Anne and Tresha

Thursday,

December 2, 2004

Central = Primary lymphoid tissue

• Site of maturation of the cells of the immune system• Thymus

– encapsulated– T cells

• Bone marrow– Bursal equivalent– B cells, monocytes, erythrocytes, granulocytes, and megakaryocytes

Peripheral = Secondary lymphoid tissue

• Filter blood and lymph• Site of antigen, immune system interaction

Peripheral = Secondary lymphoid tissue

• Diffuse lymphatic tissue (Unencapsulated)– Found in the lamina propria where pathogens

are likely to invade– GI: Tonsils, Peyer’s patches, appendix;

Respiratory tract; GU

• Lymph nodes– Encapsulated– Interposed btwn lymphatic vessels (only)

• Spleen lymphatic tissue– Encapsulated– Interposed btwn lymph and blood circulation

Lymph Vessels

• Valves• Carries Lymph from tissue

lymph nodes blood via thoracic duct– Fluid– Proteins– Ingested fats– Particulate matter– Antigen– Disease microorganisms– Cells (normal and cancerous)

Lab 11 Slide 7

Primary follicle- Naïve Lymphocytes- No germinal center

Secondary follicle- Germinal Center- Antigen has been

encountered- Looks pale! - because

of plasmablasts Lab 11 Slide 9

1

2

• Germinal Center– Dark zone = densely

packed lymphocytes separated by reticular cells

– Light zone = plasmablasts

– T cells at periphery

Tonsil

• Unencapsulated

• Stratified squamous non-keratinized epithelium

• Dense fibrous CT• CT Septum --> lobes• Crypts - invaded by

lymphocytes• Numerous Lymphoid

nodules– Germinal centers

• Lymphocytes invade the epithelium and the connective tissue

• GALT (gut associated lymphatic tissue)– In the loose areolar CT of the lamina propria– Diffuse lymphatic tissue– Solitary lymphatic nodules– Aggregates of lymphatic nodules (Peyer’s patches

and appendix)

A

B

Question 1C.Both

D.Neither

A

B

Question 1C.Both

D.Neither

Tonsil

Lymph node

• Is encapsulated = B• Contains germinal centers = C• Peripheral lymphoid tissue = C• Central lymphoid tissue = D

Question 2The region at the arrow is:

A) Peyer’s Patch

B) Germinal Center

C) Lymph Node

D) Primary lymphoid nodule

Question 2The region at the arrow is:

A) Peyer’s Patch

B) Germinal Center

C) Lymph Node

D) Primary lymphoid nodule

Lymph Node Function

• Filters lymphatic fluid• Enhance antigen presentation• Facilitate B-Cell Activation to

generate plasma cells and memory B-cells

Lymph Flow w/in Node

Afferent Lymphatics Subcapsular sinus trabecular sinuses medullary sinus efferent lymphatics

Lymph Node Structural Components

• Capsule: Dense, Irregular CT

• Trabeculae are extensions of the capsule

• Reticular cells- framework (stain black with the Silver stain)

• Hilum- efferent lymphs; entry

and exit of blood vessels

Lymph Node Parenchyma

• Cortex

– Primary, secondary nodules

• Deep cortex

• (aka paracortex, juxtamedullary cortex, thymus dependent cortex)

– No nodules

• Medulla

– Cords and sinuses.

– Where plasma cells synthesize and release Abs into lymph flowing through the sinuses.

Lymphatic Sinuses• Subcapsular sinus

– Receive lymph from afferent lymphatic vessels

• Trabecular sinuses– Drain into medullary sinuses

• Provide open communication between lymphatic drainage and parenchyma (macrophages monitor lymph as it percolates through; will phagocytose)

• Macrophages take up India ink- stained black.

The Germinal Center

• Characterizes the 2ndary nodule

• Pale staining center: plasmablasts

– Large cells, large nucleus, prominent nucleolus

– May see mitotic figures

• Dark outer zone

– Densely packed lymphocytes (sp. B-cells)

T-Cell Zone

• Comprises Deep Cortex and Paracortex

• Where T and B cells enter from the circulation

• See post capillary venules with high endothelial cells

• B cells migrate, T cells remain

Medullary Region

• Cords and Sinuses• Cords: reticular cells,

lymphocytes, plasmablasts, plasma cells

• Antibody secreted into efferent lymph

• Macrophages present• Entry/Exit of blood

vessels, nerves, efferent lymph

Summary of Lymph Node flow

Lymph Flow w/in Node

Afferent Lymphatics Subcapsular sinus trabecular sinuses medullary sinus efferent lymphatics

Question 3

The region inside the box contains which of the following upon antigenic stimulation:

A. Plasma Cells

A. Macrophages

B. T-Cells

C. Memory B-Cells

D. All of the Above