This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Diabetes Mellitus, Subject name: Medicine
Which is the common site of injection of islet cells in islet cell transplant for diabetes mellitus? 
Select and explain. 
A. Pelvis, B. Poal vein, C. Pancreas, D. Forearm muscles
B: Poal vein
Answer: B: Poal vein 
Explanation: Islet cell transplantation involves the extraction of islets of Langerhans from organ donors through a complex purification process. These are the cells responsible for the production of insulin. These cells are then injected into the recipient, usually into the poal vein. They then engraft into the parenchyma of the liver and secrete insulin.