Lymphatic System and 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.