Lymphatic System Flashcards
What are three functions of the lymphoid system?
- Antibody to antigen binding (self vs. foreign defense)
- Cell mediated immunity (T-lymphocytes, killer cells)
- Humoral immunity (B-lymphocytes)
What are the cells involved in cell-mediated immunity?
- T-lymphocytes
- Killer cells
What are the cells involved in humoral immunity?
B-lymphocytes
What are the five broad types of lymphoid tissue found in the body?
- Hematopoietic tissue (bone marrow)
- Thymus gland tissue
- Encapsulate lymphoid organ tissue
- Unencapsulated lymphoid tissue
- Diffuse lymphoid tissue
What are the two encapsulated lymphoid organs?
- Lymph nodes
- Spleen
What are the two unencapsulated lymphoid tissue types?
- Lymph nodules
- Tonsils
Where are lymphocytes and plasma cells found in the esophagus?
In LOOSE CONNECTIVE TISSUE under the esophageal epithelium
What are the two types of immunity?
- Innate immunity (granulocytes and other leukocytes)
- Adaptive immunity (lymphocytes and antigen presenting cells)
Where are lymphocytes formed? Where are they activated and proliferate?
- Formed in the primary lymphoid organs
- Activation and proliferation in the secondary lymphoid organs
What comprises mucosa-associated lymphoid tissue (MALT)?
- Immune cells located in digestive, respiratory or urogenital mucosae
What do natural killer (NK) cells do?
Destroy various unhealthy host cells (eg. infected with bacteria, virus or cancer)
What are the primary lymphatic organs/structures? (2)
- Thymus
- Red bone marrow
What are the secondary lymphatic structures? (4)
- Tonsils
- Cervical/axillary/inguinal lymph nodes
- Spleen
- MALT (mucosa-associated lymphoid tissue) in small intestine
What do leukocytes secrete?
- HCl and organic acids
- Defensins
- Lysozymes
- Complement system of proteins in blood plasma
- Interferons
What are defensins?
Short cationic polypeptides produced by neutrophils and various epithelial cells that kill bacteria by disrupting the cell wall
What are lysozymes?
Enzymes made by neutrophils and cells of epithelial barriers, which hydrolyzes bacterial cell wall components, killing those cells.
What is complement?
A system of proteins in blood plasma, mucus, and macrophages that react with bacterial surface components to aid removal of bacteria.
What are interferons?
Paracrine factors from leukocytes and virus-infected cells that signal NK cells to kill such cells and adjacent cells to resist viral infection.
What are cytokines?
Small glycoproteins and peptides that have specific functions in coordinating cell activity in innate and adaptive immune responses
What are molecules recognized by cells of the adaptive immune system?
Antigen
What do antibodies do and what secretes them?
Plasma cells secrete antibodies which interact with antigens
Once antibodies clump with antigens or cause NK cells to kill a cell, what type of cell removes the remains?
Phagocytic leukocytes
What are the two types of lymphocytes and where do they develop?
- T lymphocytes (thymus)
- B lymphocytes (bone marrow)
Both the thymus and bone marrow are primary lymphoid organs/structures
Where can lymphocytes be found?
T and B lymphocytes can be found developing in primary lymphoid organs/structures. After development they migrate to secondary lymphoid organs (eg. MALT, lymph nodes, spleen). They then circulate through blood, connective tissue and lymph throughout the body.
What type of connective tissue does most lymphoid tissue have?
Reticular connective tissue
What do helper T cells do?
Secrete cytokines
A type of T lymphocyte
What do B cells differentiate into?
Plasma cells
What do B lymphocytes do?
A part of the adaptive immune response, humoral immunity. These directly bind with antigens and begin endocytosis. A helper T cell then binds to the B lymphocyte to begin proliferation of B lymphocytes to plasma cells with cytokines. The aggregation of B cells forms primary lymphoid nodules.
The eventual aggregation of B cells and helper T cells forms secondary lymphoid nodules
Describe the stages of a lymphoid nodule?
- B cells that have binded to antigens aggregate to form a primary lymphoid nodule
- Helper T cells (Th Cells) release cytokines causing the B cells to proliferate rapidly and form a secondary lymphoid nodule
- Nonproliferating B cells are pushed to asid to produce a darkly stained peripheral mantle
- After 2 to 3 weeks of proliferation, most cells of the germinal centre and mantle are dispersed and the structure of the secondary lymphoid nodule is gradually lost
What do B lymphocytes differentiate into? (2)
- Plasma cells that secrete antibodies that bind to the same antigen epitope recognized by activated B cell (humoral immunity)
- Memory B cells are lymphocytes that allow a very rapid response upon subsequent exposure to the same antigen
How many lobes does the thymus have and where is it located?
Bilobed
In the mediastinum of the thorax, ventral to the trachea.
