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Questions and Answers
What is the function of the semilunar valves in lymph vessels?
What is the function of the semilunar valves in lymph vessels?
What is the main difference between lymph and blood plasma?
What is the main difference between lymph and blood plasma?
What is the function of stromal cells in bone marrow?
What is the function of stromal cells in bone marrow?
What type of cells are present in the thymus?
What type of cells are present in the thymus?
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What is the function of the thymus?
What is the function of the thymus?
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Where do lymph vessels return lymph to?
Where do lymph vessels return lymph to?
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What type of tissue is bone marrow?
What type of tissue is bone marrow?
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What is the term for the process of producing new blood cells?
What is the term for the process of producing new blood cells?
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What is the main function of the thymus?
What is the main function of the thymus?
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What is the main difference between the cortex and the medulla in the thymus?
What is the main difference between the cortex and the medulla in the thymus?
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Where are T cells mainly found in the lymph node?
Where are T cells mainly found in the lymph node?
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What is the function of the afferent lymph vessels in the lymph node?
What is the function of the afferent lymph vessels in the lymph node?
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What is the function of the medulla in the lymph node?
What is the function of the medulla in the lymph node?
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What is the purpose of negative selection in the thymus?
What is the purpose of negative selection in the thymus?
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Where is the thymus located in the body?
Where is the thymus located in the body?
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What is the main function of secondary lymphoid organs?
What is the main function of secondary lymphoid organs?
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Study Notes
Lymphatic System
- Consists of a large network of lymphatic vessels, lymph nodes, and lymphoid tissues.
- Carries a clear fluid called lymph, which is similar to blood plasma, containing waste products, cellular debris, bacteria, and proteins.
Lymphatic Vessels
- Consist of functional units called lymphangions, separated by semilunar valves.
- These segments propel or resist the flow of lymph by the contraction of the encircling smooth muscle, depending on the ratio of its length to its radius.
- Lymph ducts return lymph to the bloodstream by emptying into the subclavian veins.
Lymphoid Tissues
- Primary lymphoid organs: bone marrow and thymus.
- Peripheral lymphoid organs: lymph nodes, spleen, and mucosallymphoid tissues.
Bone Marrow
- A semi-solid tissue within the spongy portions of bones.
- Involved in new blood cell production (hematopoiesis) and production and early clonal selection of lymphocyte tissues.
- Stromal cells are involved in hematopoiesis, providing a microenvironment that influences the function and differentiation of hematopoietic cells.
Thymus
- Made up of immature T cells (thymocytes) and lining cells (epithelial cells) that help thymocytes develop.
- Consists of two lobes, merged in the middle, surrounded by a capsule with blood vessels extending into the interior.
- Cortex is rich with cells, and medulla is less dense with a coarser network of epithelial cells.
Functions
- T cells begin as hematopoietic precursors from the bone marrow and migrate to the thymus for maturation.
- Maturation involves positive selection (reacting against antigens) and negative selection (not reacting against antigens found on body tissue).
- Once mature, T cells emigrate from the thymus to provide vital functions in the immune system.
Lymph Nodes
- Secondary lymphoid organs that maintain mature naive lymphocytes and initiate an adaptive immune response.
- Each lymph node is surrounded by a fibrous capsule, divided into the outer cortex and inner medulla.
- B cells are mainly found in the outer cortex, while T cells and dendritic cells are found in the paracortex.
- The medulla contains plasma cells and macrophages within the medullary sinuses.
Afferent and Efferent Vessels
- Afferent lymph vessels enter the lymph node at all parts of the periphery, forming a dense plexus in the substance of the capsule.
- Efferent lymphatic vessels commence from the lymph sinuses of the medullary portion of the lymph node.
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Test your knowledge of the lymphatic system, its components, and functions.
