Gonadotropin-releasing hormone is released into the hypophyseal portal system, which is a network of capillaries connecting the hypothalamus to the hypophysis, or pituitary.
This happens because blood flow follows the path of least resistance and shunts away from the portal system and towards the systemic system of circulation.
Portal hypertension leads to the formation of Portosystemic shunts, which is when blood is diverted away from the portal venous system and backs up into the systemic veins.
Second, blood backing up in the systemic veins leads to portal systemic shunts, which happens in the three points where the systemic venous system and hepatic portal system are connected.