Blood Composition, Gas Transport, Immune Function (3B) - Bio & Biochem

1. What is the function of platelets (thrombocytes)?

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

2. What vitamin is required for hepatic synthesis of several clotting factors?

   Vitamin K. It enables gamma-carboxylation of glutamate residues in factors II, VII, IX, and X for calcium binding.

3. What are the three major formed elements of blood?

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

4. Which leukocyte is most associated with parasitic infections and allergy?

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

5. What is the main protein in plasma that maintains oncotic pressure?

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

6. What immunoglobulin class is most abundant in serum?

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

7. Which MHC class presents endogenous antigens to $CD8^+$ T cells?

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

8. What is the biconcave shape of erythrocytes best suited to increase?

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

9. What is the primary function of B lymphocytes in adaptive immunity?

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

10. What is hematocrit?

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

11. What is the primary function of cytotoxic T cells ($CD8^+$)?

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

12. What is the primary function of helper T cells ($CD4^+$)?

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

13. What immunoglobulin class is a pentamer and best at complement activation?

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

14. What are the main plasma proteins responsible for clotting?

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

15. Which MHC class presents exogenous antigens to $CD4^+$ T cells?

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

16. What are the two major components of whole blood by volume?

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

17. Which leukocytes differentiate into macrophages in tissues?

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

18. What is the immediate precursor protein cleaved to form fibrin in clotting?

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

19. What enzyme converts fibrinogen to fibrin during coagulation?

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

20. What is the primary function of erythrocytes in blood?

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

21. What immunoglobulin class mediates type I hypersensitivity via mast cells?

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

22. What is the main form of $CO_2$ transport in blood?

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

23. What is the most common leukocyte type in peripheral blood?

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

24. What is the defining specificity of an antibody (immunoglobulin)?

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

25. Which leukocyte releases histamine and heparin in allergic responses?

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

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