Lymphatic System Flashcards
What is the lymphatic system?
A group of cells, tissues, and organs that monitor the body and react to a presence of potentially harmful substances and infectious agents
What are lymphocytes?
These are the definitive cell type and the effector cells in the immune system response
What is the immune system?
An interconnection of blood and lymphatic circulation through various organs, tissues, and cells
What are the primary lymphatic organs?
Bone marrow
Thymus
What are the secondary lymphatic organs?
Lymph nodes
Spleen
Diffuse lymphatic tissue nodules (such as MALT, tonsils, and appendix)
The lymphatic system is composed of ______ vessels that transport interstitial fluid (referred to as ____)
Lymphatic, lymph
What is innate immunity (natural, nonspecific) ?
This is the first line of defence against microbial invasion ]. You are born with this ability and it does not change over time
What are mediated cells within the lymphatic system?
Phagocytic, neutrophils, macrophages/monocytes, and also NK cells
What is adaptive immunity?
Adaptive defence that targets specific invaders and foreign proteins. Acquired by gradual exposure.
With regards to adaptive immunity, what type of lymphocytes are involved? What is their purpose?
Involves B and T lymphocytes, these activate and work against specific antigens.
Specific molecules are presented to lymphocytes by ______ ______ cells
Phagocytic APC (antigen presenting cell)
What are APC cells derived from?
Mostly derived from monocytes, macrophages, kupffer cells, dendritic cells, langerhans cells
What are the two types of specific defences of adaptive immunity?
Humoral immunity—> production of proteins called antibodies (immunoglobulins) by B lymphocytes which have differentiated into plasma cells
Cell mediated immunity—> response targets transformed cell and infected cell (viral, fungal) for destruction by specific killer cells. These involve T lymphocytes
What are antigenic determinants (Epitopes)?
These are small molecular domains of the antigen immune cells that can be recognized and reacted to
What are major histocompatability? What are the two types (don’t describe)? And where does this originate?
Major Histocompatability (MHC) is produced by a super gene located on chromosome 6 in humans. It has MHC I and MHC II
Explain what MHC I means
- expressed on the surface of all nucelated cells and platelets
- presents peptide fragments to cytotoxic CD8+ T lymphocytes
- acts as a target to allow elimination of abnormal host cells
- express they are actively synthesized by the cell
Explain what MHC II is
- limited in distribution, expressed on surface of all APCs
- critical in immune interactions
- MHC II partially digest endocyted foreign peptides to CD4+ T lymphocytes
How are cells identified within the immune system?
They are identified by specific clusters of differentiation (CD) markers on their surface
What are cluster differentiation (CD) molecules?
These are designated by numbers according to an international system that relate them to antigens expressed on their surface at different stages in their differentiation
True or false:
MHC occur in strict species, variety within these species is genetic.
False, MHC proteins occur in many species
What is the humans version of MHC?
HLA—>Human leukocyte Antigen
Explain in detail some characteristics of T-Lymphocytes (T cells)
- differentiate in the thymus (but are produced in bone marrow)
- accounts for 75% of circulating lymphocytes
- involved in cell mediated immunity
- recognize antigenic epitopes via T cell receptors (TCRs)
- only recognize antigens when presented as part of MHC molecules
What are some important subsets of T Lymphocytes? (Don’t explain)
- helper T lymphocytes express CD4 markers, CD4+T cells
- Cytotoxic T lymphocytes (Killer T cells)
- Regulatory (suppressor) Lymphocytes
Helper T lymphocytes express CD4 markers, CD4+T. Explain how this is important in subset T lymphocytes.
- TCRs and CD4 bind MHC class II molecules
- assist with the immune response by producing cytokines
Activates the following 3:
- cytotoxic CD8+T cells (further activates CD4+T cells)
- activates macrophages to become phagocytic and produces cytokines
- Promotes differentiation of B cells into plasma cells
Cytotoxic T lymphocytes (Killer T cells) express CD8 marker and create CD8+ cells, How is this an important subset of T lymphocytes?
TCRs with CD8 bind to specific antigens on cancer transformed cells - MHC class 1 molecules are altered from the norm, these put on display microorganisms, parasites, and transported cells
What is the importance of regulatory (suppressor) lymphocytes for subsets of T lymphocytes?
