Lecture 8 - Lymphatic system

What are the four main components of the lymphatic system?

Lymph, lymphatic vessels, lymphoid tissues, and lymphoid organs

What are the major lymphoid organs?

Lymph nodes, thymus, and spleen

What are the three forms of lymphoid tissue?

Mucosa-associated lymphoid tissue (MALT), diffuse lymphoid tissue, and lymphoid nodules

Which structures are classified as primary lymphoid structures?

Thymus and red bone marrow

Which structures are classified as secondary lymphoid structures?

Tonsils, lymph nodes, spleen, and MALT in the small intestine

Which system returns excess interstitial fluid to the bloodstream, transports lymphocytes and immune components, and supports lymphocyte development and activation?

Lymphatic system

What is interstitial fluid called once it enters the blind-ended vessels that collect it?

Lymph

Which blind-ended, highly permeable vessels collect interstitial fluid through thin endothelial walls and have irregular, variable diameters?

Lymphatic capillaries

Which filaments extend from the lymphatic capillary wall into the surrounding tissue?

Anchoring filaments

Which thin-walled vessels contain valves and carry lymph in one direction back toward the bloodstream?

Larger lymphatic vessels

Which tissue is composed primarily of lymphocytes, antigen-presenting cells, macrophages, and reticular cells and fibers?

Lymphoid tissue

What term refers to a localized accumulation of lymphocytes?

Lymphoid nodule

Which type of lymphoid nodule consists mainly of small, resting lymphocytes and has a relatively uniform appearance?

Primary nodule

Which type of lymphoid nodule has a germinal center and mantle zone and indicates active B-cell proliferation?

Secondary nodule

Which pale-staining region of a secondary lymphoid nodule contains activated and proliferating B cells?

Germinal center

Which darker-staining region surrounds the germinal center and contains more densely packed small lymphocytes?

Mantle zone

Which primary lymphoid organ is responsible for T-lymphocyte maturation?

Thymus

Which extensions of the thymic capsule divide the organ into lobules?

Septa

Which peripheral region of a thymic lobule stains darkly and contains a dense population of developing T cells?

Cortex

Which central region of a thymic lobule stains more lightly and has fewer lymphocytes and more epithelial reticular cells?

Medulla

Which thymic cells form a supporting cytoreticulum and interact with developing T cells?

Thymic epithelial cells (TECs)

Which thymic cells help organize the cortex and medulla and produce cytokines involved in T-cell development?

Thymic epithelial cells (TECs)

Which barrier includes continuous capillary endothelium, basal lamina, perivascular connective tissue, and thymic epithelial cells?

Blood-thymus barrier

Which thymic region primarily contains the blood-thymus barrier?

Thymic cortex

Which variable-sized, often eosinophilic structures in the thymic medulla consist of concentric aggregates of epithelial reticular cells?

Hassall corpuscles

Which lymphoid tissue is associated with mucosal surfaces and provides local immune surveillance?

Mucosa-associated lymphoid tissue (MALT)

Where does mucosa-associated lymphoid tissue occur?

Tonsils, Peyer's patches, appendix, and diffuse lymphoid tissue throughout mucosa

Which lymphoid structures are associated with the upper respiratory and digestive tracts?

Tonsils

What are the three anatomically distinct tonsils?

Pharyngeal tonsil, palatine tonsil, and lingual tonsil

Which partially encapsulated tonsil has stratified squamous nonkeratinized epithelium, lymphoid follicles, and deep epithelial crypts?

Palatine tonsil

Which aggregates of lymphoid nodules lie primarily in the ileal wall and contribute to mucosal immune surveillance?

Peyer's patches

Which secondary lymphoid organs filter lymph?

Lymph nodes

What are the three major regions of a lymph node?

Cortex, paracortex, and medulla

Which dense connective tissue structure completely surrounds a lymph node?

Capsule

Which extensions of the lymph-node capsule enter the lymphoid tissue and provide structural support?

Trabeculae

Which concave lymph-node region allows blood vessels to enter and leave and the efferent lymphatic to exit?

Hilum

Which lymph-node region lies beneath the capsule and contains lymphoid nodules, B lymphocytes, and diffuse lymphoid tissue?

Cortex

Which lymph-node region lies between cortex and medulla and contains T-lymphocyte-rich diffuse tissue without prominent lymphoid follicles?

Paracortex

Which specialized venules in the lymph-node paracortex allow circulating lymphocytes to enter the node?

High endothelial venules (HEVs)

Which structures in the lymph-node medulla contain lymphocytes, plasma cells, macrophages, and reticular fibers?

Medullary cords

Which lymph-filled spaces in the lymph-node medulla drain toward the efferent lymphatic?

Medullary sinuses

Which lymph-node sinus lies immediately beneath the capsule?

Subcapsular sinus

What is the sequence of lymph flow through a lymph node?

Afferent lymphatic vessels → subcapsular sinus → medullary sinuses → efferent lymphatic vessel at the hilum

Which blood vessels form networks around lymphatic nodules in a lymph node?

Blood capillaries

Which organ is the largest accumulation of lymphoid tissue in the body and filters blood?

Spleen

Which lymphoid organ removes aged or damaged erythrocytes, recycles their components, and responds to blood-borne antigens?

Spleen

What are the two major histologic regions of the spleen?

White pulp and red pulp

Which dense connective tissue structure surrounds the spleen and contains smooth muscle and elastic fibers?

Splenic capsule

Which structures extend inward from the splenic capsule, carry blood vessels, and provide structural support?

Trabeculae

Which splenic region consists of lymphoid tissue associated with the arterial circulation?

White pulp

What are the structural components of splenic white pulp?

Lymphoid follicles, periarteriolar lymphoid sheath (PALS), and central arteries

What are the main cell populations in splenic white pulp?

B and T lymphocytes, and antigen-presenting cells

Which T-lymphocyte-rich component of white pulp surrounds central arterioles?

Periarteriolar lymphoid sheath (PALS)

Which splenic region contains splenic cords, splenic sinusoids, macrophages, erythrocytes, and other blood cells?

Red pulp

Which specialized splenic vascular channels have elongated endothelial cells aligned parallel to blood flow, with open spaces between cells, and participate in erythrocyte filtration?

Splenic sinusoids