connective tissue in red pulp o Splenic sinusoids: very permeable capillaries o Storage site for erythrocytes and platelets 25
21.4b Spleen • Monitoring blood as it flows through the spleen – Path of flow: splenic artery, central artery, sinusoids, venules, splenic vein • Function of spleen : eat foreign particles; clear defective erythrocytes and platelets; store erythrocytes and platelets – The spleen filters and monitors blood (not lymph) – White pulp monitors it for foreign materials and bacteria o Macrophages in sinusoids of red pulp remove particles o Phagocytize bacteria, debris, defective erythrocytes and platelets – In first 5 months of fetal life, spleen makes blood cells. This function can be reactivated under certain conditions o E.g., some hematologic disorders
Clinical View: Splenectomy • Surgical removal of the spleen • May be performed due to – Ruptured spleen from abdominal injury (most common) – Infection, cyst, or tumor – Lymphoma or other cancer – Blood disorders (e.g., sickle cell anemia) • May be more prone to life-threatening infection
• Tonsils – Secondary lymphatic structures – Immune surveillance of inhaled and ingested substances – Tonsillar crypts o Invaginations that trap material – Contain lymphatic nodules o Some with germinal centers 21.4c Tonsils Figure 21.8b, c
• Tonsils ( continued ) – Pharyngeal tonsil o In nasopharynx o Called adenoids when enlarged – Palatine tonsils o In posterolateral oral cavity – Lingual tonsils o Along posterior one-third of tongue 21.4c Tonsils Figure 21.8a
Clinical View: Tonsillitis and Tonsillectomy • Acute tonsillitis: inflammation and infection of tonsils • Palatine tonsils most commonly affected – Redden and enlarge – May partially obstruct pharynx • Fever, chills, sore throat, and difficulty swallowing • May be infected by viruses or bacteria • Persistent recurrent infections, chronic tonsillitis – May require tonsillectomy, surgical removal of tonsils 30
21.4d Lymphatic Nodules and MALT • Lymphatic nodules – Clusters of lymphatic cells with some extracellular matrix o Not completely surrounded by connective tissue capsule – Scattered nodules termed diffuse lymphatic tissue – Found in every body organ – Help defend against infection – In some areas, group together to form larger structures o E.g., MALT
21.4d Lymphatic Nodules and MALT • MALT – Mucosa-associated lymphatic tissue – Located in gastrointestinal, respiratory, genital, and urinary tracts o Found in lamina propria of the mucosa – Help defend against foreign substances – Prominent in small intestines , especially ileum o Peyer patches : large collections of lymphatic nodules that form bulges in ileum wall
Relationship of the Lymphatic System to the Cardiovascular System & the Immune System 33 Figure 21.9a
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- Fall '19