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Questions and Answers
What is one of the primary roles of stellate TECs in the thymus?
What is one of the primary roles of stellate TECs in the thymus?
What do the junctions formed by squamous TECs primarily consist of?
What do the junctions formed by squamous TECs primarily consist of?
What do stellate TECs provide for thymocytes?
What do stellate TECs provide for thymocytes?
How do stellate TECs contribute to T cell development?
How do stellate TECs contribute to T cell development?
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What type of barrier is formed between the cortex and medulla of the thymus?
What type of barrier is formed between the cortex and medulla of the thymus?
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What characterizes the mature T lymphocytes in the inner medulla?
What characterizes the mature T lymphocytes in the inner medulla?
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What is the role of Hassall corpuscles in the inner medulla?
What is the role of Hassall corpuscles in the inner medulla?
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Which cells in the inner medulla are described as antigen-presenting cells (APCs)?
Which cells in the inner medulla are described as antigen-presenting cells (APCs)?
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What feature do Stellate TECs lack in the inner medulla?
What feature do Stellate TECs lack in the inner medulla?
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What is the primary function of the thymus gland?
What is the primary function of the thymus gland?
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What happens to mature T lymphocytes in the inner medulla?
What happens to mature T lymphocytes in the inner medulla?
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Which of the following correctly describes the composition of the inner medulla?
Which of the following correctly describes the composition of the inner medulla?
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Which organ is responsible for the maturation of B lymphocytes?
Which organ is responsible for the maturation of B lymphocytes?
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Which type of TECs are described as supportive in the inner medulla?
Which type of TECs are described as supportive in the inner medulla?
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What defines self-tolerance in the immune system?
What defines self-tolerance in the immune system?
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What is one function of cytokines released in the inner medulla?
What is one function of cytokines released in the inner medulla?
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Which of the following is NOT a secondary lymphoid organ?
Which of the following is NOT a secondary lymphoid organ?
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Which of the following best describes the Mucosa-associated Lymphoid Organs (MALT)?
Which of the following best describes the Mucosa-associated Lymphoid Organs (MALT)?
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What anatomical condition occurs to the thymus gland after puberty?
What anatomical condition occurs to the thymus gland after puberty?
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What role does positive and negative selection play in the thymus?
What role does positive and negative selection play in the thymus?
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Which of the following functions does the spleen perform?
Which of the following functions does the spleen perform?
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Which statement about immuno-competent cells is correct?
Which statement about immuno-competent cells is correct?
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What occurs to immature lymphocytes as they exit the primary lymphoid organs?
What occurs to immature lymphocytes as they exit the primary lymphoid organs?
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What is the primary function of lymph nodes in the immune system?
What is the primary function of lymph nodes in the immune system?
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What distinguishes primary lymphoid nodules from secondary lymphoid nodules?
What distinguishes primary lymphoid nodules from secondary lymphoid nodules?
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Which statement best describes the role of high endothelial venules (HEVs) in lymphocytes?
Which statement best describes the role of high endothelial venules (HEVs) in lymphocytes?
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What type of immunity is primarily stimulated by the activation of B lymphocytes?
What type of immunity is primarily stimulated by the activation of B lymphocytes?
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How do lymphocytes contribute to the immune surveillance of the body?
How do lymphocytes contribute to the immune surveillance of the body?
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What process occurs when normal red blood cells (RBCs) are determined to be functioning properly?
What process occurs when normal red blood cells (RBCs) are determined to be functioning properly?
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Which of the following correctly describes the role of macrophages in the spleen?
Which of the following correctly describes the role of macrophages in the spleen?
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In which anatomical location is mucosa-associated lymphoid tissue (MALT) primarily found?
In which anatomical location is mucosa-associated lymphoid tissue (MALT) primarily found?
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What type of cells primarily produce secretory IgA in MALT?
What type of cells primarily produce secretory IgA in MALT?
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What is a characteristic feature of the spleen's vascular supply?
What is a characteristic feature of the spleen's vascular supply?
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What type of immunity is primarily associated with B cells?
What type of immunity is primarily associated with B cells?
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Which structure in the lymph node is associated with T cells?
Which structure in the lymph node is associated with T cells?
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What is the main role of high endothelial venules (HEVs) in the lymph node?
What is the main role of high endothelial venules (HEVs) in the lymph node?
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What type of cell acts as a scavenger in both the B cell and T cell armies?
What type of cell acts as a scavenger in both the B cell and T cell armies?
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What are the lymphoid nodules primarily found in the lymph node cortex called?
What are the lymphoid nodules primarily found in the lymph node cortex called?
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Which cell type is not considered an antigen-presenting cell (APC) in the B cell army?
Which cell type is not considered an antigen-presenting cell (APC) in the B cell army?
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What is the primary function of the lymph node's filtration process?
What is the primary function of the lymph node's filtration process?
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In which region of the lymph node would you find activated T and B cells?
In which region of the lymph node would you find activated T and B cells?
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What is the primary composition of the stroma in lymph nodes?
What is the primary composition of the stroma in lymph nodes?
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Which cytokines are primarily released by high endothelial venules (HEVs)?
Which cytokines are primarily released by high endothelial venules (HEVs)?
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Study Notes
Lymphoid Organs
- Lymphoid organs are aggregates of immune cells, specialized for protection. The primary function is defense against infections and tumors, and repair of dead cells and tissue.
