Lymphatic System Anatomy and Histology

• The lymphatic system includes structures like axillary and cervical lymph nodes, cisterna chyli, inguinal lymph nodes, MALT, the right lymphatic duct, red bone marrow, the spleen, thoracic duct, the thymus gland, and tonsils.

Lymphatic Anatomy

• Locate and describe the location of lymphatic organs using an APR assignment.
• The organs to locate are: thymus, spleen, axillary lymph nodes, pharyngeal tonsil, palatine tonsil, lingual tonsil.

Lymph Node Structure

• Lymph node structures on a diagram include the cortex, medulla, lymphatic nodules, trabeculae, afferent lymphatic vessels, efferent lymphatic vessel, lymph node artery, lymph node vein, valves in lymphatic vessels, and the hilum.
• Lymph moves through afferent vessels into the node and exits via efferent vessels.
• Structural features of a lymph node slow down lymph movement.
• Slow lymph movement through a lymph node is desirable.

Histology

• Draw and label structures using an APR assignment to complete the histology activity.
• Lymph node: capsule, cortex, medulla, lymphatic nodule.
• Thymus: thymic (Hassal's) corpuscle.
• Spleen: red pulp, white pulp.
• Ileum: Peyer's patch.

Lymphatic System Anatomy & Function

• Lymph nodes filter lymph, and the spleen filters blood.
• Lymph from a limb enters the vascular system via the right lymphatic duct.
• Valves ensure the one-way flow of lymph in lymphatic vessels.
• Fats absorbed into the small intestine's villi pass into a large lymphatic structure (lacteal), then enter circulation via the thoracic duct.
• The lymphatic system returns fluid to the circulatory system, houses immune system cells, and absorbs dietary fats.
• Unencapsulated mucosal associated lymphoid tissues (MALT) can be found in specific locations.

Defenses Against Infection

• General defense mechanisms that protect against various pathogens and function the same way upon every exposure are called nonspecific or innate defenses.
• Defenses targeting specific, previously encountered pathogens are called specific or adaptive defenses.

Antibodies

• An antibody consists of two light and two heavy chains, with variable portions combining to form antigen-binding sites.
• The stem cell genes encoding light and heavy chains recombine to yield diverse lymphocyte antigen specificities, a process called V(D)J recombination.
• The five classes of antibodies are IgM, IgA, IgD, IgG, and IgE (MADGE).
• Antibody classes' functions are determined by differences in the constant region of their chains.
• IgM, IgA, IgD, IgG, & IgE (MADGE).
• Characteristics matched with antibody classes: functions as the antigen recognition site of B cells, 1st class made in a primary immune response, pentamer with potent agglutinating capabilities, crosses the placental barrier, found in secretions, attaches to basophils and mast cells, most plentiful circulating antibody, and antibody type made in late primary & secondary immune responses.

Immune Response

• An immune response is initiated against antigens evading innate defenses.
• A dendritic cell engulfs an antigen, processes it, and presents fragments on its surface as part of a class II MHC protein.
• When encountering a CD4 Thelper cell (TH) with a fitting receptor, the antigen-presenting cell (APC) and T cell co-stimulate each other.
• The activated THs cell differentiates and proliferates to generate clones of effector Th cells.
• Effector TH cells bind cells presenting the same antigen as part of their MHC II protein, releasing cytokines/interleukins to activate the already sensitized B cell.
• The activated B cell proliferates into plasma cells and B memory cells.
• Plasma cells release soluble proteins (antibodies) that recognize & bind the antigen that sensitized the B cell.
• Antibodies may directly inactivate pathogens or target them for destruction by phagocytes.
• TH cells help APCs stimulate CD8 cells which recognize presented antigens and form clones of cytotoxic T cells.
• Memory CD8 cells and suppressor T cells also form.
• Activated CD8 cytotoxic T cells release perforin to kill virally-infected cells displaying specific antigens as part of their MHC I complex.
• Suppressor T cells activate more slowly, playing a role in ending the immune response.
• After termination via suppressor T cells, memory T & B cells remain for rapid initiation upon re-exposure.
• Natural killer (NK) cells provide constant immunological surveillance by releasing perforin to kill cells with abnormal MHC I complexes.

Primary vs Secondary Responses

• The features of a diagram represents the primary and secondary immune responses.
• Compare primary and secondary immune responses, noting speed of onset, antibody titer magnitude, and main antibody class involved.

Types of Hummanity

• Match natural vs. artificial and active vs. passive immunity types with the correct descriptions.
• Results from introduction of a weakened or killed form of a pathogen that leads to the production with few or no symptoms of the disease = Active Artificial Immunity
• Occurs when sera containing pre-made antibodies is given to provide immediate protection against a pathogen or toxin = Passive Artificial Immunity
• Results when a disease-causing pathogen triggers an immune response that leads to production of antibodies against the pathogen = Active Natural Immunity.
• Occurs when a fetus acquires antibodies via the placenta or when a nursing infant acquires antibodies in breast milk = Passive Natural Immunity