Lymphoid Organs Flashcards
Why is blood considered to be a connective tissue?
It has all of the components that characterize such tissues: fibres (though in normal blood, it is latent), amorphous matrix, and cells (RBCs, WBCs, platelets)
What is blood plasma?
55% of the total blood volume- protein-albumin, globulins, Ig, fibrinogen- carries regulatory substances, nutritional substances, salts, waste
What is the lifespan of RBCs? What happens to RBCs when their lifespan is up?
90-120 days. Senescent RBCs are engulfed by macrophages in the liver and spleen. Hb is scavenged and the residue become the iron-containing pigment, haemosiderin
What are the two main categories of leukocytes?
Granulocytes and agranulocytes
Neutrophil function (granulocyte)
First line of defence against microbial infection, actively phagocytic, and produce antimicrobial substances (lytic enzymes, bactericidal substances), modulate inflammatory responses by producing cytokines and chemokines
Eosinophil function (granulocyte)
Major role in controlling parasitic infestation, and in allergic responses. Regulate allergic and acute inflammatory processes: inactivate histamine, inhibit histamine release, cytokines, chemokines. Phagocytic: antigen-antibody complexes
Basophil function (granulocyte)
Major role in allergic and inflammatory reactions, lipid metabolism, blood coagulation, possess IgE surface receptors. Limited phagocytic and bactericidal activity.
Lymphocyte (agranulocyte)
* Responsible for immune response *T cells- effector cells–> cell mediated immune response *B cells- plasma cells–> humoral immune response (antibodies) *NK cells- cytotoxic *cell mediated innate immune response *produce cytokines, chemokines
Monocytes (agranulocytes)
Largest of the circulating formed elements in blood, 5-8%. Monocytes become tissue macrophages, or dendritic cells.
Dendritic cells (agranulocytes)
(from monocytes) not present in blood except a small number of immature cells. Antigen presenting cells, activate T cells *Present in small quantities in tissues that are in contact with the externam environment (skin, intestines, etc.)
Macrophages (agranulocytes)
(from monocytes) Antigen Presenting Cells- initiate immune response *phagocytic *RBC, granulocyte formation *cytokines
Aggregation
Associated with endothelial cell injury; formation of platelet plug
Coagulation
Initiated at larger sites of injury; formation of a clot (thrombus)
Haemopoiesis
Formation and development of RBCs and WBCs from stem cells
Where does myeloid haemopoiesis take place?
Bone marrow (myeloid- red blood cells & non-lymphocytic white blood cells)
Where does lymphoid haemopoiesis take place?
Primary- bone marrow, thymus Secondary- lymph nodes, spleen, lymphoid tissues
Where does haemopoiesis begin and end during development?
Yolk sac–> stem cells migrate to the liver and spleen during mid-gestation- as bones develop–> bone marrow–> primary and secondary lymphoid haemopoietic organs then established
Where do blood cells arise from?
Pluripotent stem cells
What tells the bone marrow how many RBCs to produce?
hormones (erythropoietin) and cytokines
What tells the bone marrow how many WBCs to produce?
hormones and cytokines. Granulocyte- macrophage colony stimulating factor (GM-CSF) is produced by activated macrophages e.g. during infection
What is the primary lymphoid organ in birds?
Bursa of Fabricius (B cells). “Cloacal Tonsil” (Bone marrow in mammals, bursa in birds)
What is the primary lymphoid organ in the chicken?
Harderian gland (B cells, chicken). A pair, located between the eye and nasal cavity. Involved in the local immune responses of the conjunctivae and upper respiratory tract. A central duct drains the gland secretion to the eye.
What are the primary lymphoid organs?
Bone marrow (B cells) and Thymus (T cells) ** the lymphoid organs where WBC produce and mature)
What is another primary lymphoid organs in ruminants, pigs, horses, dogs and humans?
Ileal Peyer’s patches near the ileocaecal junction (B Cells)
What is the secondary lymphoid organ in birds?
Caecal tonsils
What is the secondary lymphoid organ in ruminants?
Hemal nodes
What are the secondary lymphoid organs?
Lymph nodes, spleen, tonsils, MALT (mucosa-associated lymphoid tissues)- such as Peyer’s Patches ** lymphoid organs where the WBCs reside
What is produced in the thymic cortex and what is in the thymic cortex?
*heavily packed with lymphocytes. *T cells are produced in the thymic cortex. *Blood-thymus barrier restricts exposure of developing T cells to antigen.
What is the role of reticular epithelial cells?
Direct the differentiation of T cells, producing thymic hormones including thymopoietin, thymosin alpha, thymulin
Thymic (Hassall’s) corpuscles
Large, eosinophilic. Degenerate epithelial cells form clumps in the medulla. Keratinised centre surrounded by elongated epithelial cells. Seen in older animals post puberty.
What tissue makes up a lymph node?