What in involution of the thymus?
Great decrease in size during puberty. Mostly becomes filled with adipose tissue and T cell production is dramatically decreased.
What is a main function of the thymus?
Central tolerance and prevention of autoimmunity.
What type of cell proliferates in the thymus during its development? Where does it come from?
Lymphoblasts from bone marrow
What type of connective tissue does the thymus have?
- A vascular capsule that has extending septa that separate thymic lobules
- A cortex surrounding medulla of the thymus
What types of selection in the thymus promote differentiation of T lymphocytes? What regions of the thymus do these two processes take place?
- Positive selection (cortex)
- Negative selection (medulla, allows survival only of T cells that do not tightly bind self-antigens presented on dendritic cells there)
What is mucosa-associated lymphoid tissue (MALT)?
Large and diffuse collections of lymphocytes, plasma cells, antigen presenting cells (APCs) and lymphoid nodules.
These are found in the mucosa because the mucosa is the inner lining of the digestive, respiratory and genitourinary tracts, where pathogens commonly invade due to openings to the external environment.
Where are lymph nodes found?
Distributed throughout the body along the lymphatic vessels. All lymph is filtered and has antibodies added by at least one lymph node
Where are lymph nodes most commonly found? (5)
- Armpits (axillae)
- Groin
- Major vessels of the neck
- Thorax
- Abdomen (esp. mesenteries)
What do lymph nodes primarily do? (2)
- Filters lymph to defend against spread of microorganisms and tumor cells
- Provide enclosed environments that facilitate plasma cell production (and therefore facilitating antibody production)
What is the region of a lymph node where an efferent lymphatic vessel leaves? What other things penetrate the organ here?
The hilum
An artery, vein and nerve also penetrate the organ at the hilum.
What type of connective tissue is associated with lymph nodes? What is the structure of this tissue?
Dense connective tissue that forms a capsule around the node and extends trabeculae within through which blood vessels branch.
What type of cells are found in lymph nodes? (6)
- Lymphocytes of all types
- plasma cells
Dendritic cells - Macrophages
- Antigen presenting cells (APCs)
- Follicular dendritic cells (FDCs)
What are the three regions of a lymph node?
- Cortex
- Central medulla
- Paracortex between the cortex and medulla
What are the two regions of a lymphatic nodule?
- Germinal centre
- Mantle zone
What keeps lymph flow unidirectional in lymph nodes?
Valves in afferent and efferent lymphatic vessels
What structures fill most cortical areas of lymph nodes?
Lymphoid nodules in between processes of follicular dendritic cells (FDCs)
What are the two major components of a lymph node medulla?
- Medullary cords (lymphoid tissue with many B/T cells and plasma cells)
- Medullary sinuses (lined by discontinuous epithelium, lumen contains reticular fibers that contain filtering meshwork as final lymph filter, converge at hilum to form efferent lymphatic vessels)
What causes the enlargement of lymph nodes during an infection?
Rapid proliferation of B lymphocytes in germinal centres of follicles with the help of Th cells
What lymphoid organs are involved in filtration of the blood?
ONLY the spleen
What type of connective tissue fills the spleen?
Reticular tissue
What type of pulp is found in the spleen (by percent)?
- White pulp (20%)
- Red pulp (80%) (erythrocytes)
What constitutes white pulp of the spleen? (2)
- Lymphoid nodules
- Periarteriolar lymphoid sheaths (PALs) (mostly T cells)
What constitutes red pulp of the spleen? (2)
- Blood filled sinusoids
- Splenic cords
Describe the path that blood travels in the spleen (6)
- Trabecular artery
- Central arteriole (surrounded by periarteriolar lymphoid sheath (PALs) in red pulp
- Germinal centre in white pulp
- Penicillar arterioles
- Macrophage sheathed capillaries
- Splenic sinuses leading to closed circulation and trabecular vein and splenic vein or open circulation leading to red pulp
How are erythrocytes at the end of their life filtered out of the blood?
When blood passes out of open circulation capillaries in the spleen, they are dumped into red pulp. Everything is able to reenter blood through gaps in the sinusoids except stiff and swollen erythrocytes, which are blocked from passing between the stave cells and undergo selective removal by macrophages in the red pulp of the spleen.
Where are lymphoid nodules found? (3)
- MALT
- Lymph nodes (cortex)
- Spleen (white pulp only)
Where are efferent and afferent lymphatic vessels found? (3)
- Thymus (few efferents in septa)
- MALT (efferents only)
- Lymph nodes (afferents at capsule, efferents at hilum)
- Spleen (Efferents in trabeculae only)
Why is there elastin in the capsule of the spleen?
To allow it to expand up to 3X its size during infection
What mostly composes the sheath that surrounds central arterioles in the spleen?
T lymphocytes
