TBL 14: Bone Marrow Flashcards
What are the different hematopoietic organs from gestation to birth?
Blood islands in the mesoderm surrounding the yolk sac. From 2nd to 7th month of gestation, the liver is colonized by hemangioblast-derived hematopoietic stem cells. From 7th month on, the bone marrow is colonized by these stem cells
What are blood smears good for?
cells details, maturation, differential counts, ratio of myeloid to erythroid cells, morphological changes, detect anemias, leukemias, and myeloma
What are needle biopsies good for?
Panoramic view of bone marrow and normal architecture, bone marrow cellularity (index of hematopoietic cells to adipocytes)
How do autologous and allogeneic bone marrow transplants differ?
Autologous - used in lymphoma where marrow is contaminated. Harvest bone marrow and reinject it after obliterating the remaining stem cells
Allogenic - bone marrow comes from another person who matches MHC
What are the four CFU cells?
erythrocytic, granulocytic-monocytic, lymphocytic, megakaryocytes
The cells of erythropoiesis and the characterization of them
CFU-E, proerythroblasts, basophilic, polychromatophilic, orthochromatophilic, nuclear extrusion, reticulocytes (no central pallor), erythrocyte
What is the role of erythropoietin? How long does erythropoiesis last?
produced in kidneys and it stimulates and sustains erythropoiesis which takes about 7-8 days
Why is hypoxia the principal stimulus for erythropoietin secretion?
Regulation exists as a feedback loop. Hypoxia tells the kidneys that not enough O2 is delivered to tissues so it produces erythropoietin to stimulate the development of more RBCs to increase the blood’s O2 carrying capacity
Why does cytoplasmic color change from blue to reddish pink during erythropoiesis?
The RNA also absorbs the basic stain. Over time, the cytoplasm has less RNA as the nucleus is gone so the cytoplasm changes color
Describe granulopoiesis
CFU-GM, myeloblasts, promyelocytes, myelocytes, metamyelocytes, band cells and lobulation of the horseshoe shaped nuclei completes process
When do neutrophilic, eosinophilic, and basophilic granules become distinct?
Metamyelocytes
Characterize Promyelocytes
large, round nuclei and reddish blue cytoplasmic granules (lysosomes)
Characterize Myelocytes
Nuclei are eccentrically positioned and flattened on one side
Characterize metamyelocytes
The flattened side of the nucleus becomes indented and the granules become distinct
Characterize band cells
progressive deepening of the indentation results in horseshoe-shaped nuclei
What is sepsis and when can it progress to septic shock?
systemic response to infection. Blood poisoning. Infection in blood leading to inflammation. Can progress to shock if hypotension and organ dysfunction fail to respond to antimicrobial treatment
At what age are progenies of T cells established by?
Mid-twenties
Describe the thymus
Two lobes surrounded by connective tissue capsule. Short trabeculae project into outer portions of lobe subdividing them into lobules with an dark stained cortex around a pale medulla
What are epithelial reticular cells
Form a meshwork extending between trabeculae creating a scaffold supporting the T cells.. They secrete thymosin and thymopoeitin which induce T cell maturation and cell-mediated immunity
What does lymphocytopoiesis do and describe the maturation of T cells?
Generates mature B cells and immature T cells in bone marrow. Immature T cells circulate to capillaries in the thyme medulla and traverse the capillary endothelium into the cortex where they become immunocompetent.
Why do recurrent opportunist infections characterize DiGeorge syndrome?
Thymus does not develop properly and thus, there is a T cell deficiency leading to immunodeficiency
What forms the blood-thymus barrier?
tight junctions between cortical capillary endothelial cells, thick basement membranes, macrophages, ERC processes
Function of blood-thymus barrier and what happens when a T cell circumvents it?
Blocks premature exposure of non self and self antigens in the blood to maturing T cells. If a T cell is exposed, it undergoes apoptosis which prevents immune reactions in the thymus
What part of the thymus has no blood-thymus barrier and why? What is this part not stained as darkly?
Medullary capillaries so that matured T cells can enter bloodstream. T cells don’t spend a lot of time in the medulla so that explains the weak stain
What are the thymus (Hassall’s) corpuscles? Where are they? What do they do?
In the medulla and formed by clusters of ERC. Many cells undergoing degeneration. ERCs in this produce cytokines that induce development of regulatory T cells
In what systems are lymphatic capillaries particularly abundant in?
Those open to external environment. Skin, respiratory, urogenital, digestive
What are lymphangitis and lymphadenitis and why are these conditions potentially dangerous?
Secondary inflammation
Lymphangitis - lymphatic vessels
Lymphadenitis - lymph nodes
Uncontained, these conditions could lead to septicemia
What is lymphedema
a localized type of edema when lymph does not drain from a particular part of the body
What forms the MALT?
Aggregations of lymphocytes (lymphoid nodules) that join the lymphatic capillaries and vessels to form MALT
What makes up the lymphoid nodules and what else is part of MALT?
Mostly B cells that selectively bind to invading bacterial antigens and replicate. T cells are dispersed among the lymphoid nodules in MALT
What triggers a humoral immune response
Release of immunoglobulins by plasma cells that bind antigens
What occupies the paler germinal center of a lymphoid nodule
Plasma cells from the activated B cells
What is required for T cell activation?
They need to bind both non self antigen and self-antigen
Why can graft-versus-host disease (GVHD) occur after allogeneic bone marrow transplantation?
The graft T cells see the tissue of the host as foreign inducing an inflammatory response and apoptosis of the host tissue
How many lymph nodes are in the body?
500-600
Describe lymph nodes
dense connective tissue capsule (type I collagen) with dark cortex and pale medulla. Lymphoid nodules form in the cortex from activated B cells. There is also a trabeculae network and reticular fiber meshwork (Type III collagen)
What are high endothelial venules (HEV)?
venules lined with simple cuboidal endothelium around the boundary. They bind circulating lymphocytes to take them from the bloodstream into the cortex. The medullary and cortical capillaries drain into the HEV and the HEV empty into veins that exit the lymph node at the hilum
Describe the path (which sinuses) and what they are?
Afferent lymph vessels deliver to subcapsular sinus which is continuous with the trabecular sinus which are continuous with the medullary sinuses that weave among the medullary cords
What lines the sinuses?
Discontinuous epithelium
What associates with sinuses and helps filter the lymph?
Macrophages and there are some surrounding B cells
What are the medullary cords?
Linear aggregates of antigen-activated lymphocytes and plasma cells that migrated from the cortical lymphoid nodules to medulla. The lymphocytes and antibodies enter the percolating lymph through the porous medullary sinuses
What accounts for pale staining of medulla in lymph nodes?
Extensive branching of the medullary sinuses
What forms the single efferent lymphatic vessel at the hilum?
Coalescence of medullary sinuses forms the single efferent vessel that transports the lymph, lymphocytes, and Abs out of lymph nodes
What conditions can cause lymphadenopathy?
enlargement of the lymph nodes. Can be caused by metastasis or antigenic stimulation in a bacterial or viral infection
What is the course taken by activated lymphocytes from the local lymph nodes to the MALT for amplification of the humoral immune response?
Efferent vessels to leave local lymph nodes and the HEV in MALT causes the homing process where the lymphocytes bind selective cytokines to migrate to that tissue
