Blood Composition, Gas Transport, Immune Function (3B) - MCAT Biological and Biochemical Foundations of Living Systems

Bicarbonate ($HCO_3^-$) in plasma. Carbonic anhydrase converts $CO_2$ to bicarbonate in erythrocytes for efficient transport to lungs.

IgE. It triggers degranulation upon allergen binding, releasing histamine for allergic responses.

IgM. Its structure allows efficient agglutination and classical complement pathway initiation.

IgG. It provides long-term protection through opsonization, neutralization, and placental transfer.

Binds a particular epitope (antigenic determinant). The variable region confers high-affinity binding to unique molecular structures on pathogens.

MHC class II. It presents phagocytosed antigens to initiate helper T cell-mediated immune responses.

MHC class I. It displays intracellular peptides to enable immune surveillance of infected or cancerous cells.

Coordinate immune response via cytokine signaling. They release cytokines to activate B cells, macrophages, and cytotoxic T cells in adaptive immunity.

Kill virus-infected and malignant cells. They induce apoptosis in target cells via perforin and granzymes upon MHC I recognition.

Differentiate into plasma cells that secrete antibodies. Activated B cells produce immunoglobulins for humoral immunity against specific antigens.

Monocytes. Monocytes migrate to tissues and transform into phagocytic cells for pathogen clearance.

Basophil (and tissue mast cells). They degranulate to release mediators promoting inflammation in hypersensitivity reactions.

Eosinophil. Eosinophils release major basic protein and other mediators to combat helminths and allergens.

Neutrophils. They constitute 50-70% of white blood cells and act as primary phagocytes against bacteria.

Thrombin. This serine protease cleaves fibrinogen in the common pathway of coagulation to stabilize clots.

Fibrinogen. It is converted by thrombin into fibrin monomers that polymerize to form clot meshwork.

Hemostasis: platelet plug formation and clotting support. Platelets aggregate at vessel injury sites and release factors to initiate coagulation.

Fraction (percent) of blood volume occupied by erythrocytes. It indicates oxygen-carrying capacity and is measured by centrifuging blood to separate components.

Surface area-to-volume ratio for gas exchange. The discoid shape maximizes diffusion efficiency for oxygen uptake and carbon dioxide release.

Transport $O_2$ (and some $CO_2$) via hemoglobin. Hemoglobin within erythrocytes binds oxygen in lungs and releases it in tissues for cellular respiration.

Fibrinogen and prothrombin (clotting factors). These proteins participate in the coagulation cascade to form fibrin clots and stop bleeding.

Albumin. It exerts colloidal osmotic pressure to regulate fluid balance between blood and tissues.

Plasma and formed elements. Whole blood consists of liquid plasma and cellular formed elements, separated by centrifugation.

Erythrocytes, leukocytes, and platelets (thrombocytes). These cellular components are suspended in plasma and perform oxygen transport, immune defense, and hemostasis functions.