[Durgical](https://durgical.com/en/) › [DurgiPedia](https://durgical.com/en/durgipedia/) › [Histology](https://durgical.com/en/histology/) › [Lymphoid organs](https://durgical.com/en/histology/#a-lymphoid) › Thymus and tonsils under the microscope [Histology](https://durgical.com/en/histology/) · [Lymphoid organs](https://durgical.com/en/histology/#a-lymphoid) # Thymus and tonsils under the microscope - Organ The thymus is where T cells mature and it has no follicles. The tonsils are lymphoid nodules under the lining of the throat, with deep crypts. Updated 2026-11-01 **See it in 3D:** [Thymus](https://durgical.com/en/anatomy/thymus/) · [Palatine tonsils](https://durgical.com/en/anatomy/palatine-tonsil/) ## Key points - Hassall's corpuscles in the medulla: the clue that identifies the thymus. - The normal thymus has no lymphoid follicles, no germinal centres and no afferent lymphatics. - The thymic stroma is epithelial and comes from third pharyngeal pouch endoderm; it is missing in DiGeorge syndrome. - Palatine: stratified squamous epithelium and deep crypts; pharyngeal: ciliated respiratory epithelium. - In myasthenia gravis there may be thymic hyperplasia with germinal centres, or a thymoma. ## What it is The thymus is a primary lymphoid organ divided into lobules, each with a dark cortex packed with thymocytes and a pale medulla with Hassall's corpuscles; its framework is made of epithelial cells, not reticular fibres. The tonsils are mucosa-associated lymphoid tissue with no complete capsule, and follicles with germinal centres just under the epithelium. This page describes what you see under the microscope; the immune function of both is covered in the Immunology section. ## Structure - Thymus: a thin capsule with septa that divide it into incomplete lobules; the medulla of neighbouring lobules is continuous. - Thymic cortex: dark because thymocytes are densely packed, with thymic epithelial cells and macrophages that engulf dying thymocytes. - Thymic medulla: paler, with fewer thymocytes and with Hassall's corpuscles (concentric layers of epithelial cells, sometimes keratinized at the centre). - Blood-thymus barrier in the cortex: continuous capillaries wrapped by epithelial cells. - With age the thymus involutes: its lymphoid tissue is replaced by fat, although islands of thymic tissue remain. - Palatine tonsil: non-keratinized stratified squamous epithelium dipping into deep crypts; under it, follicles with germinal centres; a partial capsule on the deep side only. - Pharyngeal tonsil (adenoids): ciliated pseudostratified columnar respiratory epithelium, with folds rather than deep crypts. - Lingual tonsil: at the base of the tongue, stratified squamous epithelium with simple crypts. ## Clinical notes - The crypts of the palatine tonsil trap debris and bacteria; they are where tonsillitis and peritonsillar abscess begin. - Group A streptococcal pharyngitis and infectious mononucleosis enlarge the tonsils. - The crypt epithelium is a common site of origin of HPV-associated oropharyngeal carcinoma. ## Memory aid The thymus has no follicles, it has «onions»: Hassall's corpuscles look like concentric rings in the pale medulla. ## Test yourself Think of the answer, then tap the question to see it. ## Which structure in the medulla identifies the thymus under the microscope? Hassall's corpuscles, made of concentric layers of epithelial cells. ## Why does the thymic cortex stain darker than the medulla? It holds many more tightly packed thymocytes, whose nuclei take up the hematoxylin. ## Which epithelium lines the palatine tonsil? Non-keratinized stratified squamous epithelium that dips down to form crypts. ## What happens to the thymus with age? It involutes: its lymphoid tissue is gradually replaced by fat. [Add to my cards (4)](https://durgical.app/estudiar/?add=/en/histology/thymus-and-tonsils-under-the-microscope/) ## See it in 3D The structures of Durgical's 3D anatomy where it is found. - [Thymus](https://durgical.com/en/anatomy/thymus/) - [Palatine tonsils](https://durgical.com/en/anatomy/palatine-tonsil/) ## Related - [Lymph node and spleen under the microscope](https://durgical.com/en/histology/lymph-node-and-spleen-under-the-microscope/) - [Simple, stratified, pseudostratified and transitional epithelium](https://durgical.com/en/histology/simple-stratified-pseudostratified-and-transitional-epithelium/) - [Adipose tissue: white and brown fat](https://durgical.com/en/histology/adipose-tissue-white-and-brown-fat/) - [Oral cavity, tongue and teeth](https://durgical.com/en/histology/oral-cavity-tongue-and-teeth/) - [Enteroendocrine cells and GALT](https://durgical.com/en/histology/enteroendocrine-cells-and-galt/) ## Related conditions - [Peritonsillar abscess](https://durgical.com/en/conditions/peritonsillar-abscess/) - [Streptococcal pharyngitis](https://durgical.com/en/conditions/streptococcal-pharyngitis/) ## Microorganisms - [Streptococcus pyogenes](https://durgical.com/en/microbiology/streptococcus-pyogenes/) - [Epstein–Barr virus](https://durgical.com/en/microbiology/epstein-barr-virus/) [← All of histology](https://durgical.com/en/histology/) Educational content on normal microscopic structure and its clinical relevance; no substitute for studying slides or for a health professional's advice. Sources: [21.1 Anatomy of the Lymphatic and Immune Systems](https://openstax.org/books/anatomy-and-physiology-2e/pages/21-1-anatomy-of-the-lymphatic-and-immune-systems) (OpenStax, Anatomy and Physiology 2e, 2022); [Thymus](https://training.seer.cancer.gov/anatomy/lymphatic/components/thymus.html) (NCI SEER Training Modules, 2026); [Components of the Lymphatic System](https://training.seer.cancer.gov/anatomy/lymphatic/components/) (NCI SEER Training Modules, 2026). ## **Spotted a mistake?** We are always improving for the community. Tell us what is wrong and our team will review it. Report a mistake Representative model, for educational purposes only. --- Source: https://durgical.com/en/histology/thymus-and-tonsils-under-the-microscope/ License: CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Cite as: DurgiPedia (durgical.com), https://durgical.com/en/histology/thymus-and-tonsils-under-the-microscope/