SH Lecture - Lymphatic Structure and Organs
Introduction
This lecture will provide an overview of the lymphoid structure and histology of key cells, vessels, structures and organs lymphoid organs, including the lymph nodes, spleen and thymus, as well as extranodal lymphoid tissues including mucosal associated lymphoid tissues (MALT).
In this lecture I will go through the structures in sequence from cells through to organs, immunity itself is covered in detail elsewhere in the course.
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Structure | Function |
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Cells
Two Blood Cell Systems
- Mononuclear Phagocytic System - circulating monocytes of peripheral blood and non-circulating (fixed) tissue macrophages found throughout the body.
- Lymphoid System - lymphocytes, three major types of T, B, and NK.
Lymphoid Organs
- Central - Lymphocytes develop from precursor cells in bone marrow. (see blood marrow image)
- Peripheral - Lymphocytes respond to antigen lymph nodes or spleen.
Blood Cells |
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The blood cell information shown below in the table is shown to identify the relative proportions of different cell types in the circulating blood. This information is provided in the lecture as additional information for reference purposes only.
Blood Cell NumbersThe adult ranges of cells / 1 litre (l), total blood volume is about 4.7 to 5 litres. Blood Development | Blood Histology Red Blood Cells
Leukocytes (white blood cells)
Granulocytes
Non-Granulocytes
Lymphocytes
Platelets
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1. Mononuclear Phagocytic System
Mononuclear Phagocytic System (MPS, also called Lymphoreticular System or Reticuloendothelial System, RES)
Circulating monocytes of peripheral blood.
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Non-circulating (fixed) tissue macrophages (MΦ)
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2. Lymphoid System
Adaptive immunity functional cells are the lymphocytes (B, T, NK) and dendritic cells (process antigen and present it on their surface, monocyte precursor derived).
- Antibody-mediated - B Lymphocyte secreting antibody = Plasma Cell
- Cell-mediated - T Lymphocytes form memory cell, Cytotoxic T cells, T helper cell
B Cell Development | Germinal Centres |
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Plasma cells
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Lymphocyte Electron Micrographs |
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Histologically, there is little difference in appearance between T and B lymphocytes until activated.
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Lymphocyte Circulation
- Microbial antigens are carried into a lymph node by dendritic cells, which enter via afferent lymphatic vessels draining an infected tissue.
- T and B cells enter the lymph node via an artery and migrate out of the bloodstream through postcapillary venules.
- Unless they encounter their antigen, the T and B cells leave the lymph node via efferent lymphatic vessels, which eventually join the thoracic duct.
- The thoracic duct empties into a large vein carrying blood to the heart.
- A typical circulation cycle takes about 12–24 hours.
Links: MBoC Chapter 24 - The Adaptive Immune System | MBoC Figure 24-14. The path followed by lymphocytes as they continuously circulate between the lymph and blood | Immunobiology
Lymph Vessels
Three main types (capillaries, collecting vessels, ducts) based on size and morphology.
- Remember anatomy acronym - NAVL = Nerve, Artery, Vein and Lymph.
Lymph Capillaries
Begin as blind-ending tubes in connective tissue, larger than blood capillaries, very irregularly shaped.
Jejunum lacteal (lymphatic capillary of small intestine villi, absorbs dietary fats)
Lymph Collecting Vessels
Larger and form valves, morphology similar to lymph capillaries. Lymphangion
Lymph Ducts
Smooth muscle cells in wall, 1 or 2 layers.
Thoracic and right lymphatic ducts |
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Diffuse Lymphatic Tissue
Alimentary canal, respiratory passage and urogenital tract.
