Classification of Lymphoid Organs Quiz

Classification of Lymphoid Organs

• Primary lymphoid organs: Include bone marrow and thymus where T and B lymphocytes originate and mature.
• Bone marrow: Site of origin for T and B lymphocytes; B lymphocytes migrate directly to secondary lymphoid structures.
• Thymus: T lymphocytes mature before seeding secondary lymphoid structures.

Secondary Lymphoid Organs

• Diffuse lymphoid tissue and lymphoid nodules: Comprising solitary and aggregates of lymphocytes.
• Key structures: Tonsils, lymph nodes, and spleen play crucial roles in immune response.

Mucosa-Associated Lymphoid Tissue (MALT)

• Location: Found in the lamina propria of respiratory and digestive systems.
• Function: Clusters of lymphocytes respond to antigens, provide immune surveillance, and filter tissue fluid.

Lymph Vessels

• Structure: Fine tubes containing lymph, facilitating removal of tissue fluid and returning it to the blood.
• Distribution: Present in all tissues except CNS, eyeballs, internal ears, epidermis, cartilage, and bone marrow.

Functions of Lymphoid Tissue

• Immune defense: Provides surveillance and defense against foreign substances and microorganisms.
• Immune tolerance: Differentiates between "self" and "non-self" entities.
• Lipid absorption: Absorbs lipids in small lymphoid vessels (lacteals) of the intestines.
• Fluid balance: Helps maintain fluid balance by returning tissue fluid and white blood cells to blood.

Circulation of Lymph

• Lymph capillaries: Network of vessels draining lymph from tissues, similar to but wider than blood capillaries.
• Flow: Drains into larger lymph vessels, converging on primary lymph nodes, then secondary and tertiary lymph nodes.
• Lymphatic vessels: Return lymph to bloodstream via great veins at the neck, featuring valves to prevent backflow.

Tonsils

• Types: Pharyngeal, lingual, and palatine tonsils located at the oral cavity-pharynx junction.
• Composition: Aggregations of lymphoid nodules and diffuse lymphoid tissue supporting immune response.

Thymus

• Role: Receives immature lymphocytes (thymocytes) from bone marrow for maturation.
• Structure: Surrounded by a connective tissue capsule divided into lobules.
• Lobule components:
  • Outer cortex densely packed with thymocytes.
  • Inner medulla having fewer thymocytes.
  • Blood-thymic barrier protects developing lymphocytes from circulating antigens.

Diffuse Lymphatic Tissue

• Location: Present in lamina propria of organs opening to the exterior.
• Composition: Clusters of lymphocytes ready to respond to antigens in various tissues, including tonsils and lymph nodes.

Lymph Nodules

• Occurrence: Found in lamina propria of exterior-opening organs; can be solitary or in aggregates (e.g., tonsils, Peyer's patches).
• Types:
  • Primary nodules present before antigen stimulation, composed mainly of B lymphocytes.
  • Secondary nodules develop after stimulation, with a central pale germinal center for lymphocyte division.

Test your knowledge on the classification of lymphoid organs, including primary organs like bone marrow and thymus, as well as secondary structures such as lymph nodes and spleen. This quiz will also cover Mucosa-Associated Lymphoid Tissue (MALT) and the role of lymph vessels in immune response.