The decrease in blood clotting caused by heparin occurs at which general site of action?

The decrease in blood clotting caused by heparin occurs at which general site of action?

• A. Intracellular
• B. Extracellular
• C. Nuclear
• D. Mitochondrial

Answer: (B)

The main idea is where heparin acts to slow clotting. Heparin binds to antithrombin III in the extracellular fluid of the blood, greatly boosting its ability to inhibit key clotting enzymes, especially thrombin and factor Xa. This action occurs in the plasma outside of cells, so the site of action is extracellular. By neutralizing these proteases in the circulation, fibrin formation is reduced and clotting is decreased. Heparin does not need to enter cells or affect nuclear or mitochondrial processes to exert its effect, which is why intracellular, nuclear, or mitochondrial sites are not correct.

The main idea is where heparin acts to slow clotting. Heparin binds to antithrombin III in the extracellular fluid of the blood, greatly boosting its ability to inhibit key clotting enzymes, especially thrombin and factor Xa. This action occurs in the plasma outside of cells, so the site of action is extracellular. By neutralizing these proteases in the circulation, fibrin formation is reduced and clotting is decreased. Heparin does not need to enter cells or affect nuclear or mitochondrial processes to exert its effect, which is why intracellular, nuclear, or mitochondrial sites are not correct.