These have CD4+ and CD25+
-serve to inhibit excessive immune responses by inhibiting other immune cells
What does the activation of T lymphocytes cause?
This produces clones of memory cells. This means there is a faster response on subsequent exposures
Explain in detail some characteristics of B lymphocytes (B-cells)
- differentiate in bone marrow (bursa equivalent organs)
- accounts for 20-30% of circulating lymphocytes
- involved in humoral immunity
- each cell is covered with many B-Cell receptors (BCRs) which are monomers of IgM and IgD
How do IgM and IgD function?
Bind antigen—>endocytosed—>processed—>presenting on the MHC class II molecule of the B cell—> presenting to a T helper cell—> T helper stimulates gene recombination— >maturation into plasma and memory B cells
What are the function of plasma cells?
- produce anitbodies against the specific antigen that was originally bound and processed
What is the function of memory B cells?
These are long lived, allow a rapid response upon subsequent exposure
What does the activation of B lymphocytes cause?
This produces clones of memory B cells which means a faster response on subsequent exposure
What is the basic structure of an antibody?
Two light chains and two heavy chains form an antibody monomer
What are the two chains in an antibody connected by? What do their various ends connect?
The chains are linked by a disulfide bond.
The variable portions (Fab) bind the antigen (at a specific epitope)
The constant region (Fc) of the molecule binds to the surface receptor of the cell
Wha are the five major classes of antibodies? (Don’t explain them)
G A M E D
- IgG
- IgA (secretory)
- IgM
- IgE
- IgD
Describe the antibody IgG and its characteristics
This is the most abundant, and smallest monomer
- highly soluble and confers passive immunity
- activates phagocytosis, opsonization, neutralizes antigen
- major memory immunoglobulin
- found in fetal circulation in women
Describe the antibody IgA and its characteristics
This is present in most secretions (milk, tears, saliva)
- produced by plasma cells mainly near mucosal surfaces for protection against organisms
- can be found in a diametric form (J, joining chains) that holds two monomers together
- has a secretory piece
- mainly protects mucosae
Describe the antibody IgM and its characteristics
This is the largest immunoglobulin and exists in a pentameric form
- mainly produced in the initial response to an antigen response
- most effective antibody in activating compliment
- serves as an antigen receptor (BCR) as monomers
- found in B lymphocyte surfaces
Describe the antibody IgE and its characteristics
- these have Fc receptors on the basophils and mast cells
- when IgE binds to these cells it triggers release of substances resulting in an allergic reaction
- destroys parasitic worms and participates in allergies
Describe the antibody IgD and its characteristics
- this is the least abundant
- bound to the surface of B lymphocytes, acts as an antigen receptors (BCR) triggering B cell activation
- found in surface of B lymphocytes
What are the three actions of antibodies? (Do not describe them)
- Compliment activation
- Opsonization
- NK cell activation
Explain what “compliment activation” is
This is a system or group of roughly 20 plasma proteins that when activated, will cause a cascade of enzymatic reactions that result in cell membrane rupture of invading cells.
Explain what “opsonization” is
This is receptors on macrophages, neutrophils, and eosinophils. These allow for the facilitation of phagocytosis by Leukocytes
Explain what “NK cell activation” is
This is when antibodies bound to antigens on virus infected cells are recognized ny NK cells. NK cells; release protein that cause death of infected cells.
What are NK cells?
Constitutes for 5-10% of circulating lymphocytes
- neither T nor B cells
- these are specialized to kill certain types of targeted cells
What are lymph nodes?
Small bean shaped encapsulated lymphatic organs located along the pathway of lymphatic vessels
What are the two types of lymphatic vessels? Explain them.
Afferent lymphatic vessels: brings lymph’s into the lymph node
Efferent lymphatic vessels: brings lymph away from the lymph node at the heilum.
What is a hilum?
Concave depression on the concave surface that serves as an entrance/exit for blood and lymphatic vessels and nerves
What are the three supporting elements of lymph nodes?
Capsule—> composed of dense irregular connective tissue
Trabeculae (CT septa)—> CT extension from the capsule that extends into lymph node forming a supportive framework
Reticular tissue—> reticular cells and reticular fibres form a fine supporting mesh work
What does the parenchyma divide itself into?
The cortex and the medulla
Explain the outlayer of the lymph node, the cortex.
