Lymphatic System and Spleen Overview

Lymphatic System

• Lymph nodes are crucial components, clustered along lymphatic vessels.
• Bean-shaped, unidirectional flow.
• Filter lymph, removing microorganisms (macrophages).
• Activate immune response.
• Capsule surrounds each node, divided into compartments (cortex and medulla).
• Cortex contains B and T cells, dendritic cells.
• Medulla contains B and T lymphocytes.
• Lymph enters via afferent vessels, flows through sinuses, exits via efferent vessels.
• Fewer efferent vessels allow lymphocytes & macrophages time to act.
• Lymph flows through multiple nodes.

Spleen

• Largest lymphoid organ, fist-sized.
• Located on left side of abdominal cavity, behind stomach.
• Supplied by splenic artery and vein.
• Lymphocyte proliferation and immune surveillance.
• Blood filtration, RBC recycling for later use.
• Stores blood platelets and monocytes.
• Erythropoiesis in fetuses.
• Two compartments: white pulp (immune function) and red pulp (RBC destruction).
  • White pulp forms cuffs around central arteries.
  • Red pulp consists of splenic cords, separating splenic sinusoids.

Thymus Gland

• Located in the superior thorax, overlying the heart.
• Important for T lymphocyte precursor maturation.
• Contains epithelial cells, not reticular tissues.
• More prominent in children due to the development of the immune system.

Mucosa-Associated Lymphoid Tissue (MALT)

• Strategically located in mucous membranes.
• Protect against pathogens entering the body.

Tonsils

• Ring of lymphoid tissue around throat entrance.
  • Palatine tonsils (paired, posterior oral cavity).
  • Lingual tonsils (base of tongue).
  • Pharyngeal tonsil (posterior nasopharynx wall).
  • Tubal tonsils (surround auditory tube openings)
• Gather and remove pathogens entering the throat

Peyer's Patches

• Large clusters of lymphoid follicles, similar to tonsils.
• Located in the distal small intestine (ileum).

Appendix

• Offshoot of large intestine, rich in lymphoid follicles.
• Strategic position to prevent bacteria entry, generate memory lymphocytes.

Blood and Leukocytes

• Lymph from capillary beds flows through lymph nodes, then enters the blood circulation.
• Leukocytes (WBCs) are the only complete cells in blood.
• Protect against bacteria, viruses, parasites, and toxins.
• Can leave bloodstream to mount immune/inflammatory responses.

Granulocytes

• Spherical, larger than RBCs, visible cytoplasmic granules.
  • Neutrophils: hydrolytic enzymes, antibiotic-like proteins, phagocytes
  • Eosinophils: blue-red nucleus, red granules, immune response & parasites
  • Basophils: rarest, histamine granules, dilate vessels, attract other WBCs

Agranulocytes

• No visible granules, typically kidney-shaped.
  • Lymphocytes: large nucleus, blue cytoplasm, found in lymphoid tissues, B & T cells
  • Monocytes: largest, gray-blue cytoplasm, kidney-shaped nucleus, become macrophages, fight viruses & chronic infections

Leukopoiesis

• Hormonally regulated process of leukocyte production.
• All originate from hemocytoblasts which can become lymphoid stem cells or myeloid stem cells.

Disorders

• Leukemia: cancer of WBCs (acute from blast cells, chronic from other cells).
  • Bone marrow involvement; treated with chemo, anti-leukemic drugs, and bone marrow transplants.
• Infectious mononucleosis: Epstein-Barr virus, excess abnormal lymphocytes.
• Leukopenia: abnormally low WBC count, often caused by chemotherapy drugs.