Immunology Quiz: Thymus and Lymph Nodes

Study Notes

The lymphatic system is a network of vessels, tissues, and organs that help maintain fluid balance in the body and fight infection.
It consists of lymph, lymphatic vessels, structures and organs containing lymphatic tissue, and red bone marrow.
The lymphatic system's functions include draining excess interstitial fluid, transporting dietary lipids, and carrying out immune responses.
Lymphatic vessels begin as lymphatic capillaries, which are closed at one end.
They unite to form larger lymphatic vessels that resemble veins in structure but have thinner walls and more valves.
Lymph nodes are located along lymphatic vessels and are part of the lymphatic system.
Lymphatic nodules are not surrounded by a capsule.
They are scattered throughout the lamina propria of mucous membranes, in the mucosa-associated lymphatic tissue (MALT) of the respiratory tract, and in the appendix.
Lymphoid organs include the tonsils, thymus, spleen, and lymph nodes.
The thymus is a primary lymphatic organ where T cells mature.

Lymphocytes are the primary cells involved in the immune response and come in two main types: T cells and B cells.
T cells manage the immune response and attack foreign cells.
B cells produce plasma cells, which secrete antibodies that immobilize antigens.
Macrophages phagocytose foreign substances and help activate T cells.
Dendritic cells are spiny-looking cells similar to macrophages, capturing antigens and bringing them back to lymph nodes.
Reticular cells are fibroblast-like cells that produce stroma (a network) that supports other cell types in lymphoid organs.

Innate immunity is present at birth and provides a nonspecific, immediate defense against invading pathogens.
First line of defense includes skin and mucous membranes while the second line is composed of phagocytic leukocytes, antimicrobial proteins and the inflammatory response.
Adaptive immunity develops after exposure to a pathogen and provides a specific, long-lasting defense.
Antibody-mediated immunity involves antibody production by B cells and immune responses against extracellular pathogens.
Cell-mediated immunity involves the activation of T cells and cytotoxic T cells which attack infected body cells.

Lymphatic tissues and organs can be grouped by function into primary and secondary groups.
Primary Lymphatic Organs (where stem cells become immunocompetent): red bone marrow and thymus.
Secondary Lymphatic Organs (where most immune response occurs): lymph nodes, spleen, and lymphatic nodules.
The spleen is the largest single mass of lymphatic tissue in the body, with white pulp (lymphocytes and macrophages) and red pulp (blood-filled sinuses and cords).
The spleen cleanses the blood, stores blood platelets, and plays a role in fetal blood cell production.
Lymph nodes are bean-shaped organs located along lymphatic vessels. These bean-shaped nodes have a fibrous capsule with trabeculae extending inward, separating the nodes into compartments composed of cortex and medulla.

B cells can recognize and bind to antigens for adaptive immunity.
T cells only recognize processed antigen fragments associated with MHC molecules
Antigens are broken down into peptide fragments and associated with MHC molecules.
The pathway depends on whether the antigen is outside or inside body cells.
Antigen-presenting cells (APCs) process and present antigens.