- BALT - Bronchus Associated Lymphoid Tissue or GALT - Gut Associated Lymphatic Tissue
- Not enclosed by a connective tissue capsule
- Located in subepithelial tissue - lamina propria
- Diffuse lymphatic tissue + nodules
- Reactive - enlarge when activated (by antigen)
Lymphocytes
- travel to nodes and back again
- proliferation and differentiation
Lymph Nodules
- Organized concentrations of lymphocytes
- No capsule, covered by epithelia
- Nodules are also the unit structure seen in a node
- Oval concentrations in meshwork of reticular cells
Nodule States
- Primary Nodule - Mainly small lymphocytes
- Secondary Nodule
- Central pale region (germinal centre) - Effector cells and macrophages
- Dark outer ring (small lymphocytes)
Gastrointestinal Tract
- Oropharynx - Tonsils
- Distal small intestine (ilieum) - Peyer’s Patches
- Appendix, cecum
Mucosal Associated Lymphoid Tissues
Anatomical location - Palatine (tonsils), Lingual and Pharyngeal ( adenoids ) Ring of oral adenoid tissue:
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Palatine Tonsils
- the "tonsils", lateral wall of oropharynx
- covered by stratified squamous epithelium
- numerous crypts (10-20) infolds of surface epithelium
- Afferent lymph vessels absent
- Efferent lymph vessels are present
Lingual Tonsils
- lamina propria root of tongue
- covered by stratified squamous epithelium
- salivary glands and skeletal muscle are directly adjacent
Pharyngeal Tonsils
- adenoids or nasopharyngeal tonsils, upper posterior part of throat
- covered by a pseudostratified ciliated epithelium with goblet cells
Peyer's Patch
- located in the ileum
Peyers patches (ileocolonoscopy) | Peyer's Patch (histology) | microfold cells or M-cells (transport gut lumen organisms and particles to immune cells across the epithelial barrier). |
About Peyer's Patch |
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External Links Notice - The dynamic nature of the internet may mean that some of these listed links may no longer function. If the link no longer works search the web with the link text or name. Links to any external commercial sites are provided for information purposes only and should never be considered an endorsement. UNSW Embryology is provided as an educational resource with no clinical information or commercial affiliation.
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Lymph Nodes
- Location throughout the entire body - Concentrated in axilla, groin, mesenteries
- Encapsulated organ (1 mm - 2 cm)
- Antigen transformed lymphocytes from the blood
- In lymph vessel pathways “filter”
- Afferent- towards node
- Efferent- away from node
Lymph flow
- enters the node through afferent vessels
- filters through the sinuses
- leaves through efferent vessels
Lymph Node Structure
Connective Tissue
- Capsule - dense connective tissue (irregular CT, some adipocytes))
- Trabeculae - dense connective tissue
- Reticular Tissue - Reticular cells and fibers, supporting meshwork (collagen type III)
- Reticular cell produces reticular fibers (collagen type III) and surrounds the fibers with its cytoplasm
- reticular fibbers can also be produced by fibroblasts
Lymphocyte (T and B) Traffic
Important - Please note that the lymphocytes exit from the node by efferent lymphatic vessels. See also Image - Cell Trafficking into and out of Lymph Nodes. |
T and B motility |
T and B interaction |
High Endothelial Venules See also Lymphocyte Migration at High Endothelial Venule Model |
Links: Immunobiology - Figure 1.8. Organization of a lymph node
Thymus
Gross Anatomy
- Superior mediastinum, anterior to heart
- Bilobed lymphoepithelial organ
Histology
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Thymus Cells
Reticular cells | Macrophages | Lymphocytes |
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Development Changes
{Changes with age Overall Size
- birth 10-15 g
- puberty 30-40 g
- after puberty - decreases in size (involution)
- middle-aged 10 g, replaced by adipose tissue
Histology
Adult Thymus
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Spleen
Spleen Function
- Immune - filters blood in much the way that the lymph nodes filter lymph.
- Lymphocytes in the spleen react to pathogens in the blood and attempt to destroy them.
- Macrophages then engulf the resulting debris, the damaged cells, and the other large particles.
- Red Blood Cell Removal - spleen (and liver) removes old and damaged erythrocytes from the circulating blood.
- Blood Reservoir - The sinuses in the spleen also act as a reservoir for blood.
