Histology Flashcards
What are the organs of the haematolymphoid system?
Thymus Bone Marrow Lymph nodes Spleen Mucosa associated lymphoid tissue
What fluid drains into lymph nodes? How is this formed?
Receive a blood supply and they drain lymph from tissues
Formed by excess fluid that is left in tissues due to differences in hydrostatic and oncotic pressures from arterial to venous ends of a capillary bed
Greatest where vessels are leaky e.g. during inflammation
Contain dead cells, fragments of degraded tissue and any antigens that have broken through the physical barrier of the skin/mucosa
What fluid carries antigens to the spleen?
Blood
What are the functions of the spleen?
Production of an immunological response against blood borne antigens
Removal of particulate matter and aged or defective blood cells from the circulation
Recycling iron back to the marrow
Extra-medullary haematopoiesis in the fetus and during certain bone marrow diseases
What are antigen presenting cells? What types are there?
Present antigen to lymphocytes bound to major histocompatibility complexes
Contact of MHC-peptide complex with a T cell receptor with appropriate specificity then activates T cells
Non-professional (all cells nucleated cells)- MHC Class 1. Viral
antigens or cancer antigens would be expressed by these cells with MHC Class 1 and would invoke a response by cytotoxic T cells.
Professional APC (dendritic cells, macrophages, Langerhans cells) take in external antigen, process it and present it bound to MHC Class II receptors. Class II+ antigen promote T helper cell response, which then activate B cells
What are the classes of lymphocytes? What are the major functions of each?
B Cells: derived from bone marrow. Stimulated B cells mature into plasma cells. Once activated, mitotically divide producing a mixture of plasma cells and memory B cells (capable of mounting a secondary immune response: more rapid, greater magnitude and produces IgG)
T Cells: effector and regulatory functions. T cells migrate from bone marrow to thymus where they develop into mature T cells (or undergo apoptosis if they are self-reactive). T cells then move into secondary lymphoid organs e.g. lymph nodes and MALT, but are constantly circulating round. T helper cells- help other cells by secreting
interleukins. T cytotoxic cells- kill viral and cancer cells. Require help from TH cells to become active
What are the different types of antibody?
Ig- G, A, D, M and E
What types of interleukins are secreted by helper T cells? What functions do they have?
TH1- promote a cell mediated reaction
TH2- promote humoral immunity
TH17- acute inflammation
Describe the structure of a lymph node
Afferent lymphatic inflow on convex surface
Flow through cortical sinuses (encounter B cells and APC) into medulla
Flow out through medullary sinuses to efferent lymphatic on concave surface
Follicles contain B cells
Paracortex contain T cells
Medulla contains plasma cells
Describe the structure of a lymphoid follicle
Mantle zone: resting B cells Germinal centre: dendritic cells, centrocytes, centroblasts shouldn’t see mitiotic figures here, only class switching and maturation
What are centrocytes and centroblasts?
Centrocyte: B cell with cleaved nucleus, formed following cessation of centroblast proliferation
Centroblast: activated B cell, enlarged and proliferating. Metabolically active B cells proliferate in germinal center of a secondary lymphoid follicle following exposure to follicular dendritic cell cytokine
What type of lymphoma would occur from follicle centre cells? Would you expect this to be high or low grade?
Follicular lymphoma
Depending on the number of blasts versus centrocytes the tumour can be relatively indolent or aggressive (high number of blasts)
What cell type is found predominantly in medullary cords of lymphoid tissue?
Plasma cells
What are the characteristic micro anatomical features of the spleen?
Red pulp: interconnected sinuses, tributaries of splenic vein. Blood cells enter parenchyma from capillaries, squeeze through walls of the sinuses and drain out via the splenic vein
White pulp: periarteriolar lymphoid sheaths, mainly TH1 cells. Prominent marginal zone of medium cells
What are the characteristic micro anatomical features of the thymus?
Two regions: cortex and medulla divided into lobules.
T cell almost exclusively- maturation, division and deletion of self-reactive T cells
Squamous cells areas: Hassall corpuscles in medulla