Loose lymphatic tissue, diffuse dense lymphatic tissues and nodules. Trabeculae comprise connective tissue and form the main supportive framework. Hilus region supplied by blood vessels. Has a connective tissue capsule. Afferent vessels- in. Efferent vessels- out. * 2 regions; the outer cortex and the inner medulla
Cortex of lymph node
* Outer cortex- primary and secondary lymphatic nodules which comprise B lymphocytes (B cells)- (B cells live in the follicles) * Deep cortex (paracortex)- dense diffuse lymphatic tissue comprising T lymphocytes (T cells) * Corticomedullary junction (thymus dependent zone) contains high endothelial venules (HEV) through which reciculating lymphocytes are able to migrate from blood into the lymphatic tissues
Function of lymph nodes
* Lymph filtered through sinuses- come into contact with macrophages * Antigen uptake- carried out by macrophages, dendritic cells * Antigen uptake leads to lymphocyte formation - clonal expansion of B cells–> plasma cells–> antibody production - stimulated T cells proliferate in thymus dependent zone- leave node as recirculating lymphocytes
What is unique about a pig lymph node?
Structure is reversed- inner cortex and outer medulla. Few cells in efferent lymph.
What are hemal nodes?
Unique to ruminants and develop from LN primordia. No lymph vessels, no typical medulla- mainly sinuses filled with blood. Hemal nodes receive cells, antigens from blood, and after Ag stimulation many nodules may form. Functional significance of hemal node is not fully understood.
Lymphadenopathy
Enlarged lymph nodes- infection or neoplasia (lymphoma)
MALT
mucosal-associated lymphoid tissue. Located in subepithelial mucosal connective tissue. - Bronchial, gut, nasal, conjunctiva- associated - lymphatic nodules- solitary or aggregates - organ-like aggregated lymphatic nodules, e.g. tonsils, Peyer’s patch Function: provide means to allow early encounter of foreign antigens, leading to antibody production
Tonsilar lymphoid tissue location?
Location- lingual (base of tongue); palatine (caudolateral oropharynx); nasopharyngeal (roof of nasopharynx)
Location of Peyer’s patches?
Found predominantly in the ileum and at the ileocaecal junction
Caecal tonsils
*Aggregates of lymphatic tissues form nodular units at the caecum in check *Each nodular unit is demarcated by thin connective tissue
Spleen
Really part of the circulatory system, but it has a large population of lymphocytes. Left cranial part of the abdomen. Red pulp (loose lymphoid tissue) parenchyma, with isolated areas of white pulp (dense lymphoid tissue) interspersed through it. Function: *Antibody production- humoral immunity against blood borne antigens *filter blood- dispose of defective blood cells *preserves iron for re-use *bilirubin recirculated to liver * storage of cells- RBCs; platelets *haemopoiesis- in fetal life
What does the red pulp of the spleen do?
Haematological functions. Bulk of spleens volume and consists of splenic cords and the blood sinuses between them. Main function is removal of deteriorating red cells and platelets, and stores these cells. Contains smooth muscle- in order to contract and eject stored erythrocytes when needed.
What does the white pulp of the spleen do?
Immunological functions. Lymphatic nodules and dense tissues, evenly scattered among the loose red pulp. Splenic (lymphatic) nodules- B cell domain. Periarterial lymphatic sheath- T cell domain- diffuse dense lymphatic tissue/ surrounds central artery or arteriole.
Ellipsoids
In spleen. Sheathed capillaries. In white pulp in dog, horse, pig. Leaky capillaries
Sinusoids
Spleen of dog and human. Allowing free movement of blood. Many macrophages.
How does blood enter the spleen?
Splenic arterial supply via the splenic capsule.
Splenectomy
Can be removed without any longterm problems. Can make animal susceptible to blood-borne infections.
General lymph node function
Reacts to antigen in tissue fluid
General spleen function
Reacts to antigen in blood
General MALT function
Reacts to antigen at mucosal surfaces
Sinusoid
What is this and what is its function?
Megakaryocyte- a large bone marrow cell with a lobulated nucleus responsible for the production of blood thrombocytes (platelets). They usually account for 1 out of 10,000 bone marrow cells but can increase in number nearly 10-fold during the course of certain diseases.
Reticular epithelial cells
Direct the differentiation of T cells producing thymic hormones
Hassall’s (thymic) corpuscles- in the medulla. Degenerate epithelial cells form clumps. Keratinized centre surrounded by elongated epithelial cells. Seen mainly in older animals post puberty.
White pulp
Red pulp
How does blood flow through the spleen?
Splenic a. –> capsular and trabecular segments –> acquires periarteriolar lymphocyte sheath (PALs)–> blood delivered to red pulp i.e. splenic cords and sinuses–> veins–> trabecular veins–> splenic vein–> general circulation
Trabeculae in spleen
