Q. A 7-year-old girl is brought to her pediatrician because her parents say she is “growing breasts.” Physical examination shows not only developing breasts, but pubic hair. She is diagnosed with precocious puberty, and prescribed Leuprolide. The parents are assured while Leuprolide is usually prescribed for endometriosis or prostate cancer, it will suppress their daughter’s increased expression of sex hormones. It does so by acting on the vasculature of the hypothalamus and pituitary gland, which is uniquely designed and includes a portal system. Which of the following is the functional significance of this specialized vascular system?