- In emergencies, such as hemorrhage, smooth muscle in the vessel walls and in the capsule of the spleen contracts.
- This squeezes the blood out of the spleen into the general circulation.
Structure
- Capsule, trabeculae (dense connective tissue)
- Splenic pulp white pulp, red pulp - based on appearance and cell content.
White Pulp
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Red Pulp
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Reticular Fibers (type III collagen) act as supporting meshwork.
Spleen Development: SH Lecture Spleen | SH Adult Histology | Overview Red and White Pulp | Overview Red and White Pulp | Cords and Sinuses | Reticular Fibre overview | Reticular Fibre detail | unlabeled red and white pulp | unlabeled red pulp and macrophages | unlabeled white pulp germinal centre | unlabeled reticular fibre | unlabeled white pulp reticular | unlabeled red pulp reticular | Structure cartoon | Cartoon and stain | Category:Spleen | Histology Stains | Immune System Development |
Additional Information
Additional Information - Content shown under this heading is not part of the material covered in this class. It is provided for those students who would like to know about some concepts or current research in topics related to the current class page. |
If you have comments or questions specifically related to this lecture, please leave them on the Student lecture feedback page.
The following is not part of the lecture and is for reference purposes only.
SH Practical - Lymphatic Structure and Organs associated practical support page. Note that virtual slides will be used in the associated practical class and this linked page is provided for student self-directed learning of concepts from the virtual slides.
- Lymphatic cartoon links: Overview | Tonsil | Tonsil and MALT | Thymus | Spleen | Bone marrow | Lecture - Lymphatics | Immune System Development
- Lymph Node Cartoons: Detailed structure | Cartoon with Histology | Lymphocyte traffic | Simple structure | Simple node anatomy | Wiki node image | Internal structure | Mesenteric lymph node | Histology | Gallery | Lymph Node Development
Mouse Lymphocyte Motility Movies | |||||||||||||||
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Mouse Immune Movies: Transendothelial migration | T cell zone | Medullary sinus | Sinus endothelial barrier | Bi-directional traffic | cross the sinus endothelial barrier | T and B cell motility | T and B cell coupling |
Additional Images |
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Janeway’s Immunobiology |
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A useful resource textbook for further reading on Lymphatic Structure and Organs is Immunobiology 5th edition The Immune System in Health and Disease Charles A Janeway, Jr, Paul Travers, Mark Walport, and Mark J Shlomchik. Open links in a new tab if you wish to refer back to this lecture page.
I have included some links in this table below to specific notes and there is also available a complete list of contents. External Links Notice - The dynamic nature of the internet may mean that some of these listed links may no longer function. If the link no longer works search the web with the link text or name. Links to any external commercial sites are provided for information purposes only and should never be considered an endorsement. UNSW Embryology is provided as an educational resource with no clinical information or commercial affiliation. Immunobiology 5th edition The Immune System in Health and Disease Charles A Janeway, Jr, Paul Travers, Mark Walport, and Mark J Shlomchik. Part I. An Introduction to Immunobiology and Innate Immunity Chapter 1. Basic Concepts in Immunology
Part III. The Development of Mature Lymphocyte Receptor Repertoires Chapter 7. The Development and Survival of Lymphocytes
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Nature Immunology - Videos
These are short (5-10 min) animations showing how the immune system monitors the epithelial and environment interface at different anatomical locations.
Government Sources
These information pages provide general information to the public. See how the biology concepts have been simplified to make them more understandable.
USA
Australia
Blood Cells |
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Blood cell information shown in the table below is also additional information for reference purposes.
Blood Cell NumbersThe adult ranges of cells / 1 litre (l), total blood volume is about 4.7 to 5 litres. Blood Development | Blood Histology Red Blood Cells
Leukocytes (white blood cells)
Granulocytes
Non-Granulocytes
Lymphocytes
Platelets
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Anatomy of the Human Body (1918) - Lymphatics |
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Anatomy of the Human Body Gray (1918) Historic anatomy is good, though there are there are some functional inaccuracies.
