16 Questions
What is the function of the semilunar valves in lymph vessels?
To prevent the backflow of lymph
What is the main difference between lymph and blood plasma?
Lymph has a higher proportion of lymphocytes
What is the function of stromal cells in bone marrow?
To provide a microenvironment for hematopoiesis
What type of cells are present in the thymus?
Thymocytes, epithelial cells, and other immune cells
What is the function of the thymus?
To help immature T cells develop
Where do lymph vessels return lymph to?
The subclavian veins
What type of tissue is bone marrow?
Semi-solid
What is the term for the process of producing new blood cells?
Hematopoiesis
What is the main function of the thymus?
To mature T cells
What is the main difference between the cortex and the medulla in the thymus?
The cortex is richer in cells than the medulla
Where are T cells mainly found in the lymph node?
In the paracortex
What is the function of the afferent lymph vessels in the lymph node?
To bring lymph into the lymph node
What is the function of the medulla in the lymph node?
To store plasma cells and macrophages
What is the purpose of negative selection in the thymus?
To eliminate T cells that react to body tissues
Where is the thymus located in the body?
In the upper chest under the breastbone
What is the main function of secondary lymphoid organs?
To initiate an adaptive immune response
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.
Test your knowledge of the lymphatic system, its components, and functions.
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