During coagulation of blood, an enzyme complex thrombokinase helps in the conversion of prothrombin (present in plasma) into thrombin. Thrombin further helps in the conversion of inactive fibrinogens into fibrins which form network of threads. Renin is secreted by JG cells in response to fall in glomerular blood flow, which converts angiotensinogen in blood to angiotensin-I Epinephrine or adrenaline is secreted by adrenal medulla in response to stress of any kind and during emergency.