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- Textbook Links: MBoC Figure 24-6. The development and activation of T and B cells | [http://www.ncbi.nlm.nih.gov/books/NBK26921/figure/A4430/ Figure 24-7. Electron micrographs of nonactivated and activated lymphocytes | Immunobiology - Figure 1.9. Organization of the lymphoid tissues of the spleen
Structure - Cells, Vessels, Diffuse (extra-nodal tissue), Nodes, Organs.
- Cells
- Vessels
- Diffuse
- Mucosal Associated Lymphoid Tissues (MALT)
- Extranodal Lymphoid Tissues
- Nodules
- Lymph Nodes
- Position
- Structure
- Function
- Organs
- Position, Structure, Function
- Thymus
- Spleen
Terms
A few key terms associated with the Lymphoid system.
- adenoid - (Greek " +-oeides = in form of) in the form of a gland, glandular; the pharyngeal tonsil.
- afferent lymph - vessel carrying lymph towards a node containing antigen-presenting cells, antigen, effector and memory T cells, and regulatory T cells.
- acquired immune deficiency syndrome - (AIDS) note this is now better described as "advanced HIV disease", decrease in the number of CD4 T cells. (More? Immunobiology - AIDS)
- anastomose - joining of two tubes or structures together.
- Antibody mediated immunity - the immune function of plasma cells (active B lymphocytes) secreting antibody which binds antigen.
- antibodies - mammals have five classes (IgA, IgD, IgE, IgG, and IgM)
- antigen - any substance that is recognised by the immune system and stimulates antibody production.
- appendix - is a gut-associated lymphoid tissue (GALT) located at the beginning of the colon. The anatomy is as a finger-like structure that arises from the cecum. The length (2.5-13 cm) is longer in both infants and children and also has more abundant lymphatic tissue in early life. The wall structure is similar to the small intestine (though with no villi), nor plicae circularis. Lymph nodules surround the lumen of the gastrointestinal tract and extend from the mucosa into the submucosa.
- B cell - (B-cell, B lymphocyte) historically named after a structure called the bursa of Fabricius in birds, a source of antibody-producing lymphocytes. These immune cells develop in the bone marrow. (More? Electron micrographs of nonactivate and activated lymphocytes)
- blood - liquid connective tissue containing cells of the lymphatic system see Cardiovascular terms
- B lymphocyte - (B cell, B-cell)
- BALT - (Bronchus Associated Lymphoid Tissue) immune tissue associated with the respiratory tract.
- band cell - (band neutrophil or stab cell) immature neutrophil seen in bone marrow smear, a cell undergoing granulopoiesis, derived from a metamyelocyte, and leading to a mature granulocyte. Also occasionally seen in circulating blood.
- bone marrow sinusoid - endothelial cells and no supporting cells vascular space supplied by arteriole and capillary vessels, interconnected by inter-sinusoidal capillaries, spanning throughout the bone marrow. Radially distributed around the draining central sinus (about 100 µm in diameter). Bone marrow sinusoids are unique and are not comparable with regular veins.
- cecum - (caecum, Latin, caecus = "blind") within the gastrointestinal tract a pouch that connects the ileum with the ascending colon of the large intestine.
- cell - has a specific cell biology definition, but is often used instead of "lymphocyte" when describing B and T cells.
- cell-mediated immunity - the immune function of T lymphocytes. (More? Immunobiology - T Cell-Mediated Immunity)
- central tolerance - in thymus mediated by cortical epithelial cells, medullary epithelial cells and thymic dendritic cells, involves deletion of self reactive thymocytes (T cell) (see [https://www.ncbi.nlm.nih.gov/pubmed/30476234 PMID30476234).
- "clockface" - a term used to describe the appearance of plasma cell nuclei due to the clumping of the chromatin at the nucleus periphery. More clearly seen in tissue plasma cells that the bone marrow smear, where they are sometimes confused with the basophilic erythroblasts. Image - plasma cell
- CD - (cluster of differentiation) identifies immunological surface markers on cells. Positive (+) generally means that the substance is expressed/identified, while negative (-) means that it is missing/not identified.
