IMSE 311: Lymphoid Organs

Bone Marrow

One of the largest tissues in the body and is the main source of HSCs

Thymus

Small, flat, bilobed organ found in the chest cavity; gradually shrinks in size as humans age

Secondary Lymphoid Organs

Where main contact with foreign antigens takes place

Thoracic duct

Largest lymphatic vessel in the body and where LYMPHs pass through to return to the blood stream

2

Age when thymus development starts

Continuous recirculation

Increases the likelihood of a T-cell coming into contact with specific antigens

Lymphoiesis

Multiplication of LYMPHs that occurs in the secondary lymphoid organs

• strictly antigen-dependent

Spleen

Large discriminating filter that removes old and damaged cells and foreign antigens from the blood

• Largest secondary lymphoid organ

• 12 cm

• 150 g

Red Pulp

Splenic tissue that is rich in macrophage and destroys old RBCs, platelets, and some pathogens

• Culling

White Pulp

Splenic tissue that contains lymphoid tissue arranged around arterioles

Periarteriolar Lymphoid Sheath (PALS)

Part of the splenic white pulp that mainly contains T-cells

Primary Follicles

Attached to PALS which contain immature B-cells

Marginal Zone

Surrounds PALS and contains dendritic cells and macrophages

350 mL

The spleen receives a blood volume of approx. _____ per minute, which allows LYMPHs and macrophages to constantly survey for infectious agents

Lymph Nodes

Central collecting points for lymph fluid

• Numerous near joints and where the arms and legs join the body

• Provides ideal environment for contact with foreign antigens that have penetrated into the tissues

• 1-25 mm

Lymph Fluid

Filtrate of blood and arises from passage of water and low-MW-solutes out of blood vessel walls and into the interstitial spaces between cells

Lymphatic Vessels

Some of the lymph fluid returns to the bloodstream, but a portion flows through the tissues and is eventually collected in thin-walled vessels known as?

Lymph Node: Cortex (Primary Follicles)

Outermost layer that contains macrophages, aggregations of mature (resting) B-cells, and follicular dendritic cells

Lymph Node: Cortex (Secondary Follicles)

Consist of antigen-stimulated proliferating B-cells

Lymph Node: Germinal Center

Interior of secondary follicle where transformation of B-cells into plasma cells and memory cells take place

Lymph Node: Paracortex

Part of lymph node that contains T-cells

Plasma Cells

Actively secrete/produces antibodies when exposed to an antigen

Memory Cells

Quickly develop into plasma cells when exposed to an antigen

Lymphadenopathy

Enlarged lymph nodes due to accumulation of LYMPHs and other cells

Peyer’s Patches

Specialized type of MALT located at the lower iluem of intestinal tract

Cutaneous-associated Lymphoid Tissue (CALT)

T-cells, MONOs, MACROs, and dendritic cells that are found in the skin (epidermis)