Lymphatics PDF

lymphatics LYMPHOID TISSUES Lymphatic system: for drainage of wastes and is Composed of: part of the immune system STROMA Monitor body surfaces and internal fluid o Supporting...

lymphatics LYMPHOID TISSUES Lymphatic system: for drainage of wastes and is Composed of: part of the immune system STROMA Monitor body surfaces and internal fluid o Supporting framework compartments that react to the presence of potentially o Reticular CT (except thymus): made of collagen harmful substances (foreign substances) type three or reticulin Definitive cell types: Lymphocytes o Area where the parenchyma exists in PARENCHYMA o Functional elements o Mostly lymphocytes Lymph tissues are either in nodules/encapsulated, or diffused (not enclosed by capsules) PRIMARY / CENTRAL LYMPHOID ORGANS For production and maturation 1: BONE MARROW There are primary and secondary lymphoid organs Primary: where B and T cells are created o Thymus: where T cells mature § Majority of the circulating cells are T cells (although B cells also circulate) o Bone marrow: B and T cells created here; B cells mature here as well Jelly-like substance within cavity of long bone or Secondary organs are everything else aside from proximal area of long bones (for adults) thymus and bone marrow Types: o RED - Clusters of hematopoietic islands (more numerous in babies) o YELLOW - numerous adipocytes and dormant hematopoietic clusters Lymphatic vessels are like lined capillaries that intersperse in capillary beds since they draw out the waste from the blood vessels (remove substances or fluid à lymph system) Right picture above: Lymphatic system has many lymph nodes (aggregates of lymph tissue) that exist in several organs in lymphatic system; kidney-bean shaped o Most things that filter waste are kidney-bean shaped This is what happens in red bone marrow Flores, Cristina Angela B. (BSMLS-2C) Histology Lab  o Hematopoietic stem cells à create all of blood CAPSULE cells of body o Dense irregular CT o Envelopes lobes o They only partially separate TRABECULAE o AKA Interlobular septum o Septa coming from the capsule o Incompletely subdivides lobes into lobules LOBULES o Cortex - peripheral, DARK (outside) o Medulla - central, LIGHT (middle) Left: red; Right: yellow Red marrow (found in babies’ bones) Thymus of a young child (has cortex, medulla, capsule, o Limited in adults (can only be found in central and interlobular septum): more B cell population flat bones like skull, sternum, & proximal ends Thymus for children and adults are different of long bones) Slides for thymus are usually from children/baby or Hematopoietic cords and reticular cells (circled patients with thymic hyperplasia (thymus became pictures) bigger) 2: THYMUS Site of T cell maturation (T cells made in bone marrow) Thymus of adult: more adipocytes; no lymph nodules; no Induction of central tolerance to prevent autoimmunity antibody production o Makes T cells such that they will not recognize your body as foreign Stroma: provides network for developing T lymphocytes o Allow the existence of your blood cells called thymocytes (darker nucleus and more numerous) o If thymus does not function properly, there will be and you can find here the reticular fibers making up this autoimmune disease (body starts attacking stroma itself) Fully functional at birth but involutes or becomes smaller during puberty (made up more of adipocytes) o Common trend: as we get older à lymp organs become smaller à have more adipocytes Cells developing here are called thymocytes before they are activated to become T cells Reticular cell/macrophage: lighter cytoplasm and bigger Flores, Cristina Angela B. (BSMLS-2C) Histology Lab  COR+EX o Cells in parenchyma: o Outer portion of thymus o Area for positive selection § Larger T lymphocytes § Macrophages § Breakdown of immunocompetence § Developing cells have ability to recognize § Thymic interdigitating cell: present self- something as foreign antigens to T cells if cells pass à continue to grow and mature à go to medulla if cells fail à apoptose o Hassall’s corpuscle § Aggregates of epithelial reticular cells (the ones that produce stroma) in the medulla § Defining feature of medulla of thymus o Cells in parenchyma: § Made of keratohyalin granules: reason § Thymocytes: smaller why they are very pink § Macrophages: slightly pinker cytoplasm § Increase with age than reticular cells § Function not exactly known MEDULLA Proposed that they act for removal of apoptotic thymocytes § Swirls SECONDARY LYMPHOID ORGANS For storage, differentiation, and rapidly increase the number of lymphocytes with specific antigen presentation 1: LYMPH NODE o Inner portion of thymus o Area for negative selection § Avoid autoimmunity § Make sure that the cells will not recognize own body cells as foreign If cells fail à apoptose If cells pass à they become fully mature T cells à exit thymus as mature, immunocompetent, self- There are many lymph nodes throughout the bodies tolerant but naïve