- CD4+ - (T helper cells) refers to T lymphocytes that express CD4 (cluster of differentiation 4, a glycoprotein of the immunoglobulin superfamily) on their surface, associated with helper/inducer function. These cells can be infected by human immunodeficiency virus (HIV).
- CD4/CD8 ratio - clinical measurement of different immune cell types (ratios between 1.5 to 2.5 are considered normal). Viral infections such as HIV, cytomegalovirus, Epstein-Barr virus, and influenza virus, associated with an inversion of the ratio.
- CD8+ - (cytotoxic T cells) refers to T lymphocytes that express CD8 (glycoprotein of the immunoglobulin superfamily) on their surface, associated with cytotoxic/suppressor activity.
- "clockface" - a term used to describe the appearance of plasma cell nuclei due to the clumping of the chromatin at the nucleus periphery. More clearly seen in tissue plasma cells that the bone marrow smear, where they are sometimes confused with the basophilic erythroblasts.
- cords of Billroth - spleen cellular columns located in red pulp. surrounded by splenic sinusoids. Cords contain reticular cells, macrophages, lymphocytes, plasma cells and erythrocytes.
- cortex - outer layer, used in association with medulla (innner layer or core) a general description that can be applied to describing an organ with a layered structure.
- cortical Thymic Epithelial Cell - (cTEC, types I - IV) support and antigen presenting cells located in the cortex regions of the thymus required for positive and negative selection of maturing T cells. See also medullary epithelial cell.
- crypt - (tonsil crypt) tonsil squamous epithelium infold, with intraepithelial passages containing non-epithelial cells. Functions include: intimate contact between immune response effector cells, facilitate transport of antigens, synthesise secretory components, and contain a pool of immunoglobulins. PMID 7559106
- dendritic cell - (DC, antigen-presenting cell, APC) cells that present antigens and induce a primary immune response in resting naïve T lymphocytes. Originate from the same common progenitor as monocytes (PMID 20193011). In 2011 Ralph M. Steinman received half the Nobel Prize half of the award to to Ralph M. Steinman for his discovery of the dendritic cell and its role in adaptive immunity.
- Effector cells - the immune functioning (active) B and T lymphocytes.
- Efferent lymph - vessel carrying lymph away from a node.
- fibroblastic reticular cell - (FRC) specialized myofibroblasts that form the structural mesenchymal network "sponge" within lymphoid tissue that regulate immune cell migration, activation, and survival. Immune T cells, B cells, dendritic cells (DCs), plasma cells and macrophages move and interact.
- follicular dendritic cell - (FDC) in B cell follicles of secondary lymphoid organs, cells interspersed within the stromal cell network function: Primary - help B cells to cluster. Secondary - in GC long-term retention of intact antigen and support B cell survival.
- GALT - Gut Associated Lymphatic Tissue consisting of Peyer’s patches, isolated lymphoid follicles and mesenteric lymph nodes.
- germinal centre - (GC) centre of B cell follicles of secondary lymphoid organs, where antigen-activated B-cell clones expand and undergo immunoglobulin gene hypermutation and selection.
- haemopoiesis (hemopoiesis) formation of blood cells.
- Hassall's corpuscles - (Hassall's body, thymic corpuscle) Epithelial reticular cells located in the thymic medulla. Named after Arthur Hill Hassall (1817-1894) a British physician and chemist.
- high endothelial venule - (HEV) the specialised post-capillary venous region that enables blood lymphocytes and pre-dendritic cells to enter a lymph node. The endothelial cells express ligands that bind lymphocytes, aiding their adhesion and subsequent transmigration into the lymph node. With inflammation, monocytes and NK cells can also enter here.
- humoral immune response - production of antibody by plasma cells derived from B lymphocytes (B cells).
