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Lymphatic System and Immunity: Key Questions and Answers

What are the parts of the immune system?

• Lymph: A fluid circulating in the lymphatic system that contains water, proteins, immune cells, and waste products. It plays a critical role in transporting immune cells throughout the body and removing waste products from tissues.

• Lymph Vessels: Transport lymph throughout the body. They are equipped with valves to prevent backflow and are more permeable than blood vessels, allowing for the absorption of larger particles such as pathogens and cellular debris.

• Lymphoid Tissues/Organs:

  • Primary:

    • Thymus: A gland located behind the sternum, crucial for T cell maturation. T cells generated here are central to the adaptive immune response.

    • Bone Marrow: The site for B cell production and where innate immune cells are generated, containing hemopoietic stem cells that can differentiate into various immune cell types.

  • Secondary:

    • Spleen: Filters blood, removing old and damaged red blood cells and activating lymphocytes in response to blood-borne pathogens.

    • Lymph Nodes: Act as filters for lymph, trapping pathogens and foreign particles, and serving as sites for lymphocyte activation.

    • Tonsils: Guard the entrances to the gastrointestinal and respiratory tracts, providing an immune response to pathogens entering through the mouth or nose.

• Lymphoid Cells: Include B cells and T cells that are central to adaptive immunity, alongside natural killer cells which play a significant role in innate immunity.

How do lymphatic capillaries differ from blood capillaries?

• Lymphatic capillaries are characterized by increased permeability and the presence of flap-like valves that promote one-way flow, enabling them to absorb larger particles, including pathogens, protein, and cellular waste, which blood capillaries cannot do.

Where do superficial and deep lymphatics collect lymph from?

• Superficial Lymphatics: Collect lymph from the skin and subcutaneous tissues, playing a role in immune surveillance of surface pathogens.

• Deep Lymphatics: Gather lymph from deeper muscles and organ systems, crucial for filtering internal biological contaminants. Both types of lymphatics converge into larger lymphatic trunks.

• Right Lymphatic Duct: Drains lymph from the right side of the body above the diaphragm, while the Thoracic Duct collects lymph from the left side and from the abdominal cavity below the diaphragm.

What structure receives lymph from the inferior parts of the abdomen, pelvis, and lower limbs?

• Cisterna Chyli: An enlarged sac located at the lower end of the thoracic duct, it is the main collecting area for lymph originating from the lower body.

What is the germinal center of lymphoid tissues?

• The germinal center is a specialized microenvironment within lymphoid follicles where naive B cells undergo proliferation and differentiation into plasma cells following antigen exposure, essential for adaptive immunity.

What are the 5 tonsils and their locations?

1. Palatine Tonsils: Located on either side of the throat, these are the most commonly known.

2. Lingual Tonsils: Situated at the base of the tongue, contributing to the immune response against oral pathogens.

3. Pharyngeal Tonsils (Adenoids): Found on the posterior wall of the nasopharynx; often removed in cases of chronic infection.

4. Tubal Tonsils: Located near the openings of the auditory tubes, playing a role in defending the area from respiratory pathogens.

What is MALT and its location?

• Mucosa-associated lymphoid tissue (MALT): Comprises lymphoid tissues associated with mucosal surfaces such as the gastrointestinal tract (notably Peyer’s patches located in the small intestine) and the respiratory tract, providing localized immune protection.

What are the differences and functions of the 3 lymphoid organs?

• Lymph Nodes: Have afferent lymphatic vessels (bringing lymph in) and efferent vessels (draining lymph out). They are critical for filtering lymph and activating lymphocytes in response to detected pathogens.

• Thymus: Contains a unique blood-thymus barrier that allows T cells to mature without interference from pathogens in the bloodstream and produces the hormone thymosin to promote T cell development.

• Spleen: Divided into red pulp (responsible for blood filtration and removal of damaged red blood cells) and white pulp (rich in lymphocytes, involved in immune activation and response).

What are the main differences between innate and adaptive immunity?

• Innate Immunity: Non-specific, present from birth, and involves immediate defenses, including physical barriers (skin, mucous membranes), phagocytosis (by cells like macrophages), and the complement system.

• Adaptive Immunity: Highly specific and acquired over time through exposure to pathogens, involving specialized lymphocytes that provide long-lasting immunity (B cells and T cells).

What stem cells initiate lymphocytopoiesis, and where are they located?

• Hemopoietic Stem Cells: Located in the bone marrow, these cells divide into two lineages: one becomes B cells within the marrow and the other matures into T cells in the thymus.

What are the 7 types of innate immunity?

1. Physical Barriers: Skin and mucous membranes that act as the first line of defense.

2. Phagocytes: Include microphages, which respond immediately to infection, and macrophages, which can be stationary or mobile and engage in complex processes to eliminate pathogens.

3. Immune Surveillance: Conducted by NK cells that monitor and eliminate abnormal cells, including tumors.

4. Interferons: Cytokines produced in response to viral infections that inhibit viral replication in neighboring cells.

5. Complement System: Proteins that enhance the effectiveness of antibodies and phagocytes and contribute to pathogen lysis.

6. Inflammation: Induced by cytokines, which recruit leukocytes to the site of infection and contribute to the localized immune response.

7. Fever: Triggered by pyrogens, which help enhance the body’s immune function against infections.

What are the 3 types of T cells in adaptive immunity?