T cells (never These swell up when people are sick (rapid increase caught foreign substance before) in number of lymphocytes) If they catch foreign substance, they become active Flores, Cristina Angela B. (BSMLS-2C) Histology Lab  There are a lot of afferent vessels (exchanged with capillaries) that enter lymph nodes à filtered à go out through efferent vessels (exit) Lymph node has convex and concave/hilum surface Primary nodules (1o): highly basophilic Secondary nodules (2o): has germinal center (active follicles) GERMINAL CENTER o MANTLE ZONE § Quiescent B cells (not activated) § Intense basophilic stain Image of lymph node (see convex side where afferent like primary follicles enters and efferent vessel [black arrow]) § Has follicular dendritic cells which present ENCAPSULATED (still dense irregular CT) antigens, has T-helper Filters lymph for particulate matter and cells and macrophages microorganisms (first one to encounter with o LIGHT ZONE microorganisms that may have been seen in the § Centrocytes: B cells derived from blood) centroblasts with surface immunoglobulin Hematopoiesis: blood cell creation Already interacted with follicular Site of lymphopoiesis: proliferation of dendritic cells or antigen-presenting activated B and T cells (differentiate cells and now express intact antigen on based on the microorganism they saw) their surface Contains Centrocytes have high affinity to o Macrophages antigens presented by dendritic cells o Antigen-presenting cells (APCs) à proliferate more and become bigger T-helper cells support proliferation and differentiation of centrocytes o DARK ZONE § Centroblasts : highly mitotic Still has capsule, trabeculae, stroma Lymph node is encapsulated OUTER CORTEX Small, noncleaved lymphocytes à centroblasts (multiple nuclei) à centrocytes (small, cleaved lymphocytes and do not look like fully formed circles) PARACORTEX o Made of lymphoid nodules (1o and 2o) o Mostly B cells o Inner cortex Flores, Cristina Angela B. (BSMLS-2C) Histology Lab  o NO lymph nodules o Mostly T cells (where they proliferate and differentiate) MEDULLA Spleen has: o White pulp: has structures similar to secondary follicles; 20% o Innermost region o Red pulp: made of sinusoids, splenic cords, and o Medullary cords reticular meshwork (similar to medulla); 80% § dense lymphoid tissues between medullary sinuses (spaces) o CELLS: § Plasma cells § B and T cells (proliferated from cortex and paracortex) RED PULP o Large number of RBCs o Consists of: § Splenic cords of Billroth: made of reticular cells and fibers § Sinusoids (Splenic sinuses): spaces WHITE PULP 2: SPLEEN Also a kidney-bean shaped structure Found in upper left quadrant of abdomen (posteriorly) and hilum of spleen is in one end of the pancreas o Basophilic due to the large nuclei of lymphocytes Also ENCAPSULATED and has trabeculae o Consists of: § Lymphoid nodules Largest lymphoid organ § Periarterial lymphatic sheath (PALS): FUNCTIONS: specialized T cells covering central artery Filters blood § Macrophages Removes and § Dendritic cells destroys damaged § Also has germinal center and old RBCs and o Marginal zone platelets (spleen is § Transitional area between red & white pulp also known as graveyard of RBCs) Storage for blood Lymphopoiesis Flores, Cristina Angela B. (BSMLS-2C) Histology Lab MUCOSA-ASSOCIATED LYMPHOID TISSUE (MALT) ORGANS Still secondary lymphoid organs but specialized Mostly diffused and sprinkled within mucosa of many organs (not encapsulated anymore) MALT: TONSILS Has crypt, epithelium, secondary follicles Large, irregular masses of lymph tissue in the mucosa of the posterior oral cavity and nasopharynx Forms the Waldeyer ring o Pharyngeal/ Adenoid Pharyngeal: has shallow infoldings, NOT CRYPT! o Tubal (2) in nasopharynx (simple columnar epithelium) o Palatine (2) in either sides o Lingual near tongue or at the back of the MALT: PEYER’S PATCHES circumvallate papillae Larger in children Large, irregular masses of lymph tissue in the mucosa Distinguishing factor: lining epithelium and submucosa of the ileum (last part of small Palatine and Lingual: Simple squamous intestine, before the colon) nonkeratinized epithelium Look like large secondary follicles o Lingual tonsils lack distinct capsules (not Found also in fundus of stomach and gastroileal very obvious lining epithelium) junction Pharyngeal: Simple columnar epithelium; no crypts M-cells TONSILLAR CRYPT o Microfold cells o Dead epithelial cells o Simple columnar epithelial cells atop Peyer’s o lymphocytes patches for antigen presentation EPITHELIUM o SSE, nonkeratinized o Deep, branching invaginations (crypts) o Tonsils have “capsules” but they are still diffused since naputol sila at the crypts Flores, Cristina Angela B. (BSMLS-2C) Histology Lab MALT: APPENDIX Found in right lower quadrant Blind sac extending from the cecum Primary and secondary follicles in the lamina propria (areolar CT) and submucosa Zoom in of follicles Flores, Cristina Angela B. (BSMLS-2C) Histology Lab