LYMPHATIC SYSTEM

SCHOOL OF ANATOMICAL SCIENCES

Lymphoid tissue is made up principally of lymphocytes and macrophages enmeshed in a framework of reticular fibres. Lymphocytes produce an immune response to foreign material (antigens) in the body.

Lymphocytes are constantly being circulated, in lymphatic vessels and in blood vessels. They enter the surrounding connective tissue between the endothelial cells of the smaller vessels by amoeboid movement. B-lymphocytes differentiate into plasma cells which produce antibodies – a ‘humoral’ response, i.e. they elicit a ‘cellular’ response e.g. to parasites.

Macrophages identify and ingest foreign substances and cause the lymphocytes to react. They are derived from monocytes which are formed in the bone marrow.

Slide 45 (100x): Lymph node (H&E)

Cortex Of Lymph Node

In this section of the cortex of the lymph node, NOTE:

The dense irregular CT of the capsule (with adipose tissue) that invaginates the lymphoid tissue forming trabeculae. The capsule and trabeculae contain lymphatic and blood vessels. Dark basophilic lymphoid follicles/nodules with pale-stained germinal centres (secondary lymphatic follicles). Pale stained subcapsular and paratrebecular sinuses with diffuse lymphoid tissue.

Questions Explain the presence of germinal centres.Which lymph vessels are found in the capsule?

Slide 45 (100x): Lymph node (H&E)

Medulla Of Lymph Node

In this section through the lymph node, NOTE:

The outer dark basophilic cortex and the inner pale basophilic medulla. Dark basophilic cords of lymphoid tissue in the medulla – medullary cords. The paler basophilic regions of diffuse lymphoid tissue in the medulla – medullary sinuses. The blood vessels in the medullary cords.

Questions Name the cells found in the medulla of the lymph node.What is the function of the post-capillary venules in the lymph node?

Slide 45 (100x): Lymph node (H&E)

Hilus Of Lymph Node

In this section through the lymph node hilus, NOTE:

Various blood vessels. The large lumina of the lymphatic vessels containing homogenous lymph and valves.

QuestionsWhat lymphatic vessels are found in the hilus? Describe the flow of lymph in the lymph node. Describe the flow of blood in the lymph node.

Slide 45 (400x): Lymph node (H&E)

Reticular Cells of Lymph Node

In this section of the cortex of a lymph node, NOTE:

The dense irregular CT of the capsule in the upper part of the field. Many round and dark basophilic nuclei of lymphocytes in the lymphoid tissue. The oval, elongated and pale basophilic nuclei of the reticular cells in the subcapsular sinus.QuestionsWhat is the function of the reticular cells?What is the function of the lymph node?

Slide 84 (1000x): Duodenum (H&E)

Plasma Cells

In this section of the lamina propria (LP) of the duodenum, NOTE:

The loose CT between the secretory cells of the gastric glands. The large nuclei of a few plasma cells with the clock-faced arrangement of the pale euchromatin and dark heterochromatin and nucleolus.

QuestionsWhat do plasma cells secrete? In the lymph node, where are plasma cells found?What other cell types are evident in this section?

Supplementary slides:

Slide 34 (100x): Tonsil (H&E)

Tonsil

NOTE:

The thick, stratified squamous non-keratinized epithelium lining. The nodular and diffuse lymphoid tissue. The eosinophilic fibrous tissue of the capsule, separating the lymphoid tissue from the surface epithelium.

QuestionWhat is the function of the palatine tonsil?

Slide 47 (100x): Spleen (H&E)

Spleen

NOTE:

The basophilic mass of white pulp. A ‘central artery’ running through the white pulp. The venous sinuses and the splenic cords in the red pulp.

QuestionsWhy does the white pulp stain basophilically? How do you identify the splenic cords?

Slide 48 (100x): Spleen (Silver impregnation)

Spleen

This section demonstrates the reticular fibre framework in the spleen. Reticular fibres have been stained black. Cells are not shown by this method. Compare with the H & E section. NOTE:

The fine fibres of a mass of white pulp cut in cross section. The more coarse fibres in the tunica media of the central artery (actually an eccentrically placed arteriole). Branching penicillar arterioles entering the red pulp. The red pulp made up of venous sinuses (spaces) supported by coarse reticular fibres around the venous sinuses.

QuestionWhat are the splenic cords i.e. the cords of Billroth?