissues.

So the pathway is: heart → artery → arteriole → (capillaries) → tissues

Checking the options:

• A. Arteriole comes before artery. This is the wrong order, since the large vessel leaves the heart first.
• B. Heart → artery → arteriole → tissues. This is correct.
• C and D. Veins and venules carry blood to the heart, not away from it, so both are wrong.

**Answer: B.

Exam tip: Remember "Arteries Away". Blood going away from the heart travels from the largest to the smallest vessels (artery → arteriole → capillary). Blood returning to the heart travels from the smallest to the largest (capillary → venule → vein).