Final answer:
The incorrect statement about lymph nodes is that 'They are drained by afferent lymphatic vessels' because lymph nodes are drained by efferent vessels, not afferent.
Step-by-step explanation:
When discussing lymph nodes, it's important to understand that they play a crucial role in the immune system by filtering lymph and housing immune cells. Considering the options provided, the statement that is not correct regarding lymph nodes is that 'They are drained by afferent lymphatic vessels'. This is because lymph nodes are actually drained by efferent lymphatic vessels, and it is the afferent lymphatic vessels that bring lymph into the lymph nodes. Inside the nodes, lymphatic cells, including B cells and plasma cells, are supported by structures called medullary cords. They also contain phagocytic cells like macrophages and dendritic cells which are crucial for filtering out debris and pathogens.