Which of the following contain oxygenated blood?

A. Tonsils:Tonsils are secondary lymphoid organs that trap pathogens entering through the oral and nasal cavities. They contain lymphoid tissue and contribute to immune surveillance and response.

B. Pancreas:The pancreas is an exocrine and endocrine gland involved in digestion and blood glucose regulation. It does not contain lymphoid tissue or function in immune defense, so it is not classified as a lymphoid organ.

C. Spleen:The spleen is a secondary lymphoid organ that filters blood, removes old red blood cells, and mounts immune responses to blood-borne antigens.

D. Peyer's patches of the intestine:Peyer’s patches are lymphoid nodules in the small intestine that monitor intestinal bacteria and pathogens, making them secondary lymphoid structures involved in immune defense.

A. Lymph transport is faster than that occurring in veins:Lymph moves much more slowly than blood in veins. Its movement relies on low-pressure mechanisms rather than a central pump like the heart, so this statement is incorrect.

B. Under normal conditions, lymph vessels are very high-pressure conduits:Lymphatic vessels operate under low pressure. They have thin walls and rely on external forces, valves, and vessel contractions to move lymph, not high internal pressure.

C. Lymph transport depends on the movement of adjacent tissues, such as skeletal muscles:Lymph flow is aided by skeletal muscle contractions, respiratory movements, and rhythmic contractions of smooth muscle in the vessel walls. These mechanisms compress lymphatic vessels, helping push lymph toward the thoracic duct and ultimately the bloodstream.

D. Lymph transport is only necessary when illness causes tissue swelling:Lymph circulation is continuous under normal conditions to maintain fluid balance and immune surveillance. Swelling during illness increases demand, but transport is always required.