• Cytotoxic T Cells: Directly target and kill infected or cancerous cells through perforin and granzymes.

• Helper T Cells: Facilitate and enhance the activation of B cells and macrophages, supporting the overall immune response.

• Regulatory T Cells: Maintain homeostasis in the immune system by suppressing excessive immune responses to prevent damage to host tissues.

What specific type of immunity do cytotoxic T cells provide, and what are the steps?

1. Recognition: T cells recognize infected cells via specific antigen presentation on MHC molecules.

2. Activation: Requires signals from Helper T cells and cytokines.

3. Release of perforins and granzymes: Leads to lysis of the target cell.

What specific type of immunity do B cells provide, and what are the steps?

1. Antigen recognition: B cells identify specific antigens presented by pathogens.

2. Clonal selection and expansion: Selected B cells proliferate and differentiate into plasma cells.

3. Antibody production with T cell assistance: Plasma cells secrete specific antibodies targeting the recognized antigen.

What is clonal selection?

• A process in which specific B cells are activated by their antigen, leading to extensive proliferation and differentiation into effector cells and memory cells tailored to that antigen, creating a targeted immune response.

How do the four types of immunity differ?

• Naturally Acquired Active Immunity: Develops from natural infections where the immune system produces antibodies.

• Artificially Acquired Active Immunity: Stimulated by vaccines that expose the body to antigens without causing disease.

• Naturally Acquired Passive Immunity: Conferred by the transfer of maternal antibodies through the placenta or breast milk to the infant.

• Artificially Acquired Passive Immunity: Involves the injection of pre-formed antibodies to provide temporary immunity against pathogens.

What are the four properties of adaptive immunity?

1. Specificity: Targets very specific pathogens or antigens.

2. Versatility: Capable of responding to a wide variety of pathogens.

3. Memory: Maintains memory cells that allow for a quicker response upon re-exposure to the same pathogen.

4. Tolerance: Ensures that the immune system attacks foreign pathogens while sparing the body’s own cells.

What are the two pairs of polypeptide chains in antibodies, and what is the role of constant vs. variable segments?

• Antibodies consist of two heavy chains and two light chains. The variable segments form the antigen-binding site, determining the specificity for pathogens, while the constant segments define the class of the antibody and mediate the immune response functions.

What are the six actions of antibodies when forming an antigen-antibody complex?

1. Neutralization: Prevents pathogen entry into cells.

2. Opsonization: Marks pathogens for destruction by phagocytes, enhancing phagocytosis.

3. Complement Activation: Triggers a series of reactions that lead to the lysis of pathogen cells.

4. Agglutination: Clumps pathogens together for easier removal by the immune system.

5. Precipitation: Facilitates the clumping of soluble antigens, leading to their removal.

6. Antibody-dependent Cellular Cytotoxicity (ADCC): Recruits and activates immune cells targeted at destroying the pathogen.

What is the difference between primary and secondary immune response?

• Primary Immune Response: The immune system's initial response to a pathogen, typically slow (days to weeks) as it requires growth and differentiation of specific lymphocytes to produce antibodies, generally resulting in lower antibody levels.

• Secondary Immune Response: Occurs upon subsequent exposures; it is faster and more vigorous due to the presence of memory B and T cells, leading to quicker antibody production (often within days) and higher levels of antibodies compared to primary response.

What is antibody titer?

• Antibody titer measures the concentration of antibodies in the blood, indicating the strength of the immune response to a specific pathogen. A higher titer signifies a robust immune reaction and better protection against subsequent exposures to the pathogen.

Overall, what is the order of cells that appear when the immune system is exposed to a pathogen?

• Upon detecting pathogens, macrophages and dendritic cells are among the first responders, engaging in antigen presentation. This activates Helper T cells, which in turn stimulate B cells to differentiate into plasma cells, producing antibodies. Simultaneously, cytotoxic T cells are activated to eliminate infected cells, orchestrating a comprehensive immune response. Initially, innate immune cells respond, followed by adaptive immune cells, thereby establishing a robust defense.

Know these lymphatic conditions:

1. Lymphedema: A condition marked by the accumulation of lymph fluid in tissues due to blockages of lymphatic vessels, leading to significant swelling, often affecting limbs.

2. Tonsillitis: Inflammation of the tonsils typically resulting from infection, causing symptoms like sore throat, difficulty swallowing, and sometimes ear pain.

3. Lymphadenitis: Characterized by the inflammation of lymph nodes, usually due to infection, presenting with swelling and tenderness in the affected area.

4. Hypersensitivities (Anaphylaxis and Antihistamines): Anaphylaxis is a severe allergic reaction that can occur rapidly, manifesting with symptoms such as difficulty breathing, swelling, and systemic effects. Antihistamines are medications that counteract the action of histamines, alleviating symptoms of allergic reactions.

5. Autoimmune Disorders: Conditions where the immune system mistakenly targets and attacks the body’s own tissues, leading to inflammation and damage (for example, rheumatoid arthritis, lupus).

6. SCID (Severe Combined Immunodeficiency): A genetic disorder that severely impairs both T and B lymphocyte systems, resulting in increased susceptibility to infections from birth.

7. AIDS (Acquired Immunodeficiency Syndrome): Caused by the Human Immunodeficiency Virus (HIV), which primarily targets CD4+ T cells, weakening the immune system and making individuals vulnerable to opportunistic infections.