Antidiuretic hormone (ADH) targets the

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A. Thromboplastin: Thromboplastin (tissue factor) initiates the extrinsic coagulation cascade and promotes clot formation; injecting it would increase clotting, not prevent heart attack or stroke.
B. Fibrinogen: Fibrinogen is the soluble precursor that is converted to fibrin during clot formation; giving fibrinogen would support clot formation, not reduce it.
C. Fibrin: Fibrin is the insoluble protein that forms the mesh of a clot; injecting fibrin would directly contribute to clotting.
D. Factor X: Factor X is a key coagulation factor (when activated to Xa it drives thrombin formation); administering it would promote coagulation rather than prevent it.
E. Heparin: Heparin is an anticoagulant that enhances antithrombin activity and reduces clot formation; it is used to prevent or treat thrombosis and reduce risk of heart attack/stroke.

A. Produces plasma hormones: blood does not produce hormones; endocrine organs secrete hormones into the blood. This statement is not a function of blood.
B. Transports a variety of nutrients: this is a function of blood (plasma carries nutrients to tissues).
C. Helps to stabilize the pH of extracellular fluids: this is a function; blood buffers (bicarbonate, proteins) help stabilize pH.
D. Helps to regulate body temperature: this is a function; blood redistributes heat and helps maintain temperature.
E. Participates in the initiation of blood clotting: this is a function; platelets and plasma clotting factors in blood participate in clot formation.