The Lymphatic System and Immunity

Study Notes

The lymphatic system is a vessel system connected to the circulatory system.
It is composed of lymphatic capillaries, lymphatic vessels, lymphatic ducts, and lymph nodes.
The lymphatic system returns lymph cells (clear, colorless, alkaline fluid) from tissue spaces back into the bloodstream.

Transports proteins and fluids lost through capillary seepage back to the bloodstream.
Protects the body against pathogens through phagocytosis and immune responses.
Facilitates the absorption of fats from the small intestine into the bloodstream.

Lymphocytes are prevalent in the lymphatic system.
B-lymphocytes, when activated by an antigen, differentiate into plasma cells and B-memory cells.
Plasma cells produce antibodies targeting and destroying pathogens (humoral immunity).
T-lymphocytes, when activated by an appropriate antigen, differentiate into several types:
- Cytotoxic T cells (CD8+): kill virus-infected cells and tumor cells.
- Helper T cells (CD4+): activate B and T cells.
- Suppressor T cells: modulate the immune system.
- Memory T cells: influence the immune response.
This process is called cellular immunity.

Primary Organs: Thymus, Bone Marrow
Secondary Organs: Lymph nodes, Spleen, Peyer's patches, Appendix, Adenoids, Tonsils

Located in the upper left quadrant of the abdomen.
Major site of erythrocyte destruction and a reservoir for blood (emergency bleeding).
Essential for immune responses and blood filtration.

Composed of connective tissue stroma and parenchyma. The stroma is the framework (capsule, trabeculae, reticular CT)
Parenchyma (soft tissue filling the framework): - White pulp: B-cell area (lymphoid follicles) and T-cell area (peri-arterial lymphatic sheaths). - Red pulp: Billroth cords, a soft tissue between white pulp and blood sinusoids. lymphocytes, erythrocytes, leukocytes, plasma cells, macrophages, and dendritic cells.

Lymphoid masses in the oral cavity and pharynx, filtering bacteria.
Types: Palatine tonsils, Pharyngeal tonsils (adenoids), Lingual tonsils.
Simplest lymphoid organs forming a ring of lymphoid tissue around the pharynx.
Tonsil tissue contains follicles with germinal centers.
Not fully encapsulated.
Epithelial tissue invaginates to form blind-ended crypts that trap and destroy bacteria.

Located in the mediastinal cavity.
Crucial role in the development of the immune system in infants and young children.
Producing T cells (infection-fighting cells), essential to the immune system.
Helps distinguish normal T cells from those attacking the body's own tissues.
Consists of cortex and medulla:
- Cortex contains immature T-cells (thymocytes) and thymus epithelial cells, macrophages and dendritic cells
- Medulla contains mature T cells and thymus epithelial cells, macrophages and dendritic cells
Hassall's corpuscles (or thymic corpuscles): prominent structures in the thymus medulla, composed of concentrically arranged, often degenerated, eosinophilic epithelial reticular cells.