Assertion (A): Blood coagulates in uninjured blood vessels.
Reason (R): Uninjured blood vessels release an anticoagulant heparin.
(a) If both Assertion and Reason are correct and the Reason is a correct explanation of the Assertion.
(b) If both Assertion and Reason are correct but Reason is not a correct explanation of the Assertion.
(c) If the Assertion is correct but Reason is incorrect.
(d) If both the Assertion and Reason are incorrect.
(e) If the Assertion is incorrect but the Reason is correct.
(d) If both the Assertion and Reason are incorrect.
Explanation:
When an injury is caused to a blood vessel, bleeding starts which is stopped by blood clotting. At the site of injury blood platelets release platelet factor - 3 and injured tissues release thromboplastin.
The two combine to form prothrombinase enzyme which converts prothrombin to thrombin. The latter stimulates formation of fibrin thread or clot. Blood contains an anticoagutant heparin which prevents blood clotting in uninjured vessels.