Lymphatic and Immune Systems (3B) - MCAT Biological and Biochemical Foundations of Living Systems

Bone marrow. Serves as the hematopoietic site where B lymphocytes undergo maturation and antigen-independent differentiation.

CD$4^+$ helper T cells. Interact with MHC II on APCs to secrete cytokines that direct other immune cells' functions.

Suppress immune responses and maintain self-tolerance. Produce inhibitory cytokines like IL-10 to prevent autoimmunity and excessive inflammation.

One-way valves (with skeletal muscle and pressure aid). Prevents backflow and promotes unidirectional movement toward the heart, aided by external compression.

Filter lymph and provide sites for immune cell activation. Trap pathogens and antigens in lymph, facilitating lymphocyte interaction and adaptive immune initiation.

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.

Absorb dietary lipids as chyle from intestinal villi. Specialized lymphatic capillaries in the small intestine transport emulsified fats bypassed by blood capillaries.

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.

IgM. Appears earliest due to its pentameric structure enabling strong initial agglutination before class switching.

Secrete large amounts of antigen-specific antibodies. Arise from activated B cells to produce high-affinity antibodies for humoral defense.

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.

Innate is rapid and nonspecific; adaptive is specific with memory. Innate provides immediate defense against broad pathogens, while adaptive develops targeted responses over time.

Dendritic cells, macrophages, and B cells. Express high levels of MHC II and costimulatory molecules to effectively activate naive T cells.

Phagocytose and kill bacteria; first responders in acute inflammation. Dominate early inflammatory responses by engulfing microbes and releasing antimicrobial enzymes.

Defense against helminths; contribute to allergy/asthma. Release granule contents to combat large parasites and modulate type I hypersensitivity reactions.

Antigen activates specific lymphocyte clones to proliferate and differentiate. Ensures efficient adaptive responses by expanding only lymphocytes with matching antigen receptors.

Interstitial fluid collected into lymphatic vessels. Forms from plasma filtrate that escapes capillaries, containing water, proteins, and lipids but fewer cells than blood.

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

Release histamine and heparin; mediate allergic inflammation. Initiate immediate hypersensitivity by degranulating in response to allergens or IgE crosslinking.

Phagocytosis and antigen presentation; cytokine secretion. Bridge innate and adaptive immunity by processing antigens and activating T cells in tissues.

Kill virus-infected and tumor cells without prior sensitization. Provide innate surveillance by inducing apoptosis in stressed cells via perforin and granzymes.

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.

CD$8^+$ cytotoxic T cells. Recognize MHC I-antigen complexes and eliminate compromised cells to contain infections.