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Lymphoid organs

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Lymphoid organs

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Lymphoid organs

  1. 1. IMMUNE SYSTEM AND LYMPHOID ORGANS
  2. 2. IMMUNE SYSTEM  Has the ability to distinguish “self” (body’s own molecules) from “non-self” (foreign substance)  This system has the ability to neutralize or inactivate foreign molecules (virus, bacteria & parasites) and to destroy microorganisms or other cells (e.g. virus infested cells, cancer cell, cells of transplanted organs)
  3. 3. Continued  The cells of the immune system are: a) distributed throughout the body in blood, lymph, epithelial & connective tissue b) are arranged in small spherical nodules called ‘lymphoid nodules’ which are isolated cells of immune system found in the mucosa of GIT, respiratory system, reproductive & urinary system c) are organized in larger lymphoid organs- lymph nodes, spleen, thymus, bone marrow
  4. 4. ANTIGENS  A molecule recognized by the body as ‘foreign’ and is capable of eliciting a response is called an ANTIGEN.  Antigen may consist of proteins, polysaccharides & nucleoproteins  It may be bacteria, protozoa, tumor cells or virus infested cells
  5. 5. ANTIBODIES  Are “glycoproteins” that interacts specifically with an antigen to destroy or inactivate it.  B lymphocytes produce plasma cells which then produce antibodies  The antibodies: a) may circulate in the plasma and reach tissues b) present in secretions of glands i.e. salivary and mammary gland c) integral membrane proteins of the surface of lymphocytes
  6. 6. CLASSES OF ANTIBODIES  Ig G 75-80%. Is only immunoglobulin to cross the placental barrier.  Ig A is found in secretions i.e. nasal, bronchial, intestinal, prostatic & colostrum, saliva, vaginal fluid  Ig M 10%. Found on surface of B lymphocytes functions as its specific receptor for antigen.  Ig E. Present on surface of mast cells & basophils  Ig D. Its functions not completely understood. Found on cell membrane
  7. 7. CELLS OF IMMUNE SYSTEM  Lymphocytes  Plasma cells  Mast cells  Neutrophils  Eosinophils  Cell of mononuclear phagocyte system
  8. 8. LYMPHOCYTES  T lymphocytes  B lymphocytes  NATURAL KILLER lymphocytes  PRECURSORS OF ALL LYMPHOCYTES TYPES ORIGINATE IN THE BONE MARROW
  9. 9. B LYMPHOCYTES  mature & become functional in the in the bone marrow  leave bone marrow & enter circulation  colonize C.T. epithelia, lymphoid nodule, lymphoid organ  After encountering an antigen, they redifferentiate into PLASMA CELLS  Activation of B lymphocytes require assistance of T helper cells  Some lymphocyte differentiate into B memory cells
  10. 10. T LYMPHOCYTES  leave bone marrow & enter circulation  reach thymus & undergo intense proliferation & differentiation / die  after maturation leave thymus  distributed in C.T. & lymphoid organs  constitute 65-70% of blood lymphocytes SUBPOPULATIONS OF T LYMPHOCYTES: - Helper T lymphocytes - Cytotoxic T lymphocytes - Regulatory T lymphocytes
  11. 11.  PRIMARY /CENTRAL LYPHOID ORGANS: - bone marrow - thymus  SECONDARY / PERIPHERAL LYPHOID ORGANS: - spleen - lymph nodes - solitary lymphoid nodules - tonsils - appendix - peyer’s pathces of ileum
  12. 12. TYPES OF IMMUNE RESPONSES  INNATE RESPONSE  ADAPTIVE RESPONSE
  13. 13. INNATE RESPONSE  Include the action of complement system & cells such as neutrophils, macrophages, mast cells & natural killer cells  Is fast  Is non- specific  Does not produce memory cells
