What structure primarily drains lymph from the distal sigmoid colon and upper rectum?

The inferior mesenteric nodes are primarily responsible for draining lymph from the distal sigmoid colon and upper rectum. This is because the lymphatic drainage pathways from the distal portions of the colon generally follow the vascular supply, which is provided by the inferior mesenteric artery. The lymphatic vessels from these regions converge towards the inferior mesenteric nodes, allowing lymph fluid to be filtered through these nodes before entering the systemic circulation.

When considering the other options, the superficial inguinal nodes primarily drain the lower abdomen and lower extremities, specifically areas below the inguinal ligament. The para-aortic nodes collect lymph from the abdominal organs, mainly the kidneys and testes, as well as the pelvic organs to some extent, but they are not specifically involved in the drainage of the distal sigmoid colon and upper rectum. The celiac nodes primarily drain lymph from the stomach, liver, spleen, and parts of the pancreas and duodenum, which are not directly involved in the drainage of the sigmoid colon or rectum.

Thus, the correct answer reflects the anatomical relationships and lymphatic drainage patterns associated with the regions indicated in the question.