This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Misc., Subject name: Physiology
The primary form of cortisol in the plasma is that which is: 
Select and explain. 
A. Bound to albumin, B. Bound to transthyretin, C. Free in solution, D. Bound to corticosteroid-binding globulin (CBG)
D: Bound to corticosteroid-binding globulin (CBG)
Answer: D: Bound to corticosteroid-binding globulin (CBG) 
Explanation: Ans. D. Bound to corticosteroid-binding globulin (CBG)Cortisol, like other steroid hormones, is carried in the blood largely bound to carrier proteins, although a small percentage exists free in solution. The majority of cortisol is bound to a specific carrier protein, corticosteroid-binding globulin (CBG), while smaller amounts are bound nonspecifically to albumin. Few, if any, cortisol receptors would be expected in the plasma and transthyretin binds primarily thyroxine.