  14. 14. ADAPTIVE RESPONSE  Depends on initial recognition of antigen by B & T lymphocytes  Is more complex  Is slower  Is specific  Produces memory cells LEADS TO ELIMINATION OF ANTIGENS  HUMORAL RESPONSE  CELLLULAR RESPONSE
  15. 15.  HUMORAL IMMUNITY: - accomplished by antibodies produced by plasma cells  CELLULAR IMMUNITY: - mediated by T lymphocytes
  16. 16. LYMPHOID TISSUE  is C.T. charecterized by rich supply of lymphocytes  lymphocytes are lying within rich network of reticular fibres (type III collagen produced by reticular cells)  in thymus reticulum is formed by epithelial reticular cells
  17. 17. NODULAR LYMPHOID TISSUE  Groups of lymphocytes are arranged as spherical masses called LYMPHOID NODULES  Lymphoid nodules contain B LYMPHOCYTES  Antigen arrives →B lymphocytes recognizes antigen → nodule becomes activated →B lymphocytes proliferate in centre of nodule→ it stains lighter & is called GERMINAL CENTRE  Lymphoid nodules are found in many C.T. and within lymph nodes, spleen & tonsils. NOT IN THYMUS
  18. 18. THYMUS  bilobed organ  is central or primary lymphoid organ  dual embryological origin  surrounded by connective tissue capsule that sends septae into the parenchyma and divides it into lobules
  19. 19.  capsule consists of collagen & elastic fibres, blood vessels  intra-lobular trabeculae  reticular frame work  each lobule has a cortex & medulla  cortex richer in small lymphocytes, stains darkly  medulla lighter staining
  20. 20.  thymic cortex contains t lymphocytes, macrophages, epithelial reticular cells
  21. 21.  epithelial reticular cells are stellate or squamous with long processes  have large nucle  long procecesses form cytoreticulum
  22. 22.  thymic medulla also contains cytoreticulum of epthelial reticular cells  less densly packed T lymphocytes  has structures called thymic (Hassall’s) corpuscles
  23. 23.  Hassall’s corpuscles consists of epithelial reticular cells arranged concentrically  they are a charecteristic feature of medulla  T LYMPHOCYTES PROLIFERATE & MATURE IN CORTEX. ONLY 2-3% MIGRATE TO MEDULLA WHERE THE ENTER THROUGH THE WALL OF VENULES INTO THE CIRCULATION. REST DIE
  24. 24. BLOOD THYMIC BARRIER  arterioles & capillaries in thymic cortex are sheathed by epithelial reticular cells with tight junctions  capillary endothelium is continuous  basal lamina is thick  these features create a blood thymic barrier  it prevents most of circulating antigens from leaving the blood vessels and entering the cortex  NO such barrier exists in the MEDULLA  THYMUS HAS NO AFFERENT LYMPHATIC VESSELS
  25. 25. THYMUS OF ELDERLY
  26. 26. TONSILS  are organs composed of aggrates of lymphoid tissue which is incompletely encapsulated. they lie beneath & in contact with the epithelium of the initial part of digestive tract  Types:  palatine  pharyngeal  lingual  tubal
  27. 27. PALATINE TONSILS  location  epithelium is stratified squamous  epithelium rests on basal lamina  thin fibrous connective tissue layer deep to epithelium  epithelium in crypts intensly infiltrated with lymphocytes
  28. 28.  10-20 tonsillar crypts  lining of crypt same as surface  secondary crypts  diffuse mass of lymphoid tissue surround crypts  lymph nodules are embedded in them  nodules may contain germinal centres
  29. 29.  CAPSULE  incomplete  Made of dense C.T.
