Blood flow in the hepatic portal vein

Steps:

• Identify the vein as part of the hepatic portal system based on the section diagram.
• Direction 1 traces upstream to the first organ draining blood into the vein: the intestine.
• Direction 2 traces downstream to the first organ receiving blood from the vein: the liver.
• Confirm this matches the portal circulation where intestinal blood flows to liver before heart.

Why A is correct:

• In the hepatic portal vein, blood flows from intestines (direction 1) to liver (direction 2), per the definition of portal circulation carrying nutrient-rich blood to the liver.

Why the others are wrong:

• B: Identical to A, but listed as duplicate; not a distinct option.
• C: Renal vein flows from kidney directly to heart, bypassing another organ.
• D: Pulmonary vein flows from lung directly to heart, not involving liver.

Final answer: A