Lymphatic system 2.pdf

The Spleen A) – Stroma The spleen is covered by capsule of dense connective tissue. It sends trabeculae which divide the spleen into incomplete splenic lobules. The capsule and trabeculae contain smooth muscle fibers. The contraction of these muscle fibers leads to the delivery of the blood from the...

The Spleen A) – Stroma The spleen is covered by capsule of dense connective tissue. It sends trabeculae which divide the spleen into incomplete splenic lobules. The capsule and trabeculae contain smooth muscle fibers. The contraction of these muscle fibers leads to the delivery of the blood from the spleen into circulation under certain conditions. The reticular connective tissue forms networks to support the parenchyma. B)-Parenchyma 1-White pulp (splenic nodule). i)-Periarterial lymphatic sheath; formed of reticular connective tissue which supports the artery. ii)Lymphatic nodules scattered within the periarterial sheath and contain a concentration of "B" lymphocytes. Lymphatic nodules push the central arteries toward the periphery thus becoming eccentric in position. 2- Red pulp Consists of a network of branching and anastomosing sinuses separated by highly cellular partitions called the cords of Billroth or splenic cords. The red pulp is looser in texture. It is supported by networks formed by the reticular fibers and cells. Functions of the spleen: 1-The spleen acts as a blood reservoir. The stored blood in the spleen is very rich in RBCs as the contraction of the splenic vein leads to sweeping of the plasma through the walls of the venous sinuses. 2-The spleen is a haemopoietic organ. It produces lymphocytes and monocytes. The lymphocytes are formed mainly in the white pulp. The monocytes are developed from the haemocytoblasts in the red pulp. 3- It filters the blood by its free and fixed macrophages (III) Tonsils Types 1) One pharyngeal tonsil 2) Two palatine tonsils: 3) Many lingual tonsils Tonsils are incompletely encapsulated aggregates of lymphoid tissues that guard the inlet of the oro- pharynx They react to the air- born and ingested Ags, by forming lymphocytes and creating an immune response. palatine tonsils The bilateral palatine tonsils. palatine tonsil is isolated from the surrounding C.T. by a dense fibrous capsule. The superficial aspect of the tonsils is covered by a stratified squamous, non keratinized epithelium presenting 10-12 deep crypts that invaginate the tonsillar parenchyma. palatine tonsils The tonsil is composed of numerous lymphoid nodules, many of which have germinal centers Thank you