  30. 30.  LINGUAL TONSIL: covered by stratified squamous epithlium - has single crypt  PHARYNGEAL TONSIL: - lined by pseudostratified columnar ciliated epithelium - no crypts  TUBAL TONSIL: - ciliated columnar epithelium
  31. 31. LYMPH NODE  Are encapsulated kidney shaped organs  Lye along the course of blood vessels  Are inline filters  Have a convex side where afferent vessels enter  and concave side (hilus) where efferent vessels leave
  32. 32.  Capsule sends in trabeculae  Framework is made of reticular fibers and macrophages  Parenchyma divided into:  Outer cortex  Inner cortex  Medulla
  33. 33.  Outer cortex  Subcapsular sinus formed by macrophages, reticular cells & fibres  Communicates with medullary sinus through intermediate sinus  Outer cortex made of reticular fibres  Populated with B lymphocytes  Lymph nodules with germinal center present CORTEX
  34. 34.  Inner cortex:  Contains few if any nodules  Many T lymphocytes
  35. 35. MEDULLA OF LYMPH NODE  Medullary cords  Branched extensions of inner cortex  Contain B lymphocytes  Medullary sinuses  Are dilated, irregular spaces containing lymph  Lined by reticular cells & macrophages that form network
  36. 36.  Afferent lymph vessels pour lymph into subcapsular sinus  Lymph pass through intermediate sinus into medulla  Subcapsular sinus slows flow of lymph through node  Lymph collected by efferent lymphatic vessels  As lymph flows through sinuses 99% or more antigens are removed
  37. 37. SPLEEN  FUNCTIONS:  Filtration of blood  Destruction of aged RBC  Produces antibodies & activated lymphocytes
  38. 38. SPLEEN  Location  Surrounded by capsule  Trabeculae  Incomplete division of parenchyma or splenic pulp  Hilum
  39. 39. SPLEEN  Splenic pulp divided into:  White pulp  Red pulp  WHITE PULP  Lymphoid nodules  Periarteriolar lymphatic sheath  RED PULP  Sinusoids  Splenic cords
  40. 40. WHITE PULP  Splenic artery divide to trabecular artery  Enter parenchyma  Enveloped by sheath of T lymphocytes (PALS)  Called ‘central arterioles’  PALS receive B lymphocytes & form nodules  Penicillar arterioles
  41. 41. RED PULP  Splenic cords composed of reticular fibres, T & B lymphocytes, macrophages etc  They are seperated by irregular shaped sinusoids  Sinusoid lined by elongated endothelium called ‘stave cells’  Incomplete basal lamina
  42. 42. BLOOD FLOW IN RED PULP  CLOSED CIRCULATION:  Pencilar arterioles connect directly to sinusoids  OPEN CIRCULATION:  Pencillar arterioles dump blood into stroma
  43. 43. ESOPHAGUS  Is muscular tube  Extent  Wall has four layers:  Mucosa  Epithelium  Basement membrane  Lamina propria  Muscularis interna or muscularis mucosae  Submucosa  Muscularis externa  serosa
  44. 44. UPPER 1/3 OF ESOPHAGUS  MUCOSA  Epumithelium: Stratified squamous non-keratinized  Lamina propria: scattered lymphocytes, few lymphatic nodules, mucous glands, blood vessels  Muscularis mucosae: thick, striated muscles  SUB-MUCOSA  Collagen & elastic fibres, mucous glands, blood vessels, nerves  MUSCULARIS EXTERNA  Skeletal /striated muscles  ADVENTITIA  Collagen & elastic fibers, blood vessels
  45. 45. MIDDLE 1/3 OF ESOPHAGUS  MUCOSA  Epithelium: stratified squamous non- keratinized  Lamina prppria: : scattered lymphocytes, few lymphatic nodules, mucous glands, blood vessels  Muscularis mucosae: thick, striated muscles  SUB-MUCOSA  Collagen & elastic fibres, mucous glands, blood vessels, nerves  MUSCULARIS EXTERNA  Skeletal striated muscles, smooth muscles  ADVENTITIA  Collagen & elastic fibers, blood & lymphatic vessels
  46. 46. LOWER 1/3 OF ESOPHAGUS  MUCOSA  Epithelium: Simple columnar  Lamina prppria: : scattered lymphocytes, few lymphatic nodules, mucous glands, blood vessels  Muscularis mucosae: thick, striated muscles  SUB-MUCOSA  Collagen & elastic fibres, mucous glands, blood vessels, nerves  MUSCULARIS EXTERNA  smooth muscles  ADVENTITIA/ SEROSA  Collagen & elastic fibers, blood & lymphatic vessels
  47. 47. TRACHEA  Rigid tube  Extent  Patency maintained by C shaped cartilagenous rings  Between rings is fibroconnective tissue
  48. 48. MUCOSA  Epithelium: pseudo-stratified columnar ciliated with goblet cells  OTHER CELLS:  Columnar non-ciliated cells  Immature cells  Basal cells  Neuroendocrine (APUD)  Lamina propria:  Collagen fibres, elastic fibres, lymphatic nodules, mucous, serous glands  Muscularis mucosae:  Smooth muscles
  49. 49. SUB-MUCOSA  Loose connective tissue  Serous & musous glands  Blood & lymph capillaries
  50. 50. CARTILAGE  Hyline cartilage covered with perichondrium  Trachealis (smooth) muscle  ADVENTITIA:  Loose connective tissue  Blood & lymph vessels

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