Human Anatomy
Glands and Lymphoid Tissue Histology
Glands and lymphoid tissue histology for MBBS: exocrine gland types, serous and mucous acini, lymph node, spleen, thymus and tonsil, mapped to NMC codes AN70.1 and AN70.2.
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Glands and Lymphoid Tissue Histology
Glands and lymphoid tissue histology for MBBS: exocrine gland types, serous and mucous acini, lymph node, spleen, thymus and tonsil, mapped to NMC codes AN70.1 and AN70.2.
This chapter classifies exocrine glands and distinguishes serous, mucous and mixed secretory units. It then describes the microscopic structure of the lymph node, spleen, thymus and tonsil and their roles in immunity.
High-yield: Glands and Lymphoid Tissue Histology
- Glands are classified as exocrine, which secrete through ducts, and endocrine, which release into the blood.
- Exocrine glands are grouped by shape into tubular, acinar and tubuloacinar, and by branching into simple and compound.
- Serous acini secrete a watery, enzyme-rich fluid and have rounded nuclei and a narrow lumen.
- Mucous acini secrete viscid mucus and have flattened basal nuclei and a pale cytoplasm.
- Mixed glands, such as the submandibular gland, have serous demilunes capping mucous acini.
- The parotid gland is purely serous while the sublingual gland is predominantly mucous.
- Lymphoid tissue includes lymph nodes, spleen, thymus, tonsils and diffuse mucosa-associated lymphoid tissue.
- A lymph node has an outer cortex with lymphoid follicles, a paracortex and an inner medulla with cords and sinuses.
- The germinal centres of lymphoid follicles are sites of B lymphocyte proliferation.
- The paracortex of the lymph node is the thymus-dependent zone rich in T lymphocytes.
- The spleen has white pulp of lymphoid tissue around arteries and red pulp that filters blood.
- The splenic white pulp includes periarteriolar lymphatic sheaths of T cells and follicles of B cells.
- The thymus has a cortex densely packed with lymphocytes and a medulla containing Hassall's corpuscles.
- Hassall's corpuscles are whorls of epithelial reticular cells unique to the thymic medulla.
- The palatine tonsils are covered by stratified squamous epithelium with deep crypts and underlying follicles.
Secretory acini and lymphoid landmarks
- **Serous acinus:** Watery enzyme-rich secretion; rounded nuclei, narrow lumen. Parotid gland is purely serous.
- **Mucous acinus:** Viscid mucus; flattened basal nuclei, pale cytoplasm. Serous demilunes cap mixed glands.
- **Lymph node zones:** Cortex with B-cell follicles, paracortex rich in T cells, medulla with cords and sinuses.
- **Thymus:** Cortex packed with lymphocytes; medulla contains distinctive Hassall's corpuscles.
NMC competencies in this chapter
- **AN70.1:** Identification of exocrine glands and distinction between serous, mucous and mixed acini
- **AN70.2:** Microanatomy of lymph node, spleen, thymus and tonsil with structure-function correlation
Frequently Asked Questions
How do serous and mucous acini differ under the microscope?
Serous acini have rounded, basal nuclei and a granular cytoplasm and secrete a watery enzyme-rich fluid. Mucous acini have flattened basal nuclei and a pale, foamy cytoplasm and secrete viscid mucus.
What are Hassall's corpuscles?
They are whorled clusters of epithelial reticular cells found only in the medulla of the thymus, and they are a reliable histological marker of thymic tissue.
How is a lymph node organised?
It has an outer cortex with B-cell follicles and germinal centres, a paracortex rich in T cells, and a medulla with medullary cords and sinuses through which lymph filters.
What is the difference between white and red pulp of the spleen?
White pulp is lymphoid tissue arranged around arteries and mounts immune responses, while red pulp filters the blood and removes old red cells.
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