Lymphatic and Immune Systems (3B) - Bio & Biochem

What is the primary role of regulatory T cells (Treg) in immune function?

Suppress immune responses and maintain self-tolerance. Produce inhibitory cytokines like IL-10 to prevent autoimmunity and excessive inflammation.
What is the function of lymph nodes in the immune response?

Filter lymph and provide sites for immune cell activation. Trap pathogens and antigens in lymph, facilitating lymphocyte interaction and adaptive immune initiation.
Which organ is the primary site of T cell maturation?

Thymus. Provides a specialized environment for T lymphocyte development and selection to ensure self-tolerance.
What is the primary immune function of basophils (and related mast cells)?

Release histamine and heparin; mediate allergic inflammation. Initiate immediate hypersensitivity by degranulating in response to allergens or IgE crosslinking.
Which T cell subtype primarily coordinates immune responses via cytokines?

CD $4^+$ helper T cells. Interact with MHC II on APCs to secrete cytokines that direct other immune cells' functions.
What is lymph, in terms of its origin and composition?

Interstitial fluid collected into lymphatic vessels. Forms from plasma filtrate that escapes capillaries, containing water, proteins, and lipids but fewer cells than blood.
What is the function of the right lymphatic duct?

Drains right head/arm and right thorax into right subclavian vein. Collects lymph from the right upper quadrant to return it to venous circulation at the brachiocephalic vein junction.
What is clonal selection in adaptive immunity?

Antigen activates specific lymphocyte clones to proliferate and differentiate. Ensures efficient adaptive responses by expanding only lymphocytes with matching antigen receptors.
What is the function of the thoracic duct?

Drains most of the body into the left subclavian vein. Serves as the main lymphatic drainage pathway, emptying into the venous system to maintain overall fluid balance.
What is the function of plasma cells in humoral immunity?

Secrete large amounts of antigen-specific antibodies. Arise from activated B cells to produce high-affinity antibodies for humoral defense.
What is the key structural feature that ensures one-way flow in lymphatic vessels?

One-way valves (with skeletal muscle and pressure aid). Prevents backflow and promotes unidirectional movement toward the heart, aided by external compression.
What is the defining feature of innate immunity compared with adaptive immunity?

Innate is rapid and nonspecific; adaptive is specific with memory. Innate provides immediate defense against broad pathogens, while adaptive develops targeted responses over time.
What is the role of lacteals in the lymphatic system?

Absorb dietary lipids as chyle from intestinal villi. Specialized lymphatic capillaries in the small intestine transport emulsified fats bypassed by blood capillaries.
What is the primary immune function of natural killer (NK) cells?

Kill virus-infected and tumor cells without prior sensitization. Provide innate surveillance by inducing apoptosis in stressed cells via perforin and granzymes.
What is the key difference between MHC class I and MHC class II antigen presentation?

MHC I: endogenous to CD $8^+$ ; MHC II: exogenous to CD $4^+$ . MHC I displays intracellular peptides to cytotoxic T cells; MHC II presents extracellular peptides to helpers.
What is the primary immune function of eosinophils?

Defense against helminths; contribute to allergy/asthma. Release granule contents to combat large parasites and modulate type I hypersensitivity reactions.
Which T cell subtype directly kills infected cells via perforin and granzymes?

CD $8^+$ cytotoxic T cells. Recognize MHC I-antigen complexes and eliminate compromised cells to contain infections.
What is the function of the spleen in immunity and blood maintenance?

Filters blood; removes old RBCs; mounts immune responses to blood antigens. Acts as a blood filter in the white pulp for immune surveillance and red pulp for erythrocyte recycling.
What is the primary immune function of macrophages?

Phagocytosis and antigen presentation; cytokine secretion. Bridge innate and adaptive immunity by processing antigens and activating T cells in tissues.
Which immune cells are professional antigen-presenting cells (APCs) in MCAT context?

Dendritic cells, macrophages, and B cells. Express high levels of MHC II and costimulatory molecules to effectively activate naive T cells.
Which organ is the primary site of B cell maturation in humans?

Bone marrow. Serves as the hematopoietic site where B lymphocytes undergo maturation and antigen-independent differentiation.
What is the primary immune function of neutrophils?

Phagocytose and kill bacteria; first responders in acute inflammation. Dominate early inflammatory responses by engulfing microbes and releasing antimicrobial enzymes.
Which antibody class is first produced in a primary immune response?

IgM. Appears earliest due to its pentameric structure enabling strong initial agglutination before class switching.
What is the primary function of the lymphatic system in fluid balance?

Returns interstitial fluid (lymph) to the bloodstream. Maintains fluid homeostasis by recycling excess fluid and proteins from tissues back to circulation, preventing edema.

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