Boyd W H
Anat Anz. 1976;140(1-2):224-30.
A dual system of hypophyseal anterior lobe veins is suggested for bovine. One system is associated with the gland at large and utilizes the capsular plexus of veins, while the other, not utilizing the capsular plexus, is associated with the sinusoids of the hypophyseal portal veins. As they reach the capsule of the gland, those veins not utilizing the capsular plexus, are lined, at their terminal segment by endothelial cells with contractile and secretory elements. The contractile endothelial cells subserve a valve-like action on demand of glandular function.
有人提出牛垂体前叶存在双重静脉系统。一个系统与整个腺体相关联，并利用静脉的被膜丛，而另一个不利用被膜丛的系统则与垂体门静脉的血窦相关联。那些不利用被膜丛的静脉在到达腺体被膜时，其末端部分由具有收缩和分泌成分的内皮细胞排列。收缩性内皮细胞根据腺体功能的需要起到类似瓣膜的作用。
