Skip to main content
UploadLanguage (EN)Support
BusinessMobileSocial MediaMarketingTechnologyArt & PhotosCareerDesignEducationPresentations & Public SpeakingGovernment & NonprofitHealthcareInternetLawLeadership & ManagementAutomotiveEngineeringSoftwareRecruiting & HRRetailSalesServicesScienceSmall Business & EntrepreneurshipFoodEnvironmentEconomy & FinanceData & AnalyticsInvestor RelationsSportsSpiritualNews & PoliticsTravelSelf ImprovementReal EstateEntertainment & HumorHealth & MedicineDevices & HardwareLifestyle
Uploaded byemdadhussain840
PPTX, PDF152 views

Thymus presentation ajajksskksksks THYMUS.pptx

The thymus is a primary lymphoid organ responsible for the maturation of T lymphocytes, fully formed at birth and beginning to involute after puberty. It consists of a bi-lobed structure with a connective tissue framework, including a cortex densely packed with developing thymocytes and a medulla containing Hassall's corpuscles. The thymus is crucial for developing immunocompetent T cells, with implications for conditions such as DiGeorge's syndrome and the effects of thymectomy in autoimmune diseases.

Education◦
Download to read offline
THYMUS Dr. Pradipta Ray Choudhury MBBS, MD, PhD Associate Professor of Anatomy, SMCH, Silchar
• Thymus is a primary lymphoid organ & the site of maturation of T lymphocytes. • thymus is fully formed & functional at birth (c.f. LN, spleen, tonsil etc. are under-developed at birth) continues to grow until puberty then begins to involute & replaced by fatty tissue.
Thymus - It is a bi-lobed structure in thorax. - It has only efferent lymphatic. Child
STRUCTURE A. Connective tissue framework - Capsule - septae/trabeculae - cellular reticulum- formed by epithelial reticular cells. B. Parenchyma 1. Cortex 2. Medulla and Hassall’s corpuscle.
 Covered by a connective tissue capsule. From capsule many septa/ trabeculae extend to the interior.  capsule and trabeculae contain blood vessels, lymphatics and nerves. A. Connective tissue framework
• These septa divide thymus into many incomplete lobules. • Each lobule has an outer dark stained cortex & an inner light stained medulla.
The medulla of adjacent lobules are continuous
• The supporting stroma of the organ within the lobule is formed by epithelial reticular cells. • These are stellate cells & their cytoplasmic processes come in contact with the processes of neighbouring cells thus forming a cellular reticulum within the thymus.
This reticulum is different from the reticulum of other lymphoid organs where it is formed by reticular fibres.
• In between the epithelioreticular cells, developing T lymphocytes (Thymocytes) are found.
Epithelioreticular cells/ Epitheliocytes: • Form the structural framework of thymus. • 6 types are recognised: Type I to type VI. • Secrete hormones like Thymulin, Thymopoietin, Thymosin etc. necessary for T lymphocytes differentiation.
The epithelioreticular cells envelop the thymic blood capillaries to form the blood- thymic barrier.
Blood–Thymic Barrier • It protects developing T lymphocytes in the thymus from exposure to antigens present in blood (which may influence the developing T lymphocytes) It is formed by: 1. Endothelium with basal lamina 2. perivascular space containing Macrophages 3. Type I Epithelio-reticular cells
Perivascular connective tissue with macrophage lined by endothelium
Parenchyma: Cortex The cortex is darkly stained because it is densely packed with developing T-lymphocytes (thymocytes). - Also contain few macrophages and epithelioreticular cells(type I,II,III).
T lymphocytes
T-lymphocyte of thymus/Thymocyte: T cell precursors (lymphoblasts) arrive in thymus from bone marrow. • thus the outer cortex contains larger lymphocytes divide to form smaller maturing lymphocytes which then move into deeper cortex & then the medulla.
ultimately the thymocytes leave the thymus as immunocompetent T lymphocytes are released in circulation through blood vessels & lymphatics.
Medulla and Hassall’s Corpuscle Medulla is lightly stained because the lymphocytes are less densely packed. - For this reason the epitheliocytes (type IV, V & type VI) in the medulla appear to be numerous.
MEDULLA
- The most characteristic feature of the medulla is the presence of thymic (Hassall’s) corpuscles. - these are acidophillic (pink stain) small rounded structures - are made up of closely packed, concentrically arranged epithelio-reticular cells (type VI).
MEDULLA WITH CORPUSCLE
• Each corpuscle has a central core formed by degenerating epitheliocytes & macrophages. • number of Hassall’s corpuscles increases with increasing age. • functional significance of Hassall’s corpuscles is not known.
FUNCTIONS of thymus: • thymus receives stem cells from bone marrow mature T lymphocytes are formed (involved in cell mediated immunity). • mature T lymphocytes are then carried to the lymph node, spleen and other lymphatic tissue. in thymus
• Thus Thymus is considered as a central lymphoid organ and is essential till puberty. • After puberty the other lymphatic tissues of the body are fully developed; hence thymus gets atrophied.
• Removal of thymus in newborn → failure of seeding of other lymphoid organs with immunocompetent T cells → deficiency in immunological competence to fight against invading pathogens → infection → death.
Applied importance: 1.DiGeorge's syndrome : Congenital failure of the thymus to develop. 2. Thymectomy is done in severe autoimmune diseases.
The End EDUCATION OF T LYMPHOCYTES
Thymus in children Thymus in adult
Mucosa-Associated Lymphoid Tissue (MALT) • Mucosa-associated lymphoid tissue (MALT) is localized lymphocyte aggregation in the mucosa of the gastrointestinal, respiratory tracts. • Types: Gut-associated lymphoid tissue (GALT), Bronchus-associated lymphatic tissue (BALT).
MALT In GIT – gut associated lymphoid tissue(GALT): - Aggregated nodules (Peyer’s patches) - Lymphoid nodules in vermiform appendix - tonsils: form Waldeyer’s lymphoid ring at the entrance of pharynx
Tonsils: • These are a number of collection of lymphoid tissues at the junction of the oral cavity and pharynx. • they guard the entrance to the pharynx. • They produce immune response against the airborne and ingested antigens.
• Types: palatine, pharyngeal, lingual, & tubal tonsils. lingual tonsil: present on the dorsum of posterior 1/3rd of tongue. pharyngeal tonsil: single mass situated in the posterior wall of the nasopharynx. Tubal tonsil: around the pharyngeal opening of auditory tube
• The largest of these are the right and left palatine tonsils, present on either side of the oropharyngeal isthmus.
Palatine tonsil • palatine tonsils are paired structures • The outer surface is covered by a connective tissue capsule.
• The superficial aspect of the tonsils is covered by stratified squamous nonkeratinized epithelium. • The epithelium dips into the substance of tonsil in the form of several tonsillar crypts (10 - 12 in number)
• The parenchyma of the tonsil is composed of numerous lymphoid nodules, many of which display germinal centres. Tonsillitis: enlargement of tonsils due to infection/allergy.
The End EDUCATION OF T LYMPHOCYTES