- The immune system may abnormally attack normal cells causing inflammatory diseases like rheumatoid arthritis and systemic lupus erythematosus. This happens when immune system attacks self-antigens.
- Self-tolerance means immune system doesn't react against self-antigen.
Learning Objectives
- LO1: Importance of lymphoid organs - defense against infections and tumors, tissue repair
- LO2: Types of lymphoid organs
- LO3: Structure and function of thymus gland, role in T cell maturation and selection
- LO4: Structure and function of lymph nodes
- LO5: Structure and function of spleen
- LO6: Mucosa-associated lymphoid organs (MALT)
- LO7: HEVs and lymphocyte recirculation
Classification of Lymphoid Organs
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Primary Lymphoid Organs (Lymphocyte Differentiation):
- Also called central lymphoid organs
- Sites of immature lymphocyte development, proliferation, and maturation of stem cells
- Includes thymus and bone marrow
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Secondary Lymphoid Organs (Lymphocyte Activation):
- Sites where antigens are localized for effective exposure to mature lymphocytes.
- Initiate adaptive immune responses.
- Includes lymph nodes, tonsils, appendix, Peyer's patches, and mucosa-associated lymphoid tissue (MALT).
Thymus Gland
- Site: Superior mediastinum, behind the sternum.
- Shape: Bilobed. Present in children; atrophied in adults.
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Function:
- Promotes T lymphocyte production and maturation.
- Educates developing thymocytes through positive and negative selection.
- Promotes central tolerance (prevents autoimmunity) by selectively removing T cells reactive against self-antigens.
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Structure:
- Stroma (thin capsule, septa/trabeculae, epithelial cells)
- Parenchyma (thymic lobules, cortex, medulla).
Thymic Lobule
- Contains cortex and medulla
- T-lymphocytes are in the cortex, mature T cells move to medulla.
- Inner cortex- squamous TECs, form cortico-medullary barrier.
- Outer cortex- stellate TECs, present self/non-self antigens to test efficiency, act as antigen-presenting cells.
- The cortex and medulla are crucial for T cell development.
Inner Medulla
- Mature T lymphocytes (fewer, less densely packed, larger and lightly stained)
- Medulla lacks blood thymic barrier; lymphocytes easily leave for the blood.
- Stellate TECs do not secrete cytokines.
- Hassall corpuscles (unique to medulla) support development of dendritic cells and the maturing of T cells.
Lymph Node Structure
- Site: Various locations throughout the body.
- Shape: Bean-shaped.
- Surfaces: Convex and concave.
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Structure:
- Stroma (capsule, trabeculae, supporting reticular tissue)
- Parenchyma (cortex, paracortex, medulla)
- 3 distinct regions (cortex, paracortex, medulla)
- Cortex has B cell zones, paracortex has T cell zones
- Medulla has medullary cords, consisting of T cells, B cells, antibodies, macrophages, etc.
Lymph Node Function "Antigen Supply"
-
Humoral Immune Response (B cells):
- B cell activation leads to plasma cell production and distribution of antibodies.
-
T cell activation and interaction:
- T cells activated in the paracortex of the lymph node.
- Lymph node acts as a filter for microbes.
High Endothelial Venules (HEVs)
- Major source of lymphocytes in lymph nodes (90%)
- Involved in lymphocyte recirculation; found in paracortex
- Allows lymphocytes to enter lymph nodes
Spleen
- Site: Left upper quadrant of the abdomen.
-
Structure:
- Stroma (capsule, trabeculae, supporting reticular tissue)
- Parenchyma (white pulp, red pulp - responsible for the red color)
-
Function:
- Filtration of blood; removal of damaged red blood cells (RBCs); lymphocyte activation and antibody production.
- Provides environment for B and T cell activation, antibody production, and removal of worn/damaged RBCs.
Spleen Vascular Supply and Function
- Closed circulation: Filtered blood communicates with spleen sinusoids for filtration and then returns to the vascular system
- Open circulation: Blood diffuses freely into the red pulp, allowing for filtering and processing of blood components.
Mucosa-Associated Lymphoid Tissue (MALT)
- Non-capsulated collections of lymphocytes, plasma cells, antigen-presenting cells (APCs) and lymphoid nodules.
- Located in respiratory, genitourinary, and gastrointestinal tracts.
- Dominant cell type is B cells, producing secretory IgA, targeting pathogens.
Peyer's Patches
- Specialized tissue in the ileum (part of the small intestine).
- Composed of lymphoid follicles and M cells (modified epithelial cells).
- Antigens pass through M cells to trigger immune responses.
Lymphocyte Recirculation
- Lymphocytes continuously circulate between blood, spleen, lymph nodes, and other lymphoid organs.
- Provides constant monitoring of the body and enhances exposure to foreign antigens.
T Cell Selection and Maturation
- Selection process educates T cells not to recognize/strongly bind to self-antigens.
- Positive Selection (Cortex): T cells test receptor efficiency; If they bind to self-antigen (negative outcome), they are marked for apoptosis (programmed cell death).
- Negative Selection (Medulla): Dendritic cells present self/non-self antigens; if they bind to self antigen (negative outcome) they die by apoptosis, otherwise they are kept.
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Description
This quiz explores the lymphoid organs and their crucial role in the immune system. You'll learn about the types, structures, and functions of key lymphoid organs like the thymus, lymph nodes, and spleen. Additionally, it covers the implications of immune system dysfunction and self-tolerance.