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What is the primary function of the thymus in the lymphoid system?
What is the primary function of the thymus in the lymphoid system?
What is the function of Hassall's corpuscles in the thymus?
What is the function of Hassall's corpuscles in the thymus?
What is the purpose of the blood-thymic barrier in the thymus?
What is the purpose of the blood-thymic barrier in the thymus?
Which of the following is NOT a function of the spleen during fetal life?
Which of the following is NOT a function of the spleen during fetal life?
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What occurs to the thymus after puberty?
What occurs to the thymus after puberty?
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What is the main function of the white pulp in the spleen?
What is the main function of the white pulp in the spleen?
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What is the primary function of epithelial reticular cells in the thymus?
What is the primary function of epithelial reticular cells in the thymus?
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Which of the following zones is rich in T-lymphocytes and plasma cells?
Which of the following zones is rich in T-lymphocytes and plasma cells?
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What is the primary function of the cortex in the thymus?
What is the primary function of the cortex in the thymus?
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What is the function of the reticular stroma in the spleen?
What is the function of the reticular stroma in the spleen?
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What is the relationship between the trabeculae and the capsule in the thymus?
What is the relationship between the trabeculae and the capsule in the thymus?
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What is the function of the trabeculae in the spleen?
What is the function of the trabeculae in the spleen?
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Study Notes
Lymphoid (Immune) System
- Responsible for protecting the body against invading microorganisms or foreign bodies
- Distributed throughout the body, consisting of aggregations of lymphocytes (B and T lymphocytes) and epithelial cells
Lymphatic Tissues (Organs)
- Classified into primary or central lymphoid organs and secondary or peripheral lymphoid organs
- Primary lymphoid organs: thymus and bone marrow, where B and T lymphocytes develop
- Secondary lymphoid organs: spleen, lymph nodes, tonsils, appendix, Peyer's patches, and solitary lymphatic nodules, where B and T lymphocytes settle
Thymus
- Flattened bilobed organ lying behind the sternum
- Large in infants, grows until puberty, then diminishes in size
- Consists of stroma and parenchyma
- Stroma:
- Capsule: thin connective tissue (C.T.)
- Trabeculae: thin septae of C.T. dividing the gland into 2 main lobes and incomplete lobules
- Parenchyma:
- Cortex: outer dark part, contains thymocytes (T lymphocytes), epithelial reticular cells (APCs), and macrophages
- Medulla: inner pale part, contains thymocytes (T lymphocytes), epithelial reticular cells (APCs), macrophages, and Hassall's corpuscles
- Hassall's corpuscles: large rounded structures composed of concentric layers of epithelial reticular cells around a central hyaline acidophilic mass
- Functions:
- Site for development and differentiation of T lymphocytes
- Production of T lymphocytes
- Secretion of thymic hormones
- Formation of Blood-thymic barrier: protects newly formed T-lymphocytes from circulating antigen
Spleen
- Single intra-abdominal organ covered by peritoneum
- Consists of stroma and parenchyma
- Stroma:
- Capsule: covered by peritoneum, formed of dense C.T. and smooth muscle fibers
- Trabeculae: radiate from the hilum, carrying blood vessels
- Reticular stroma: supports the organ
- Parenchyma:
- White pulp (splenic nodules or Malpighian corpuscles): formed of 4 zones
- Thymus-dependent zone: rich in T-lymphocytes
- Germinal center zone: rich in B-lymphocytes
- Follicular zone: rich in B-lymphocytes
- Marginal zone: rich in T-lymphocytes and plasma cells
- Red pulp:
- Blood sinusoids: wide blood spaces lined with flat cells and phagocytic cells
- Splenic cords: lymphatic tissue containing blood cells, plasma cells, and macrophages
- White pulp (splenic nodules or Malpighian corpuscles): formed of 4 zones
- Functions:
- Hemopoiesis of blood elements during fetal life
- Production of lymphocytes (role in humoral and cell-mediated immunity)
- Destruction of abnormal, damaged, and aged blood cells
- Blood filtration from bacteria, foreign bodies, old RBCs, WBCs, and platelets
- Storage of blood
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Description
This quiz covers the lymphoid system, responsible for protecting the body against microorganisms, and its primary and secondary organs, including the thymus, bone marrow, spleen, and lymph nodes.
