inguinal nodes in the groin, the axillary nodes in the armpit, and the cervical nodes in the neck. Lymph nodes are surrounded by a connective tissue capsule, and are divided into nodules composed of dense masses of lymphocytes and macrophages separated by lymph sinuses (spaces). Afferent lymphatic vessels carry lymph to the modes and enter on the convex side. Lymph is filtered through the node and collected by a single efferent lymphatic vessel which leaves the node at the hilum. Because there are several afferent vessels and only one efferent vessel, passage of lymph through the node is slow. The nodes filter out infectious agents, damaged cells, cancer cells, and cell debris. The lymphocytes react against bacteria, viruses, and cancer cells, and the macrophages engulf and destroy pathogens, damaged cells, and cell debris.
The spleen is surrounded by a capsule of connective tissue which extends inwards to divide the spleen into lobules (Applegate, 2000, 290). The spleen consists of red pulp and white pulp: the red pulp is composed of venous sinuses filled with blood and cords of lymphatic cells (lymphocytes and macrophages), and the white pulp consists of lymphatic tissue, which is mainly lymphocytes surrounding arteries. Blood enters the spleen through the splenic artery, enters the sinuses, and leaves through the splenic vein.
The spleen filters blood in the same way the lymph nodes filter lymph (Applegate, 2000, 290). Lymphocytes within the spleen destroy pathogens in the blood. Macrophages engulf the resulting debris, as well as damaged cells and other large particles. The spleen also produces lymphocytes, especially in response to pathogenic invasion. The sinuses of the spleen serve as a reservoir for blood which can be delivered to the general circulation in the case of emergencies by contraction of the capsule and the smooth muscle in the vessel wa
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