1.2.3 GI Histology III Flashcards
The lymph nodes are secondary lymphoid organs which play important roles in antigen presentation and activation of the adaptive immune response:
• Possesses outer capsule (dense connective tissue), afferent and efferent lymphatic vessels, cortex and medulla held together by ___________
• Lymph enters via afferent lymphatic vessels, then ________________, and runs through the cortical and medullary sinuses and leaves via efferent lymphatic vessels
• Lymphocytes enter the lymph nodes via blood vessels (90%; ________________) and lymph (10%) from the bone marrow (B cells) and thymus (T cells)
reticular fibres;
subcapsular sinus;
high endothelial venule
The cortex usually contains numerous lymphoid follicles (primary and secondary), with a _____________ surrounded by a zone of small B lymphocytes forming the mantle:
• Germinal centres are formed especially during infections, causing _______________ and maturation into plasma cells within the lymph node
• B cells within the mantle are ‘resting’ and not participating in the current response
The germinal centres are sites of intensive proliferation and differentiation of B cells, and contain other cells (e.g. follicular dendritic cells) which aid this process:
• Primary follicles contain ____________, while secondary follicles usually contain a germinal centre with _____________________
germinal centre;
B cell clonal expansion;
inactive B cells;
large numbers of active B cells
[Cells in cortex]
Centroblasts: Cells with ______________ that proliferate when activated
• Resting B cells enter the lymph node via the HEV and undergo the cycle of blast transformation when the cognate antigen is met
• Naïve B cells → centroblasts → _____________ → ______________ → plasma cells (gradual movement into medullary cords)
• Undergo somatic hypermutation and immunoglobulin class switching to produce variation and specificity of antibodies
Tingible body macrophages: Possess larger cytoplasm with numerous apoptotic bodies to digest phagocytosed materials (centroblast T cells which do not have the ______________) after T cell proliferation/cloning
Follicular dendritic cells: __________ which possess long cytoplasmic processes to trap antigens and present them to B cells (major APCs of the follicles):
• May be involved in maintaining memory cell activity and stimulating a primary immune response
Others: ___________ (dividing cells) and small follicle centre cells (centrocytes with _____________)
multiple nucleoli;
centrocytes; immunoblasts
anti- apoptotic Bcl2 protein;
CD21+ cells;
Mitoses;
cleaved nuclei
PARACORTEX
The paracortex lies between cortical follicles and mainly consists of small T lymphocytes:
• Circulating T cells enter the lymph node through the walls of the post-capillary venules (HEV) → possess high __________________ which express specialised receptors (for lymphocyte extravasation)
Paracortical reaction: when activated, T cells enlarge to form immunoblasts and undergo clonal expansion, causing the expansion of the paracortical zone
Interdigitating dendritic cells: Derived from macrophage precursors (e.g. Langerhans cells) and possess ________________ (main APCs in the paracortex)
endothelial (cuboidal) cells;
irregular grooved pale nuclei
The lymph node medulla has branching medullary cords separated by irregular _______________, along with _____________extending from the collagenous capsular supporting tissue:
• Plasma cells and their precursors (plasmablasts) which have migrated from the germinal centres in the cortex are the major cell types:
o B cells complete final stages of maturation in the cords to form plasma cells (differentiated antibody-secreting B cells; usually not detected in blood)
o Some plasmablasts migrate to peripheral tissues via ______________
Cords (darker stained): Lymphocytes and plasma cells (synthesise antibodies which are carried to the general circulation in efferent lymph)
Sinuses (lighter stained): lined with ______________ (filtering system)
medullary sinuses;
trabeculae;
efferent lymph;
macrophages;
STAINING FOR CELLS
Various immune cells express different Cluster of Differentiation (CD) markers on their surface, which may be used to differentially stain for them on histology:
B lymphocytes
- Mainly in lymphoid follicles
- CD ___
T lymphocytes
- Mainly in paracortex/interfollicular area
- CD___
Follicular dendritic cells In follicles
- CD___
Actively proliferating cells
- Mainly in follicles
- Ki-67
20;
3;
21
The spleen is the largest lymphoid organ, and serves as a haematopoietic (blood-forming) organ in the foetus and destroys effete RBCs in adults:
• Possesses a fibrous capsule with ____________ that dip into the parenchyma
• Receives a rich blood supply via the splenic artery and is drained by the splenic vein into the ________________
• Splenic parenchyma is made of red pulp, with small macroscopically visible white nodules (white pulp) scattered throughout its substance
trabeculae;
hepatic portal venous system
WHITE PULP
The white pulp consists of aggregates of lymphoid cells around small arteries/arterioles:
• T cells(mostly small T helper cells) surround the central arteries to form the __________(less well organised in humans)
• B cells form follicles (usually at the edge of the PALS), with a _____________ (small lymphocytes) and marginal zone (less densely packed medium-sized lymphocytes)
Cell Area
T cells: Periarteriolar lymphatic sheath (PALS)
B cells: Lymphoid follicles (____________________)
PALS;
mantle zone;
Malpighian nodules
RED PULP
The red pulp is the largest compartment containing a network of vascular sinusoids for filtering blood:
• Arterial system terminates in the cords (reticular fibres, fibroblasts, macrophages, blood cells in transit) as open capillaries with ___________________
• Blood then passes into an _________________ which drain into larger sinuses, tributaries of the splenic vein, and finally the hepatic portal vein
• Made of loose tissue (supported by ___________) permeated by capillaries
o Reticulin fibres of the sinusoidal basement membrane are arranged circularly and are continuous with the parenchymal reticulin meshwork
discontinuous endothelium;
interconnected network of sinuses;
reticulin fibres;
BLOOD CIRCULATION
The spleen is supplied by the splenic artery (entering at the hilum), which divides into ____________, then penicillar arteries which end as ___________:
• Spleen possesses an open and a closed circulation
• Sheathed capillaries are part of the open circulation as they end with no endothelial cells, but rather surrounded by _______________ (filter blood as it enters red pulp)
It is then drained via ___________, which in turn drain into the venous sinuses then the splenic vein:
• Endothelial cells lining the venous sinuses are elongated (stave) cells with intervening slits (for RBCs to pass through)
• Aging or abnormal cells (less deformable) and particulate matter are unable to pass and are phagocytosed by macrophages
central arteries;
sheathed capillaries
macrophages;
splenic cords;
FUNCTIONS
The spleen serves the following four main functions:
• Removal of _________________ and particulate matter from blood via phagocytosis
• Storage of _______ from recycled RBCs (breakdown of haemoglobin)
• Initiation of adaptive immune response (responding to circulating antigens)
• _______________ (in foetal life)
abnormal RBCs;
iron ;
Haematopoiesis
