Lesson 2: Lymphoid organs and development

1. Primary Lymphoid Organs

2. Secondary Lymphoid Organs

2 types of Lymphoid Organ

Primary Lymphoid Organs

where maturations of of lymphocytes occurs

1. Bone Marrow

2. Thymus

Primary Lymphocyte organs

1. Spleen

2. Lymph Nodes

3. MALT (Mucosal Associated Lymphoid Tissue)

Secondary Lymphoid Organs

Lymphocytes needs to be recirculated

if not, there will be no recognition between antigens and the naive T lymphocytes will die

Bone Marrow

• main source of the hematopoietic stem cells

• place where B cells maturation occrs

CD34

CD marker of the hematopoietic stem cell

Thymus

small, flat, bilobed organ found in the thorax

Thymus gland

change with aging

Reticular structure of the thymus

allows significant number of lymphocytes pass through to become fully immunocompetent

Thymus derived T-cell

passes through the reticular structure of the thymus and become fully immunocompetent

1. Cortex (outside)

2. Medulla

2 man zones of the thymus

Spleen

• located in the upper left quadrant

• largest secondary lymphoid organ

• large discriminating filter that removes senescent cells and foreign antigens from the blood

Red pulp

• more than ½ the volume

• destroys senescent RBCs

2 main types of spleen

1. Red pulp

2. White pulp

White pulp

• contains the lymphoid tissue

• found around the periarteriolar lymphoid sheath

Lymph nodes

• central collecting point for lymph fluids

• provides the ideal environment for contact with foreign antigens that have penetrated into the tissue

Lymph fluid

filtrate of blood and arises from passage of water

Urine

ultrafiltrate of blood

Sinuses

spaces where lymph fluids slowly flows in line with macrophage, creating an ideal location where phagocytosis can take place

Cortex

contains the macrophages and aggregations of B-cells

Primary follicle

aggregation of B-cells

Secondary follicle

contains antigen stimulated proliferating B-cells (germinal center)

Paracortex

contains T-cells

Lymphadenopathy

enlargement of the lymph nodes

Other Secondary Lymph Organs

1. CALT

2. BALT

3. GALT

CALT

Cutaneous Associated Lymphoid Tissue

BALT

Bronchus-Associated Lymphoid Tissue

GALT

Gut-Associated Lymphoid Tissue

Mucosal Associated Lymphoid Tissue

serves as the main ports of entry for foreign antigens

1. gastrointestinal

2. respiratory

3. urogenital tract

where MALT can be found

1. Tonsils

2. Appendix

3. Peyer’s

Example of MALT

Cutaneous Associated Lymphoid Tissue

contains intraepidermal lymphocytes