Final answer:
The spleen is a secondary lymphoid organ that filters blood and contains red pulp and white pulp. White pulp is arranged in nodules and contains germinal centers, while red pulp functions as a filtration system for the blood.
Step-by-step explanation:
The spleen is a secondary lymphoid organ that filters pathogens from the blood. It contains two types of tissue: red pulp and white pulp.
The white pulp is about lymphoid tissue arranged in nodules containing germinal centers of dividing B cells, surrounded by T cells and accessory cells such as macrophages and dendritic cells.
The red pulp consists of reticular fibers with fixed macrophages attached, free macrophages, and all the other cells typical of the blood, including lymphocytes. It functions as a filtration system for the blood, removing damaged red blood cells and pathogens.