- IEL - Intraepithelial Lymphocyte are T lymphocytes located in the gastrointestinal tract epithelium. Natural IELs (previously ‘type b’ IELs) acquire activated phenotype during development in the thymus in the presence of self antigens. Induced IELs (previously ‘type a’ IELs) progeny of conventional T cells activated post-thymically in response to peripheral antigens.
- IgA - the main class of antibody released at mucosal surfaces and in secretions (saliva, tears, milk, and respiratory and intestinal secretions) and the most abundantly produced antibody (70%). PMID 22566964
- IgD - the immunoglobulin B cell starts to produce as a cell-surface molecule after leaving the bone marrow.
- IgE - bind Fc receptors (surface of mast cells in tissues and basophils in the blood) release of potent pro inflammatory molecules mediators of allergic reactions.
- IgG - the major class of immunoglobulin in the blood.
- IgM - the first class of antibody made by a developing B cell, which may switch to making other classes of antibody.
- immunodeficiency - when one or more components of the immune system is defective. (More? Immunobiology - immunodeficiency)
- immunoglobulin - (antibody, Ab) protein produced by plasma cells.
- immunosenescence - in ageing and disease, refers to a weaker immune responses producing a progressive deterioration and increased susceptibility to infectious diseases, neoplasia, and autoimmune diseases.
- innate lymphoid cells - (ILCs) subset of lymphocytes that lack antigen-specific receptors, are located in peripheral tissues and abundant at barrier surfaces, decrease in number with age. PMID 29924974
- intraepithelial lymphocyte (IEL) immune cells residing in the gastrointestinal tract epithelium. image - Intraepithelial lymphocyte differentiation
- involution - in the thymus refers to the replacement, mainly in the cortex, of cells by adipose tissue. (More? PubMed- thymus involution) | Cancer Medicine - Thymomas and Thymic Tumors)
- Kupffer cells - stellate macrophage cells located in the liver sinusoids, named after Karl Wilhelm von Kupffer (1829 - 1902) a German anatomist who originally identified these cells. (More? Liver Development)
- lacteal - term used to describe the lymphatic vessels of the small intestine.
- lamina propria - a layer of loose connective tissue found underneath an epithelium, together with the epithelium described as mucosa.
- Langerhans cell - (LC, dendritic cell) Antigen-presenting immune cell found mainly in the basal/suprabasal layers of adult skin and mucosa. Cells lie in the basal/suprabasal layers of stratified epidermal and mucosal tissues. First in the innate antiviral immune defines and can migrate to lymph nodes and induce a T cell–mediated adaptive immune response. (More? Integumentary | Immune System Development)
- Leukocyte - (Greek, lukos = clear, white) white blood cell.
- lingual - related to the tongue, as in lingual tonsil, forms part of Waldeyer’s ring.
- lymph node - connective tissue encapsulated lymphoid organ (1mm - 2cm in size), positioned in the pathway of lymph vessels. (More? Lymph Node Development)
- lymphangion - the functional unit of a lymph vessel that lies between two semilunar (half moon-shaped) valves.
- lymphangiogenesis - formation of new lymph vessels from pre-existing lymphatic structures. During embryogenesis and in adult tissues as reaction to inflammation or injury.
- M cell - (microfold cell) found in the follicle-associated epithelium of the Peyer's patch. Function to transport gut lumen organisms and particles to immune cells across the epithelial barrier.
- macrophage - a large highly motile white blood cell which engulfs foreign material (bacteria etc) and both degenerating cells and cell fragments. Differentiates from a monocyte and found in many different tissues and locations. Current theory suggests tissue macrophage is also derived from resident stem cell population in many tissues. More? Immunobiology - Defects in phagocytic cells are associated with persistence of bacterial infection)
- MALT - Mucosa Associated Lymphoid Tissue.
- medulla - inner layer or core, used in association with cortex (outer layer) a general description that can be applied to describing an organ with a layered structure.
- medullary Thymic Epithelial Cell - (mTEC, types I-VII) support and antigen presenting cells located in the medullary regions of the thymus, required for central tolerance (negative selection) of maturing T cells (PMID 11375064). See also cortical thymic epithelial cell.
