Haematopoiesis

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3rd week of embryogenesis
Blood begins to circulate
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Extramedullary haematopoiesis
Haematopoiesis occurring outside of the medulla of the bone
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Primary lymphoid organs
Site of immune cell production and development
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Secondary lymphoid organs
Sites of lymphocyte maturation, antigen entrapment (trapping of pathogens) and blood cell destruction).
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Primary site of adult haematopoiesis
• Pelvis • Sternum • Vertebrae • Ribs • Heads of femur / humerus
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Chemotherapy
Cytotoxic drugs used to “kill” fast growing cells (ie cancer cells). However, act on other fast growing cells too (causing side effects)
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Post chemotherapy
Bone marrow becomes active as it tries to replace blood cells.
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Bone marrow
Spongy tissue inside bones that produces blood cells.
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Red marrow
Found in flat bones (and heads of long bones) produces most blood cells.
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Yellow marrow
Found in long bones produces some white cells.
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Stromal cells
Form the extracellular matrix and secrete growth factors.
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Macrophages
Clear debris
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Fibroblasts
Secrete extracellular matrix to give the area structure.
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Adipocytes
Energy source
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Endothelial cells
Compartmentalisation / structure
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Bone marrow transplants
Used to reconstitute the immune system of leukaemic patients. Can be harvested from sites of red marrow
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Thymus
Site of T-cell development and maturation - immature T-cells are called “thymocytes”
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Thymocytes
Traverse through the cortex (positive selection), through the cortex-medulla border (negative selection) into the medulla (differentiation). There are many thymocytes in the cortex but few in medulla. 95% are destroyed by apoptosis.
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Thymic Involution
Decline in immune function with old age.
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Secondary lymphoid organs
Sites of lymphocyte maturation, antigen entrapment (and blood cell destruction).
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Lymphatic system
Travels in lymphatic vessels (valves, lymph nodes). Collects in thoracic duct and drains back into left subclavian vein.
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Main sites of lymph nodes
Axillary, inguinal, submandibular (abdomen, chest)
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Lymph nodes
Clean the lymphatic system. B and t cells scan the fluid for pathogens. Site of activation and division of antigen activated T cells and B cells.
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Thoracic duct
Brings all the fluid from the lower part of the body back to the subcalavinan vein.
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Cortex
Contains primary follicles containing mostly B- lymphocytes. After antigenic challenge enlarge to form secondary follicles containing a germinal centre.( cluster in the middle deviding into active b cells).
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Paracortex
Contains mainly T-lymphocytes.
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Medulla
Contains mainly macrophages. Clear up any pathogens – phagocytosis
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The Spleen
Largest “filter” of blood in the body. Removes old or damaged blood cells. Windows are 3 ym, a healthy blood cells can squeeze through all the gaps, an old cells can not and gets destroyed.
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The structure of the spleen
Outer capsule with projections (trabecula) forming a compartmentalised structure. Blood enters via the splenic artery, giving rise to arterioles which end in cords Blood passes through the white pulp, into the red pulp, and re-enters circulation
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White pulp
Surrounds the splenic artery forming a periarteriolar lymphoid sheath (PALS) containing mainly T-lymphocytes.
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Marginal zone
Contains mainly B-cells, macrophages.
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Red pulp
Meshwork of splenic sinuses and splenic cords. The cords are packed with macrophages and Ab-secreting plasma cells.
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Mucosal Associated Lymphoid Tissue (MALT)
Mucous membranes lining digestive, respiratory and urogenital systems have a huge surface area (400m2). This is the major site of entry for pathogens.
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Tonsils
Meshwork of reticular cells fibers interspersed with lymphocytes, macrophages, granulocytes and mast cells Function of the tonsils is to defend against antigens entering through the nasal and oral epithelial routes.
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Peyer’s Patches
The GI tract can endocytose antigen from the lumen where an immune response can be raised and antibody can be exported to the lumen. Germinal centres contain lots of B-cells.
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Lamina propria
Contains large numbers of B cells, plasma cells, activated TH cells and macrophages.
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Submucosal layer
Below the lamina propria contains Peyer’s patches (groups of lymphoid follicles).
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M cells
Lack microvilli and endocytose Ag from gut lumen. Take in antigen and identify pathogens.
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Plasma B cells
Release IgA (secretory Ig molecule) into the gut.
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Myeloid
Granulocytes, macrophages, megakaryocytes (platelets), erythrocytes.
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Lymphoid
t-cells, b-cells and nk cells.
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CFU
Colony forming unit (a colony of cells generated from one progenitor cell).
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CFUGEMM
CFU that can make myeloid cells (granulocytes, erythrocytes, monocytes, megakaryocytes).
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Estimated total haematopoietic cell production
around 3.7x1011 cells per day .
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Haematopoietic growth factors
Produced by bone marrow stromal cells
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Erythorpoietin
Synthesised by kidney, tells cells to become red blood cells due to low oxygen levels in the blood.
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Thrombopoietin
Synthesised by liver, tells the cells to become platelets
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Cytokines
Secreted proteins that induce immune / inflammatory responses including cell proliferation, communication and cell death.
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IL-3 and GM-CSF
Multi potential growth factors. myloide cells.
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IL-7
Stimulates differentiation of the multipotential haematopoietic stem cell to lymphoid progenitor cells.
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Tpo
Increases production of platelets
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Epo
Increases production of red blood cells
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IL-4
Increases production of B-lymphocytes
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IL-2
Increases production of T-lymphocytes
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Other cards in this set

Card 2

Front

Extramedullary haematopoiesis

Back

Haematopoiesis occurring outside of the medulla of the bone

Card 3

Front

Primary lymphoid organs

Back

Preview of the front of card 3

Card 4

Front

Secondary lymphoid organs

Back

Preview of the front of card 4

Card 5

Front

Primary site of adult haematopoiesis

Back

Preview of the front of card 5
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