The cortex is comprised of the sub scapular sinus—immediately below the capsule and receives lymph from the afferent lymphatics
What is the function of cortical sinuses in lymph nodes?
These branch among the lymphatic nodules within the trabeculae
What are lymphatic (lymphoid) nodules?
These are round aggregations of lymphocyte, which are mostly B-Lymphocytes
What are the two types of lymphatic nodules? Explain them.
- Primary lymphatic nodule—> currently no immune response
- Secondary lymphatic nodules—> immune response to antigen presentation; these are paler and germinal centre of proliferating lymphocytes surrounded by cornea (mantle) of small mature lymphocytes
What is the paracortex? What does it contain?
This is a deeper extension of the cortex, there is no lymphatic nodule, diffuse. These are mostly T cells.
This contains highendothelial venules (HEVs) that are specialized post capillary venules, entry point for most circulating lymphocytes.
What is the medulla? (Not the brain portion)
The medulla is the inner region of the lymph node
What are the three components of medulla? Explain them.
- Medullary cords—> branching cordlike masses (reticular fibre) contain mostly B lymphocytes and plasma cells, T lymphocytes, Macrophages, and dendritic cells
- Medullary sinuses—> dilated lymphatic vessels that contain lymph with a discontinued endothelium and extends from the cortical sinuses. These converge and empty into the efferent lymphatic vessel at the hilum
- Thymus—> bi lobed organ in superior mediastinum. These are the site of T cell differentiate (thymocytes) and proliferation. Only T lymphocytes resides in the thymus. These are fully formed and functional at birth.
What is the general description of the thymus?
- Bi lobed organ in superior mediastinum anterior to the heart
- site of T cell differentiation (thymocytes) and proliferation
- only T lymphocytes reside in thymus
- fully formed at birth
- around puberty is when T cells differentiate and proliferate
What is the general architecture of the thymus? Only give a brief outline.
—A connective tissue capsule surrounds the thymus —trabeculae CT septa —epithelioreticular cells —cortex —medulla
What are epitheliorecticular cells?
These are features of reticular cells and epithelial cells that are supportive cells.
What is the function of epithelioreticular cells?
Line capsule, trabeculae, and surround microvasculare to form blood thymus barrier. These form a cytoreticulum to support thymocytes
Are there true CT fibres within a thymic lobule?
No
Each lobule has an outer darker staining region, more densely packed thymocytes is found here. What is this called?
Cortex
What is the medulla?
This is a paler inner staining area. It has epithelioreticular cells. This also contains Hassan’s corpuscles.
What are Hassalls corpuscles?
These are large aggregates of concentrically wrapped epithelioreticular cells. These are thought to produce factors that promote T cell development
What is the largest lymphatic organ in the body? What is the function of this?
THE SPLEEN!
This functions as a filter for blood and reacts immunologically to blood borne antigens (white pulp) . This is the main site of destruction and removes old and damaged RBC.
What is the general architecture to the spleen? What are the two features?
This has a connective tissue capsule that surrounds the spleen as well as a trabeculae (CT septa).
The CT septa branches extends into parenchyma of spleen and contains myofibroblasts and is contractile which helps release RBCs
What is the hilum of the spleen?
This is the indentation on the medial surface where the splenic artery entres
What does the parenchyma of the spleen consist of? (3 factors)
Red pulp and white pulp
What is white pulp?
This is a lymphatic nodule that may be primary or secondary, but mainly B lymphocytes.
What are the two features of White Pulp?
Central artery—> a branch of the trabecular arteries.
Periarterial Lymphatic Sheath (PALS)—> cylindrical aggregation of lymphocytes around central artery. Mainly T lymphocytes.
What is the pathway for the central artery in white pulp?
Here is the pathway: Splenic artery—> Trabecular Arteries—> Central Arteries—>Penicullar Arterioles—>Sinusoids
What is red pulp made of? (3 factors)
- Splenic cords (billroth cords)—> reticular tissue that contains large numbers of RBCS rich in macrophages and lymphocytes.
- Splenic sinusoids (sinuses)—> sinusoidal capillaries that are discontinuous where old RBCs are removed
- Diffuse lymphatic tissue—> this includes MALT and the tonsils.
What is MALT?
Mucosa Associated Lymphatic Tissue:
-this is where lymphocytes are dispersed diffusely throughout connective tissue or aggregated into nodules. These are not permanent cells.
