Areas of lymphoid tissue specifically found in the gastrointestinal tract are termed:

A. The appendix is an organ that contains lymphoid tissue and plays a role in immune function, but it does not specifically refer to macrophages and monocytes.
B. The reticuloendothelial system (also known as the mononuclear phagocyte system) consists of macrophages and monocytes found throughout the body. These cells are part of the immune system and are responsible for phagocytosis, or the engulfing and digesting of pathogens, dead cells, and debris.
C. Peyer's patches are clusters of lymphoid tissue found in the small intestine that monitor and respond to pathogens in the digestive tract.
D. Tonsils are lymphoid tissues located in the throat, playing a role in immune defense, but they are not part of the reticuloendothelial system.

A. Lymphatic capillaries do contain cells, specifically endothelial cells that form the walls of the capillaries.
B. Lymphatic capillaries are blind-ended, meaning they have an open end that begins the collection of interstitial fluid (lymph), unlike blood capillaries, which form continuous loops.
C. Lymphatic capillaries are highly permeable to water, solutes, and larger particles, which is one reason they are efficient at collecting interstitial fluid.
D. Lymphatic capillaries do not contain a muscular layer. Instead, they rely on the surrounding tissues and valves to help move lymph through the system