Primary lymphoid organs Secondary lymphoid organs Secondary lymphoid organs Bone marrow Thymus Lymph node Spleen Tonsils

lymph node Tonsils Spleen

1.Lymph nodes are bean-shaped, encapsulated structures 2. generally 2–10 mm in diameter 3.distributed throughout the body along the course of the lymphatic vessels, in the chest, neck, pelvis, axilla (armpit), groin region, and in association with the blood vessels of the intestines

 The lymph node consists of lymphoid follicles in an outer portion called the "cortex.“, and the inner portion called the "medulla," which is surrounded by the cortex on all sides except for a portion known as the "hilum.“  The hilum presents as a depression on the surface of the lymph node, which makes the spherical lymph node, bean- shaped or ovoid.  The efferent lymph vessel, arteries and veins supplying the lymph node with blood enter and exit through the hilum.

1.Lymph nodes have the primary function of producing lymphocytes which help protect the body against microorganisms and harmful foreign particles. 2. Lymph nodes normally swell when they are actively responding to infection as they fill with the pathogenic cells they filter from the lymph.

These lymphoid masses are named according to their location as : 1.Palatine tonsils 2.Pharyngeal tonsil 3.Lingual tonsil

TonsilLocationEpitheliumCrypts Pharyngea l In the midline on the roof of the nasopharynx Ciliated pseudostratified columnar epithelium typical of the respiratory tract, with some patches of stratified squamous epithelium observed Numerous folds of pharyngeal epithelium, not true crypts Lingual Posterior third of tongue Stratified squamous non-keratinising Multiple monocryptic 'units' PalatinePaired at oropharynx Stratified squamous non-keratinising deep and sometimes branching crypts (Polycryptic)

Spleen is the largest lymphoid organ in the body It is the only organ specialized for filtering blood