- Memory Cell - effector T cell (lymphocyte)
- mesenteric lymph nodes - Part of GALT as well as being involved in gut-draining. image - mesenteric lymph nodes
- Mononuclear Phagocytic System - (MPS, Lymphoreticular System, Reticuloendothelial System, RES) Consists of circulating monocytes in the peripheral blood and non-circulating (fixed) tissue macrophages (MΦ) located in tissues and organs.
- NAVL - (naval) mnemonic to remember the neurovascular bundle components Nerve Artery Vein Lymph found travelling together within organs and tissues.
- negative selection - T cells bearing autoreactive T cell antigen receptors (TCRs) are eliminated during their development in the thymus, protects against autoimmunity.
- normoblast - seen in bone marrow smear, a developing erythroblast (red blood cell) that still retains a nucleus.
- nude mice - (nu/nu) mice which are congenitally hairless and athymic, therefore they do not reject tissue and tumor grafts.
- PALS - acronym for PeriArterial Lymphoid Sheath in the spleen white pulp.
- parenchyma - (Greek = enkeim "to pour in") cells forming the functional cells of an organ or tissue. These cells carry out the function of the organ at a cellular level, and are not the structural cells, connective tissue, extracellular matrix (stromal).
- periarterial lymphoid sheath - (PALS) in the spleen the white pulp that surrounds the central arteries. (T-lymphocytes,macrophages and plasma cells)
- pharyngeal pouch III - origin of endodermal component of the thymus (also formed from neural crest). Pharyngeal arches
- Plasma Cell - active B cell (lymphocyte) which is secreting antibody. Located in either bone marrow or peripheral lymphoid tissues, these cells have and increased cytoplasmic volume (due to increase rough endoplasmic reticulum) in comparison to the inactive (non-secreting) lymphocyte.
- primary follicle - follicle that does not contain germinal centre, secondary follicles do germinal centre.
- red pulp - spleen region, organized as cell cords (splenic cords, cords of Billroth) and vascular sinuses.
- regulatory T cells - (Tregs) maintain self tolerance and suppress pathological immune responses by control of immune response to non-self antigens.
- reticular fibres - reticular cells secrete this extracellular matrix protein, composed of type III collagen.
- right lymphatic duct - drains most of the right upper quadrant. See also thoracic duct.
- secondary follicle - contain germinal centre, primary follicle does not contain germinal centre.
- sentinel lymph node - the hypothetical first lymph node or group of nodes reached by metastasizing cancer cells from a primary tumour.
- sinus - a larger vessel or space usually curved that may contain air, blood, or lymph. e.g. splenic medullary sinus, lymph node medullary sinus, sub-capsular sinus, trabecular sinus.
- sinusoid - a tiny vessel with a tortuous path and many connections to similar vessels. e.g. hepatic and bone marrow sinusoids.
- splenic capillary sheaths - in spleen around capillary endothelium and consist of three main cell types: CD271+ stromal capillary sheath cells, CD68+CD163− macrophages and recirculating B-lymphocytes. Sheaths may; 1. allow interaction among sheath macrophages and B-lymphocytes, 2. attract recirculating B-lymphocytes from the open circulation of the red pulp to start migration into white pulp follicles. 30356180
- splenic sinusoids - enlarged splenic spaces located in red pulp and surrounding cords of Billroth.
- sphingosine-1-phosphate - (S1P) sphingolipid secreted into the extracellular space establishing a gradient acting through G protein-coupled receptors to attract lymphocytes out of lymphoid organs (lymph node, thymus, spleen) into the circulation.
- stroma - (Greek = "a cover, table-cloth, bedding") tissue forming the framework/support of an organ or tissue. That is the structural cells which form connective tissue and secrete extracellular matrix, rather than the functional cells (parenchymal). All organs can therefore be functionally divided into these 2 components, stromal/parenchymal.
- Subcapsular sinus (=marginal sinus) space lying under the connective tissue capsule which receives lymph from afferent lymphatic vessels.
- T cell - (T-cell, T lymphocyte) named after thymus, where they develop, the active cell is responsible for cell-mediated immunity (killer T cells and helper T cells). Cells express T-cell receptor on surface and directly kill virally or bacterially infected cells. These cells can themselves be infected by HIV. (More? Electron micrographs of nonactivate and activated lymphocytes)
- TEC - (Thymic Epithelial Cell) thymus support and antigen presenting cells further divided anatomically and functionally into medullary TEC (mTEC, types I-VII, for central tolerance) and cortical epithelial cell (cTEC, types I-IV, positive and negative selection) populations (see PMID 28800929 PMID 30308217).
- T cell activation - (T lymphocyte activation)The activation process begins with T-cells searching for and encountering antigen-bearing dendritic cells within lymph nodes.
- thoracic duct - (TD) largest and main lymphatic vessel, drains the lower body including the extremities and abdomen. Intra-thoracic tributaries include: intercostal, mediastinal, and bronchomediastinal trunks.
- Thymic corpuscle - (Hassall's corpuscle) a mass of concentric epithelioreticular cells found in the thymus. The number present and size tend to increase with thymus age. (see classical description of Hammar, J. A. 1903 Zur Histogenese und Involution der Thymusdriise. Anat. Anz., 27: 1909 Fiinfzig Jahre Thymusforschung. Ergebn. Anat. Entwickl-gesch. 19: 1-274.)
- thymic epitheliocytes - reticular cells located in the thymus cortex that ensheathe the cortical capillaries, creating and maintain the microenvironment necessary for the development of T-lymphocytes in the cortex.
- T helper cells - (helper T-cells) (Th cells, CD4+) refers to T lymphocytes that when mature express CD4 (glycoprotein of the immunoglobulin superfamily) on their surface.
- T lymphocyte - (T cell, T-cell) regulate cell-mediated immunity.
- thymus - an immune/endocrine (thymic hormone, thymosins) organ involved in the maturation (differentiation) of T lymphocytes (T-cells).
- tonsils - lymph nodules embedded in the mucus membranes located at the back of the mouth and top of the throat. The overlying epithelium helps identify the location.
- tonsillitis - a common bacterial infection of the palatine tonsils, occurring mostly in children and young adults and can also become recurrent tonsillitis.
- vermiform appendix - see appendix, anatomical region containing gut-associated lymphoid tissue located within the gastrointestinal tract at the beginning of the colon. The anatomy is as a finger-like structure that arises from the cecum. The length (2.5-13 cm) is longer in both infants and children and also has more abundant lymphatic tissue in early life. The wall structure is similar to the small intestine (though with no villi), nor plicae circularis. Lymph nodules surround the lumen of the gastrointestinal tract and extend from the mucosa into the submucosa.
- VDJ recombination - (variable, diversity and joining gene segments) genetic recombination event that occurs in immune cell maturation in primary lymphoid organs, B cells ((bone marrow) and T cells (thymus).
- Waldeyer’s ring - ring of lymphoid tissue in the pharyngeal wall: palatine tonsils, nasopharyngeal tonsil (adenoid) and lingual tonsil. First described in 1884 by von Waldeyer-Hartz.
- white pulp - (Malpighian follicles, Malpighian bodies of the spleen, white nodules, splenic lymphoid nodules) spleen lymphoid region, organized as lymphoid sheaths with both T-cell and B-cell compartments, around the branching arterial vessels (resembles lymph node structure).
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Cite this page: Hill, M.A. (2024, April 19) Embryology SH Lecture - Lymphatic Structure and Organs. Retrieved from https://embryology.med.unsw.edu.au/embryology/index.php/SH_Lecture_-_Lymphatic_Structure_and_Organs
- © Dr Mark Hill 2024, UNSW Embryology ISBN: 978 0 7334 2609 4 - UNSW CRICOS Provider Code No. 00098G